John Sayers' Recording Studio Design Forum Archive

BriHar wrote:I get the impression that we're not yet quite on the same page, so let me try and answer your questions.

1. Only MSM. One leaf of gypsum board will have to come off the old wall. In my previous post I indicated this would probably be easier to do on the mixing side, as you already have framing constructed on the tracking side. The remaining leaf of gypsum board on the tracking side of the old wall will have to be beefed up, but again this is no longer possible from the tracking room side - again because of the new framing. So, the beefing up will have to be done from the mixing side, and attached to the other side between the studs of the framing. Forgive the crude drawing:

No, it wouldn't be to much of an effort to unscrew the poles of the new frame to remove the plates from the tracking room side. So, I will remove those. I am not to lazy to do extra work for a better solution! It is just the parallel-wall-on-the-mixing-side solution you suggested, that would have made the whole frame I built futile - a waste of material and money. And the door problem ...

2. 14mm is better than ordinary 12 and in this case would suggest to use 3 or 4 layers for each leaf. Although your reasoning seems logical by adding the thicknesses together, it is only partly the case, because the resonance of the individual boards will still be present. (check out Stuart's answer to my own question in this regard http://www.johnlsayers.com/phpBB2/viewt ... 5&start=45)

Thanks for the hint. I will stick with my 14mm boards, because I would not only have to see, if "Bauhaus" will take them back, but also do the carrying again. However, I only bought enough for two layers on each side ... So, would it be a good idea to buy the 18mm boards you suggested for an additional third layer?

4. The MSM structure must be airtight. You said you cut the ceiling, but you must be referring to a drop ceiling, the wooden framing must go up to the actual ceiling. All edges (floor ceiling walls) should be caulked.

Yes, it is a drop ceiling. And yes: Caulking each layer of leave with gypsum cement was planned and done before on the initial wall. But Stuart suggested, it could be not enough as a seal.

5. Using decoupling materials as I proposed in the DIY example in an earlier post or purchase decoupling braces (e.g. Mason Industries). If you can get a stethoscope, or contact mic, you could check for transmission by tapping to see if your rubber decoupling works. Otherwise, if you can see that it compresses somewhat under the weight of the wall (remember the layers of drywall will add considerable weight), it's probably sufficient.

Could you point me to that DIY example you refer to? Stuart indicated, it would not be enough to guess here, calculation was needed. But I don't know the formula and certain factors (the weight of the hung ceiling partly resting on the frame and -potentially - heavy absorbers I might have to attach to that wall later) are difficult to predict ...

6. Again, decoupling is always good, and the method of shrouding the screw /bolt shank plus rubber washer into a plastic anchor does work.

Ok, so you mean the usual screw/dubel thing is preventing the decoupling here, right? Can you give me a picture/product link what you mean by that? I think I understand, but I am not sure what to buy.

Hopefully, to make the interaction between ceiling frame, old wall frame and new wall frame a little clearer, let me add these new pictures: When I understand you correctly, the decoupling has to be between ...
... new wall frame and floor (correctly calculated sylomer) ...
... new wall frame and sidewall (those decoupling screws with rubber shaft ...
... new wall frame and ceiling frame (???) ...
... to be complete on this side of the view. Hope, I got the whole picture this time ...

For the old wall: I would have to take it apart completely to achieve the same result on that side. Would a correct decoupling on only one wall frame be worth the effort? Or is the separation only working, if both sides were decoupled?

I called my building center. I may bring the 1.4 cm gypsum boards back and buy fermacell instead. But they only have 2cm plates (1,5x0.5m), which are actually made for the floor and are cement based. Are these ok, too? Or should I rather stick to my 1.4 cm gypsum boards and add 3-4 layers?
Another hardware store might have the 1.8cm boards, but I am not sure, if they take the excessive 1.4 boards back without me buying something else ...
And finally, what about mixing different plates: 1 or 2 layers of the 1.4 cm and one fermacell on top. Wold that make any sense?

I would strongly recommend you get a copy of Rod Gervais' Home Recording Studio, Build it Like the Pros

In addition I propose you post some detailed cross-sections of the current state of the wall-ceiling, wall-floor, and wall-wall interfacing, both old wall and new proposed.

You indicate opting for removing the new framing temporarily to facilitate removal of the drywall on the tracking side. That will make adding the additional layers of drywall to the mix side easier and less work.

I don't think you mentioned the thickness of the drywall on the old wall.
I think you'll be alright using the 14mm in two layers particularly if you add an additional layer of 18mm Fermacell (the 20mm would also work but the panel dimensions may not be ideal, you should perhaps do a cost analysis to determine which is best).

You mention

Caulking each layer of leave with gypsum cement

I think your missing the whole picture.
A Gypsum compound is used to fill the cracks between panels, this is referred to as mudding. When we mention caulking, we refer to an acoustic caulking compound used to fill spaces between sections or at junctions between floor and wall, often in conjunction with backer rod. Acoustic Sealant or caulking never hardens but stays rubbery when it cures or dries.

No you aren't building a room in room, but the technique is similar, and there should be no flanking i.e. transmission path between the two rooms via the wall acting as a bridge. Perhaps it will be easier to think of each side of the wall as a diaphram, picking up all the vibrations in the room. If there is a mechanical connection between the two sides, this vibration will conduct and be reproduced on the other side. If there is no connection, the only path is a sealed air space filled with a absorbing material which combine to retard the transmission. Remember the speed of sound is faster and more efficient (fewer losses) in harder materials - the opposite of what we are trying to achieve. Try to think of two paper cups joined by a string, if the string is taught, it transmits sound back and forth, let the string go slack and the transmission is impeded.

Regarding the choice of decoupling material, think of the rigidity of typical metal springs. Place a spring against a window and hit it with a hammer (best just use your imagination here ) If the spring is very rigid the full force of the hammer blow will transfer through the spring as if it were a spike, and shatter the glass. If the spring is to soft, the hammer will cause the spring to completely compress and the full force of the blow will shatter the glass. Now if the spring is just right, it will compress enough to be able to absorb the force of the hammer and virtually none of the energy will be imparted to the glass, so it will not shatter. Same effect here with your decoupling.
There is another mechanism in operation involved in decoupling which is often overlooked, or better said, overshadowed by the sping mechanism. Every interface between two dissimilar materials forces sound vibrations to repropagate and results in a loss of energy. This effect is not as effective as a proper spring, but it is the mechanism in operation when the spring fails. For this reason I alway suggest the use of a decoupling material at all junctions, preferably rubbery or spongy, so long as the structural or mechanical integrity is not compromised.

The use of rockwool to be blown into the ceiling cavity is the correct choice of material, however, don't confuse this with mass. It is always the spring between two mass leaves (your ceiling and the floor above) and not used to increase mass. You don't want this packed tight otherwise you'll be defeating it's purpose. It will still have a damping effect on your ceiling due to simple contact.

DIY Bolt decoupling: The hole drilled through the framing should be oversized.

Very helpful! Thank you.

BriHar wrote:I would strongly recommend you get a copy of Rod Gervais' Home Recording Studio, Build it Like the Pros

I'll look into that, but might not be able to read (and understand) the whole book before doing at least this wall.

In addition I propose you post some detailed cross-sections of the current state of the wall-ceiling, wall-floor, and wall-wall interfacing, both old and new.

Will do!

You indicate opting for removing the new framing temporarily to facilitate removal of the drywall on the tracking side. That will make adding the additional layers of drywall to the mix side easier and less work.

I don't think you mentioned the thickness of the drywall on the old wall.

The old drywall is the standard 1.2 cm thick. And, yes! I have decided to definitively build the extra-frame on the tracking side. Removing the excessive gypsum boards is no problem.

I think you'll be alright using the 14mm in two layers particularly if you add an additional layer of 18mm Fermacell (the 20mm would also work but the panel dimensions may not be ideal, you should perhaps do a cost analysis to determine which is best).

Great to know! That will enable me to use all the boards already there and buy better ones for additional layers. This will spare me some extra back pain!

