John Sayers' Recording Studio Design Forum Archive

I'm starting a new thread despite having some old threads on this forum about this same space, so please ignore any previous posts as the situation has changed.

Briefly, I purchased 4 offices in a pod of 6 on the penthouse level of an office building with amazing views and generous wrap around balconies. Wishing to build my 3rd studio in 27 years there, I had 2 problems - keeping the spill from drums and loud amps down to a manageable level for the other occupant of level 7, and also to keep my neighbours on level 6 happy. With a live load of 650 kg per m2, it was becoming increasingly apparent that I could either minimise leakage to level 7, or to level 6, but not both due to the load restriction.

And so I got by recording drums after hours and waited for the other 2 offices to be up for sale. They eventually were and recently I purchased one and a colleague purchased the other. So now we don't have to worry so much about the spill to level 7, and can focus on a floated design for a drum room and a couple of small booths (for amps etc). I was planning on hiring a studio designer and contracting an experienced builder, but 2 lean years as well as the new acquisition has left me with less funds than I anticipated, yet still enough to build it properly.

I have an acoustician who is a friend and has offered his services at a discount, which is great however I am concerned he lacks experience with upper level builds. So I'd like to check with the forum members that his ideas are sound. If you view the attachment you will see the main control room with a side view into the Performer's Area and drum room / booths. Firstly, let me say that we will definitely be going with that configuration so please resist the urge to recommend alternative layouts The rest of the layout showing the various production suites are planned for the future, but will not be of concern at present. The have been shown, however, in order to flag any future concerns should we decide to go that way. But for the time being, the grey area is the first thing to be built, which will be the floated drum room and 2 booths. The performers area and the control room will not be floated, maybe just some sort of damped deck. I can't build the control room until after the drum room and booths are complete as I'm currently using the space allocated for the CR as an after hours drum room, and need to keep using it that way to keep up with my repayments.

OK, so the grey area is only 22 m2 but we have decided we need a floated floor atop a 100mm gap that has the equivalent density of 75mm concrete. We have decided for several reasons that concrete is not appropriate, so we will go instead with 6 layers compressed fibre cement boards totalling 112 mm (187 kg per m2). The mounts will be properly engineered for the job and will be steel spring in rubber housing and the floor has been quoted by an experienced company that does many jobs where vibration is the concern, although they assure me that their designs work equally well for airborne sound. So I'm thinking the floor should be enough to minimise drums through the floor, particularly as I've built a test floating booth that only had 120kg /m2 for the floor and that was tested to show that the low frequencies from kick drum or snare were less than the air conditioning noise from level 6 when taking SPL readings from the 6th floor.

Assuming that the floor is fine, we then come to the walls and ceiling. It looks like we cannot hang the ceiling from the roof for structural reasons, so the full weight of the walls and ceiling for the 22 m2 will add extra load upon the floated slab. So far the structural engineer has assessed a design that has the walls and ceiling weighing 35 kg per m2. Now this is my main concern at this stage... that 35kg/m2 is not enough! The acoustician has explained that 35kg for the walls and ceiling is enough mass and is proportional to the 187 kg floor mass because of the way sound behaves when going through a wall, and then down below. Remember our primary concern is that level 6 doesn't hear drums and bass, which probably means that other room in our level 7 pod will. Now from my own research, and reading through threads on this forum, I would have guessed something closer to 60 kg for the walls, but the acoustician says it will make little difference through the floor. Does anyone agree? Even if so, it would obviously be desirable to minimise sound spill into the other future production rooms, so how much difference would 60kg as opposed to 35kg make in that regard?

The diagram shows an outer leaf but doesn't show that the entire top wall is a glass facade onto the balcony, and at 10.38mm (laminated), is only around 27kg/m2. However, here I'm hoping that the allocated air gap between leaves of 150mm will make up for the light density of the outer leaf on that side.

I can supply a lot more data, but will leave it there for now as I'm anticipating some questions . Suffice it to say that the floor may go down in the coming weeks (if permits don't slow us down) which means I need to be certain of the density of the walls and ceiling pretty soon so I can have the SE assess accordingly should we decide to go heavier. I'll just add at this stage that the plan is for the perimeter walls to be inside out modules but the partition walls (between drum room and booths) to be double walls where one side is decoupled via soundclips / hat channel. The total density of both sides of the partition walls has been calculated to be only 35kg, so say 12 kg for the inside wall on the hat channel, and 24 kg fixed to the stud on the outside (obviously filed with insulation). This sounds too light to me, I would have thought 30 kg per side. I suppose we can always add layers later on?.....

Anyway, happy to hear some thoughts and field the inevitable questions. So fire away!

It's good to see you back again! I always wondered what the end outcome was going to be with your place. That was a smart move to buy the other offices on your same level, so you have the entire floor to yourself.

With that in mind, and even though you said the basic layout is already locked in and you don't want suggestions for changing it,... I would suggest that you change it! With the extra space, you now have so many more options for doing an amazing studio up there, without being limited to "the way it would have been" before. I realize that you are probably really desperate to get started on building, and get the place running (after having bought the original space such a long time ago), but rushing now seems to not be a smart move. There are many ways I can see of making large improvements, just from the very basic diagram you provided. You've already invested large amounts of money in this, and will still be investing many more "large amounts of money" to get it built, treated and tuned, so it just seems reasonable to do a reality check, and make sure that you really are making it the best it can be. Yes, I get it: you already put a lot of work into that design, and you fell in love with it, and you'd really hate to have wasted all that effort for nothing and start over with a clean slate... but the question you should be asking yourself is this: Is that really the best possibly layout? I can answer that question for you, but you won't like the answer... Second question: Could it be a lot better if I got some professional help to re-resign or properly? You probably wouldn't like my answer to that question either. I guess it boils down to how deeply in love you are with the current design and the emotional and mental effort you put into it, versus how good you want the studio to be in the end, after you pour all those many thousands of dollars into it... Are you willing to settle for it being merely OK, when it could be great? That's your decision, of course: your money, not mine! But once the place is finished, and you start noticing the problems, do you really want to be kicking yourself every day, and wondering how much better it could have been, if only....

please resist the urge to recommend alternative layouts

Sorry! I couldn't resist it... It's too important to resist, I think... You probably can't see it from where you are, as you are too close to the entire project, but from my perspective, as an impartial outside observer, the questions are SO very valid, they can't be ignored. There's huge potential in that space now, with the added area. You seem to not be seeing the potential, and are just focused on building something, anything, even if only mediocre at best, right now, just to at least have something to show for your troubles! My most important advice would be: take a second look at this. Take a step back, and re-evaluate.

That said, if you do decide to just stick to the proposed layout with blinkers on, there are still many large red flags waving at me from that diagram, and from what you said in your text. Big flags. Very red.... I certainly see why you came back here for a second opinion... some of your doubts and concerns are very valid. Some of those you already noticed yourself, obviously, and you are rightfully concerned about them. But there's other stuff you haven't' noticed, that is just as important.

First point, about "the way sound behaves when going through a wall, and then down below". The way it actually behaves is pretty simple to understand: we are talking about low frequency sound here: that's your number one concern. Not high frequencies, which travel more or less like rays or cones. Low frequencies travel roughly like a balloon being pumped up and down, or even simpler, like blowing into then sucking out of a paper bag: when you blow into it, the entire bag inflates, all sides equally, not just the side directly opposite your mouth. And when you suck out, the entire bag deflates, the same all around, not just the side opposite your mouth. The same thing happens with low frequencies after they get through a low-mass single-leaf wall. The air on the other side is like a paper bag, that inflates and deflates roughly equally, all over: directly in front of the thin wall, as well as off to the sides, and up towards the ceiling... and yes, down towards the floor too. It's a pressure front, not a ray of light. It goes out all over, roughly equally everywhere. (Remember, we are talking about low frequencies here: highs are different). So whatever sound makes it through the low mass walls and into the cavity beyond, will expand and contract as a pressure wave, not as rays or cones of sound. Thus, it will reach your outer-leaf floor.

Illustration: Set up a full range speaker on a stand in the middle of a large empty space: preferably outdoors. Play loud contemporary music through that, with plenty of bass and drums. Stand in front of the speaker, and you hear all frequencies. Now walk all around that speaker. As you move far off axis, you hear less and less of the highs and mids. When you get around behind it, all you are hearing is the lows: the highs and mids are completely gone (since they project forward, as rays and cones) but the lows are there, just as loud and strong as they were around the front. Stand up on a tall ladder right above the speaker, or lie flat on the ground with your head under it, and you hear the lows exactly the same in all directions. This effect is partly due to the baffle step issue of the speaker itself, as well as other speaker-related issues, but the basic point is still valid: low frequency sound expands equally in all directions, including down. If you have low frequency sound in the wall cavity, then it will do the same. Truck loads of suitable damping in the cavity reduces that somewhat, but there WILL still be airborne sound hitting your floor. Not to mention that the building floor slab itself is a resonant drum head, which cannot be damped.... If the resonant frequencies of that floor slab itself happen to be close to the frequencies in the wall cavity... well, use your imagination....

Add to the above: drums at 115 dBC, bass amp turned up to eleven, growling electric guitars, deep roaring keyboards, foot-stomping musicians, pumping subs.... Well, you sure do have a lot of bass energy in that cavity: Let's look at the mass-law math for a 35 kg/m2 partition, for the 63 Hz band (the low bass region).

TL(dB)= 20log(M) + 20log(f) -47.2
= 20Log(35) + 20Log(63) -47.2
= 30.881 + 35.986 - 47.2
= 19.666 dB

So the TL will be less than 20 dB for that situation. Is that enough? Only you can say. Yes, that sound is just in the cavity, and still has to make the concrete slab vibrate in order to get through to your neighbors below, and there's background noise down there too, and there's the equal loudness curves to consider.... So how much will they actually hear? Hmmm.... There's a LOT of energy going out.... Hmmmmm....

the control room will not be floated, maybe just some sort of damped deck.

Hmmmm.... so you are worried about the very loud music in the live room disturbing your neighbors, but you are not worried about the very loud music in the control room disturbing your neighbors? The sound waves don't care where they originated from: just because the bass came out of the control room speakers, not the bass cab in the live room or booth, does not mean that it will behave any differently... it will, in fact, behave exactly the same. There's no difference. The bass guitar played in the LR and the resulting track played in the CR at the same level, will still travel around the building in the same way...

OK, so the grey area is only 22 m2 but we have decided we need a floated floor atop a 100mm gap that has the equivalent density of 75mm concrete.

Math time again! 75 mm concrete is about 2300*.075 = 172 kg/m2. Assuming steel springs, with 15% static deflection down to 100mm, that gives you natural resonant frequency of around 4 Hz, along with the MSM resonance from the air (which is in parallel with the springs, don't forget), at around 14 Hz, so combined roughly 18 Hz resonant frequency for your floor system. Is that low enough? Hmmm.... Should be fine for impact noise, but is it OK for air-borne noise?

we will go instead with 6 layers compressed fibre cement boards totalling 112 mm (187 kg per m2).

Your fiber-cement board must be more dense in Australia... The nominal density for fiber-cement in most other places is normally taken to be about 1550 kg/m3, so 112mm should get you about 173 kg, not 187. Not a huge error, but 8% is 8%...

The mounts will be properly engineered for the job and will be steel spring in rubber housing

I guess there must be a typo in there some place, because putting steel springs inside a rubber tube doesn't make much sense... I would suspect that you are referring to a combination isolator that has a steel sprint plus also a rubber pad of some type? Those are commonly used for floating floors: the steel spring deals with the low frequency resonance and the rubber pad (often Neoprene) deals with the high frequencies.

Also, fiber-cement board is brittle, and not very strong. How will you support that, prevent it from cracking, and what will the final floor surface be? You can't use the board itself as the actual floor...

an experienced company that does many jobs where vibration is the concern,

I hope they also have experience in acoustics: vibration isolation is one thing, but full acoustic isolation is something else. I assume they gave you some type of engineering report with the predicted resonant frequency: what does that report say? What is the expected resonant frequency for the floor system? And what isolation are the predicting for the frequencies of concern for the studio? Did they give you a predicted TL curve? What is the resonant frequency of the original floor slab itself, without considering the new floating floor that will sit on top of it? That's an rather important factor here, that I haven't seen you mention yet. You say this company is experienced: Did they give you a list of other recording studios they have isolated like this, so you can contact those clients and check the outcome? Did all of those use the same fiber-cement board in a metal frames with steel springs in rubber casings? Or did the other studios use different floating floor methods? Did you actually contact those other studios, and go visit them, or at least talk to them?

although they assure me that their designs work equally well for airborne sound.

Ooops! Isolating impact noise and structure-borne vibration is not really the same as isolating airborne sound.

It looks like we cannot hang the ceiling from the roof for structural reasons,

I suspected as much, when we first spoke a couple of years ago. That's unfortunate, but not unexpected. On the bright side, floating the entire room will likely get you better isolation than floating individual parts of it separately, and having all the weight resting on the floating floor increases the total floated mass, which is good.

So far the structural engineer has assessed a design that has the walls and ceiling weighing 35 kg per m2. Now this is my main concern at this stage... that 35kg/m2 is not enough!

I concur. Your concerns are valid. Having a floor with a surface density of 175 kg/m2 and walls with just 35 kg/m2, doesn't make a lot of sense.

You didn't mention the ceiling, which is just as important as the floor and walls, but I'm assuming it will be something similar to the walls? How much MSM gap are you leaving for the ceiling? And what is the total height you have available for you, in the empty shell? (floor surface to ceiling surface). Will your final inner-leaf ceiling height be sufficient for good acoustics, especially in the drum room?

The acoustician has explained that 35kg for the walls and ceiling is enough mass and is proportional to the 187 kg floor mass because of the way sound behaves when going through a wall, and then down below.

Sound waves don't really understand much about "up", "down", "left" or "right". Sound waves travel pretty much the same way in all directions. I'm not at all sure what he means by 35 kg/m2 being "proportional" to 187 kg/m2.... (in fact, the proportion is only about 18%....!!!) nor how he expects that to change the way sound travels once it gets through each of those... maybe you could ask him to explain that in simple terms, or better still to show you his calculations that shows how this proportionality works, and why sound would end up moving differently in different directions. I'd be very curious about that math and the explanations, if I were you.

Remember our primary concern is that level 6 doesn't hear drums and bass, which probably means that other room in our level 7 pod will

If loud drums are going to be getting into the other parts of level 7, then what is going to prevent that from getting down through the floors, HVAC, plumbing, electrical and stairways, into level 6? I'm not following the logic here. If you have drum sounds getting out into the stairwell on level 7, for example, that's going all the way down to level 1, not just level 6.... Ditto for loud sounds getting into the building core ducts and passages. Red flags.

Now from my own research, and reading through threads on this forum, I would have guessed something closer to 60 kg for the walls,

Agreed. Your concerns are valid....

but the acoustician says it will make little difference through the floor.

I don't follow the logic there. Maybe ask him to explain, and give you his calculations for that.

it would obviously be desirable to minimise sound spill into the other future production rooms, so how much difference would 60kg as opposed to 35kg make in that regard?

The math doesn't lie:

TL(dB)= 20log(M) + 20log(f) -47.2
= 20Log(60) + 20Log(63) -47.2
= 35.563 + 35.986 - 47.2
= 24.349

So about 5 dB better, for the same one-third octave band centered at 63 Hz., assuming a single-leaf barrier Of course, we are not talking about single-leaf barriers here, but rather tuned MSM systems, so the increase is much more dramatic. Whatever isolation he was predicting for the 35 kg/m2 wall, I would expect an increase of about 15 dB if the system is well designed. So assuming that you were going to get 25 dB at 63 Hz before, I'd expect more like 40 dB at 63 Hz with the increased wall mass. That's pretty darn good.

The diagram shows an outer leaf but doesn't show that the entire top wall is a glass facade onto the balcony, and at 10.38mm (laminated), is only around 27kg/m2 here I'm hoping that the allocated air gap between leaves of 150mm will make up for the light density of the outer leaf on that side.

I'd need to know more about that laminated glass, but assuming that it proper uses acoustic PVB, I would expect MSM resonance at about 40 Hz, so it would isolate from about 80 Hz upwards. Is that what you want? Total TL would be about 54 dB, give or take. The isolation is good, but the frequency seems a bit high to me. Increasing the gap to 200 mm and increasing the mass to 60 kg would push that down to 31 Hz MSM F0, meaning that it isolates well from 62 Hz up. Total isolation would be about the same (56 dB), but the lower MSM would make a big difference for drums, bass, electric guitars, low keyboards, etc.

I'll just add at this stage that the plan is for the perimeter walls to be inside out modules but the partition walls (between drum room and booths) to be double walls where one side is decoupled via soundclips / hat channel.

So basically single-leaf walls? You are asking "Why is the dummy calling that single-leaf, if they have clips on one side?". The issue is not the clips: it is how you will manage to pull of the trick of combining an outer perimeter dual wall (fully decoupled) that somehow has to tie in to non-decoupled inner-leaf walls that are also outer leaf walls to each other... that's going to be interesting.... What is your plan there? How will you expose the cavities between your "partition" walls to the cavity for the outer-leaf?

The total density of both sides of the partition walls has been calculated to be only 35kg, so say 12 kg for the inside wall

So you are saying that you do not actually need any isolation at all between the drum booth and the vocal booths?

Once again the math doesn't lie: With only 17.5 kg/m2 on each side of a partly-coupled two-leaf wall done with clips, MSM resonance is about 70 Hz, so there's no isolation below about 140 Hz... and total TL is maybe 40-something. I do hope you never plan to have mics on in the booths while the drums are playing! There's going to be upwards of 70 dB of drum sound inside those booths...

Red flags.

This sounds too light to me, I would have thought 30 kg per side.

Yup! Me too...

I suppose we can always add layers later on?.....

Thus increasing the load on your floor system, which is already close to the load limit apparently.

I also note that the wall between the two booths is marked as "folding wall"... Ummm... how do you plan to make a wall movable and also isolate? How do you plan to seal the folding part air-tight? Unless you have some really good magical incantations from Harry Potter, I don't see you getting even 30 dB isolation between the booths like that. I do hope you were not planning to have, for example, a guitar cab in one booth and a vocalist in the other... for example.... Add to that drums in the booth, and the result is chaos. From that point of view, it would be better to forget the internal walls entirely, and just have one large room with a few gobos, and track the vocalist in the CR. The normal bleed between mics in such a single-room live-room setup would not be very different from the bleed into the booths, and between the booths.

I'm also really curious about what the "performers area" is, and why it needs to go in between the CR and live room / booths, totally blocking the sight lines. Is that supposed to be some type of green room? Or is that some type of secondary live room? If not, then why is it floated on the same slab as the LR and booths?

There's MANY other issues I noticed in there, but those are the ones you asked about, so I'll limit myself to that for now. You'll probably be so upset about what I already said above that you won't be interesting in getting yet more of the same about the other red flags, so I'll stop here...

I was planning on hiring a studio designer and contracting an experienced builder, but 2 lean years as well as the new acquisition has left me with less funds than I anticipated,

Studio designers aren't as expensive as you seem to think! Maybe some are, but not all of them. And the fee you pay a good studio designer is well worth it: the advice you get and the design he produces, can save you his fee many times over, just from NOT making numerous mistakes in the design, build, and tuning. In addition to getting a better studio in the end.

- Stuart -

There's MANY other issues I noticed in there, but those are the ones you asked about, so I'll limit myself to that for now. You'll probably be so upset about what I already said above that you won't be interesting in getting yet more of the same about the other red flags, so I'll stop here...

I can't resist pointing out the orientation of the control rooms (minus #3). You should have the speakers firing down the long length of the room. Also, where you have the soffit mounted speakers in #1 are in the wrong spot in the room. Along with the soffit you've drawn, you need what is often referred to as "soffit wings" in order to achieve an RFZ.

I'm a little confused looking at your layout as I'm not sure what are windows and what are doors. In #2 and #3 it appears there may be doors in the corners. Don't have doors in corners unless there is no other option.

For suite #4, that oddly shaped corner is causing all sorts of problems for you. Get rid of it.

Greg

Soundman2020 wrote:It's good to see you back again! I always wondered what the end outcome was going to be with your place. That was a smart move to buy the other offices on your same level, so you have the entire floor to yourself.

HI STUART! - I MISSED OUR CORRESPONDENCES AND AM GLAD YOU REMEMBER PLEASE SEE MY COMMENTS IN BOLD CAPITALS BELOW.

With that in mind, and even though you said the basic layout is already locked in and you don't want suggestions for changing it,... I would suggest that you change it! With the extra space, you now have so many more options for doing an amazing studio up there, without being limited to "the way it would have been" before. I realize that you are probably really desperate to get started on building, and get the place running (after having bought the original space such a long time ago), but rushing now seems to not be a smart move. There are many ways I can see of making large improvements, just from the very basic diagram you provided. You've already invested large amounts of money in this, and will still be investing many more "large amounts of money" to get it built, treated and tuned, so it just seems reasonable to do a reality check, and make sure that you really are making it the best it can be. Yes, I get it: you already put a lot of work into that design, and you fell in love with it, and you'd really hate to have wasted all that effort for nothing and start over with a clean slate... but the question you should be asking yourself is this: Is that really the best possibly layout? I can answer that question for you, but you won't like the answer... Second question: Could it be a lot better if I got some professional help to re-resign or properly? You probably wouldn't like my answer to that question either. I guess it boils down to how deeply in love you are with the current design and the emotional and mental effort you put into it, versus how good you want the studio to be in the end, after you pour all those many thousands of dollars into it... Are you willing to settle for it being merely OK, when it could be great? That's your decision, of course: your money, not mine! But once the place is finished, and you start noticing the problems, do you really want to be kicking yourself every day, and wondering how much better it could have been, if only....

please resist the urge to recommend alternative layouts

Sorry! I couldn't resist it... It's too important to resist, I think... You probably can't see it from where you are, as you are too close to the entire project, but from my perspective, as an impartial outside observer, the questions are SO very valid, they can't be ignored. There's huge potential in that space now, with the added area. You seem to not be seeing the potential, and are just focused on building something, anything, even if only mediocre at best, right now, just to at least have something to show for your troubles! My most important advice would be: take a second look at this. Take a step back, and re-evaluate.

That said, if you do decide to just stick to the proposed layout with blinkers on, there are still many large red flags waving at me from that diagram, and from what you said in your text. Big flags. Very red.... I certainly see why you came back here for a second opinion... some of your doubts and concerns are very valid. Some of those you already noticed yourself, obviously, and you are rightfully concerned about them. But there's other stuff you haven't' noticed, that is just as important.

I KNOW YOU HATE THE IDEA OF COMPROMISING, BUT ALAS WE MUST. I HAVE MY WIFE USING ONE OF THE LOTS WHILE I BUILD, AND ANOTHER PARTNER WHO WISHED TO LEAVE HIS LOT ALONE UNTIL THE DRUM ROOM IS BUILT...

First point, about "the way sound behaves when going through a wall, and then down below". The way it actually behaves is pretty simple to understand: we are talking about low frequency sound here: that's your number one concern. Not high frequencies, which travel more or less like rays or cones. Low frequencies travel roughly like a balloon being pumped up and down, or even simpler, like blowing into then sucking out of a paper bag: when you blow into it, the entire bag inflates, all sides equally, not just the side directly opposite your mouth. And when you suck out, the entire bag deflates, the same all around, not just the side opposite your mouth. The same thing happens with low frequencies after they get through a low-mass single-leaf wall. The air on the other side is like a paper bag, that inflates and deflates roughly equally, all over: directly in front of the thin wall, as well as off to the sides, and up towards the ceiling... and yes, down towards the floor too. It's a pressure front, not a ray of light. It goes out all over, roughly equally everywhere. (Remember, we are talking about low frequencies here: highs are different). So whatever sound makes it through the low mass walls and into the cavity beyond, will expand and contract as a pressure wave, not as rays or cones of sound. Thus, it will reach your outer-leaf floor.

Illustration: Set up a full range speaker on a stand in the middle of a large empty space: preferably outdoors. Play loud contemporary music through that, with plenty of bass and drums. Stand in front of the speaker, and you hear all frequencies. Now walk all around that speaker. As you move far off axis, you hear less and less of the highs and mids. When you get around behind it, all you are hearing is the lows: the highs and mids are completely gone (since they project forward, as rays and cones) but the lows are there, just as loud and strong as they were around the front. Stand up on a tall ladder right above the speaker, or lie flat on the ground with your head under it, and you hear the lows exactly the same in all directions. This effect is partly due to the baffle step issue of the speaker itself, as well as other speaker-related issues, but the basic point is still valid: low frequency sound expands equally in all directions, including down. If you have low frequency sound in the wall cavity, then it will do the same. Truck loads of suitable damping in the cavity reduces that somewhat, but there WILL still be airborne sound hitting your floor. Not to mention that the building floor slab itself is a resonant drum head, which cannot be damped.... If the resonant frequencies of that floor slab itself happen to be close to the frequencies in the wall cavity... well, use your imagination....

Add to the above: drums at 115 dBC, bass amp turned up to eleven, growling electric guitars, deep roaring keyboards, foot-stomping musicians, pumping subs.... Well, you sure do have a lot of bass energy in that cavity: Let's look at the mass-law math for a 35 kg/m2 partition, for the 63 Hz band (the low bass region).

TL(dB)= 20log(M) + 20log(f) -47.2
= 20Log(35) + 20Log(63) -47.2
= 30.881 + 35.986 - 47.2
= 19.666 dB

So the TL will be less than 20 dB for that situation. Is that enough? Only you can say. Yes, that sound is just in the cavity, and still has to make the concrete slab vibrate in order to get through to your neighbors below, and there's background noise down there too, and there's the equal loudness curves to consider.... So how much will they actually hear? Hmmm.... There's a LOT of energy going out.... Hmmmmm....

THE ACOUSTIC ENGINEER (LET'S CALL HIM THE AC) DID SHOW HIS CALCULATIONS FROM A SPREADSHEET REGARDING T/L (INCL LOW FREQUENCIES) WHICH SEEMED TO SHOW THAT DOUBLING THE MASS OF THE WALL WOULD MAKE LITTLE DIFFERENCE TO THE TOTAL SPILL FINDING IT'S WAY DOWN BELOW. HE WORKS FOR A PROFESSIONAL COMPANY AND RELIES ON THESE CALCULATIONS ALL THE TIME. I CAN TRY TO GET THEM IN A FORM WHERE I CAN FORWARD THEM TO YOU IF YOU LIKE.

the control room will not be floated, maybe just some sort of damped deck.

Hmmmm.... so you are worried about the very loud music in the live room disturbing your neighbors, but you are not worried about the very loud music in the control room disturbing your neighbors? The sound waves don't care where they originated from: just because the bass came out of the control room speakers, not the bass cab in the live room or booth, does not mean that it will behave any differently... it will, in fact, behave exactly the same. There's no difference. The bass guitar played in the LR and the resulting track played in the CR at the same level, will still travel around the building in the same way...

YOU SHOULD KNOW THAT CR LEVELS ARE USUALLY MUCH LOWER THAN DRUM OR BASS ROOMS! I HAVE BEEN MIXING IN A TEMP UNTREATED ROOM DURING THE DAYS WITH NO PROBLEM, EVEN AT 90dB. OF COURSE THIS IS WITH MY NEAR FIELDS ONLY. THE MAINS WILL ONLY BE FIRING AT NIGHT

OK, so the grey area is only 22 m2 but we have decided we need a floated floor atop a 100mm gap that has the equivalent density of 75mm concrete.

Math time again! 75 mm concrete is about 2300*.075 = 172 kg/m2. Assuming steel springs, with 15% static deflection down to 100mm, that gives you natural resonant frequency of around 4 Hz, along with the MSM resonance from the air (which is in parallel with the springs, don't forget), at around 14 Hz, so combined roughly 18 Hz resonant frequency for your floor system. Is that low enough? Hmmm.... Should be fine for impact noise, but is it OK for air-borne noise?

187 KG/M2 / 100mm AIR GAP / STEEL + RUBBER SPRING AND INSULATION / 125 mm EXISTING SLAB .... SURELY 50HZ AND OVER SHOULD BE ATTENUATED ENOUGH? THE EXISTING NOISE FLOOR DOWN TO THAT FREQUENCY WAS MEASURED AT 39 dB...

we will go instead with 6 layers compressed fibre cement boards totalling 112 mm (187 kg per m2).

Your fiber-cement board must be more dense in Australia... The nominal density for fiber-cement in most other places is normally taken to be about 1550 kg/m3, so 112mm should get you about 173 kg, not 187. Not a huge error, but 8% is 8%...

DENSITY OF THE QUOTED CFC IS RATED AT 1680 KG / M2. SOME TYPES ARE HEAVIER STILL...

The mounts will be properly engineered for the job and will be steel spring in rubber housing

I guess there must be a typo in there some place, because putting steel springs inside a rubber tube doesn't make much sense... I would suspect that you are referring to a combination isolator that has a steel sprint plus also a rubber pad of some type? Those are commonly used for floating floors: the steel spring deals with the low frequency resonance and the rubber pad (often Neoprene) deals with the high frequencies.

YES, COMBO OF STEEL AND RUBBER...

Also, fiber-cement board is brittle, and not very strong. How will you support that, prevent it from cracking, and what will the final floor surface be? You can't use the board itself as the actual floor...

SUPPORTED ON STEEL CHANNELS. I'VE BEEN SHOWN ACTUAL ON SITE PICS OF HOW THEY DO THIS. EVENTUAL SURFACE WILL BE SOME KIND OF WOOD FLOORING...

an experienced company that does many jobs where vibration is the concern,

I hope they also have experience in acoustics: vibration isolation is one thing, but full acoustic isolation is something else. I assume they gave you some type of engineering report with the predicted resonant frequency: what does that report say? What is the expected resonant frequency for the floor system? And what isolation are the predicting for the frequencies of concern for the studio? Did they give you a predicted TL curve? What is the resonant frequency of the original floor slab itself, without considering the new floating floor that will sit on top of it? That's an rather important factor here, that I haven't seen you mention yet. You say this company is experienced: Did they give you a list of other recording studios they have isolated like this, so you can contact those clients and check the outcome? Did all of those use the same fiber-cement board in a metal frames with steel springs in rubber casings? Or did the other studios use different floating floor methods? Did you actually contact those other studios, and go visit them, or at least talk to them?

THEY ARE BASING EXPECTED PERFORMANCE UPON TESTS ALREADY CONDUCTED. THEY HAVE DONE MANY FLOORS WITH EITHER CONCRETE OR CFC. PERFORMANCE IS VERY CLOSE IN THEIR OPINION.

although they assure me that their designs work equally well for airborne sound.

Ooops! Isolating impact noise and structure-borne vibration is not really the same as isolating airborne sound.

THEY ARE AWARE OF THIS AND HAVE ASSURED ME NOT TO BE CONCERNED.

It looks like we cannot hang the ceiling from the roof for structural reasons,

I suspected as much, when we first spoke a couple of years ago. That's unfortunate, but not unexpected. On the bright side, floating the entire room will likely get you better isolation than floating individual parts of it separately, and having all the weight resting on the floating floor increases the total floated mass, which is good.

So far the structural engineer has assessed a design that has the walls and ceiling weighing 35 kg per m2. Now this is my main concern at this stage... that 35kg/m2 is not enough!

I concur. Your concerns are valid. Having a floor with a surface density of 175 kg/m2 and walls with just 35 kg/m2, doesn't make a lot of sense.

You didn't mention the ceiling, which is just as important as the floor and walls, but I'm assuming it will be something similar to the walls?

YES.

How much MSM gap are you leaving for the ceiling?

100mm.

And what is the total height you have available for you, in the empty shell?

JUST OVER 3 METRES.

(floor surface to ceiling surface). Will your final inner-leaf ceiling height be sufficient for good acoustics, especially in the drum room?

NOT IDEAL - BUT STILL OK...

The acoustician has explained that 35kg for the walls and ceiling is enough mass and is proportional to the 187 kg floor mass because of the way sound behaves when going through a wall, and then down below.

Sound waves don't really understand much about "up", "down", "left" or "right". Sound waves travel pretty much the same way in all directions. I'm not at all sure what he means by 35 kg/m2 being "proportional" to 187 kg/m2.... (in fact, the proportion is only about 18%....!!!) nor how he expects that to change the way sound travels once it gets through each of those... maybe you could ask him to explain that in simple terms, or better still to show you his calculations that shows how this proportionality works, and why sound would end up moving differently in different directions. I'd be very curious about that math and the explanations, if I were you.

'PROPORTIONAL" WAS MY BAD CHOICE OF WORDS... HE DID SHOW CALCULATIONS THAT SUGGESTED ANY MORE THAN 35KG FOR THE WALLS WOULD LEAD TO AN INSIGNIFICANT INCREASE IN T/L THRUGH THE FLOOR ON THE OTHER SIDE OF THE WALL...

Remember our primary concern is that level 6 doesn't hear drums and bass, which probably means that other room in our level 7 pod will

If loud drums are going to be getting into the other parts of level 7, then what is going to prevent that from getting down through the floors, HVAC, plumbing, electrical and stairways, into level 6? I'm not following the logic here. If you have drum sounds getting out into the stairwell on level 7, for example, that's going all the way down to level 1, not just level 6.... Ditto for loud sounds getting into the building core ducts and passages. Red flags.

Now from my own research, and reading through threads on this forum, I would have guessed something closer to 60 kg for the walls,

Agreed. Your concerns are valid....

but the acoustician says it will make little difference through the floor.

I don't follow the logic there. Maybe ask him to explain, and give you his calculations for that.

it would obviously be desirable to minimise sound spill into the other future production rooms, so how much difference would 60kg as opposed to 35kg make in that regard?

The math doesn't lie:

TL(dB)= 20log(M) + 20log(f) -47.2
= 20Log(60) + 20Log(63) -47.2
= 35.563 + 35.986 - 47.2
= 24.349

So about 5 dB better, for the same one-third octave band centered at 63 Hz., assuming a single-leaf barrier Of course, we are not talking about single-leaf barriers here, but rather tuned MSM systems, so the increase is much more dramatic. Whatever isolation he was predicting for the 35 kg/m2 wall, I would expect an increase of about 15 dB if the system is well designed. So assuming that you were going to get 25 dB at 63 Hz before, I'd expect more like 40 dB at 63 Hz with the increased wall mass. That's pretty darn good.

THANKYOU FOR SHOWING THIS CALCULATION! YES, IT WOULD BE DISASTROUS TO GET THIS WRONG AT THE OUTSET, HOWEVER, DUE TO THE TYPE OF SPRING MOUNTS, EXTRA WEIGHT CAN BE ADDED ON (UP TO 20% TOTAL LOAD) WITHOUT BOTTOMING OUT...

The diagram shows an outer leaf but doesn't show that the entire top wall is a glass facade onto the balcony, and at 10.38mm (laminated), is only around 27kg/m2 here I'm hoping that the allocated air gap between leaves of 150mm will make up for the light density of the outer leaf on that side.

I'd need to know more about that laminated glass, but assuming that it proper uses acoustic PVB, I would expect MSM resonance at about 40 Hz, so it would isolate from about 80 Hz upwards. Is that what you want? Total TL would be about 54 dB, give or take. The isolation is good, but the frequency seems a bit high to me. Increasing the gap to 200 mm and increasing the mass to 60 kg would push that down to 31 Hz MSM F0, meaning that it isolates well from 62 Hz up. Total isolation would be about the same (56 dB), but the lower MSM would make a big difference for drums, bass, electric guitars, low keyboards, etc.

200mm IS TOO MUCH! BUT I AGREE THAT 60KG/M2 WILL BE MUCH BETTER, AT LEAST FOR THE PERIPHERAL WALLS. FOR THE WAY I WORK, DRUMS AND AMPS ARE NOT USUALLY RECORDED AT THE SAME TIME EXCEPT FOR GUIDE PASSES, SO I'M NOT AS CONCERNED ABOUT SPLILL B/N DRUMS AND BOOTHS.

I'll just add at this stage that the plan is for the perimeter walls to be inside out modules but the partition walls (between drum room and booths) to be double walls where one side is decoupled via soundclips / hat channel.

So basically single-leaf walls? You are asking "Why is the dummy calling that single-leaf, if they have clips on one side?". The issue is not the clips: it is how you will manage to pull of the trick of combining an outer perimeter dual wall (fully decoupled) that somehow has to tie in to non-decoupled inner-leaf walls that are also outer leaf walls to each other... that's going to be interesting.... What is your plan there? How will you expose the cavities between your "partition" walls to the cavity for the outer-leaf?

EXCELLENT QUESTION! THE AC HAS SIMILAR CONCERNS THAT WE HAVE YET TO SOLVE SINCE THE DESIGN HAS RECENTLY CHANGED. GIVEN THAT THE PERIPHERY OF THE GREY AREA MUST BE SINGLE LEAF (INSIDE OUT MODULES), WHAT WOULD YOU SUGGEST FOR THE PARTITION WALLS BETWEEN THE DRUM ROOM AND BOOTHS? IF THEY WERE SINGLE LEAF THEY WOULD NEED TO BE VERY HEAVY. DECOUPLED DOUBLE WALLS WOULD TAKE UP TOO MUCH SPACE. SO THE IDEA WAS FOR DOUBLE WALL WITH SOUND CLIPS ON ONE SIDE. I ASSUMED THERE WOULD BE SOME TYPE OF RUBBER BARRIER CONNECTING THE INSIDE DECOUPLED SOUNDCLIP WALL TO THE CORNER OF THE INSIDE OUT SINGLE LEAF PERIPHERAL WALL. IS THERE ANOTHER WAY TO ACHIEVE THIS WITHOUT COMPROMISING WEIGHT OR SPACE?

The total density of both sides of the partition walls has been calculated to be only 35kg, so say 12 kg for the inside wall

So you are saying that you do not actually need any isolation at all between the drum booth and the vocal booths?

HAHA - SOME ISOLATION WOULD BE NICE YES IF WE CAN MAKE THESE INTERNAL WALLS WORK AS DOUBLE SOUNDCLIP WALLS, THEN PERHAPS 30 KG PER SIDE IS BETTER?

Once again the math doesn't lie: With only 17.5 kg/m2 on each side of a partly-coupled two-leaf wall done with clips, MSM resonance is about 70 Hz, so there's no isolation below about 140 Hz... and total TL is maybe 40-something. I do hope you never plan to have mics on in the booths while the drums are playing! There's going to be upwards of 70 dB of drum sound inside those booths...

Red flags.

This sounds too light to me, I would have thought 30 kg per side.

Yup! Me too...

I suppose we can always add layers later on?.....

Thus increasing the load on your floor system, which is already close to the load limit apparently.

AS STATED EARLIER, THE FLOOR EXPERT ASSURES ME THAT THE SPRINGS CAN COPE WITH AN EXTRA 20% LOAD WITHOUT COMPROMISING PERFORMANCE. GIVEN THAT THE FLOOR WIL BE FAR HEAVIER THAN THE WALLS, ADDING 25KG TO THE WALLS LATER ON (IF NEED BE) SHOULD STILL BE OK...? BUT YEAH, WOULD RATHER GET IT RIGHT TO BEGIN WITH...

I also note that the wall between the two booths is marked as "folding wall"... Ummm... how do you plan to make a wall movable and also isolate? How do you plan to seal the folding part air-tight? Unless you have some really good magical incantations from Harry Potter, I don't see you getting even 30 dB isolation between the booths like that. I do hope you were not planning to have, for example, a guitar cab in one booth and a vocalist in the other... for example.... Add to that drums in the booth, and the result is chaos. From that point of view, it would be better to forget the internal walls entirely, and just have one large room with a few gobos, and track the vocalist in the CR. The normal bleed between mics in such a single-room live-room setup would not be very different from the bleed into the booths, and between the booths.

WAS LOOKING AT COMPANIES LIKE LOTUS OR HUFCOR THAT MAKE HIGH PERFORMANCE FOLDING WALLS WITH SEALS AND PASS DOORS. THEY HAVE RATINGS UP TO 45 DB (PROBABLY ONLY STC, BUT STILL...)

I'm also really curious about what the "performers area" is, and why it needs to go in between the CR and live room / booths, totally blocking the sight lines. Is that supposed to be some type of green room? Or is that some type of secondary live room? If not, then why is it floated on the same slab as the LR and booths?

PERFORMER'S AREA IS WHERE PLAYERS WILL BE SITUATED WITH THEIR HEADPHONES AND INSTRUMENTS WHILE THEIR AMPS ARE IN BOOTHS. THERE MAY BE A VOCALIST OR A PIANO OR KEYBOARD PLAYER, OR OTHER ACOUSTIC INSTRUMENT. IT IS EXPECTED THAT THE PERFORMER'S AREA WILL BE SUBJECT TO A MANAGEABLE DEGREE OF SPILL SUCH THAT A SINGER OR ACOUSTIC INSTRUMENT MAY BE RECORDED SIMULTANEOUSLY. HOWEVER, MOST OF THE TIME THE SPACES WILL BE USED SIMULTANEOUSLY MAINLY FOR GUIDES OR RUN THROUGHS (TO CHECK FOR ARRANGEMENT ISSUES ETC). ONCE GUIDES ARE RECORDED, THEN DRUMS RECORD ALONE, THEN EACH INSTRUMENT ONE AT A TIME. FOR "LIVE" RECORDINGS, I'D STILL HOPE THAT THERE WOULD BE ENOUGH ISOLATION B/N ROOMS THAT WOULD MAKE ANY SPILL MANAGEABLE...

There's MANY other issues I noticed in there, but those are the ones you asked about, so I'll limit myself to that for now. You'll probably be so upset about what I already said above that you won't be interesting in getting yet more of the same about the other red flags, so I'll stop here...

NOT AT ALL, I SAW MOST OF THESE RED FLAGS COMING, AND ITS GREAT TO HAVE SOMEONE ELSE WAVE THEM IN MY FACE IN THE END, I'LL BE HAPPY TO COMMENCE MY BUILD HAVING WEIGHED UP ALL THE WARNINGS, EVEN IF I DECIDE TO IGNORE SOME OF THEM. PLEASE DON'T BE INSULTED WHEN I SAY THAT I MAY STILL END UP NOT TAKING UP CERTAIN SOUND ADVICE. THERE HAS GOT TO BE COMPROMISES WITH THIS BUILD, WHERE THE PRIORITY IS TO KEEP DRUMS AND BASS AWAY FROM MY LEVEL 6 NEIGHBOURS WITH A DESIGN THAT HAS A PERMISSIBLE LOAD
. I'LL HAVE TO LIVE WITH THE LESS THAN IDEAL OUTCOME IN MOST OTHER RESPECTS...

I was planning on hiring a studio designer and contracting an experienced builder, but 2 lean years as well as the new acquisition has left me with less funds than I anticipated,

Studio designers aren't as expensive as you seem to think! Maybe some are, but not all of them. And the fee you pay a good studio designer is well worth it: the advice you get and the design he produces, can save you his fee many times over, just from NOT making numerous mistakes in the design, build, and tuning. In addition to getting a better studio in the end.

THIS IS OBVIOUSLY TRUE. BUT I WAS HOPING THAT BETWEEN MY AC, AND THE SOUND ADVICE FROM THIS FORUM, I CAN COME UP WITH SOMETHING THAT WILL NOT BE A TOTAL DISASTER ...

Gregwor wrote:

There's MANY other issues I noticed in there, but those are the ones you asked about, so I'll limit myself to that for now. You'll probably be so upset about what I already said above that you won't be interesting in getting yet more of the same about the other red flags, so I'll stop here...

I can't resist pointing out the orientation of the control rooms (minus #3). You should have the speakers firing down the long length of the room. Also, where you have the soffit mounted speakers in #1 are in the wrong spot in the room. Along with the soffit you've drawn, you need what is often referred to as "soffit wings" in order to achieve an RFZ.

THANKS FOR THESE THOUGHTS GREG.
#1 IS MOST IMPORTANT, AND I MAY TRY 2 DIFFERENT ORIENTATIONS PRIOR TO FINISHING INTERNAL TREATMENT. SAME GOES FOR THE OTHER ROOMS. WHAT DO YOU MEAN BY "SOFFIT WINGS"?

I'm a little confused looking at your layout as I'm not sure what are windows and what are doors. In #2 and #3 it appears there may be doors in the corners. Don't have doors in corners unless there is no other option.

SORRY, IT'S MY CRAPPY WAY OF SHOWING DOORS THAT WILL PROBABLY HAVE WINDOWS IN THEM. THE SIDE WINDOWS FOR #1 MAY END UP BEING SLIDING GLASS DOORS, OR JUST WINDOWS WITH A DOOR NEXT TO THEM... WHY DO YOU THINK DOORS IN CORNERS ARE TO BE AVOIDED?

For suite #4, that oddly shaped corner is causing all sorts of problems for you. Get rid of it.

THE PARTNER LIKES IT BECAUSE IT WILL BE HIS ROOM AND AS WE NEED THE SOUND LOCK AND VOCAL BOOTH IN THAT SPACE, HE WISHES TO NOT LOSE ANY MORE ROOM IN THERE, WHICH HE WOULD IF WE HAD A STRAIGHT WALL THERE INSTEAD OF THE WEIRD CORNER.... MAYBE WE COULD PLACE THE CONSOLE SOMEWHERE ELSE IN THAT ROOM?... ROOMS #2, 3 AND 4 NEED NOT BE WONDERFUL ACOUSTICALLY, THEY WILL BE FOR LOW LEVEL POST TYPE PROJECTS THAT CAN BE MIXED AND MASTERED IN THE MAIN CONTROL ROOM WHERE THE ACOUSTIC TREATMENT WILL BE BETTER (IF NOT PERFECT). I'VE WORKED IN LESS THAN PERFECT CONTROL ROOMS FOR DECADES AND I DO FINE...


Greg

I had a think about the wall loads and have sent off a letter outlining some revised loads to the SE. While I await his response (he's notoriously slow), I have also sent the attached diagram off to the AC. Accepting the layout for the time being, are we happier with these walls?

.... and for Stuart, you got me thinking if there is a way to create a workable junction between an RC wall meeting and inside out wall module.
The best idea I could come up with is a rubber barrier or "plug" to join the RC side to the non RC wall. Presumably this rubber barrier would also be requires to line the ceiling junction (horizontal) as well... In this instance (see attached) if both sides were 30kg each with one side RC, then surely this would perform considerably better than a single leaf 60 kg wall? Is it worth the few extra centimetres width?

Gregwor wrote:
For suite #4, that oddly shaped corner is causing all sorts of problems for you. Get rid of it.

Greg

Maybe this? (see attached)

WHAT DO YOU MEAN BY "SOFFIT WINGS"?

The "walls" that extend past your main baffles in which your speakers are mounted. These wings allow you to reflect the sound towards your back wall. Their position and angle is determined through ray tracing.

Maybe this? (see attached)

For a balanced (left and right) listening experience, the first half of your control room needs to be symmetrical. The way that wall angles, the speakers will shoot right into the angled wall and then reflect the sound back at the mixing engineer. You should have all of the sound reflected towards the back wall.

Has your acoustician friend seen your layout plan?

Greg

Gregwor wrote:

WHAT DO YOU MEAN BY "SOFFIT WINGS"?

The "walls" that extend past your main baffles in which your speakers are mounted. These wings allow you to reflect the sound towards your back wall. Their position and angle is determined through ray tracing.

Maybe this? (see attached)

For a balanced (left and right) listening experience, the first half of your control room needs to be symmetrical. The way that wall angles, the speakers will shoot right into the angled wall and then reflect the sound back at the mixing engineer. You should have all of the sound reflected towards the back wall.

Has your acoustician friend seen your layout plan?

Greg

Not yet, maybe I'll send him this re #4 (see attached):

Suite #4 is now a near perfect square. That's very very bad. The desk still isn't in the middle of the wall at which point you still lack symmetry.

Suite #1 is still oriented incorrectly. Flip the desk 90 degrees so that you're firing down the long length of the room. Also, put your door on your side wall or very front wall so that your rear wall is able to house very thick (2'+ if possible) insulation/hangers.

Your friend should be able to point all of this stuff out. There are pretty strict guidelines to designing listening rooms so all of these suggestions that have been made are based off of that.

Greg

I KNOW YOU HATE THE IDEA OF COMPROMISING, BUT ALAS WE MUST. I HAVE MY WIFE USING ONE OF THE LOTS WHILE I BUILD, AND ANOTHER PARTNER WHO WISHED TO LEAVE HIS LOT ALONE UNTIL THE DRUM ROOM IS BUILT...

You'd be surprised how much I have to compromise when designing studios. In fact, "compromise" is what it's all about! Studio design is basically just juggling a whole bunch of compromises, all at once. One of those many compromises, is getting the build sequence right so that it doesn't interfere with the operation of the studio... There's no reason to NOT include those other spaces in the design. They could, indeed, be used, and the studio could be built without messing with the need to use them until the time comes... A good studio designer can figure that out...

I CAN TRY TO GET THEM IN A FORM WHERE I CAN FORWARD THEM TO YOU IF YOU LIKE.

I'd love to see them, yes. Color me "skeptical" until then....

YOU SHOULD KNOW THAT CR LEVELS ARE USUALLY MUCH LOWER THAN DRUM OR BASS ROOMS! I HAVE BEEN MIXING IN A TEMP UNTREATED ROOM DURING THE DAYS WITH NO PROBLEM, EVEN AT 90dB. OF COURSE THIS IS WITH MY NEAR FIELDS ONLY. THE MAINS WILL ONLY BE FIRING AT NIGHT

So you are the only one who will ever be sitting at the console, pushing the faders? No other engineer will ever be in there, doing some mixing at the levels he/she likes? Most of the engineers I know want to "check the bass" every now and then, which is their secret code for pushing things to insanely high levels.... You might not do that, but many engineers and producers do. And the band will never ask you to "turn it up to eleven" so they can hear the toms pumping and the bass roaring? You've never had a band in your CR that wanted to hear their song just as loud as it was when they played it in the LR (or as loud as they think they remember it, when they rehearsed in their garage....)? You seem to be assuming that you'll never have anything over 85 dBC in the CR. I'm betting that such a restriction will be broken within very short order...

187 KG/M2 / 100mm AIR GAP / STEEL + RUBBER SPRING AND INSULATION / 125 mm EXISTING SLAB .... SURELY 50HZ AND OVER SHOULD BE ATTENUATED ENOUGH?

If your entire room was going to be 187 kg/m2 (floor, walls, ceiling), then yes: not a problem. But your walls are only 30 kg/m2. And 50 Hz is not that low: a 5 string bass goes down to 31 Hz (B0). Even for that, you'd still be fine for 30 Hz with your 187 kg/m2 setup if it was the entire room... but it ain't gonna be the entire room! Your low mass walls and ceiling... Hmmmm.... And we haven't even mentioned your HVAC silencer boxes, or your electrical system, or your windows / doors between rooms.... Hmmmm....

I know you really, really want this to work, but wishing won't make it so...

THE EXISTING NOISE FLOOR DOWN TO THAT FREQUENCY WAS MEASURED AT 39 dB...

You have 39 dBC background at 50 Hz without any isolation, in a commercial building in a major city? That's a little hard to believe: that's something like NR-5... How was that measured? And that's just one frequency.... What does the frequency spectrum look like for your background noise? Not just at 50 Hz, but from 31 Hz all the way up to 4k.

DENSITY OF THE QUOTED CFC IS RATED AT 1680 KG / M2. SOME TYPES ARE HEAVIER STILL...

I wish I could get dense stuff like that here. (I think you mean kg/m3, not kg/m2, though... ).

YES, COMBO OF STEEL AND RUBBER...

So something like this? Is that what you are talking about? Steel springs with Neoprene pads on top?

THEY HAVE DONE MANY FLOORS WITH EITHER CONCRETE OR CFC. PERFORMANCE IS VERY CLOSE IN THEIR OPINION.

I would expect the multiple layers of fiber-cement to perform a bit better than solid concrete, since there's advantages to having individual layers that can slide past each other along sheer planes. I'm curious as to why their tests don't show the expected advantage... (It's similar to the situation of gluing layers of drywall together, and getting worse performance as compared to the same layers not glued.)

THEY ARE BASING EXPECTED PERFORMANCE UPON TESTS ALREADY CONDUCTED.

You skipped over a few critically important questions, and just gave a vague generic answer, so here they are again:

1) I assume they gave you some type of engineering report with the predicted resonant frequency: what does that report say? What is the expected resonant frequency for the floor system?

2) What isolation are the predicting for the frequencies of concern for the studio?

3) Did they give you a predicted TL curve?

4) What is the resonant frequency of the original floor slab itself, without considering the new floating floor that will sit on top of it?

5) Did you actually contact other recording studios that this company has built, and go visit them, or at least talk to them on the phone?

#4 there is very important: Your existing floor right now, just as it is, already has a resonant frequency. It is a drum head: a membrane stretched over a frame. Therefore it resonates. You MUST find out what that frequency is! It doesn't matter how well the new floating floor isolates, if that existing resonant frequency happens to be an unpleasant one....

THEY ARE AWARE OF THIS AND HAVE ASSURED ME NOT TO BE CONCERNED.

Sorry to be cynical, but whenever a company I'm considering buying stuff from tells me "Don't worry about it! We got it!", that makes me VERY concerned! To me, that's a red flag right there...

I hope Greg reads this, and can tell you about his experience with contractors that told him before hand: "Don't worry about that! It will all be OK"... (Over to you Greg! )

YES.

So ceilings will rest only on the inner-leaf walls, and will be about 30 kg/m2?

JUST OVER 3 METRES.

So you will be ending up with something like 260 cm inner-leaf ceiling height? Then treatment below that?

HOWEVER, DUE TO THE TYPE OF SPRING MOUNTS, EXTRA WEIGHT CAN BE ADDED ON (UP TO 20% TOTAL LOAD) WITHOUT BOTTOMING OUT...

I thought your number one concern here was the loading on the existing structural floor? And now you are saying that if your floating floor doesn't float, you will fix that by adding even more weight?

And speaking of the existing structural floor: your springs will act on that mostly like a series of point loads... what is the plan for dealing with that? How will you spread the load so that you are not putting too much stress on just a relatively few spots?

200mm IS TOO MUCH! BUT I AGREE THAT 60KG/M2 WILL BE MUCH BETTER, AT LEAST FOR THE PERIPHERAL WALLS.

I'm not sure if you are aware of what you get by increasing the air gap, and what you get by increasing the mass. If you are looking at an imaginary TL curve, then increasing the air gap mainly lowers the resonant frequency (slides the curve to the left), while increasing the mass mainly raises the isolation (lifts the curve)... but ONLY if you increase both masses by similar amounts. If you have non-symmetrical mass distribution, meaning that one leaf has a significantly higher mass than the other, then things get a little more complex: increasing the mass on the side that has the LOWEST mass has the GREATEST effect. Increasing the mass on the side that has the most mass already, doesn't help that much...

FOR THE WAY I WORK, DRUMS AND AMPS ARE NOT USUALLY RECORDED AT THE SAME TIME EXCEPT FOR GUIDE PASSES, SO I'M NOT AS CONCERNED ABOUT SPLILL B/N DRUMS AND BOOTHS.

Then why do you have separate drum booths and isolation booths? As I already mentioned, if that's the case then it would be better to have one large LR, rather than several small ones. Small LR's sound lousy. Small rooms need stacks of treatment (which makes them even smaller...) Bigger ones sound better. It would also be cheaper, and simpler to skip all the dividing walls, windows, doors, HVAC complexity, electrical complexity, etc.

EXCELLENT QUESTION! THE AC HAS SIMILAR CONCERNS THAT WE HAVE YET TO SOLVE SINCE THE DESIGN HAS RECENTLY CHANGED.

Yup! There's a LOT of stuff that you still have to solve! Probably way more than you realize. That's just one small issue that I highlighted.

GIVEN THAT THE PERIPHERY OF THE GREY AREA MUST BE SINGLE LEAF (INSIDE OUT MODULES), WHAT WOULD YOU SUGGEST FOR THE PARTITION WALLS BETWEEN THE DRUM ROOM AND BOOTHS?

So let's see here: you have issues that a studio designer would resolve for you, but you haven't been able to resolve them, and instead of hiring a studio designer to resolve your problems, you want even more freebies from a studio designer on an Internet forum? Interesting approach to getting your studio designed...

IF THEY WERE SINGLE LEAF THEY WOULD NEED TO BE VERY HEAVY.

Right. So I would not make them single-leaf!

DECOUPLED DOUBLE WALLS WOULD TAKE UP TOO MUCH SPACE.

Are you SURE about that?

Besides, there's a well know saying that applies here: "You can't eat your cake and have it too!". You can use space, or mass. Or both. There's no magical acoustical materials that can give you 80 dB of isolation in a panel 1cm thick that weighs only 1 kg/m2... It would be wonderful if there was such a thing, but the laws of physics inside this universe prevent that from happening. So either you have to find a different universe with different laws of physics to build your studio in, or you have to live with the laws that govern this one. And the only variables that you are allowed to play with, are: mass, thickness, damping, resilience, and rigidity. There are some tricks that can combine those parameters into optimized performance, and a good studio designer can work with them to get you the best isolation, but there are limits.

SO THE IDEA WAS FOR DOUBLE WALL WITH SOUND CLIPS ON ONE SIDE.

... Which gets back to the issue of how you tie that in with the outer-leaf, as well as the structural issues, and the practical issues. If you go that route, you will paint yourself into a corner. For example, how would you manage to support the inner-leaf ceiling of a room on top of just drywall on clips? You can't do that, obviously, but you also can't support it from joists that touch the walls of the other rooms, because then you trash your isolation. And how does all of this work with your local building codes, for unsupported wall tops in tall commercial buildings? You don't have a major earthquake problem where you are, like I do where I am, but even so there will be seismic issues to deal with, and even issues from other types of building movement. Do you need seismic snubbers on your floated slab? And on your wall tops? What about your HVAC silencers, that will probably be hung from the existing ceiling? How do you tie those into the rooms, without creating flanking paths? These are all things that a studio designer would do... if you had one!

I ASSUMED THERE WOULD BE SOME TYPE OF RUBBER BARRIER CONNECTING THE INSIDE DECOUPLED SOUNDCLIP WALL TO THE CORNER OF THE INSIDE OUT SINGLE LEAF PERIPHERAL WALL.

Nope! I can't see that working. I can't see it passing code, either. Even if you could do that, it still doesn't solve the issue of coupling your wall cavities properly.

IS THERE ANOTHER WAY TO ACHIEVE THIS WITHOUT COMPROMISING WEIGHT OR SPACE?

I'm sure there is! I'm sure a studio designer would be able to come up with something. You might want to give John another try....

HAHA - SOME ISOLATION WOULD BE NICE YES IF WE CAN MAKE THESE INTERNAL WALLS WORK AS DOUBLE SOUNDCLIP WALLS, THEN PERHAPS 30 KG PER SIDE IS BETTER?

That's not the approach I would take... You need more isolation than clips can give you, and clips do take up quite a bit of space anyway, that you don't seem to be taking into account...

AS STATED EARLIER, THE FLOOR EXPERT ASSURES ME THAT THE SPRINGS CAN COPE WITH AN EXTRA 20% LOAD WITHOUT COMPROMISING PERFORMANCE. GIVEN THAT THE FLOOR WIL BE FAR HEAVIER THAN THE WALLS, ADDING 25KG TO THE WALLS LATER ON (IF NEED BE) SHOULD STILL BE OK...?

Well, did you do the math on that? Your room is 22m2, and I'll assume that it is 3m x 7m (which is only 21m2) to keep the math simple. I'll also assume walls 2.8m high. So you have 20 linear meters of wall, 2.8m high = 56 m2, plus 21 ms ceiling, for a total of 77 m2 surface area. You want to an additional 25kg/m2 to that, which implies an additional 1,400 kg load on your existing structural floor.... Didn't you say that it was already getting close to being overloaded?

Also, if you just consider pure mass law, starting with 35 kg/m2 then adding another 25 kg/m2, gives you an increase of maybe 3 to 4 dB...

WAS LOOKING AT COMPANIES LIKE LOTUS OR HUFCOR THAT MAKE HIGH PERFORMANCE FOLDING WALLS WITH SEALS AND PASS DOORS. THEY HAVE RATINGS UP TO 45 DB

And have you noticed the WEIGHT of such a system? Have you also noticed that most of those systems assume that there is a very solid, rigid, substantial ceiling above, to attach the top end to, but all you'll have is drywall on clips?

PERFORMER'S AREA IS WHERE PLAYERS WILL BE SITUATED WITH THEIR HEADPHONES AND INSTRUMENTS WHILE THEIR AMPS ARE IN BOOTHS.

If that's the concept, then don't isolate that area at all! Just put them in a non-isolated room somewhere, and make your live room even bigger. Or put them in the CR.

You don't actually have any real live room in your studio at all right now: Just a bunch of small booths, none of which is big enough to have good acoustics. They will all need to be dead, since they aren't big enough to be live. On the other hand, if you remove all the partitions between the "performer's are", the "drum booth" and the other two booth, you have a fairly decent sized live room, where you actually could track a band. Assuming you hired a studio designer worthy of the name, he would probably then tell you that after you completed that LR and the CR, then you could use the remaining spaces in the new section of the building that you just bought, to create your "performer's area" and the booths...

ONCE GUIDES ARE RECORDED, THEN DRUMS RECORD ALONE, THEN EACH INSTRUMENT ONE AT A TIME.

Pretty much the way I used to record, way back when I pretended to be an engineer... So I "get it", yes.

I'D STILL HOPE THAT THERE WOULD BE ENOUGH ISOLATION B/N ROOMS THAT WOULD MAKE ANY SPILL MANAGEABLE...

With the current plan, I would not count on that....

PLEASE DON'T BE INSULTED WHEN I SAY THAT I MAY STILL END UP NOT TAKING UP CERTAIN SOUND ADVICE. THERE HAS GOT TO BE COMPROMISES WITH THIS BUILD,

Not insulted... just frustrated. Because I can picture then way things could be, and I'm seeing a studio that you are not. It's frustrating to know that there are much better ways of doing what you are trying to achieve, but you don't seem to be interested. You seem to be focused just on what you have already decided is the one-and-only, best possible layout, and despite what other people are telling you, you are still convinced that you have a great design. I'm not at all insulted if you don't want to listen to what I have to say, or what John has to say, or Greg has to say, or what others have to say! After all, it's your money, and you can spend it any way you want! I'm not insulted if you decide to put all your cash in a big pile and burn it, or maybe shred it for compost, or use to to build what you are showing right now, or use it any anther way! That doesn't insult me at all! It frustrates me, because I can see better ways of putting the money to use, but it seems you have already decided that there are no better ways...

WHERE THE PRIORITY IS TO KEEP DRUMS AND BASS AWAY FROM MY LEVEL 6 NEIGHBOURS WITH A DESIGN THAT HAS A PERMISSIBLE LOAD. I'LL HAVE TO LIVE WITH THE LESS THAN IDEAL OUTCOME IN MOST OTHER RESPECTS...

Sorry, but I don't see the conflict here. Why does your control room have to be laid out so badly, in order to get good isolation for your drums? Why does the studio have to have clumsy traffic paths and poor sight lines, just because there's a weight limit on your floor? Why do there have to be multiple tiny rooms with poor acoustics in each, just because you want to track drums at mid-day on the 7th floor? In short, you are imagining conflicts that don't actually exist. There's no reason why you have to have a lousy, poorly functional studio just because you need to track drums on a load-limited floor. You are imposing limits on yourself, that don't have to be there, and imaging conflicts that don't actually exist. Or that don't have to be there, if the place is designed correctly.

Studio designers aren't as expensive as you seem to think! Maybe some are, but not all of them. And the fee you pay a good studio designer is well worth it: the advice you get and the design he produces, can save you his fee many times over, just from NOT making numerous mistakes in the design, build, and tuning. In addition to getting a better studio in the end.

THIS IS OBVIOUSLY TRUE. BUT I WAS HOPING THAT BETWEEN MY AC, AND THE SOUND ADVICE FROM THIS FORUM, I CAN COME UP WITH SOMETHING THAT WILL NOT BE A TOTAL DISASTER

So you'd still rather mooch and beg for freebies, instead of paying a designer to design your place properly? John is a great designer, and there are other designers here too. I'd really suggest that you contact John again, and see if you can get him interested. If you hire him, you'd get a very, very different layout than what you have now, and it would work much better.

#1 IS MOST IMPORTANT, AND I MAY TRY 2 DIFFERENT ORIENTATIONS PRIOR TO FINISHING INTERNAL TREATMENT.

That's a really, really, REALLY bad way of approaching the design for a control room! You are basically saying: "To hell with good acoustics! I'll just build any old shape and size of room that I can fit in, throw around some furniture, racks and speakers randomly, then happily end up with lousy sound and mixes that don't translate, and I really don't care, because that's what I have decided is the best way to do it!" Maybe it would be better to ask somebody who knows about studio design and acoustic response, to design your studio so it has good acoustic response?

Have you ever heard of ITU BS.1116-3? Google it. Look at chapters 7 and 8. That's what you should be aiming for. If your room does not meet those specs (or at least come close to them), then it is not a critical listening room, and hence is not a usable control room. There's a reason for every single one of those specs: some are practical, some are physical, some are acoustic, but many are psycho-acoustic. If you want to understand those specs, and what they mean, and why they are like that, then read the book "Sound Reproduction" by Floyd Toole. You'll also get to understand why your studio would be lousy if it does NOT meet those specs.

Rooms like that don't just happen magically by building any old rectangle then "maybe trying 2 different orientations"! The control room of your studio is the most important room of all. That's where the creative decisions happen. That' where the "magic" happens. How can you hope to mix sound in there, if you can't even hear it properly because the room is coloring it? How can you expect to turn out great mixes every time, if the room is lying to you?

A control room has one single reason for existing: to NOT be there acoustically! It must be neutral, transparent, flat. The number one thing that it MUST do is to transmit the sound from the speakers to your ears without altering it in any way: Not adding anything to it, and not taking anything away from it. Frankly, it's just plain laughable to expect that you can achieve that by just "maybe trying 2 different orientations". In reality, it takes weeks for an experienced designer to design the acoustic response of a control room, then weeks more to tune it once it is built. Here's an example: thread about Studio Three Productions' studio. That room meets all of those specs I mentioned, and exceeds many of them. That didn't happen by accident! And it mostly certainly didn't happen by "trying 2 different orientations". It happened through a careful process of design, and construction, and tuning. There simple is no way on this planet that you can hope to get world-class acoustic response in your control room without taking the time to design it that way. And if you don't want a world-class studio, then why are you going to all this trouble to build it?

WHAT DO YOU MEAN BY "SOFFIT WINGS"?

Red flag! BIG one! But this time, it's in your own side of the court. You are designing speaker soffits, and you don't yet know what the "wings" are, or what they do, or how to position them, or how to angle them, or why! That's a big red flag.

As Greg pointed out, your speakers are set up in a terrible layout, for oh-so-many reasons... start with being located in the room corners ( ), and angled at 45° ( ), aiming at the geometric center of the room ( ), and firing across the short axis of the room ( ), etc., etc. etc.

WHY DO YOU THINK DOORS IN CORNERS ARE TO BE AVOIDED?

Red flag! Studio Design 101, on the very first day of class, in the very first hour of instruction, you learn that room corners are sacrosanct, reserved for treatment, because that's the place where you get the biggest, bestest, most optimal performance from treatment! Room corners give your treatment at least a 12 dB boost, and probably 18 db boost. So you never, ever put anything in a corner that would interfere with the treatment, because there's no better place for it. If you can't put it in the corner, then it will have to be two to three times bigger in order to do the same job.

For this very reason I often get clients to move existing doors, and they happily do so, because it's just such a darn good idea to NOT have doors in the places where acoustic treatment works best.

THE PARTNER LIKES IT BECAUSE IT WILL BE HIS ROOM AND AS WE NEED THE SOUND LOCK AND VOCAL BOOTH IN THAT SPACE,

You do NOT need a sound lock there, because that area is not isolated from anything! And even if it were isolated, you still don't need a sound lock. That's a myth from the 1970's. Sound locks are just a wast of space, if the isolation is done correctly. Very few studios designed and built these days, have sound locks.

That's why Greg was questioning that: because it's a useless, needless waste of space that accomplishes nothing.

HE WISHES TO NOT LOSE ANY MORE ROOM IN THERE,

Then why, in heaven's name, is he wasting space by having sound lock?????

PROJECTS THAT CAN BE MIXED AND MASTERED IN THE MAIN CONTROL ROOM WHERE THE ACOUSTIC TREATMENT WILL BE BETTER (IF NOT PERFECT)

Nope. Sorry. Not with the current layout and tuning plan! The acoustics in that room will be FAR from perfect. Because you are not making any attempt to design them so that they will be perfect! As Greg pointed out, there's a very specific set of acoustic specifications that control room needs to meet (see above: ITU BS.1116-3, and other similar specs). Those are very tight specs: Very hard to meet. And if you don't meet them, they it is not "perfect", because that set of specs is the very definition of "perfect"! That's the perfect set of characteristics that a critical listening room must have, based on decades of research. That's what "acoustically neutral" looks like. Getting a room to meet that is really hard to do. Take it first hand from somebody who does it for a living, all day, every day. It's easy to write those specs on paper, but a whole different thing to design and treat and tune a room to meet them! And it does NOT happen by "maybe trying 2 different orientations"!

.... and for Stuart, you got me thinking if there is a way to create a workable junction between an RC wall meeting and inside out wall module.
The best idea I could come up with is a rubber barrier or "plug" to join the RC side to the non RC wall. Presumably this rubber barrier would also be requires to line the ceiling junction (horizontal) as well... In this instance (see attached) if both sides were 30kg each with one side RC, then surely this would perform considerably better than a single leaf 60 kg wall? Is it worth the few extra centimetres width?

That's not what I would do, no. You are only looking at one tree, not the entire forest. You are attempting to fix one small aspect of the underlying issue, without seeing all of the other aspects. You can't design a studio like that. You need to be taking the large overview of everything into account with ever single design decision you make, and you need to be checking each aspect on several levels, that you are just ignoring right now. Even if you could use rubber to do that, what characteristics would you specify for the rubber? What would the compressive modulus need to be, in order to ensure that it doesn't flank? What shape factor would you use to calculate the dynamic compressive stiffness, so you can figure out the deflection correctly, and ensure that the resonant frequency is low enough? You can't just throw any pieces of rubber in there, and hope it would do the job!

What's really surprising here is that you say you have an acoustician friend who is helping you here, yet he's not flagging the things we are. I'm wondering how much experience he has designing recording studios? It's one thing to do acoustics design for schools, shops, performance halls, theaters, factories, and offices. It's quite another thing to do it for recording studios.... Has your friend designed recording studios before? Are you showing him the same diagrams you are showing us? Even more interesting: Why are you asking us, if you have him? Hmmmmm.... more red flags....


- Stuart -

I hope Greg reads this, and can tell you about his experience with contractors that told him before hand: "Don't worry about that! It will all be OK"... (Over to you Greg! )

I have been told "don't worry" by pretty much every contractor that has worked on my place and every single one of them has screwed up royally.

Greg

I gotta say that I’m a little offended that you (Stuart) seem to think I’m “mooching” for free advice … Sheesh, I’ve seen dozens of threads where people are building much bigger projects than my tiny space, where they have been helped in fine detail through dozens of pages over several years. Am I wrong to assume that these people were receiving “free” advice? Have I given you the impression perhaps that I should be able to afford $13K for a 2 room design? Perhaps I indicated that I could afford it prior to purchasing the other office (along with my wife), but I did write in my recent return post that I’m now broke. I think I can afford materials and cheap labour, but not $13K for a design. To be honest, I cannot afford to build the main control room just yet, let alone the other Production Suites! … That’s way down the track, but thought I should show my current hopes for the future…

You bring up great points, and I’d like to respond to most of your questions, but for the short term they are just not pressing… After 2 years of mulling this over, I will build the first thing that needs building, and that is the floated room. If this sounds unacceptable to anyone, then please stop reading, I don’t wish to waste your time. The rest of the space has to happen later, many months later, so I don’t want to be distracted about details regarding the Control Room. Obviously studio design needs to take into account the whole design, which is why I provided an outline. But the exact size of the CR or it’s orientation, or the treatment, soffit wings etc can wait. You keep saying they can’t, and I keep saying they HAVE to. Here’s why, if the floated room doesn’t work, then I WILL NOT BUILD THE REST OF THE ROOMS! I will make good and resell…

So can we PLEASE restrict the discussion for the time being to be mainly about the floated room design? I can simplify things further, I’m not even concerned so much about the internal partitions for the 2 booths. I may decide not to have them. I just want to see if I can build a floating room roughly 4.6M x 4.9M (yes, almost square) to have 2.7 M ceilings inside a 3.1 M shell where one whole side is a 10.38 mm lam glass facade and the existing slab is 125mm reinforced concrete. I have done enough tests and research and have had people like you agree that 187 kg /m2 for a floating slab should suffice, provided it has the proper rubber/spring mounts and at least 100mm air gap filled with appropriate insulation. I have signed off on that and am not asking for further advice about that part. You say you need the slab's resonant frequency, but your maths can predict it, right?

I came back to the forum for some free advice (yes FREE advice! ) regarding the density of the walls and the ceiling on top of this floating floor. Naturally I’m aware that the doors and windows need to match the wall densities, but I am also aware that the walls can be less dense than the floor, and also that the ceiling can be less dense than the walls - at least in terms of T/L through the floor. I’m pretty sure John himself concurs with this. Even if this were NOT true, the structure will not allow the walls and ceiling to be 187 kg/m2. The structure has been okayed by the SE at 35kg /m2 for the walls and ceiling (including partition walls), with a “maybe” so far regarding heavier walls. All I need to do is to submit another load proposal and my SE will assess it. Unfortunately he doesn’t like to offer suggestions, he just assesses what is submitted. Hire another SE? Too late, I’ve already invested $ and time and will see the relationship through. If he assesses 60kg walls with 35 kg ceilings and says that’s too much, I then need to ask for a separate assessment.

So that is really what I’m asking. You have said 35kg is not enough, and you have inferred 60kg is much better (how about 50 kg?). I also understand there is no way for you or anyone else to give precise data as it depends on so many factors. But you do have faith in the maths, and there is a way to express what I’d like to figure out with maths where the maths would ideally be able to predict the T/L outcome through the floor for a number of different wall options, at least in laboratory-like conditions. Heck, I’d pay you or anyone to show me the maths for that one ! Particularly if you could also explain why my acoustic engineer comes to very different conclusions! I would like to think that the maths for acoustic theory is rather black or white, but it seems, unfortunately, that many engineers come to very different conclusions. For example, I built a test booth (I told you about this) very carefully with no weak spots. I gave 5 different “experts” the exact dimensions, densities as well as information regarding the air gap , mounts, isolation etc etc and I got 5 very different predictions! Even worse is that when I actually had the booth expertly tested, the results for pink noise as well as for specific frequencies were nothing like any of the expert predictions. When I reported the results back to each expert they all, without exception, blathered on about user error, or wrong method of testing etc etc.

OK, so you’d be wondering, given that I have so little faith in the “maths”, then why am I asking for it here? Well, what I did find was that, strangely, the real test figures resembled a kind of average of all the wrong predictions. So I figure if I get a few different predictions, then experience has taught me to take a punt on the average of these. Oh yes, I said “punt”, because I know that no-one can be sure when it comes to this stuff, not even you Stuart! If after all that I get it wrong, then it’s my fault entirely, and I will live with that...

With the caveat that other unknown factors will surely make predictions impossible, can anyone take an educated guess about how dense my walls and ceiling need to be, upon this floating deck, to attenuate drums and/or bass down to 39dB (no weighting - the masking background noise from level 6) ? And show the maths??

Oh, and remember to send me the bill….

Have I given you the impression perhaps that I should be able to afford $13K for a 2 room design?

13k for design of a two-room studio totaling around 65 m2 or so (as best I can estimate from your rough diagrams), seems rather steep, to be very honest! That's very much on the high side... Very...

I think I can afford materials and cheap labour,

As a point of reference on that, total costs vary by country, city, site, and complexity, of course, but as a very rough rule of thumb, based on what my clients from various places around the world tell me, a studio build in most places seems to cost around US$ 500 to US$ 1500 per square meter. The higher number is more for a ground-up studio build, starting from an empty piece of land. The lower number is for building within an existing structure where there are no major complications. Yours would fall somewhere in between. So, for a 65m2 studio, the cost in materials and labor would be something like US$ 35,000 to US$ 70,000. Those are realistic numbers. You are on the seventh floor with no elevator (it only goes to floor 6, then stairs, as I recall), so add a good delta for that complication: there's going to be a lot of labor costs in simply hauling up the materials (several tons, all hand-carried), as well as tools and equipment, plus hauling down the waste. Those costs would not apply to a ground-level build. Labor is usually about 40% of the total cost (give or take a few points), so assuming that the material-hauling and stair-climbing time adds 25% to the labor costs, that's another 10% of the total: That pushes the estimate to somewhere in the range 40k to 80k (I'm rounding liberally here). That's US$. At today's exchange rate, that works out to something like AU$ 55 k to 110 k. Those are realistic numbers, and should give you a reasonable ball-park estimate. I am not considering the floating floor(s) in there: that's just for a typical high-end studio build. You already have cost estimates for your floating floor, so add that to the above.

I'm not sure if that's what you had in mind for your budget here, but that's what it will probably cost.

I’ve seen dozens of threads where people are building much bigger projects than my tiny space, where they have been helped in fine detail through dozens of pages over several years. Am I wrong to assume that these people were receiving “free” advice?

Possibly, yes. Some paying clients do want to have build threads on the forum to document their progress. Some prefer to keep that private. You might have seen a few of those. There are also many threads where people do get help for a long time, but it's often basic help. Your case is rather specialized! I very much doubt you can point to another thread here on the forum where somebody got extensive, comprehensive, detailed help with floating an entire studio on the top floor of an office building with structural load restrictions!

You bring up great points, and I’d like to respond to most of your questions, but for the short term they are just not pressing…

And there's part of the issue! You might not think they are pressing, but you are only looking at the trees, not the forest. From your perspective, the shape and size of the control might not seem like it is in the least important right now, but from the point of view of a studio designer, it IS important... right now. Even if you won't be able to build it for a year or three, it's still important to have it designed NOW, since it has a substantial impact on how the live room(s) should be designed.

After 2 years of mulling this over, I will build the first thing that needs building, and that is the floated room. ... Here’s why, if the floated room doesn’t work, then I WILL NOT BUILD THE REST OF THE ROOMS! I will make good and resell…

I'm not sure how to explain this in more understandable terms, but that's very short-sighted. What if it DOES work? Are you then prepared to tear it down again and rebuild it, if it turns out that it just won't work together with the control room? Or would you just settle for a lousy studio?

What you are saying is sort of like you want to by a car, but you are just going to buy the engine first, and test run it to see if it works OK, then later you'll by some other random car pieces and sort of string them together with chewing gum and baling wire, roughly in the shape of a car, and then you'll rent that out to customers as a luxury limo... Sorry to be a bit over-the-top with the illustration, but that's not far off from what you are proposing. The "possible" future control room is every bit as important now as the floated drum booth, because hopefully it WILL work OK... but if there's no design for the rest, then you'd be screwed if it turned out to be unworkable when coupled with the other room... And yes, chances are it WOULD end up unworkable, because great studios don't just happen by random: they happen by design.

