Can Sound Isolation design be used as the final room shape?

I know that room shapes have to follow some constraints, if we want to avoid as much room modes as possible:No parallel walls, and ideal ratios are the main rules. -I am about to build isolation walls/floor/ceiling in my incoming recording studio, and then, modify the room shape, as described above. But before starting everything, i am just wondering if the isolation step couldn't be made in the same time than the design step: When building isolation wall,with included Mass-air-mass rule, why couldn't it be designed and built as it should be for a good design room (with right angles,breaking parallel walls, etc..), instead of doing things twice? Some people don't hesitate to keep the '2 step' attitude: they build isolation wall still parallel, then they start the room shape modifications on top of that... so i am wondering if there would be a special reason for that?? Thank you

Nightmusic wrote:

Some people don't hesitate to keep the '2 step' attitude: they build isolation wall still parallel, then they start the room shape modifications on top of that... so i am wondering if there would be a special reason for that??

Night - generally when you see that taking place - what they are doing afterwards is treating the space - not installing walls that would (in effect) create a three leaf system. One of theproblems with designing a studio with walls out of parallel is that you cannot then use established room ratios as a part of the design. All room ratios are designed based on rectangular rooms - if you start sloping ceilings and installing walls at 6 degree (minimum) splays you change all of that. The idea that you can average out the room dimensions and have that represent a room ratio (or that you can do that and use it to determine room modes) is incorrect and false on the face of it. so you pick one and proceed - or you pick the other and proceed...... I hope that helped to clearthings up for you. sincerely, Rod

Rod, I totally agree with your opinion, and furthermore, i would even say that original walls (in my case reinforced concrete ones), have to be considered as the strongest walls in a room modes calculation. Indeed, i would tend to think that isolation walls are much more less massive than concrete wall behind. And even if the total isolation wall thickness is large enough to be very massive, that mass would be spread over few inches anyway, leading to an average room dimension not so accurate to use for room modes.(Who's gonna say that sound waves would reflect 100% from the outer part of isolation, which is often made with gypsumboard??) Of course, I would use the same principle for floor and ceiling... That is why i am thinking about that option-Please tell me if i am totally lost there! -: 1) Calculate room modes from the original dimensions of the room -before any isolation-and consider the results as the strongest room modes of the room(even after the isolation put). 2) Try to reduce the effect of these room modes by designing right angles with the isolation walls.(Aren't sloping ceiling/angled walls what they do in big recording studios?) 3) Analyse the results for room modes and comb filtering with a dedicated calibrated mic and analysis software (as ETF): -Before the isolation step, -After the isolation step (which gives Mass-Air-Mass process, 2 leef system, as you suggested to me in a recent post), -After the treatment made (thanks to absorption, bass traps, diffusors...) Given this, if i am still in the right direction- or i may not at all !!- well... if i'm still right, do i have to keep the same isolation wall thickness all along the sloping design, or does the mineral wool thickness have to follow the varying cavity? Stuck at that point, another question arises: let's assume that there's some varying cavity behind isolation wall, filled with varying mineral wool thickness, what would miss to that isolation wall-or a part of it-, to become a kind of slat resonator in the same time? (if we put adapted slats on it, of course).That would do the trick of absorbing sounds with less material? Am i in the right direction, or totally lost? Well, Something tells me that my idea is kind of crazy, but, who knows... I know that bass traps/resonators don't have the same principle as sound isolation (bass traps do trap low frequency in a cavity), but i try to imagine something in between, especially for those of us who don't have that much space for special treatment. Hope i wasn't too confuse in my explanations,well i hope these questions would help others also anyway...

Nightmusic wrote:

I totally agree with your opinion, and furthermore, i would even say that original walls (in my case reinforced concrete ones), have to be considered as the strongest walls in a room modes calculation.