You mention

Caulking each layer of leave with gypsum cement

I think your missing the whole picture.
A Gypsum compound is used to fill the cracks between panels, this is referred to as mudding. When we mention caulking, we refer to an acoustic caulking compound used to fill spaces between sections or at junctions between floor and wall, often in conjunction with backer rod. Acoustic Sealant or caulking never hardens but stays rubbery when it cures or dries.

Alright! I guessed you meant this with using the term acoustic sealant. Is this like an acrylic "fugendichter"? And by backer rod you probably mean something like a rubber stripe or pieces to fill bigger gaps and make them airtight. Could you maybe tell me the german word for "backer rod"? Couldn't figure that out with google.
Hope, I got it this time ...

Regarding the choice of decoupling material, think of the rigidity of typical metal springs. Place a spring against a window and hit it with a hammer (bet just use your imagination here ) If the spring is very rigid the full force of the hammer blow will transfer through the spring as if it were a spike, and shatter the glass. If the spring is to soft, the hammer will cause the spring to completely compress and the full force of the blow will shatter the glass. Now if the spring is just right, it will compress enough to be able to absorb the force of the hammer and virtually none of the energy will be imparted to the glass, so it will not shatter. Same effect here with your decoupling.
There is another mechanism in operation involved in decoupling which is often overlooked, or better said, overshadowed by the sping mechanism. Every interface between two dissimilar materials forces sound vibrations to repropagate and results in a loss of energy. This effect is not as effective as a proper spring, but it is the mechanism in operation when the spring fails. For this reason I alway suggest the use of a decoupling material at all junctions, preferably rubbery or spongy, so long as the structural or mechanical integrity is not compromised.

I think I got that before, but two questions:
Stuart pointed out that the decoupling of the wall would work only, if the used material (like sylomer) is calculated appropriately in its "bouncing factor" in correlation with the weight of the whole wall. So far, i don't know the formula to calculate this correctly. Also, I am not sure how the partly resting weight of the ceiling on the wall frame has to be taken into account as well. So, I basically don't know if this will be just an ...

expensive but useless decoration under your wall

Same goes for the other spots of decoupling spots. That's why I wonder if this is beyond my abilities and financial possibilities (I can spend something between 2000 - 3000€, but there are other things to be done as well) or if a non-calculated decoupling will be not as good as the real thing, but bring some improvement, that is worth it. I could figure out the elastic property of the rubber mats I bought, as well as the weight of the wall construction. But I am in need of the right formula ...

The use of rockwool to be blown into the ceiling cavity is the correct choice of material, however, don't confuse this with mass. It is always the spring between two mass leaves (your ceiling and the floor above) and not used to increase mass. You don't want this packed tight otherwise you'll be defeating it's purpose. It will still have a damping effect on your ceiling due to simple contact.

Remember, that the ceiling is in my case not so much important for isolation (because I already have no problems with neighbors), but rather to stop the one layer of gypsum boards from resonating and hopefully absorbing some low end. My ceiling is not very high already and there will be another 4cm added on the floor with the parquet, so I would like to avoid having to build a "Plattenschwinger" above my head, if possible. Under these circumstances - would you still recommend the stone wool to be loose?

DIY Bolt decoupling:

That is what I needed! Thanks again!

I'll look into that, but might not be able to read (and understand) the whole book before doing at least this wall.

I hope this doesn't come off as sounding harsh and unfriendly, since that isn't the intention at all. Quite the opposite. But here goes anyway:

Stop. If you build that wall, or anything else, BEFORE you understand what you are doing, then you would be absolutely wasting your time, your money, and a lot of hard work, all for nothing.

Brian has been trying to tell you the same thing diplomatically, but the bottom line is this: there are many, many things that you are talking about doing that simply do not make sense, some of which you have done already, some still planning to do. It is because you don't have a good grasp yet of the basic principles behind acoustic isolation. I'm not trying to insult you, or bring you down: just pointing out that there are things you need to learn first, BEFORE attempting to go any further at all with your build. You aren't ready to be building yet.

So I agree with Brian: first of all, just stop building. Don't waste any more time, money, effort, materials etc. Then get Rod's book, read through it a couple of times, ask questions here (or ask Rod himself), until you understand the concepts. Then design your entire room properly, taking into account ALL of the factors, concepts, potential problems, etc., Then post the complete design here, and only when everyone agrees that you have a good design, only then should you be picking up a hammer to start actually building. It will take a lot more time, for sure: weeks, perhaps months. But that is MUCH better than roaring ahead at full steam, doing things that will not produce the results you are hoping for. The solution then will be even worse: Rip it all down and start again, doing it right the second time.

I hope that came out right: I'm just trying to help you here, but I seem to have this bad habit of "telling like it is" without much sugar coating, and some people don't like that.

- Stuart -

I agree with you, that I indeed should take the time to study a book like that completely. I am not at all insulted by this. Both of you have been so kind and patient with me!
But the thing is, I have a fixed amount of time to do at least the basic structure (building the separation wall between both rooms, painting and doing the parquet in the tracking/teaching room. That has to be done by the 4th of November, because I will continue teaching then. I already stopped building anyway, since I realized myself, that it was not any good, if the basic things, like isolation between those rooms, didn't turn out well. Now, studying a technical book in english (I already have three books about room acoustics, which I partly read) could turn out a long time project. I am not that fast with scientific texts in another language! Maybe I will have been through with it, when it comes to building room treatment elements. But I simply cannot just take the time needed until I continue with the wall.
But I agree with you, thats why I made an appointment with a professional acoustic consultant tomorrow. He will give me the information to build that wall right, I hope. I will post the results of course and will continue with my questions, as soon as I did catch up with the learning. Thanks, guys!

The main reason I suggested Rod's book is primarily because it is one of the most practical (real world) works in this area, doesn't get too deep or involved with the mathematics to spin your head. Just practical "how do I build this?" type information and written in an easy to follow narrative.
BTW your comprehension of english is really not too shoddy

Regarding the acoustic sealant, use silicon Fügedichtung rather than acrylic.
The backer rod is a closed cell foam extrusion (like a long foam worm) and is used in conjunction with the caulking. You do have to realize that most of the advice given so far is based on, or involves compromise. Compromise is ok if you understand what's being compromised, but if you don't, you might be very dissapointed in the end when the results do not meet your expectations.

Take the Advice of a pro that sometimes posts here named Avare (Andre) whos signature line reads:
"Good studio building is 90% design and 10% construction."

What is the formula to calculate the needed material for floating? I tried finding it in the forum search unsuccessfully. I gathered from your answer, the mass of the wooden frame including all gypsum boards attached must be a variable in it, the rubbers deflection strength is in combination with the area of the rubber.

Exactly. The manufacturer of the rubber should publish the basic numbers here, which tell you how much the rubber must deflect ("squash down") in order to float. It will be something like "10% to 20% optimum deflection. Loading of 5 kg/cm2 will cause 10% deflection" or something like that. That's just an example that I made up in my head, so do NOT take those figures as being valid! So you then need to calculate the total mass of the wall, figure out how many cm2 of that specific rubber you need, then place the rubber in the correct location. But it is more complex than that, since some parts of the wall might be heavier than other parts. For example, the area under window and door frames might be different, and places where you have heavy things hanging on the wall might also be different, so you need to calculate the correct amount of rubber for each part of the wall.

This might help you understand the issues:
http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

That is about floated floors, not floated walls, but the concepts are the same.

However, when I cut the ceiling wood construction between both rooms, the mass of that side of the ceiling will also partly have to rest on that wall frame. But how can I calculate that "partly"?

Exactly! You need a structural engineer to calculate that. That's why floating a wall is not easy: there are many, many ways to get it wrong, and only one way to get it right....

I thought it would only be a room-in-room construction, if the whole system was closed (floor, ceiling, 4 walls). Are you suggesting the whole thing won't work at all for insulation, when I don't do that (continue the wall around the whole tracking room and to a new ceiling? Don't get me wrong: I do not need "perfect" isolation. I will be enough, if I can monitor people in the recording room without too much cross talk.

