Warehouse Studio Conundrum

tardishead · Post by **tardishead** » Mon Nov 30, 2015 9:05 am

Hi all. Before I post a detailed design I wanted to ask some advice on how to deal with a certain situation. I am throwing ideas around at the moment as for an overall construction method.
I am based in London. I have access to a warehouse in which I would like to build myself a control room and build 2 extra rooms that are isolated that can be used for mixed media - potentially live room, or mix room, or both. I have 10k UKP for budget at the moment but I am a pretty decent builder/carpenter and have plenty experience in the labour side of building studios. Also I have 4 very heavy sound doors and frames which will help greatly.
The warehouse has nice thick walls about 300mm but unfortunately the ceiling is the weak link. It is thin metal panels and has 4 large skylights which are only made of 18mm transparent plastic. But I would like to keep the skylights so that people can have a natural light section/lounge area to use as well. In studios with no natural light this creates a nice facility. This area also has drains which need to be available to access in case of emergency and on top of that fire safety has stated that there needs to be separate access to all rooms. So therefore I have decided that this part of the space is not right for building and would be better used as a recreational area.

warehouse studio SHUFFLE6.jpg

Ceiling height 3650mm is available height before large steel beams which hold up an apex metal roof peaking about 6m total height.

So building three rooms with isolated stud walls and ceiling would not be a problem - and would provide isolation from each other I understand that. However ideally when outside in the lounge/corridor it would be great if the noise from each room was attenuated enough as to not be unpleasant for those occupying the recreational corridor space. To achieve this I need another leaf that encloses all 3 rooms.
At this point a word about the outer building leaf. I don't consider this to be a valid outer leaf because of the ceiling which essentially nullifies it acting as a leaf. There are plenty of air gaps in this outer leaf and there is a lot of space between it and my proposed renovation building. Ceiling starts 2m above the 3 proposed rooms and the outer wall on the other side of the recreational corridor is another 2m as well. It is an industrial area but pretty quiet. I have experienced the room which has been used for storage for some time and the loudest noise is definitely the rain hitting the metal roof.

So the outer leaf which will enclose the three rooms: Ok so I think the best way would be to build completely independent stud walls and separate ceiling from the 3 studio rooms. The ceiling and walls could be attached to the building's masonry walls acting as the same leaf. But doing this way - especially the ceiling - would be very expensive and time consuming. Also 2 lots of 9x2" joists one under the other would considerably reduce the available ceiling height. So I wondered what can be achieved with one layer of stud and joist carcassing? At this point I wondered about using resilient clips - genie clips or Isomax? I have experience of using Isomax before and although at first intimidating it just takes a bit of application and attention to detail.
So I would separate the 3 rooms as usual with separate stud walls but the walls being close enough so that on the outside of these stud walls I could join the plasterboard layers so they join together to present one overall surface/leaf.

So considering the isolation between adjacent rooms. 2 layers plasterboard/resilient clips/studs/insulation/gap/insulation/studs/resilient clips/2 layers plasterboard. Now I could not find any data on this wall construction. But I would presume that this behaves like a separate 2 stud wall construction which can have a STC of 69. I have read that there is no gain to adding resilient clips either side of an already separated wall construction but the clips would be used for the purpose of isolating the inner leaves form the outer leaves in my case. Is there any reason why clips might compromise this double stud wall construction and isolation between the studio rooms themselves?
Also would there be a problem if all the outer leaves were joined together. Can sound from one room excite the outer leaf and be reflected back into another room? I presume not because all studios are built this way that is with a constant outer leaf. Surely the important aspect is that the inner plasterboard layers are decoupled from the the stud walls?

Now consider the isolation between the studio rooms and the recreational/corridor area. In the performance tests on the Genie Clip website it states 2 layers plasterboard/clips/stud with insulation/2 layers plasterboard can give STC of 64. 80HZ 30DB TL 100HZ 39DB TL.
So unless someone can tell me how badly I have thought this through it would seem to me with this approach I can create double stud levels of isolation and low frequency performance between studio rooms themselves; and ok but not quite as good isolation between the rooms and the recreational area outside.

Soundman2020 · Post by **Soundman2020** » Mon Nov 30, 2015 11:45 am

You seem to be missing some of the concept here: With "room-in-a-room" construction, you have ONE SINGLE outer leaf that encloses ALL of the individual rooms, each of which consists of just one single inner-leaf. You do NOT need a separate outer-leaf for each room. That will cost a huge amount extra, and produce worse isolation.

So in your case, all you need to do to complete the outer leaf, is this:

tardishead-fixed.jpg

You would also put a ceiling on top of that new wall, completely enclosing the three rooms, and you'd be done!

Yes, each inner-room would have its own ceiling, which would also be a single-leaf, just like the walls.

but unfortunately the ceiling is the weak link.

Right. That's why you'd be building a new ceiling across all of the rooms. Fortunately, you have plenty of height to work with, so that won't be too much of a problem. Technically, you would have a 3-leaf roof, but the third leaf (tin) would be so far away as to not be a problem.

So building three rooms with isolated stud walls and ceiling would not be a problem - and would provide isolation from each other I understand that.

There will only be isolation of you enclose all three of them with an outer leaf, as per the diagram above.

However ideally when outside in the lounge/corridor it would be great if the noise from each room was attenuated enough as to not be unpleasant for those occupying the recreational corridor space.

That's what the above wall accomplishes: It completes the "envelope", fully enclosing all three rooms, and thus creating a proper 2-leaf MSM system for each room.

To achieve this I need another leaf that encloses all 3 rooms.

Correct. But you only need ONE SINGLE leaf here that surrounds ALL of the rooms. Not a separate one for each.

I don't consider this to be a valid outer leaf because of the ceiling which essentially nullifies it acting as a leaf.

No, it does not nullify it: it merely means that you'd have a 3-leaf system, which is tuned differently from a 2-leaf system, but since you would set the distance between the tin "outer" leaf and the new "middle" leaf to be large, and the mass on the outer leaf is so low, the 3-leaf effect would be minimal. For all practical purposes, it would still act like a 2-leaf system.

There are plenty of air gaps in this outer leaf and there is a lot of space between it and my proposed renovation building

Excellent! Even more reason why it would not have much effect.

Ok so I think the best way would be to build completely independent stud walls and separate ceiling from the 3 studio rooms.

Exactly: A single stud frame wall, enveloping all 3 rooms, with drywall on only one side of that framing, is what you need. Ditto for the ceiling. One single unit that covers all three rooms.

The ceiling and walls could be attached to the building's masonry walls acting as the same leaf.

Correct. That is indeed the right way to do it.

But doing this way - especially the ceiling - would be very expensive and time consuming.

Why? It's just a simple stud frame! Not hard to do at all. Why do you say that it would be expensive and complicated? Even working all by yourself, you could have that framing up in a couple of days, and drywall on it in another few days. If you have a couple of helpers, it would go even faster. I don't see why this is "expensive and time consuming". Especially considering that there is no other way to do it!

Also 2 lots of 9x2" joists one under the other would considerably reduce the available ceiling height.

Why ? Why do you need such large framing members for the inner-leaf ceilings on the rooms? Youd' only be spanning something like 4m, nax, so it would be possible to do that with 2x6 even. Why do you need 2x9? That might be needed for the outer-leaf, depending on spam, but NOT for the individual inner leaf-ceilings.

And what's the problem anyway? You have 3650 mm to play with! So what if you lose a foot or so? You still have more than enough height to have very decent rooms. If you build the inner-leaf ceilings "inside-out", then from the acoustic point of view you'd only lose about a foot in total (assuming you really do need 9x2 joists for the outer leaf. However, I don't see it that way: Assuming that you need to span 5m for that, I don't see why you'd need 9x2s: 2x8s would seem to do the trick, assuming reasonable parameters. So if you place the new outer-leaf ceiling at 30cm below the tin, then acoustic height of your inner-leaf ceiling could still be 3100 mm (assuming you build it inside-out). That's plenty high, unless you have some unusual requirements. Even allowing for the 2x6 inner joists, the visible ceiling would still be above 2.9 meters. That's way higher than most houses today.