That is a mistaken belief on your part. When you build the inner wall assembly it changes everything. The sum total of the parts is greater than the part considered seperately. Indeed, i would tend to think that isolation walls are much more less massive than concrete wall behind. But massive in and of itself is not everything - otherwise we wouldn't need isolated construction other than concrete. And even if the total isolation wall thickness is large enough to be very massive, that mass would be spread over few inches anyway, leading to an average room dimension not so accurate to use for room modes.(Who's gonna say that sound waves would reflect 100% from the outer part of isolation, which is often made with gypsumboard??) Of course, I would use the same principle for floor and ceiling... That is why i am thinking about that option-Please tell me if i am totally lost there! -: You are 100% completely totally lost - and making things much more difficult than they need be. It isn"t that difficult. 1) Calculate room modes from the original dimensions of the room -before any isolation-and consider the results as the strongest room modes of the room(even after the isolation put). Nope. 2) Try to reduce the effect of these room modes by designing right angles with the isolation walls.(Aren't sloping ceiling/angled walls what they do in big recording studios?) Sure, nothing wrong with that....... as long s you have the room to spare to do it right. 3) Analyse the results for room modes and comb filtering with a dedicated calibrated mic and analysis software (as ETF): -Before the isolation step, 100% off in la-la land again......... -After the isolation step (which gives Mass-Air-Mass process, 2 leef system, as you suggested to me in a recent post), You can do that - -After the treatment made (thanks to absorption, bass traps, diffusors...) you can also do that - Listen - any way you look at it - you are going to have to do basic treatments to the room - I believe we have already been through what those are - and you can't get away form that - so personally - I wouldn''t bother testing until that was done. Given this, if i am still in the right direction- or i may not at all !!- well... if i'm still right, do i have to keep the same isolation wall thickness all along the sloping design, or does the mineral wool thickness have to follow the varying cavity? Nope - keepp it the same thickness. Stuck at that point, another question arises: let's assume that there's some varying cavity behind isolation wall, filled with varying mineral wool thickness, what would miss to that isolation wall-or a part of it-, to become a kind of slat resonator in the same time? (if we put adapted slats on it, of course).That would do the trick of absorbing sounds with less material? Am i in the right direction, or totally lost? Well, Something tells me that my idea is kind of crazy, but, who knows... You're totally lost again. I know that bass traps/resonators don't have the same principle as sound isolation (bass traps do [u]trap low frequency in a cavity), but i try to imagine something in between, especially for those of us who don't have that much space for special treatment.[/u] Sorry, isolation is isolation - and room treatments are room treatments. The better you make your isolation - the more room treatments you need in the end........ There is no magic "one size fits all - one assembly does both jobs" that exists in the universe.

Rod, Thank you for correcting me as you do, cause my confusions about that might have lead me directly to tha wall -lol- Well, seriously, i know that these confusions aren't mine only, all these come from different interpretations around in forums, so ur explanations will be useful for other too. Nevertheless, i may still precise some of my thoughts:

Nightmusic wrote: I totally agree with your opinion, and furthermore, i would even say that original walls (in my case reinforced concrete ones), have to be considered as the strongest walls in a room modes calculation.

That is a mistaken belief on your part. When you build the inner wall assembly it changes everything. The sum total of the parts is greater than the part considered seperately

Actually i wanted to ask more about the fact that isolation walls are precisely made with different material all way long its own thickness ('sum total of the parts'), so if we want to calculate room romes from the starting point of these walls, it seemed to me difficult to get an proper dimensions to use for that.Sure the isolation wall may do a good job in stopping waves (changing some into energy, reflecting the rest of them), but from which inner point of the wall should we make measurement? Wouldn't waves reflect differently as long as they hit the inner parts of the isolation walls? That is why i wrongly started from the principle that concrete walls would be easier to consider for room modes. But you may think that i complicate all this, so i stop there! :oops:

But massive in and of itself is not everything - otherwise we wouldn't need isolated construction other than concrete.

I wasn't speaking about isolation efficiency on that part, but room modes calculation.That is why i focused on mass, and the ability for a wall to reflect the sound waves into the room.

Listen - any way you look at it - you are going to have to do basic treatments to the room - I believe we have already been through what those are - and you can't get away form that - so personally - I wouldn''t bother testing until that was done

I will follow that conclusion anyway, but thanks to your advices i will do the things much more in the classic way, i think. I would still go for analysis room with software between isolation step and treatment step, in order to know things much more 'physically' than 'theorically'. Anyway, I will post a new thread asap to resume all the building plan i will start, and all the learning that i got till today, thanks to that forum.:wink: