TL through wall, then through floor...

[princeplanet]

heavy bottom wall best.pdf

This question was on the end of another thread which isn't getting noticed, so I thought I'd re ask here. Please refer to the attached diagram, it shows a Control Room on the left and a floated studio on the right. It is to be built on an upper level with no levels above. I am ONLY concerned with the low frequency (sub 250 hz) TL via the studio through the existing slab floor, both through the floated floor and through the wall to the control room and then through the floor. I'm even concerned with the sound leaking through the gap between the 2 walls and down through the existing slab.

I'd like the studio walls to be clad with 60kg/m2 materials (probably compressed cement sheet) but if it can be shown that 35kg/m2 is sufficient, that will keep my Structural Engineer (and my neighbours below) very happy. My proposed compromise is that these walls might be 35kg/m2 except for the bottom 500mm which might be 60kg/m2. The idea for this comes from the fact that the further away 2 leaves are from from each other, the greater the TL. This is surely why, when considering only TL through a floor, that a wall can be less dense that a floor, and a ceiling can be less dense than a wall. Obviously if we're concerned with TL through the wall, or ceiling, then consistent density is imperative. But as my concern is only regarding TL through the floor, I'd like to know if its true that the bottom part of a wall being heavier than the top part will make a difference to what eventually leaks through the floor on the other side of the wall. The higher up the wall, the greater the distance between said wall section and the floor. If this is true, then maybe I can have the bottom 500mm of the wall at 60kg/m2 in density, and the rest of the wall up to the inner ceiling might be only 35kg/m2.

Does this make sense? Or is there some principle that can demonstrate how this "heavy bottom / light top" wall idea would make little difference. Remember, I'm only concerned about leakage through the floor (loud drums, bass amps etc). I don't mind leakage through to the control room, and leakage elsewhere on my level is also not an issue.

Thanks.

[Soundman2020]

It is not an MSM system, thus you are limited by Mass Law on each surface. It's that simple. There's no MSM benefit here.

I kinda think that if this curious plan had any merit at all, you'd see studios everywhere built that way, all around the world. And it would be discussed extensively in all the usual texts. There would also be research papers on it, and equations for calculating it, and lab-tested examples.... The fact that you searched and can't find any of that, should be telling you something...

Something tells me you are being sold a pig in a poke...

- Stuart -

[princeplanet]

It is not an MSM system, thus you are limited by Mass Law on each surface. It's that simple. There's no MSM benefit here.

I kinda think that if this curious plan had any merit at all, you'd see studios everywhere built that way, all around the world. And it would be discussed extensively in all the usual texts. There would also be research papers on it, and equations for calculating it, and lab-tested examples.... The fact that you searched and can't find any of that, should be telling you something...

Something tells me you are being sold a pig in a poke...

- Stuart -

You saw the attachment? What makes you say it is not not a MSM system? As for why there's scarce information regarding the "heavy bottom - light top" wall idea, that may have to do with the fact that most isolated rooms are equally concerned with TL through walls as well as through floors?

And yes, I am curious as to why this idea would not have merit. Consider the gobo - that is the very definition of "heavy bottom - light top"- You can't get any lighter than an opening!
The last time I checked, a good gobo managed to attenuate all frequencies. Granted there's a big difference b/n 500mm and 2M, but surely the principle is the same?

As for being sold a pig in a poke, are you referring to the acoustician who assures me a 35kg wall will work? Or the heavy bottom wall idea? If the latter, then that's my own idea. I'm happy to be shown where it doesn't hold water (to use your analogy), apart from the fact that there's scarce evidence of its potential efficacy.

[Soundman2020]

You saw the attachment?

Yes I did: that's not the way sound works. You are still not seeing the big picture. Sound doesn't go only where you want it to go: it goes everywhere, in all directions. Especially low frequency sound: it moves in the same way a balloon moves when you pump it up then deflate it rapidly: expanding and contracting equally all over. The sound from your sub (in your diagram) will not go through the floor and lower wall as a series of rays, but rather it will also go through the window, upper wall, ceiling, doors, HVAC system, etc. as pressure waves It will exit through ALL the surfaces of your room, not just the ones you'd like it to exit through. And once it is out on the other side, it does the same thing: once again expanding in all directions equally as a PRESSURE wave, not a bunch of rays. If you measure the pressure changes inside a balloon, you'll find that it is the exact same value at all points. There's no difference between the pressure just inside the neck of the balloon, or right in the middle, or towards the bottom, or the top: it's the same everywhere.

What makes you say it is not not a MSM system?

Because it isn't! There's no spring involved: just two masses. Sound that went out loudly through the low-mass upper wall, or window, or ceiling, or wherever, and is now in the cavity, has no MSM relationship with the structural floor. It is just sound waves in air. When it reaches the floor, it simply sees "here be Mass Law!", and behaves accordingly. You only get MSM between surfaces where there is a spring that couples them.