I have done enough tests and research and have had people like you agree that 187 kg /m2 for a floating slab should suffice, provided it has the proper rubber/spring mounts and at least 100mm air gap filled with appropriate insulation.

I do agree with that... PROVIDED THAT the walls and ceiling are also built suitably, as well as the rest of the studio. All designed to work together.

What you seem to be missing here, is that the entire studio is a system, where all the parts affect each other. You are not taking into account that whatever results you get from having JUST the booth floated, will change drastically WHEN YOU BUILD THE REST! The isolation WILL be different, because you'll be adding many more tons of mass to the same structural floor, and you'll building new walls right next to the booth walls, plus adding new HVAC ducts and silencers, and other new stuff. All of that will have SUBSTANTIAL impact on what you got with your initial stand-alone floated booth. It will completely change the resonant characteristics. And you'll never know what those new characteristics will be, UNLESS YOU DESIGN THE ENTIRE STUDIO FIRST! That's what you are not seeing here. Adding new parts to a tuned system will ALWAYS re-tune it. There's no way round that. Put a pillow inside your floor tom, or a brick inside your acoustic guitar, if you want a practical example. Adding the other rooms later WILL change the way your booth isolates.

So here's the likely scenario if you don't design it all first. You build the floated booth, and it works fine. Then you build the control room next to it, and all of a sudden you start getting complaints from downstairs.... Then what? What's your plan in that situation?

Hopefully you see the point...

You say you need the slab's resonant frequency, but your maths can predict it, right?

No. That's something your structural engineer will have to measure right now, before you even start: I can't predict that, since I know nothing about the building. I don't know where the support columns are, nor the thickness of the slab, nor the density of the concrete, nor anything else about it. Before you do ANYTHING in there, you should get that tested. It's rather important that you know the resonant characteristics of that existing slab, before you start. What happens if there's an unexpected resonance in that, which happens to be close to the way you normally tune your kick? Or close to a common note on the bass? There's no way to predict that easily. It's a lot simpler to just measure it. Your acoustician friend will know how to do that. Or your structural engineer.

but I am also aware that the walls can be less dense than the floor, and also that the ceiling can be less dense than the walls - at least in terms of T/L through the floor.

I'm not sure where you are getting your information from, but it's not correct. You seem to be assuming that the floor is the only issue. It isn't. Sound that gets out through your thin glass into the air outside, can just as easily get back in through the equally thin glass of the offices one floor down... Sound that gets out through the low-mass door can then get down the stair well, and into the offices one floor down. Sound that gets out through the HVAC duct and into the buildings service core, can then go wherever it wants in the entire building... Ditto for sound that gets out through your thin ceiling into an electrical conduit... Etc.

It would be nice if the floor was the only path that sound could take on its wat to annoy your downstairs neighbor, but that's simply not the case. There are multiple other paths that sound can take. And if you only have low-mass walls and ceiling, then there's a high probability that the sound will simply bypass your wonderful floor, and take another route.

Simple fact: isolation is only as good as the weakest link... in ANY direction. Sound is 3D, and expands in all directions equally. Once it is out of your room, then it is out everywhere.

I'm not sure how to put that in more simple terms.

Even if this were NOT true, the structure will not allow the walls and ceiling to be 187 kg/m2. The structure has been okayed by the SE at 35kg /m2 for the walls and ceiling (including partition walls), with a “maybe” so far regarding heavier walls. All I need to do is to submit another load proposal and my SE will assess it.

How about if you just ask him what the point load limit is, and what the line load limit is, and what the area load limit is? If you have to go back to him every single time you are considering a change, it's going to take an awful long time to get anywhere! n the other hand, if he would just tell you: "You cannot exceed ZZZ kg on any given square cm, or YYY kg on any given square meter, or XXX kg on any given 1m long line, 1cm wide". That would go a long way to simplifying things. Yes, it's actually rather more complex than that! For sure! But at least that would give us some maneuvering room, and he can then do his number crunching just a couple of times, based on probably designs.

If he assesses 60kg walls with 35 kg ceilings and says that’s too much, I then need to ask for a separate assessment.

All of that is resting on the floated floor, and the floated floor is resting on several springs, which are basically point loads on the structural floor below. Or maybe small area loads, if there's some type of base pad there to spread the load. So, all you need to get from him is the maximum permitted point load on any given spring base. That's it. For example, if each spring is going to rest on a 10cm x 10cm steel plate, then all you need to know is: what's the maximum load that you can put on each plate, regardless of where it is located on the floor? (In other words, the worst-case load limit) And also: What's the total weight that you can have spread across all such plates? He'll probably also need to tell you what the minimum distance is between such plates, and that's fine.

So that is really what I’m asking. You have said 35kg is not enough, and you have inferred 60kg is much better (how about 50 kg?). I also understand there is no way for you or anyone else to give precise data as it depends on so many factors. But you do have faith in the maths, and there is a way to express what I’d like to figure out with maths where the maths would ideally be able to predict the T/L outcome through the floor for a number of different wall options, at least in laboratory-like conditions.

You are asking the impossible, because you are not considering the full picture! I can't predict unknowns, base on other unknowns. Nobody can. I'm not a prophet. If I told you that your floated drum booth in the middle of the empty space up there, with nothing around it for several meters in each direction, was going to isolate 58.35 dB to the rooms below, that might be right. But as soon as you build another wall inside the same space, close to the booth, everything changes. The isolation might now only be 49.219 dB, or it might be 64.985 dB.... there's no way of knowing, because that wall has not been designed yet! It's the control room wall, and since you don't want to design the control room yet, there's no way of knowing WHAT effect it will have on the drum booth isolation.

That's the point you seem to not be getting here: anything you do to the studio AFTER you build the drum booth all by itself, will CHANGE when you build something else next to it. In what way will it change? There's no way of knowing unless you design it first. I can estimate the resonant frequency of a wall if I know how it is built, but if there's no information about that wall, then there's no way to predict it.

Maybe your structural engineer can convince you of this. He's already done the floor load calculations for your current scenario, with just the drum booth. Ask him if he would need to change anything if you decided to install a 10 ton concrete block on the floor right next to the drum booth...

I would like to think that the maths for acoustic theory is rather black or white,

It is... if you know ALL of the variables! Maybe not exact, but close. But the more variables you add, the more uncertainty you add too. It's dead easy to calculate the resonant frequency of a weight bouncing up and down from a spring: that's a SDoF case (Single Degree of Freedom). Now add a second weight hanging below the first, and you have 2 DoF... that's more complex. Ad yet another weight hanging from yet another spring below the first two, and it gets even more complex. There are now SEVERAL resonances, not just one, so there's no simple answer! If you ask me what the resonant frequency of the first case is, I can give you a very accurate answer, but if you ask me for "the resonate frequency" of the last case, I can't give you an answer, because there is no single resonant frequency! I can give you a set of frequencies, and that set can be very accurate again, but since it is now a complex system, they change over time... Add yet another motion to the system, such as nudging the first weight to the left as it also bounces up and down, while also nudging the second weight to the right, and putting a bucket of water under the third weight, so it dips in a bit each time it reaches the bottom of its travel... and things get REALLY complicated!

The point being that, as things get more complex, so do the answers. You might not get the answer you are expecting, simply because you are asking the wrong question! If you look at that last hypothetical system, with three weights all bouncing up and down on springs AND ALSO swinging sideways AND damping on one of them, and you ask three different engineers "What's the resonant frequency of that system", you might well get three different answers. And they would all be correct, because each of them understood your question in a different way. Maybe one gives you the lowest frequency of any part of the system that is bouncing up and down, while another gives you the frequency of the overall pendulum swinging, an the third guy gives you just the damped resonance of the lowest weight.... all are correct, but all are different.

Yes, I do get that you just want to know "How much sound is getting from my drums into the office below?", and you think that's a simple question, but it isn't. There are way, way more variables involved here than just three weights bouncing and swinging on springs!

So, yes: you might well get different answers from different people, but it's entirely possible that they are all correct.

However NONE of them can be correct if they don't have all the data. Such as knowing how heavy the control room will be, and how massive the walls will be, and how far away they will be from the drum booth walls, and what type of insulation will be in the cavity, and how much of that cavity will be filled, and, and, and, and.... (If you really want to go to extremes, then you'd even need to know the air temperature and humidity, to be more accurate...)

but it seems, unfortunately, that many engineers come to very different conclusions.

Yup! See above: they might all be correct.... or they might all be wrong, if that data is incomplete, or erroneous.

For example, I built a test booth (I told you about this) very carefully with no weak spots. I gave 5 different “experts” the exact dimensions, densities as well as information regarding the air gap , mounts, isolation etc etc and I got 5 very different predictions! Even worse is that when I actually had the booth expertly tested, the results for pink noise as well as for specific frequencies were nothing like any of the expert predictions. When I reported the results back to each expert they all, without exception, blathered on about user error, or wrong method of testing etc etc.

And the ones who complained about wrong method of testing are the ones you should have listened to! Your method is flawed. Pink noise is NOT a good way of testing isolation for a drum booth! Drums are all transients, not steady-state. Drums are impact noise AND resonance, with rapidly fluctuating levels. Nothing at all like pink noise. Even the spectrum is different. Way different. Pink noise has equal energy per octave. Drums most certainly don't. And it's really hard to use pink noise for isolation measurements in the real world anyway, because pink noise sounds exactly like background ambient noise...

I would agree with the guy that said your method was flawed.

can anyone take an educated guess about how dense my walls and ceiling need to be, upon this floating deck, to attenuate drums and/or bass down to 39dB (no weighting

You are starting with a flawed question! How can anyone predict that, when you specifically state that the target level is 39 dB, but without specifying weighting! That's like going to the grocery store and asking for 39 kilograms, but not telling the what type of produce you want! Is that 39 kg of grapes, or 39 kg of mushrooms, or 39 kg of watermelon? You at least have to specify the units that you are using. Do you want the level in the target room to be 39 dBC, or dBA, or dBZ, or something else?

You also have to define "bass". Are we talking about electric bass guitar, which is pretty much pure single tone sine wave, and steady state... or are we talking kick drums and floor toms and snares and crash cymbals, which are impact, transient, resonant, with multiple frequencies all at once, and very far from steady state?

Also, what's the starting level in the source room? If this is an electric bass guitar, what's the SPL level, and what note is it playing? It might be 31 Hz, at 50 dBA, or it might be 196 Hz at 100 dBC?

It would be a lot easier to give you an answer for a specific situation, such as "6 string bass playing an open E1 at 80 dBC measured 1m from the speaker, aiming for a level of 39 dBC at the same frequency in the target room". That can be calculated. But "... attenuate drums and/or bass down to 39dB (no weighting" is actually a meaningless question... There is no answer to that, because the question is not valid.

Off topic: I would not be too worried about a level of 39 dBC at 31 Hz .... But I would be concerned about a level of 39 dBC for 500 Hz!
Mssrs Fletcher and Munson can probably explain why that is...

Oh what the hell, ... let's give your badly flawed question a stab anyway, (with caveats)! What is the surface density and thickness of your EXISTING structural floor? That's one parameter I don't have. And the resonant frequency of that floor, too. And the same for the existing ceiling, and the existing walls around where the drum booth will be. Give me those, and I'll give you a very rough and very inaccurate answer.

- Stuart -