For any room, isolation is only as good as the weakest part. So if you have fantastic MSM walls around all 4 sides that get you 65 dB of isolation, but the ceiling only gets 40 dB of isolation then the entire room only gets 40 dB of isolation. It is that simple. Sound is like water: it always takes the easy path out. If water is running down a hill, and you put a rock on the way, it will simply move to one side and go around the rock. Same with sound. If you want to isolate a room, then all sides of the room must be isolated to the same level. If your ceiling is already done, and is coupled to the rest of the building, then it does not matter how good your walls are: the ceiling is the weak link, and that is how the sound will get out. You could build six-foot thick concrete walls around the room, and it would make no difference at all to the isolation, as the sound will just take the easy way out: through the ceiling.

But what about the ceiling? There, it is more about absorbing the sound and about putting more mass on the gypsum boards to prevent them from resonating at low frequencies. Also, I really cannot redo the ceiling, which I would have to do, to put fiberglass in by hand. My Question: Is this approach of injecting material suited for the ceiling then? What material is best blown in there? I gathered here, the more mass, the better, hence, the guy recommended rock wool.

You seem to be confusing the issues here: In an MSM wall, the mass is in the leaves, not the insulation. The insulation is there for one purpose only: to damp resonance inside the wall. Using insulation that has more mass is not going to increase the isolation of the wall. There is an optimum mass for each type of insulation, and for rock wool it is roughly 50 kg/m3. If you use rock wool that is a lot more dense, then your isolation will DECREASE, since it will no longer be damping the resonance optimally. And the same if you use insulation that is too light: either very heavy of very light means the the acoustic absorption characteristics are no longer optimum, and the wall will no longer isolate as well as it should. Or the ceiling in this case. Same principle.

What product/material do you refer to for that "acoustic sealant"?

the Green Glue Company also makes another product, which is acoustic sealant. Other companies make acoustic sealant too. But if you can't get proper acoustic sealant, then you can use ordinary caulk, then type used in bathrooms and kitchens to seal around the edge of sinks, bath tubs, toilets, etc. Use a type that never gets hard, and always remains soft and flexible, even when it is completely dry.

Especially, how can I seal off the air between the wall and the detached ceiling?

The same way. Except that the "detached ceiling" should be resting ONLY on the inner-leaf walls, and not attached to the structure of the building in any manner. If that's what you have, then just run a bead of acoustic sealant (or bathroom caulk) into the gap between the gypsum board on the ceiling and the gypsum board on the walls. When you put the gypsum board on the ceiling joists, you should have left a small gap all around the edge, just a couple of mm wide. Use the caulk to seal that. You should really put backer rod in that gap first, then sealant on top of the rod. That's the correct way of doing it.

Nothing. The frame just rests on the rubber mat on the floor.

Then you have a MAJOR problem! Apart from being unsafe, that is probably also illegal. The walls must be attached to the floor. Each time you open and close the doors, the entire wall can move across the floor. Heavy vibrations can cause the wall to move across the floor. And if there is even an earthquake, the entire room will collapse ore be severely damaged, since the wall will be bouncing up and down, smashing into the floor with each wave. You really, really should fix that, and do it urgently! I would never work in a room where the walls are not fixed to the floor. I'm surprised that your framing passed inspection like that. Didn't the inspector notice that your walls are not bolted down? Very surprising.

- Stuart -

BriHar wrote:The main reason I suggested Rod's book is primarily because it is one of the most practical (real world) works in this area, doesn't get too deep or involved with the mathematics to spin your head. Just practical "how do I build this?" type information and written in an easy to follow narrative.
BTW your comprehension of english is really not too shoddy

I am already reading the book you recommended and I must say THANK YOU!!! again. It is really way better than all the others before. I don't have any problems understanding anything - contrary to earlier reading experiences of that topic. My appointment with the acoustic consultant will be next monday. I think by then I will have figured out way more and he will only have to make some fixes and extra advices to my plan.