So I wondered what can be achieved with one layer of stud and joist carcassing?

I don't understand the question: that's exactly what we are talking about so far! One single stud wall surrounding all your rooms, with a single-joist ceiling on top, all sheathed on only one side of the framing. There is no simpler way of doing it.

At this point I wondered about using resilient clips - genie clips or Isomax?

Once again: Why? How? Where would you put those, and what would the purpose be? If you have a proper 2-leaf system, then you don't need clips. Once again, you are greatly increasing your costs unnecessarily, for no perceivable reason, and perceivable benefit.

So I would separate the 3 rooms as usual with separate stud walls but the walls being close enough so that on the outside of these stud walls I could join the plasterboard layers so they join together to present one overall surface/leaf.

I'm not sure I understand what you are saying there: Why would you go to all that expense, trouble and complication, in order to get less isolation? Why not just go the easy way? That sounds for all the world like you are proposing to build a complex system of interconnected three-leaf walls...

2 layers plasterboard/resilient clips/studs/insulation/gap/insulation/studs/resilient clips/2 layers plasterboard.

And yet again, I ask the same question: Why would you do that? If your frames are decoupled, then why go to all the expense, time, and complication of using clips plus hat channel in addition to the isolated frames? What for? What do you hope to gain by that?

Now I could not find any data on this wall construction.

Probably because it makes no sense?

I very much doubt that an acoustic lab would go to the trouble of testing something that makes no sense in theory, and has no purpose in practice.

But I would presume that this behaves like a separate 2 stud wall construction which can have a STC of 69.

I very much doubt it, and there's not way to know unless someone has tested it. You cannot extrapolate the performance of a complex interconnected 3-leaf wall from a simple 2-leaf wall. There is no logical connection between the two, and no mathematical model for even predicting it. If you want to know how such a wall would perform, you'd have to pay an acoustic lab to build one inside their test facility, and test it for you.

Also, STC is a really lousy way of measuring sound isolation for music. The following quote comes from ASTM-E-413, which is the STC specification itself. This is what STC says about STC:

ASTM E 413 – 04
Classification for Rating Sound Insulation

4. Significance and Use
4.1 These single-number ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television, and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling allies, power transformers, musical instruments, many music systems, and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands

In other words, you should never use STC ratings for deciding on studio isolation, since it is basically meaningless, according to STC spec itself!!!

I can build you two different walls, both rated at STC 50, but one of them will be 30 dB better at isolating the complete audio spectrum than the other.... That's a huge difference! One thousand times more energy blocked, three orders of magnitude in intensity reduction, eight times better subjectively... but both walls have the exact same STC rating.

STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio. The ONLY way to determine that, is by look at the Transmission Loss curve for it.

I have read that there is no gain to adding resilient clips either side of an already separated wall construction

Correct.

but the clips would be used for the purpose of isolating the inner leaves form the outer leaves in my case

Not the way you described it! You described two separate frames, each with drywall on only one side, plus clips...

Also would there be a problem if all the outer leaves were joined together.

What is "all outer leaves"???? There is only ONE outer leaf here, not multiple. There is one single "shell" that encloses all three inner-leaf rooms. It is that simple.

It sounds like you want to build a separate "outer-leaf" around each of your rooms, but that makes no sense at all. What are you hoping to save by doing it that way? In reality, you would double your total costs, at least, and that's just in materials, without considering labor.

I don't understand why you want to complicate things so greatly, increase your costs enormously, slow down construction considerably, and end up with a poorer solution: I can't understand the motivation behind that.

So unless someone can tell me how badly I have thought this through it would seem to me with this approach I can create double stud levels of isolation and low frequency performance between studio rooms themselves;

No you cannot, because you would have four-leaf systems between the individual rooms, thus greatly reducing your low frequency isolation. People often assume that if one-leaf is bad, and two-leaf is good, then three-leaf must be better and four leaf must be fantastic. It does not work like that. Three-leaf is actually worse than two leaf, all other factors being equal, and four leaf is even worse than that: The issue is "resonance". Resonant systems are not intuitive, and can do things that you never would expect. Such as trashing your low-frequency isolation...

If you absolutely have no choice, and must do a 3-leaf system at some point, then you can compensate for the lost isolation by adding more mass to all leaves and increasing the air gap, but that costs extra money and extra space. You would also have to extend that increased mass and increased air gap up to the new outer-leaf ceilings, in order to maintain surface density and MSM resonant frequency, thus complicating matters even more (and increasing expense even more).

The ONLY way to get good isolation at reasonable cost is to build a simple, basic fully-decoupled two-leaf system. There is no cheaper way than that. Anything else is going to either cost you a lot more money, or isolate a lot worse. Or both.

Two other things: the shape of your control room is rather strange, and wont' work very well, and you do not need to splay the walls of your rehearsal rooms like that: that's a myth. You are wasting space and complicating construction, for no acoustical benefit. Just make your two rehearsal rooms rectangular, and install proper treatment, and make your control room a ore conventional shape, to optimize acoustics and isolation, and minimize cost. You are on a very, very tight budget anyway, so you can't afford to complicate anything in any way.

- Stuart -

tardishead · Post by **tardishead** » Mon Nov 30, 2015 8:57 pm

Thanks for your reply Stuart
Actually you have misunderstood me completely. The outer leaf system which you describe is exactly what I perceived - not a 3 leaf or 4 leaf system. I just wondered if this could be achieved with one stud wall/ceiling with the inner leaf decoupled from the structure with resilient bars or clips but of course this would never be as good as a double stud wall. Anyway you're right theres no point in experimenting - 2 separate wall system is totally the way to go. Its a no brainer.

STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio. The ONLY way to determine that, is by look at the Transmission Loss curve for it.

Yes I'm well aware of that. I am just referencing IR761 from NRCC. Look at the best STC figures and then check the low frequency performance. Double stud wall STC 69 . 26.7db TL @50hz 39db TL 100HZ
Out of interest what are the most economical options for improving the transmission loss for a double stud wall? Greenglue?

Two other things: the shape of your control room is rather strange, and wont' work very well, and you do not need to splay the walls of your rehearsal rooms like that: that's a myth. You are wasting space and complicating construction, for no acoustical benefit. Just make your two rehearsal rooms rectangular, and install proper treatment, and make your control room a ore conventional shape, to optimize acoustics and isolation, and minimize cost. You are on a very, very tight budget anyway, so you can't afford to complicate anything in any way.

Not rehearsal rooms. Project studio rooms - most likely mixing programming and some live recording. Occupants might change over time. Splayed the walls 6 degrees to take flutter out of the equation. Ratio 1:1.3:1.9 . Then I planned to put about 500mm hangers/bass trapping on the back wall of each. Possibly some diffusion in front of bass trapping. Using stand mount near field monitors would make front wall absorptive and create basic reflection free zone with broadband absorbers on first reflection points. Ceiling cloud. With splayed walls at least part of the room will remain more live without the need to put up absorbers to control flutter. Is my logic really that unsound?

the shape of your control room is rather strange

Ok so with the corridor I have to keep the 3 rooms will be about 200 SQFT each - can't really go over that. I've messed around with some RFZ designs which tend to be shorter and fatter and I don't have the square footage to build along the length of the unit without making the mixed media rooms smaller. I want to make the other 2 rooms at least 200SQFT and so unfortunately I don't have enough space to build an RFZ room that would be large enough for my needs. The more typical RFZ designs tend to suit closer to 1:1.44:1.66 (one of Wes Lachots favourites) ratio and from all the examples I have seen on the web the smaller ones are populated with minimal gear and racks etc. Now I have a lot of large format analogue rack equipment and a large console. I need length in order to fit all the gear in and people and couches etc. My design is based on 1:1.3:1.9 like the other rooms. Planned putting 500mm hangers behind couch as well.

warehouse CR 1.jpg

warehouse CR 2.jpg

Realistically there will be more low racks either side of the couch, either side of the desk and under the desk as well. I'm an outboard nut!
Really that bad? So I made the front half of the room a bit fatter to try implement a RFZ style room but had to taper in the back end of the room in order to fit into the available space beside the unit entry door and also so the width averages out at the same ratio and eliminates flutter. Is there any reason why this would sound bad? Speakers are ATC SCM150 passives. As shown would like them to be soffit mount. Opinions vary on how big the room needs to be to accommodate them but the ATC design engineers themselves have told me 200 SQFT is fine just ensure a lot of trapping. I kinda wish I had smaller speakers but I bought them very cheap quite a few years ago and I absolutely love them. I never listen to them very loud but the mid range is unbeatable and the freq range is amazing. Speaker angles are 30 degrees. Listening position is 38% length from speaker to end wall (behind trapping). RFZ is not huge I know.
Love to see/hear some other suggestions.