As for why there's scarce information regarding the "heavy bottom - light top" wall idea, that may have to do with the fact that most isolated rooms are equally concerned with TL through walls as well as through floors?

No. It's because TL is a system, not a bunch of parts. The isolation in a system is only as good as the worst part, or "weakest link" if you prefer. Its because isolated rooms are concerned with isolation of the room as a whole, not isolation in one or two directions only. Think in terms of my fish-tank analogy. You can't build a fish tank that only holds water on one side, because that's the only side you want to look at the fish through. You still have to make all of the other sides equally water-tight, even though you don't care if the fish can be seen, or not seen, from the other sides.

Consider the gobo - that is the very definition of "heavy bottom - light top"- You can't get any lighter than an opening!
The last time I checked, a good gobo managed to attenuate all frequencies.

You must have a very curious gobo, then! The last time I checked, gobos are not very good at all at isolating low frequencies. The last time I put a floor tom behind a rather large gobo, I could still here all of the reverberation.... the actual "smack" of the drumstick hitting the head was attenuated somewhat, yes, but all of the "boooom" was still there, on the other side of the gobo... Because the highs were attenuated reasonably well, since they travel in ray-like patterns, and can be stopped with relatively low mass any way, but the lows got through because they travel as pressure waves, not rays, and can't be stopped by low mass... Plus: diffraction...

As for being sold a pig in a poke, are you referring to the acoustician who assures me a 35kg wall will work? Or the heavy bottom wall idea? If the latter, then that's my own idea. I'm happy to be shown where it doesn't hold water (to use your analogy), apart from the fact that there's scarce evidence of its potential efficacy.

I'm referring to the fact that you are really, really, really desperately wanting to buy into any old fantasy, myth, or invented "snake-oil science" theory, because you really, really, really desperately want to make your studio do things that it can't actually do! You believe that if you can just find some magical combination of building materials, and arrange them "just so", then all will be well, you will achieve 85 dB of isolation while not overloading your structural floor, and also designing it all on your own, for under 20k$! That's the real issue here.

Yes, I get it! You need to make your place work because you already invested so much time, and money, and emotion into it. But your desperation and enthusiasm will not make the laws of physics go away. There are limits, but you reject them, and instead insist that everyone else is wrong, the theory is rong, the experts are wrong, the books are wrong, and there really is a way to o it... so you clutch at straws that you think might work: You buy the pig in the poke, in the sense of "buying" something that you totally hope will be one thing, but when you look into the bag with the light of reality shining bright, it is actually something very different.

There are very well known principles of acoustics, tried and true. Many of them are complex, but can still be expressed as simple rules of thumb, such as "isolation is only as good as the weakest link" or "you need 15dB below ambient to be inaudible" or "highs travel as rays, lows travel as balloons" or "MSM must be half the lowest needed isolation frequency" or "spring rate is governed only by gravity" or "you get 6 dB improvement for each mass doubling" or "you get 6 dB drop for each distance doubling" or "increasing 10dB sounds like twice as loud". There are solid, sound, reliable, tested, demonstrated research and equations behind all of those, and they are all absolutely correct, but they still need to be used within certain constraints. It seems you want to ignore those constraints, and also ignore the rules themselves! In your hope that there just might be something that the scientists and acousticians and researchers have missed. And you'll be the one to find it....

I'm really sorry that you have this situation, where the physical building itself and the laws of physics and the budget prevent you from doing what you want to do. But there is no way around it. Either you have to accept that you cannot achieve the massive isolation that you want to achieve to avoid annoying your neighbors and thus lower your sights, or you sell the place and move to one that DOES allow you to achieve what you want to achieve.

Getting very high isolation on the 7th floor of an office building is only possible if there is sufficient structural integrity to support the hugely massive floors AND walls AND ceiling AND windows AND doors AND HVAC system. Your structural engineer has said that there isn't enough structural integrity in your building to do that. Period. That's what this all boils down to. Either except the limitations on isolation that are imposed on you by the building and the laws of physics, making do with less isolation than what you want (which can still be pretty good isolation, by the way, but won't be perfect), or find another place where you don't have those limitations.

This is why you see numerous posts here on this forum, and all the other forums about studio design and construction, recommending that a studio needing high isolation should always be built on the ground floor, slab-on-grade, never on an upper floor. Because upper floors just do not provide the conditions that you need. Yes, there are cases of studios built on upper floors with high isolation... but with high budgets too, that extend to modifying the building structure itself to produce the needed conditions. It seems you can't do that in your case...

In a nut shell: Your studio can sound fantastic, be isolated very well, and be cheap to build. Pick any two. Or just one.

I wish I had better news for you, but reality is stark.

Short summary: You need greater than 80 dB TL to make your studio viable in the manner you want to use it (assuming rock band at 115 dB, target in the room below at less than 35 dB). I suspect that you can probably get TL into the high 60's for your place, within the limitations imposed by the building. Certainly you can get way over 50, perhaps even approaching 70, but it just isn't possible to go higher, because you can't get enough mass into the place. To go higher, you'd have to spend serious money to reinforce the floor, and switch out all the exterior glass, and modify other aspects of the building too, probably. I don't see that happening. If someone is telling you that you can get 85 dB from 35kg/m2 walls, I'd run. Laugh first, then check my wallet is still in my pocket, then run.


- Stuart -

[princeplanet]

You saw the attachment?

Yes I did: that's not the way sound works. You are still not seeing the big picture. Sound doesn't go only where you want it to go: it goes everywhere, in all directions. Especially low frequency sound: it moves in the same way a balloon moves when you pump it up then deflate it rapidly: expanding and contracting equally all over. The sound from your sub (in your diagram) will not go through the floor and lower wall as a series of rays, but rather it will also go through the window, upper wall, ceiling, doors, HVAC system, etc. as pressure waves It will exit through ALL the surfaces of your room, not just the ones you'd like it to exit through. And once it is out on the other side, it does the same thing: once again expanding in all directions equally as a PRESSURE wave, not a bunch of rays. If you measure the pressure changes inside a balloon, you'll find that it is the exact same value at all points. There's no difference between the pressure just inside the neck of the balloon, or right in the middle, or towards the bottom, or the top: it's the same everywhere.

What makes you say it is not not a MSM system?

Because it isn't! There's no spring involved: just two masses. Sound that went out loudly through the low-mass upper wall, or window, or ceiling, or wherever, and is now in the cavity, has no MSM relationship with the structural floor. It is just sound waves in air. When it reaches the floor, it simply sees "here be Mass Law!", and behaves accordingly. You only get MSM between surfaces where there is a spring that couples them.

As for why there's scarce information regarding the "heavy bottom - light top" wall idea, that may have to do with the fact that most isolated rooms are equally concerned with TL through walls as well as through floors?

No. It's because TL is a system, not a bunch of parts. The isolation in a system is only as good as the worst part, or "weakest link" if you prefer. Its because isolated rooms are concerned with isolation of the room as a whole, not isolation in one or two directions only. Think in terms of my fish-tank analogy. You can't build a fish tank that only holds water on one side, because that's the only side you want to look at the fish through. You still have to make all of the other sides equally water-tight, even though you don't care if the fish can be seen, or not seen, from the other sides.

Consider the gobo - that is the very definition of "heavy bottom - light top"- You can't get any lighter than an opening!
The last time I checked, a good gobo managed to attenuate all frequencies.

You must have a very curious gobo, then! The last time I checked, gobos are not very good at all at isolating low frequencies. The last time I put a floor tom behind a rather large gobo, I could still here all of the reverberation.... the actual "smack" of the drumstick hitting the head was attenuated somewhat, yes, but all of the "boooom" was still there, on the other side of the gobo... Because the highs were attenuated reasonably well, since they travel in ray-like patterns, and can be stopped with relatively low mass any way, but the lows got through because they travel as pressure waves, not rays, and can't be stopped by low mass... Plus: diffraction...

As for being sold a pig in a poke, are you referring to the acoustician who assures me a 35kg wall will work? Or the heavy bottom wall idea? If the latter, then that's my own idea. I'm happy to be shown where it doesn't hold water (to use your analogy), apart from the fact that there's scarce evidence of its potential efficacy.

I'm referring to the fact that you are really, really, really desperately wanting to buy into any old fantasy, myth, or invented "snake-oil science" theory, because you really, really, really desperately want to make your studio do things that it can't actually do! You believe that if you can just find some magical combination of building materials, and arrange them "just so", then all will be well, you will achieve 85 dB of isolation while not overloading your structural floor, and also designing it all on your own, for under 20k$! That's the real issue here.

Yes, I get it! You need to make your place work because you already invested so much time, and money, and emotion into it. But your desperation and enthusiasm will not make the laws of physics go away. There are limits, but you reject them, and instead insist that everyone else is wrong, the theory is rong, the experts are wrong, the books are wrong, and there really is a way to o it... so you clutch at straws that you think might work: You buy the pig in the poke, in the sense of "buying" something that you totally hope will be one thing, but when you look into the bag with the light of reality shining bright, it is actually something very different.