Soundman2020 · Post by **Soundman2020** » Tue Dec 01, 2015 2:10 am

Actually you have misunderstood me completely. The outer leaf system which you describe is exactly what I perceived - not a 3 leaf or 4 leaf system. I just wondered if this could be achieved with one stud wall/ceiling with the inner leaf decoupled from the structure with resilient bars or clips but of course this would never be as good as a double stud wall.

From that comment, it looks like I did, in fact, understand you perfectly!

Let me try again: the outer leaf is NOT a double stud wall! The outer leaf is a SINGLE stud wall. It does not have any drywall on the other side of the studs: it has drywall on only ONE side if the studs. That's it. That's all. That is the complete, entire, finished outer leaf. Nothing else at all.

Inside of that, each room is also built as a single-stud frame, which also has drywall on only one side of it, never on both sides.

This is the concept:

MSM-two-leaf-WallChunk-conventional-.png

That's for "conventional" construction. If you were to do the same thing using the "inside-out" construction technique, then it would look like this:

MSM-two-leaf-WallChunk-inside-out-.png

Both of those cases, that represents exactly your situation. The single-leaf wall across the front completes the outer-leaf shell around the three rooms, and each of those is built as a single-leaf wall.

Since you say that this is exactly what you were describing, please explain where you wanted to put the RC and additional drywall on this, because I'm not understanding what you are trying to say. Any place you put it would make it into a 3-leaf or 4-leaf system.

Project studio rooms - most likely mixing programming and some live recording. Occupants might change over time. Splayed the walls 6 degrees to take flutter out of the equation.

... and thus wasting valuable floor space! Once again, it is a myth that you need to splay walls: since flutter echo is easily dealt with using wall treatment, and since you will need wall treatment anyway, regardless of what the room will be used for, there is zero need for splayed walls.

Ratio 1:1.3:1.9

Ratios only apply to rectangular rooms. If you angle one of more of your walls, ratios are no longer valid for calculating modal behavior. Standard calculators only work for perfectly rectangular rooms. If your room is not rectangular, you will need FEM/FEA software to do that, plus an operator who knows how to set teh boundary conditions correctly for acoustical calculations, and who knows how to interpret the results.

In any event, 1:.3:1.9 is Louden's second ratio, it is outside the Bolt area, and it fails one of the three basic tests for usability as a critical listening room ( 1.1w / h < l / h < ((4.5w / h) - 4) ). You might want to rethink that.

Then I planned to put about 500mm hangers/bass trapping on the back wall of each.

That would be a start, but you'll need a lot more bass trapping than that in such a small room. You will need large traps in several of the twelve corners, and since some of them are concave (due to the splayed walls) those will need even larger traps.

Possibly some diffusion in front of bass trapping.

The room is too small to be able to use numeric-based diffusers, such as Schroeder, Skyline, QRD, BA, etc. According to Cox and D'Antonio, the spatial and time-domain lobing artifacts are too great within ten feet of such diffusers regardless of tuned wavelength, and at least three times the lowest tuned wavelength. So no listening position should be within ten feet of a diffuser anyway, no matter how you tune them. Since your rooms are only 16 feet long, that leaves only a very small part of the room where you could be more than ten feet away... So you don't really have the option of using those diffusers. In any event, in such a small room, diffusion doesn't really happen: there can be no statistically valid diffuse sound field in small rooms. You could maybe do some randoms scattering, but that's about it.

Using stand mount near field monitors would make front wall absorptive and create basic reflection free zone with broadband absorbers on first reflection points.

You cannot create an RFZ room using absorption. The basic concept of RFZ is that the room geometry itself creates the RFZ, not things inside it. And since absorbers, by definition, do not reflect, it is impossible to use absorption to do that. If you want an RFZ room, it has to be designed as an RFZ room, by correctly placing the reflective surfaces at the front and sides of the room, and the absorptive treatment at the rear of the room.

With splayed walls at least part of the room will remain more live without the need to put up absorbers to control flutter. Is my logic really that unsound?

You will need 483 sabins of absorption in that room to bring it within ITU and EBU specs. That's nearly 500 square feet of perfect absorption. The entire surface area of the room is roughly one thousand square feet. Therefore roughly half of the entire surface will need treatment. Discounting the floor (you probably don't want to be walking on a porous absorption floor!

), you only have 800 square feet left, so two thirds of the walls and ceiling will need treatment. If you do an RFZ design, then the front wall is, by definition, not absorptive, so you lose another 125 square feet. You are down to under 700 square feet of available surface area, so most of it is going to be covered with treatment. If you wanted a room that is more live than ITU specs, you could leave off maybe 20% of that, but that's still a lot of surface area.

So yes, your walls will, undoubtedly need a lot of treatment, meaning that flutter echo will not be a problem anyway. By splaying your walls, you are trying to deal with a problem that won't even be there. And since a room with splayed walls has lower volume than one without, you are actually increasing the amount of absorption you need by splaying your walls...

If you want part of the room to be more live, then reduce the coverage area in that region while increasing it elsewhere, and "checkerboard" the treatment to ensure that there is no flutter while still keeping it live. Or do slot walls in that area.

Ok so with the corridor I have to keep the 3 rooms will be about 200 SQFT each - can't really go over that

200 square feet of floor area is fine for a control room. ITU and EBU specs call for a minimum of 215, but at 200 you are still fine. Not a problem. And floor area is not the issue: it is the shape of the room that is an issue.

I've messed around with some RFZ designs which tend to be shorter and fatter

RFZ rooms do not necessarily need to be short and fat: they can be if you want, but the can also be long and thin. There are several ways of getting there.

I want to make the other 2 rooms at least 200SQFT and so unfortunately I don't have enough space to build an RFZ room that would be large enough for my needs.

Yes you do! John has built RFZ-type rooms inside a shipping container!!! I have built RFZ-type rooms in far less than 200 ft2. It can be done. Just not like you are trying to do it. Your basic premises are not correct, and the design you show is not for an RFZ room anyway.

ONLA--V2323-CR.png

This is a true RFZ-type room in about 200 square feet, and it includes a Hammond organ with Leslie, and a full-size vertical piano, plus a client seating area. That's one I designed for a customer in the USA a couple of years back, and it works just fine. I have also designed true RFZ rooms even smaller than that, which also work fine, but I don't have the owner's permission to show them in public. But believe me, it can be done.

The more typical RFZ designs tend to suit closer to 1:1.44:1.66 (one of Wes Lachot's favorites) ratio and from all the examples I have seen on the web the smaller ones are populated with minimal gear and racks etc.

Not true. see the case above. Even with the organ, Leslie unit, piano sofa, side tables, et. al. there is still plenty of room for other stuff. Not visible in that image is the rack gear installed under the desk. And the above room is closer to Sepmyer 1, if you really wanted to look at it in terms of room ratio. But once again, room ratios are not valid for rooms that are not rectangular, and by definition RFZ rooms cannot be rectangular.

Now I have a lot of large format analogue rack equipment and a large console.

How large? I have done a room in 140 square feet based around a Mackie 32.8. That's a 32 channel, 8 bus console, analogue. It can be done.

I need length in order to fit all the gear in and people and couches etc.

Fine! Then make it longer and thinner, but still do it as RFZ. There's no problem with that.

Planned putting 500mm hangers behind couch as well.

The room shown above does indeed have 50mm hangers behind the client couch. As does the 140 square foot room with the giant Mackie console...

So I made the front half of the room a bit fatter

... which implies that the rear of the room is thinner!

Small control rooms should NEVER be narrower towards the rear! That creates issues with focusing, bass build-up, etc. Control rooms should only ever stay the same width going back, or get larger. Never smaller, There's a reason why Tom Hidley stopped using compression ceilings in his designs....

but had to taper in the back end of the room in order to fit into the available space beside the unit entry door and also so the width averages out at the same ratio and eliminates flutter. Is there any reason why this would sound bad?

Yep. See above. The tapered wall forces the bass energy (and any wavelength longer than the width of the room) to be compressed, which causes distortion, increases pressure build-up, focuses the energy (instead of diffusing it), and generally does the opposite of what you should be doing. There's a reason why you never see that in small control rooms, and rarely see it even in very large control rooms (which is the only place where it could be done, validly). The only exception is with the "corner control room design" concept, but that is based on a different shape and principle anyway, so it is not an issue... And yours is not a corner design either...

Speakers are ATC SCM150 passives

Nice, but those things are pretty darn big! Perhaps too big for a small room like that? I'd take a careful look at the specs, and see if they can be acoustically matched to that room. They also don't go down that low, considering their size: only 60 Hz, according to the specs, so you'll need a sub to go with them, or better still, a couple of subs. What did you plan to use for that?

As shown would like them to be soffit mount.

That's excellent. It is practically impossible to do a true RFZ room without soffit mounting. But your soffits will have to be pretty big to accommodate those large speakers.

Opinions vary on how big the room needs to be to accommodate them but the ATC design engineers themselves have told me 200 SQFT is fine just ensure a lot of trapping.

Did they mention anything about Q and room loading? I guess if they say it is OK, then it can be done, but since the Q is likely to be all over the place for those, you are going to need to give careful attention to how you mount them, and how you design the RFZ area.

I kinda wish I had smaller speakers

Maybe sell those and buy something else? Big speakers can be used in small rooms, not a problem, but they do need to be matched to the job. I'm not convinced those are.

the mid range is unbeatable and the freq range is amazing.

Specs say: "60Hz – 17kHz", rolling off to -6 dB at 25Hz and 22k. Of course, you wont' get that in your room anyway, but maybe a smaller speaker with better high end and low-end would be more suitable? I'm not saying you can't use those: just that it would be a challenge to do so in that room.

Speaker angles are 30 degrees.

It's a long thin room: 30° is too much. That's why you had to put your speakers where they are, instead of in a more suitable location.

Listening position is 38% length from speaker to end wall (behind trapping)

The room length is about 540cm from what I can see. 38% would be 205cm, but the circle on your diagram is at about 220 cm, so it is too far back. Also, your speaker axes seem to be intersecting in the middle of your head, which would be fine if you can relocate your ears to where your eyeballs are, but if you want to keep your ears on the sides of your head, then the intersect point needs to go further back. And if you want to get a decent sized, wide, smooth sweet spot, then the intersect needs to go about 12 to 18" behind your head. Maybe more, for a long thin room.

38% is just a rough guideline. it is not written in stone. And it only applies to rectangular rooms in any case. Your room is far from rectangular, as are all RFZ rooms.

RFZ is not huge I know.

It needs to be at least as large as the sweet spot, and preferably larger! It also needs to completely cover the mix-position range, allowing for your head movement from side to side as you operate that large format console you mentioned, at both extremes, and it also needs to cover the front-to-back head movement as you lean over the console to get to the gain controls, or lean back to listen....

An RFZ room where the RFZ is small, isn't much use!

Love to see/hear some other suggestions.

Switch places with one of your "multi-purpose" rooms. Put the CR in the middle, between them, shape and size it conventionally for an RFZ room, do not narrow it down at the back, change the shape/size of one or both of the "multi-purpose" rooms to better accommodate the CR, make those other rooms rectangular, or closer to rectangular, forget about flutter echoe since it won't be an issue, consider using smaller speakers, or at least make sure to match those big ones as close as possible to the acoustic loading of the room, consider using subs to extend the bass, consider having windows or doors between the CR and the two other rooms for better access, etc.

That's a good space with good possibilities: designing it right could make it great.

- Stuart -

tardishead · Post by **tardishead** » Tue Dec 01, 2015 8:36 am

Re the isolation issue. A complete breakdown in semantics. I understand the 2 leaf situation and have built studios with it in a building with a concrete ceiling so not like what I am using now with a weak ceiling. This was indeed my first instinct I then went on to overcomplicate this. I stated that I understood this and would drop the other idea and realise that it was stupid. Please lets drop this.

This is a true RFZ room in about 200 square feet, and it includes a Hammond organ with Lesly, and a full-size vertical piano, plus a client seating area. That's one I designed for a customer in the USA a couple of years back, and it works just fine. I have also designed true RFZ rooms even smaller than that, which also work fine, but I don't have the owner's permission to show them in public. But believe me, it can be done.

Umm there is no link or jpg am I missing something? I would love to see design.

Ratios only apply to rectangular rooms. If you angle one of more of your walls, ratios are no longer valid for calculating modal behavior.

Ok from what I have read from Wes Lachot and others you take the average width of the room and length from the speaker to the end of the room. https://www.gearslutz.com/board/studio- ... walls.html
Is this categorically incorrect?

You cannot create an RFZ room using absorption. The basic concept of RFZ is that the room geometry itself creates the RFZ, not things inside it. And since absorbers, by definition, do not reflect, it is impossible to use absorption to do that. If you want an RFZ room, it has to be designed as an RFZ room, by correctly placing the reflective surfaces at the front and sides of the room, and the absorptive treatment at the rear of the room.

For those 2 rooms I did not say I wanted to create an "RFZ room" or a "Reflection Free Zone". I said I wanted to create a "reflection free zone" (by absorbing the first reflections). Again this is semantics right? Ethan Winer is always going on about this. RFZ is a particular room design and actually a trademark. The words without capitals just mean a zone without reflections. I deliberately used lower case in order to express this.
For the mixed utility rooms I was inspired by this although very different room ratios. And I envisaged similar absorptive treatment at the front of the rooms.
http://realtraps.com/art_studio.htm

How large? I have done a room in 140 square feet based around a Mackie 32.8. That's a 32 channel, 8 bus console, analogue. It can be done.

Giant. OMG I have a vintage Neve - it is 900x1100x1910mm. But I take your point.

The room length is about 540cm from what I can see. 38% would be 205cm, but the circle on your diagram is at about 220 cm, so it is too far back. Also, your speaker axes seem to be intersecting in the middle of your head, which would be fine if you can relocate your ears to where your eyeballs are, but if you want to keep your ears on the sides of your head, then the intersect point needs to go further back. And if you want to get a decent sized, wide, smooth sweet spot, then the intersect needs to go about 12 to 18" behind your head. Maybe more, for a long thin room.

I read in a few threads the length in question is between the centre axis of the speaker and the end of the solid room
Again is this incorrect. Can you point me to evidence?

Yep. See above. The tapered wall forces the bass energy (and any wavelength longer than the width of the room) to be compressed, which causes distortion, increases pressure build-up, focuses the energy (instead of diffusing it), and generally does the opposite of what you should be doing.

Ok excellent. I had not read this. This helps me a lot
So I think I am at nearly a RFZ design so long as I correct the tapering of the back of the room and make the third angles from the front of the room more extreme so they create a wider RFZ - no? But please please point me to some designs that might help me. Similar footprint or thereabouts.

tardishead · Post by **tardishead** » Tue Dec 01, 2015 9:21 am

Rear of control room tapered
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=742
I knew I'd seen it somewhere. But I understand why this wouldn't be the best. You see many other CR designs on this forum where the bass trapping at the back of the room makes the room seem tapered at the back - but the solid walls behind the trapping is not tapered.
I think this is where the confusion set in.

Soundman2020 · Post by **Soundman2020** » Tue Dec 01, 2015 10:58 am

Umm there is no link or jpg am I missing something? I would love to see design.

Damn! I must have forgotten to upload that image the first time! I just fixed that, and it seems to be showing now. Sorry about that!

Ok from what I have read from Wes Lachot and others you take the average width of the room and length from the speaker to the end of the room. ... Is this categorically incorrect?

I guess that depends on what you mean by "categorically incorrect"!

How accurate do you want the results, and how far out of rectangular is the room? Clearly, if one wall is out of parallel by half a millimeter between one end and the other on a wall 5m long, the effect will be infinitesimally small. On the other hand, if it is out by a meter, then yes, there's a big difference. And if there are more than four walls, one ceiling and one floor, then all bets are off. So if your room has six walls and two ceilings, there's basically no point looking to a simple modal calculator to get realistic answers. There's also the situation where only part of the wall is out of parallel, but it is way out of parallel, such as with an RFZ room. The soffits most certainly count as walls (so you have six sides, not four), and they are at least 30° out or parallel. How do you deal with that in a simple calculator meant for rectangular rooms? Answer: you do so intelligently, by considering only those results that are valid. For example, the vertical axial modes will still be 100% valid (assuming the ceiling is parallel to the floor), the side-to-side axial modes will be mostly valid, since most of the side walls remains parallel, but the front-back axial modes will be very inaccurate, since most of the front wall is way out of parallel with the rear wall. The tangential modes associated with the side walls, ceiling and floor will be mostly valid, but the tangentials associated with the side walls, front and back will be way off, as will those associated with the front and back walls, ceiling and floor. And the obliques will be all over the place, very, very inaccurate. To someone who understand the implications, such as Wes Lachot or F. Alton Everest, the results are very useful. To the average home studio builder, they are meaningless. The spread shown on the graphs and charts will be very much incorrect, and not suitable at all.

That's the issue.

For those 2 rooms I did not say I wanted to create an "RFZ room" or a "Reflection Free Zone". I said I wanted to create a "reflection free zone" (by absorbing the first reflections).

splitting hairs. And sorry, but you cannot create either a "Reflection Free Zone" or a "reflection free zone" by absorption on the first reflection points. It is not possible to do that, since there is no such thing as a perfect absorber. Even if you could do that, the results would be disastrous, since you would have no diffuse field / reverberant field / whatever you want to call it. The entire point of modern studio design is that early reflections do not get to the engineer's head, since they are re-directed away from his head in some manner, and arrive at his ears in a more diffuse manner, at a level of at least 10 dB lower, and outside of the Haas time (however you want to interpret that). It is not about completely eliminating the first reflections, which is what perfect absorption would do), nor about coloring it, which is what partial absorption does: it is about delaying it, attenuating it, and diffusing it such that it does not mess up the psycho-acoustic perception of sound.

These are the basic concepts behind RFZ, CID, NER, MR, TB, and many others. They all aim for the same goal, and it cannot be achieved through total or partial absorption at the first reflection points. If it is total absorption, there is no diffuse field and the room is very dead and unpleasant. If the absorption is partial, then by definition it colors the sound, so the returned energy is mostly mid-lows and lows: the room sounds muddy, dull.

So sorry, it cannot be done the way you say you want to do it.

Again this is semantics right? Ethan Winer is always going on about this. RFZ is a particular room design and actually a trademark.

It's not semantics: it is avoiding using the trademark, which as far as I know is still held by D'Antonio, or perhaps by RPG. trying to pretend that RFZ and rfz are different things is disingenuous. They are the same thing, under different names. If somebody makes an exact replica of a Jeep in their workshop, but then calls it a Joop to avoid infringing copyright and trademarks, that does not make it any different: it is still a Jeep, just made by somebody else. RFZ is rfz, without the trademark. And it is not accomplished by absorption at first reflection points.

I also wouldn't take everything that Ethan says as gospel truth: I admire and respect him a lot, and he's a valued member of this forum too, but he does say some strange things every now and then that fly in the face of the science of acoustics. For example, he says that oblique and tangential modes are not important at all, and the calculator on his web site therefor only shows axials. He's been called out on that by many top acousticians, among them Eric Dessart. So don't rely too much on what you see on his website. He does make good products, though!

For the mixed utility rooms I was inspired by this although very different room ratios. And I envisaged similar absorptive treatment at the front of the rooms.

I have seen that many times before, yes. But that is not a reflection free zone room, nor is it an RFZ room.

I read in a few threads the length in question is between the centre axis of the speaker and the end of the solid room. Again is this incorrect. Can you point me to evidence?

Yes it is incorrect. There's a basic misunderstanding of what a mode is: it has absolutely nothing at all to do with speakers (apart from that fact that they provide the sound source!). It has only to do with room dimensions. A mode is simply a path that a sound wave can take around the room and arrive back at its starting point, in phase with itself, and going in the same direction. Room modes are standing waves. They are created by the solid, rigid, massive boundaries of the room, nothing else. The simplest mode is the axial mode, which runs along one of the three major axes of the room: front-back, left-right, up-down. It is a standing wave that occurs between parallel walls, and is directly related to the distance between the walls. If you have walls that are ten feet apart, you will have a mode that occurs between them at exactly 56.5 Hz. It does not matter where you put the speaker, or what speaker it is, or which way you point it, or who made it: the only thing that matters is that if the speaker produces a tone at 56.5 Hz, it will excite the mode between those two walls: the standing wave will form. (OK, if you want to split hairs, it would not happen if you put the speaker at the modal null point in the room for that frequency.... but for all other locations, the mode will be excited, to one extent or another.

The above are axial modes: there are also oblique modes, where the wave follows a path that bounces between four surfaces, instead of just two. And there are also tangential modes, that bounce between all six surfaces.

So wherever you read that modes are related to speakers and their axes, was dead wrong. Or you misunderstood it.

This should be clear from using a room mode calculator: the ONLY data that you enter is the dimensions of the room. There is no place for you to enter the location of the speaker or its axis, or the orientation, or anything else about it, since it is irrelevant to the modal response.

So I think I am at nearly a RFZ design so long as I correct the tapering of the back of the room and make the third angles from the front of the room more extreme so they create a wider RFZ - no?

... and also angle the front walls such that they direct the early energy from the speakers around the mix position, to the rear wall, where it can be either absorbed, or diffused, or both.

You see many other CR designs on this forum where the bass trapping at the back of the room makes the room seem tapered at the back - but the solid walls behind the trapping is not tapered.

Correct!

- Stuart -

tardishead · Post by **tardishead** » Tue Dec 01, 2015 10:54 pm

The room design with the hammond organ etc. That listening position looks very far forward. Like exactly 1/3 room length.
I thought that was a no no
Also what are the angles of the speakers? Is there a SKP file for that. I don't want to copy it just learn from taking measurements etc.
Or do you have a link for the whole project thread?

Soundman2020 · Post by **Soundman2020** » Wed Dec 02, 2015 1:25 am

The room design with the hammond organ etc. That listening position looks very far forward. Like exactly 1/3 room length.
I thought that was a no no

The engineer here is shown leaning forward over the desk, but still within the sweet spot, so that might be confusing you. His normal position would be a few cm back from there, sitting more upright.
But even so, I'm not sure where you are getting all this incorrect information from, since there is nothing at all wrong with the location of the listening position in that room, as borne out by the results. There is also nothing wrong with having the listening position at 33% of the room depth, even though that isn't the case here (closer to 37%, if you must know).
Please explain why you think 33% is bad location, acoustically.
The bad modal locations are 25%, 50%, and 75%, which are the nodal points of a sound wave.
But once again, all of those apply to RECTANGULAR rooms. This is an RFZ type room, and therefore it is NOT rectangular. It has eight walls and two ceilings, for a total of ten boundary surfaces. A rectangular has only six boundary surfaces. The 38% "rule" (which Wes regrets ever having made public, since it never was meant to be a rule at all) applies to the front-back axial modes, but since the front wall is segmented into five different pieces, instead of just one, there is no clear single modal null or peak for the x.0.0 modes: There are more tangential nodes associated with that plane, certainly, both x.x.0 and x.0.x, but the actual x.0.0 modes are simply not present sharply at all. Plus, the rear wall is deeply trapped, as I already mentioned, so even if there was a strong x.0.0 modal response from the room dimensions, it would be very well damped.