There are very well known principles of acoustics, tried and true. Many of them are complex, but can still be expressed as simple rules of thumb, such as "isolation is only as good as the weakest link" or "you need 15dB below ambient to be inaudible" or "highs travel as rays, lows travel as balloons" or "MSM must be half the lowest needed isolation frequency" or "spring rate is governed only by gravity" or "you get 6 dB improvement for each mass doubling" or "you get 6 dB drop for each distance doubling" or "increasing 10dB sounds like twice as loud". There are solid, sound, reliable, tested, demonstrated research and equations behind all of those, and they are all absolutely correct, but they still need to be used within certain constraints. It seems you want to ignore those constraints, and also ignore the rules themselves! In your hope that there just might be something that the scientists and acousticians and researchers have missed. And you'll be the one to find it....

I'm really sorry that you have this situation, where the physical building itself and the laws of physics and the budget prevent you from doing what you want to do. But there is no way around it. Either you have to accept that you cannot achieve the massive isolation that you want to achieve to avoid annoying your neighbors and thus lower your sights, or you sell the place and move to one that DOES allow you to achieve what you want to achieve.

Getting very high isolation on the 7th floor of an office building is only possible if there is sufficient structural integrity to support the hugely massive floors AND walls AND ceiling AND windows AND doors AND HVAC system. Your structural engineer has said that there isn't enough structural integrity in your building to do that. Period. That's what this all boils down to. Either except the limitations on isolation that are imposed on you by the building and the laws of physics, making do with less isolation than what you want (which can still be pretty good isolation, by the way, but won't be perfect), or find another place where you don't have those limitations.

This is why you see numerous posts here on this forum, and all the other forums about studio design and construction, recommending that a studio needing high isolation should always be built on the ground floor, slab-on-grade, never on an upper floor. Because upper floors just do not provide the conditions that you need. Yes, there are cases of studios built on upper floors with high isolation... but with high budgets too, that extend to modifying the building structure itself to produce the needed conditions. It seems you can't do that in your case...

In a nut shell: Your studio can sound fantastic, be isolated very well, and be cheap to build. Pick any two. Or just one.

I wish I had better news for you, but reality is stark.

Short summary: You need greater than 80 dB TL to make your studio viable in the manner you want to use it (assuming rock band at 115 dB, target in the room below at less than 35 dB). I suspect that you can probably get TL into the high 60's for your place, within the limitations imposed by the building. Certainly you can get way over 50, perhaps even approaching 70, but it just isn't possible to go higher, because you can't get enough mass into the place. To go higher, you'd have to spend serious money to reinforce the floor, and switch out all the exterior glass, and modify other aspects of the building too, probably. I don't see that happening. If someone is telling you that you can get 85 dB from 35kg/m2 walls, I'd run. Laugh first, then check my wallet is still in my pocket, then run.


- Stuart -

[princeplanet]

Do you remember I made a test booth? I had to tweak it a little and get the floating height right, but the last time it was tested by an esteemed 40 year veteran from ARUP, the 110dB noise source was not detectable from below. This construction was 120kg/m2 for the floor (100mm air gap on isolators and insulation filled) and 60kg/m2 for the walls and ceiling. His appraisal was that a larger room with similar specs would also work, even without such a heavy ceiling. I wish I could have afforded him to design the build, but he was far too expensive. He does concert halls and very large facilities.

As for the SE appraisal, well, as hard to believe as I'm sure it is to you, he still hasn't calculated the max load for the walls! I have been waiting for many months and apparently he is preparing something for me to see this week. He may indeed say 60kg is not permissible, but he has already indicated that 35kg is, and that if the walls are on the beams then they will not affect the load on the floor. I just wanted to be ready with another question for him straight away because he takes too long to consider things...

So yeah, that question was to be if he'd allow a hybrid wall (heavy bottom...). I find gobos actually do attenuate some lows, obviously not as much as the highs for the obvious reason you cite-that being that lows are spherical waves and highs are rays. Otherwise gobos would be useless for live rock recordings (hey, didn't you actually advise me to do away with booth partitions and just use gobos instead? ). I'm not in denial of the laws of physics, I'm just in search of them, in this case the laws pertaining to the question of TL through a wall then floor in relation to the proximity of the wall height in relation to the floor. I'm sure there must be a BBC test somewhere. I'll try to see if my Concert Hall guy can help...

But I'm willing to concede that the miniscule increase in TL from a reinforced lower wall may not be worth the trouble. However, I'll never accept that the art/science of Acoustics as it relates to building a better/smarter studio has reached a point where there are no new discoveries to be had .

BTW, the proposed build has the studio as a room in a room, and a control room which is not. However, there is a sealed wall between them. I can't say I understand your insistence that this somehow does not represent an MSM system. A room in a room, where all inner leaves are surrounded by air tight outer leaves, is inherently MSM by default, no? There is still an air spring between the wall and the floor, no?

[princeplanet]

Turns out that there is a way to predict the answers I was asking, despite the limited information, and I was thankfully given it on another forum by a veteran studio designer.
Just wanted to say thanks to those on this forum that tried to help.