Here's the spectrogram for nearly completed room (before the final round of treatment), showing the actual response in the low end, as well as the predicted modal response as if it were a rectangular room using the average dimensions:

ONLA-V2323-SPECTRO.jpg

As you can see, there simply is no correlation with the lowest modes and the predicted modes. The cursor is marking the point where the lowest mode should be, at 34.75 Hz, and there isn't even a trace of it. That's the exact location where the 1.0.0 mode should be, according to standard room mode calculators. It simply is not there, because the room is NOT a rectangle.

So much for being able to take "average dimensions" to accurately predict room response!

The lowest modal issue here is clearly at 57.8 Hz, which is obviously the 1.1.0 tangential mode (so much for Ethan's claims that tangential modes are not important....). It is predicted to be at 56.5 Hz, but is a little higher due the extra walls creating a slightly shorter path.

At 44 Hz. there's a slight hint of the 0.1.0 mode, but it's not a problem in the least.

For that size room, that's a pretty darn good low end response: I think you'd have to agree!

Here's the decay plot, if you are interested. It is well within ITU specs:

ONLA-V2323-RT60.jpg

And the actual impulse response:

ONLA-V2323-IR.jpg

The first reflection visible on there is at 3.3ms, but note that it is over 90% down from the impulse itself, in terms of energy, and is therefore well within specs.

Here's the same data represented as dB:

ONLA-V2323-IRdb.jpg

Once again, you can see that the earliest reflections are more than 20 dB down, and the decay is smooth and clean, with no strong reflections at all. The design is, indeed "reflection free". Mission accomplished.

So clearly, there is nothing at all wrong with the listening position in this room. It is where it is supposed to be, where acoustic conditions are best, and the results bear out the calculations and reasoning I followed in locating it there.

It seems to me that you are relying far too much on things you read on the Internet, from questionable sources, which only apply to 6-sided regular rectangular rooms anyway, and you are trying to extrapolate them to non-rectangular rooms with more than 6 sides, which all RFZ-type rooms are, by definition. Those simple "rules" just do not apply to rooms that have more than 6 boundary surfaces, some of which are non-parallel. They only apply partially, as I mentioned a few posts back, and have to be interpreted with clear understanding of which results are applicable and which are not.

So, to summarize: The information you got that having the listening position at 33% of room depth is a bad thing, is not correct. That's not the best position for a rectangular room, but it isn't necessarily bad, and in any case this is not a rectangular room, and the mix position is not at 33%! The "bad" modal locations are at the half-wavelength and quarter-wavelength points, which are 0%, 25%, 50%, 75%, and 100%. There is no acoustic reason why one-third of a wavelength would be bad, since there are no acoustic effects at that point from a standing wave. Modal nulls and peaks can only ever occur at points where the standing wave itself is at either a pressure null or pressure peak, which mathematically can only happen at nodal points: half of the wavelength (null) and a quarter of the wavelength (peak).

Also what are the angles of the speakers?

In this specific case they are angled at 29°, which turned out to be just right. They are 208 cm apart, and 178cm from the engineer's ears at the center of the sweet spot: The sweet spot is an oblate spheroid, roughly 61cm in diameter, and there is a "semi-sweet spot" beyond that, roughly 97 cm in diameter, where the response is still very smooth, with only minor issues. As I mentioned before, the engineer in the above image is shown leaning forward over the desk, as though he were reaching to the back of the console (not shown), but his head is still within the inner sweet spot. He can move back about a meter from there and still have good precision, and he can also move about 30cm either way and still have good precision.

Is there a SKP file for that.

Yes there is, but I can't share it with you, unfortunately, since it was a design that I did specifically for one of my paying customers. He doesn't mind me sharing overall views and results, since he is very happy with his studio, but obviously he is not too keen on having all the details that he paid for, given away to others for free. That's his decision, and his right. Sorry. I hope you understand.

Put it this way: If you wanted a similar design done for your room, you'd either have to do it yourself, or pay a designer to do it for you, which implies that either you invested a lot of time in it, or you invested money in it, and in either case I'm sure you would not want all that investment to be spread around the internet for others to use for free.

I don't want to copy it just learn from taking measurements etc.

It would not help you at all, even if I was at liberty to share it with you. All rooms are different, each needs it's own individual design. Unless you were planning to build an exact copy of this room, using the exact same speakers, dimensions, furniture, treatment, etc., then it would be of no help to you.

Or do you have a link for the whole project thread?

For the same reason as above, I can't give that to you, and it wouldn't help you anyway. You'd still have to go through the same process I did for this room, doing all the math, estimates, and trade-offs, adjustments, compromises, checking, etc. based on your speakers, your available space, your needs, etc. The only other thing I can do is give you this picture of the finished room:

ONLA-V2323-20131218--Panorama-CR-1-ENH1-SM.jpg

That's a composite panoramic view taken from the client sofa at the rear, using a wide-angle lens, so things are somewhat distorted, but you can see how the room turned out.

Here's another room I designed, for a different customer, using the same principles:

RD-CR-Final-690x400.png

Once again, the mix position appears to be too far forward, according to the criteria you mentioned. Once again, that is not the case. Once again, it is an RFZ-type design. And once again, the results prove that the design is correct. In this case, I was hired part way through the project to "fix" the original design, which was not working, so I inherited some things that could not be changed. But the room worked out great. The owner is currently upgrading his speakers, and I'm working on slight changes in the soffit design to accommodate them, but I expect that the results will be even better response, which is hard to do since it is already really, really good! (Graphs available on request...

)

- Stuart -

tardishead · Post by **tardishead** » Fri Dec 04, 2015 10:29 am

Ok. Thanks
Here are some of the places I got my mistaken facts/ideas from.

Care to comment on that link I posted of one of John's designs. Tapered back of control room. One side has bass trapping the other does not.
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=742

Is this a compromise? No good/spec?

Also in John's Rec Manual there a re some designs of Control Rooms.

http://johnlsayers.com/Recmanual/Titles/Plans.htm

One design ,THE CORNER CONTROL ROOM has a massively tapered back end? This design not appropriate? Dated?

This thread is used as a sticky at Gearslutz and presided over by some pretty amazing brains.

https://www.gearslutz.com/board/studio- ... lls-3.html

Its has comments such as

The absorption for RFZ is in orange

Oxymoron? A large section on importance of tuned room ratios even though modes are hard to predict. Averaging of widths/lengths to fit in with certain ratios. Splayed walls all over the place as well as this website.

Also this is a nice looking and pretty thorough design

https://www.gearslutz.com/board/studio- ... tric+chair

But not true RFZ design hey? But they talk about the RFZ even though it has been created by absorbers at first reflection points.
It seems strange that they did not go true RFZ
Oh yeh it has a diffuser on the back wall 10ft away - so long as the engineers doesn't take a step back should be ok. I have read on GS that 3 x the lowest design wavelength works.
Curious to know what you think of this.

Soundman2020 · Post by **Soundman2020** » Fri Dec 04, 2015 2:42 pm

Tapered back of control room. One side has bass trapping the other does not.

For bass trapping, that isn't too much of a problem. Symmetry is critical in the front of the room, up to the point where everything is going past the ears of the engineer already. From there on back it isn't quite as critical for mids and highs, and not critical at all for lows. The mids and highs will be attenuated/diffused/scattered at the back, and come back as a smooth, even diffuse field, whereas the lows just don't matter, since low frequency sound is not very directional to start with, our ears are not so good at figuring out directionality for lows, our ears are not so good at figuring out directionality for sounds coming from behind, and above all, for modal damping it isn't critical where the damping takes place, because modes are standing waves, so damping any part of it will reduce the entire wave. In other words, putting bass trapping on only one side if the back of the room does not affect symmetry: it isn't as effective as having traps on both sides, but it does not cause any discernible asymmetric response, psycho-acoustically.

One design ,THE CORNER CONTROL ROOM has a massively tapered back end? This design not appropriate? Dated?

I did mention corner control rooms a few posts back: Here's what I said: "The only exception is with the "corner control room design" concept, but that is based on a different shape and principle anyway, so it is not an issue... And yours is not a corner design either...". Acoustically, that is very different from a room that just gets narrower at the back.

Its has comments such as: "The absorption for RFZ is in orange"

Yes it does. ... to which Wes replied: "you can't create an RFZ with that one skinny piece of fiberglass in the one spot per side.". Correct. I agree. You can't do that: And note that what Wes calls "skinny" is actually may inches thick!

A large section on importance of tuned room ratios even though modes are hard to predict.

Plus the very apt advice in response: "Don't over-think the ratio. Yes, it is the basis of a good room, and an important early choice to make. However, there are many other factors to consider, and if you are going to properly treat the room, then the choice between these two ratios won't end up making that big a difference in the end. ... You can't take a ratio in isolation, any more than you can take any other element of an acoustical design in isolation. ". Very true. Pretty much what I said already. And an additional comment: "Ratios, while being significant, certainly aren't at the top of my list... Just pick a decent one and move on. As Jay points out, once you start treating and shaping your room, the variables are going to change/evolve anyway."

Also, Wes likes to tune his ratios to musical scales. Most other designers I know of don't do that, for various reasons. So a lot of what you read there by Wes is about doing that. Not really applicable to your case.

And notice that Wes would prefer to see soffits in that room....

In addition, notice how that room evolves over the course of the thread, away from multi-splayed walls, towards a more conventional RFZ-type room... but then went beyond that, into unrealistic shapes and sizes....

Notice also that Wes bowed out of that thread and never came back after the shape and size got too crazy to be workable...

And notice that the room was never actually built. That's a good thing, actually, as it would not have worked after people stopped listening to Wes and went down silly paths...

But not true RFZ design hey?

Correct. it is not. At one point on page 4 it nearly was again, but without soffits.. hence Wes's comment on soffits.

But they talk about the RFZ even though it has been created by absorbers at first reflection points.

Some of the posters do, but the real experts there don't. And Wes points out that you cannot create an RFZ like that....

It seems strange that they did not go true RFZ

Yes. It would have been better to do that, but the OP's insistence on having glass up front, on not angling his walls enough, on using absorption up front where it would not work, on not heeding Wes's advice on how to the the rear of the room, etc. lead to the room being unworkable. And that's when Wes stopped posting on that thread.

I have read on GS that 3 x the lowest design wavelength works. Curious to know what you think of this.

You should probably read Cox and D'Antonio's book on the subject. They pretty much invented the concept of diffusion! Their conclusion is that you need at least ten feet, and that you also need at least 3 full wavelengths of the lower cut-off frequency of the diffuser. In other words, if the "3 wavelengths" rule gives you a distance of less than ten feet, then you need ten feet. And if it gives you a distance of more than ten feet, then you need whatever distance it tells you. They later revised that to seven wavelengths, since further research uncovered the issue that a diffuser can still be scattering at frequencies one octave lower than the cut-off for diffusion.

So either you have to tune your diffusers high enough that the cut-off is seven wavelengths, in which case you are still stuck with the ten foot rule, or you have to make your room big enough that seven wavelengths is not a problem for the frequency that you wanted to tune them to.

I'm just wondering, and I have to ask, but please don't take this the wrong way: did you come here to get help with your project, and to learn a better way of doing it? Or did you come here to argue about your pre-conceived misinterpretations of things you have read on the internet? If you are here for the former, then I'd be happy to carry on helping you, but if you are here for the later then there isn't much point in my carrying on: I don't have the time to be explaining each and every issue that you come up with, especially when you don't even acknowledge the issues that I have already dealt with, and just seem to want to move on to ever-more esoteric points that don't have any real application in your build. I have shown you what is wrong with your design, and how to fix it, and I have shown you several studios that I have designed where these principles have been implemented, and shown to work. If you don't want to modify your place to incorporate these best practices, then that is entirely your choice, of course. But I'm not sure that I want to spend any more time trying to show you why you should modify it, what is wrong with it, or how to fix it, if you are convinced that it is perfect already, just like it is...

- Stuart -

tardishead · Post by **tardishead** » Fri Dec 04, 2015 8:29 pm

please don't take this the wrong way

Ha. You're too polite. I have been rude. I did not mean to be petulant. I did not reference those links in order to contest you - rather to show you some examples of where I picked up misconceptions and confusion and for you to explain. To be honest I was very frustrated with myself for being so misinformed. My professional life has been blown apart the last few years - my son is special needs, requires a great deal of care and devotion and consequently my time is super precious. Time picking up bad information is time wasted. I have learnt so much through your replies. I am so grateful. More and more these days I find it very difficult to access the correct information through the internet. Proliferation of information - right and wrong. And I should have known that GS should be taken with a big pinch of salt. Theres correct information posted by pros and then theres a whole lot of loose talk that is misleading. I know this from the things I do specialise in. And the pros don't have time to go through and categorically correct people. However you have done so with me and thats been very helpful. Sorry if its been arduous. And sorry if I aggravated you or wasted your time.
I feel like we should start the thread again. I did not know where to post queries because I thought the posts were supposed to be project specific. I should have started it way simpler. I was not at all set on room design and should not have posted them - I was really wanting to get my head around isolation first and then move onto layout later. And also because there are some other subtle design issues that I did not include in the first post and will explain some of why I was trying to do things a certain way. What do you think?

Soundman2020 · Post by **Soundman2020** » Sat Dec 05, 2015 1:43 am

my time is super precious. Time picking up bad information is time wasted.

I hear you! Definitely "been there and done that". That's the trouble with the internet: on the one hand, there's a huge amount of information on any given topic. On the other hand, a lot of it is total garbage, and it's really hard to figure out gems from dross... unless you already know which is which! Catch-22....

More and more these days I find it very difficult to access the correct information through the internet. Proliferation of information - right and wrong.

Yep. You would not believe the number of videos there are on YouTube, about "how to make a studio", with the vast majority of them providing terrible information. Some of it is harmless, and just waste's the DIY builder's time and money, but a LOT of it is counter-productive, and can actually harm the acoustics or the isolation of the room... or both! For example, the famous "you must float your floor" myth. In reality it is "No you must not, unless you actually have one of the very few cases where that really is needed, and also have a very big budget to be able to do it!". But there they are, dozens of videos showing the exact WRONG way to float a floor, and practically none showing the right way. We have even had a couple of those video-makers come on the forum trying to defend what they did, insisting that a light wooden deck sitting on rubber pucks is a great floated floor

Strangely enough, when we challenge them to actually do some acoustic tests on their wonderful floors and post the results here on the forum, they seem to get very silent all of a sudden... I wonder why?

And I should have known that GS should be taken with a big pinch of salt. Theres correct information posted by pros and then theres a whole lot of loose talk that is misleading

Yep. There are a few good guys over there, some not-so-good ones, and quite a few people without much of a clue, but who comment anyway, diluting the expertise. And of course, there's also a LOT of people who want to learn, asking questions, and trying to make sense out of it with discussions and comments, such as the OP in that thread: he started out well, with good intentions, and started out following the advice of the good guys, but then got distracted into the not-so-good, and ended up not building anything! At one point, Wes even told him to "just go for it", as his design was workable. But then...

and it got sidetracked...

And the pros don't have time to go through and categorically correct people. However you have done so with me and thats been very helpful. Sorry if its been arduous. And sorry if I aggravated you or wasted your time.

No problem! It happens. I don't consider it wasted time, if it was helpful for you, and you learned useful stuff from it!

I feel like we should start the thread again. I did not know where to post queries because I thought the posts were supposed to be project specific.

It's better to keep all your questions in your own thread, so that you know where to find the answers in the future! Some people ask questions all over the forum, in dozens of places, but then don't remember it the answer to their question about SBIR was in the "Speakers" thread, or the "Soffits" thread, or the "Room Acoustics" thread, or some other thread that the hijacked! So just keep all your questions in this thread, even if they aren't directly related to your specific build.

I was not at all set on room design and should not have posted them - I was really wanting to get my head around isolation first and then move onto layout later.

That's fine! Isolation, layout, and treatment are all different aspects of studio design, but they are interconnected: changing your isolation plan can have repercussions on your layout and also on your treatment. And changing your treatment plan can, in turn, have unexpected effects on your isolation. For example, something as simple as deciding to put a large membrane trap on a wall could potentially reduce the isolation of the wall in that location, due to resonance effects, so you might need to improve the isolation plan there, just because you did some treatment. A lot of things about acoustics are not intuitive. So it's actually a good thing to work on all of the issues together, since modifying one aspect can have an impact on others.

Case in point: I'm working on the design for a barn conversion in New Zealand right now, and I had trouble fitting in the HVAC silencer boxes above the CR ceiling. So I had to lower part of the ceiling, which affected both the structural situation as well as the isolation, and most of all the acoustics. Complete revamp of the acoustic plan is now needed...

And also because there are some other subtle design issues that I did not include in the first post and will explain some of why I was trying to do things a certain way. What do you think?

Carry on in this same thread, updating your design as you move along. It's also very interesting for others who want to follow your build in the future, as thye can see how your thinking changed as you moved forwards, and understand the decisions you made along the way: why you changed this, or did not change that, why you chose "X" material instead of "Y" material, etc. It's useful for you, and also for others.

I'm looking forward to following your thread, since you have a really nice sized space and a good basic plan, that just needs refining.

- Stuart -

PS. I keep meaning to mention that I love your handle! I'm a bit of a "Tardis Head" myself... I love the Doctor! Been following him since the early 70's, and really enjoying the re-boot over the last few years.... Maybe you should put a blue police box in for your avatar!

tardishead · Post by **tardishead** » Tue Dec 08, 2015 10:06 am

Ok will do.Thanks Stuart
A few questions.
A speaker soffit box/wall. Would that compromise the isolation of the room at the nearest wall because of 3 leaf effects?
If so is there anything I can do to increase the isolation? More mass on that particular wall?

Sliding doors. Single glazed right! To stop multiple leaf effects
I think John recommends a minimum thickness 8mm. I have found quite standard uPVC sliders in UK with 24mm glass. 4-20-4. Does that sound right - sounds massive hey! Maybe they do it thicker in UK.
And also preferable to have a large air gap and two different thicknesses and also at an angle.
This is just a thought at the moment. Probably won't pursue it because its hard to get TL data from manufacturers.

And a couple more qs from that design of Johns.
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=742
The tapered back. Is it the point that so long as the back wall is wider than the front wall you can add width in the middle of the room and you don't get the compression artefacts?
The angles of the walls don't look big enough to create much of an RFZ. I've seen those slighter angles on some of Johns designs. Also they only have 2 steps rather than 3 like in your room design you posted before. I wondered why they were less steep. Have I seen those less steep angles after the soffit box angle used with slot resonators. Does that deflect/absorb the sound enough to create a larger quasi RFZ (frequency dependant)? I see you have used slots on your design on those angles after the soffit walls.
And lastly when drawing out RFZ ray traces - how wide do you need to go with the angles of rays emanating from the speakers? Or potentially must you go all the way because bass frequencies are omnidirectional?

Tom Baker is the man

Soundman2020 · Post by **Soundman2020** » Tue Dec 29, 2015 12:31 pm

A speaker soffit box/wall. Would that compromise the isolation of the room at the nearest wall because of 3 leaf effects?

Not if you build it correctly!

There's plenty of mass in there, and the distances are large, plus the faces are angled steeply, so the resonant effects have a low Q and are low level. Also, if you think about it, from the speaker's point of view it is NOT a 3-leaf wall: it is just a 2-leaf wall...

If so is there anything I can do to increase the isolation? More mass on that particular wall?

It has to be massive anyway: the front face of the soffit is an attempt to emulate an "infinite baffle", so it must have a lot of mass on it, and it needs to be thick and rigid.

Sliding doors. Single glazed right! To stop multiple leaf effects

Correct.

I have found quite standard uPVC sliders in UK with 24mm glass. 4-20-4. Does that sound right?

Nope! Because that ain't single leaf! That's a two-leaf "double-glazed" window. Two panes of 4mm glass, separated by a 20mm air gap. If you have two of those (one in each leaf) then you have a FOUR-leaf window!

When John speaks of 8mm glass, he's probably talking about the thickness of the glass layers in the laminate sandwich: In other words, 8mm thick glass, the interlayer, then another 8mm glass, for a total thickness of a bit over 16mm. Yes, you need laminated glass here, and yes it must be thick. That 16mm laminated glass pane would be about right for a wall leaf that has two leaves of 5/8" drywall on it.

And also preferable to have a large air gap and two different thicknesses and also at an angle.

Larger air gap is good, definitely. Different thicknesses is debatable, but not really necessary (it's unlikely you'd have problematic coincidence dip issues with such a system anyway, and even if you did, they'd be fairly high up the spectrum). Angled glass? Why? You are aware that angling your glass REDUCES your isolation, right?

This is just a thought at the moment. Probably won't pursue it because its hard to get TL data from manufacturers.

You don't actually need that. You just need to do the math (or get someone to do it for you) and design the windows (or get someone to design them for you) so that they will achieve the correct TL that you are looking for. It's not rocket science!

The tapered back. Is it the point that so long as the back wall is wider than the front wall you can add width in the middle of the room and you don't get the compression artifacts?

As Steve said about that: "You should probably ask John about this, it's his design. "

I also agree with his next comment: "There shouldn't be a problem with non-symmetrical bass traps, since those frequencies tend to be non-directional."

I suspect that John had no choice but to narrow down the one wall there, in order to fit in the iso booth and LR reasonably. Studio design is always about trade-offs: he probably needed to trade off the angle back there for an improved LR, then did the extra trapping in the other side of the room to compensate. That would be my guess.

In fact, John actually did answer on that thread, saying: "The right hand one is a slot resonator whereas the rear one is heavy absorption." And that makes perfect sense: so it is not acting as a compression wall at all., or only to a minor degree, since one side is not "solid" and the other is heavily damped.

The angles of the walls don't look big enough to create much of an RFZ.

It's tight, but I'd say that there is a decent sized RFZ in there, depending on what speakers were used. If they are high-Q, then the RFZ could be very decently sized at all but the lowest frequencies.

Also they only have 2 steps rather than 3 like in your room

... and they go further back than in my designs. I like to save as much space as possible by keeping the angled parts to a minimum, and as far forward as I can, within reason. John's older designs tend to opt for longer angled sections. Both approaches can work. John's are easier to build, mine take up less space but are more complicated. 6 of one, half a dozen of the other... Trade-offs...

But if you look carefully, you'll see that in this case, John is also using a two-step design...

I wondered why they were less steep.

All rooms are different. the wider the room is, then less steep the angle needs to be. You can also move the mix position and re-angle the speakers to allow for lower wall angles. Or higher angles. There are many parameters that cab be adjusted. And of course, the speakers themselves play a huge part in design decisions. It's a different matter to design a room for high-Q speakers, as compered to low-Q speakers....

I see you have used slots on your design on those angles after the soffit walls.

Yes, I sometimes do, but in some cases they are not really tuned slots, as the cavity behind is not sealed. I do that when I need a bit of reflection, a bit of diffusion, but not tuned mid-range absorption, only low end absorption. I only tune them (seal the cavity) if I need help with a specific mid-range issue. I sometimes even have a "slot wall" where part of it is tuned resonant slats, but other parts are not tuned. Don't forget that you are only looking at the surface, and can't see what is going on behind. Of the cavity is not sealed on purpose, then there is no resonance going on...

And lastly when drawing out RFZ ray traces - how wide do you need to go with the angles of rays emanating from the speakers?

That depends on the speakers, and also on the room! High-Q speakers in a wide room, and you only need to go out to maybe 40° or so. Low-Q speakers in a narrow room, I'd be out to 60° or even 70°.

Or potentially must you go all the way because bass frequencies are omnidirectional?

Well... yes and no...

That's a huge subject, all by itself. And it also brings up the issue: are you using a sub (or several subs) in your room? Do you have a bass management system? Is it a multi-channel room? Also issues of genre, come into play. I really can't give you a much better answer than that, without writing a paper about it!

- Stuart -

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