Regarding the acoustic sealant, use silicon Fügedichtung rather than acrylic.
The backer rod is a closed cell foam extrusion (like a long foam worm) and is used in conjunction with the caulking.
You do have to realize that most of the advice given so far is based on, or involves compromise. Compromise is ok if you understand what's being compromised, but if you don't, you might be very dissapointed in the end when the results do not meet your expectations.

Thanks! Now I think I have - also with the help of the book - a way better understanding what needs to be done. I think my expectaions might be a little lower than what you guys would think. But with starting this project i kind of got eager to get it even better than initially planned. I f that turns out to be that way, great!

Soundman2020 wrote:

Nothing. The frame just rests on the rubber mat on the floor.

Then you have a MAJOR problem! Apart from being unsafe, that is probably also illegal. The walls must be attached to the floor. Each time you open and close the doors, the entire wall can move across the floor. Heavy vibrations can cause the wall to move across the floor. And if there is even an earthquake, the entire room will collapse ore be severely damaged, since the wall will be bouncing up and down, smashing into the floor with each wave. You really, really should fix that, and do it urgently! I would never work in a room where the walls are not fixed to the floor. I'm surprised that your framing passed inspection like that. Didn't the inspector notice that your walls are not bolted down? Very surprising.

Stuart, I think this is no problem. Germany is not known for heavy earthquakes! In my 35 years I never experienced a single one. My mother told me of one, which made the tea pots in the cupboard rattle slightly. Also, the original wall (which stands since 5 years like an oak) is completely non-structural. It is just built with a wood frame (which is connected on the sides to the concrete walls by heavy bolts) under the hung ceiling. The new one I will connect to the wood frame, because I realized the transmission via this frame between the two rooms. However, I already had a friend over who really knows this stuff and he didn't have any complains towards me.
I guess Germany is considered a very burocratic country, but ... there was no inspector visiting. I just asked the owner, if I may do this and he was fine with it.

I read your hints and link about decoupling. This is what I gather from it:
My floor consists of heavy Tiles on concrete. While I assume, the tiles will transmit some low end, my situation is probably closer to concrete slab (I am in the basement) than anything else. I will probably not be able to really calculate the needed rubber deflection and area to get it floating. There are simply to many unknowns (maybe the consultant will on monday?).
I understand now (at least I hope, I do) that probably the leaves of gypsum being decoupled from the frame by a resilient channel are probably more important that grounding the frame on sylomer (which is also expensive. So I guess I turned my attention to the wrong spot here. Thanks for making that clear!

Regarding the ceiling and the stuffing material: Isolation is not important here. The only isolation I need is between the tracking room and the mixing room. I already have no problems with my neighbours. That is why I was asking, if - in this case - tighter might be even better, because I crave absorption here, not reflection. It might still be better lighter packed. I just wanted to make sure there is no misunderstanding here.

Hi guys,

back again for more trouble!

While I hopefully start soon on the soffit mount in my mixing room, I would like to think two more things a little ahead of time:

The first thing would be my ceiling, which I earlier described here. It unfortunately is already a hung ceiling with just one layer of gypsum. It resonates as hell with sub woofer frequency and (arghh!!) the builder did not put any insulation inside! It is just a wooden framework, that separates the gypsum by about 10cm from the conrete above.
However, I have no problems with neighbors or much sound coming in that I would disturb my work, as it is in the basement and very quiet, as it is now. I also couldn't afford to take the hole ceiling off as to do it properly (with more than one layer and - I guess - heavier gypsum boards.
Thats why I am thinking of two measures:
1) Are there any smaller acoustic tiles available, that could be attached to bare drywall (glueing would be the easiest, but I am not sure if something like that would work without coming down on me!!!)? I have googled a lot, but found nothing. THe idea would be to increase the mass of the ceiling without having to do it all over again. If my idea with smaller tiles is for some reason rubbish: What else would you recommend doing for that matter.
2) To insert insulation without having to remove the gypsum there is an approved method of injecting insulation grains (different materials available) into the ceiling from just a few holes. I already had a guy here to evaluate, if that was possible and the frame would carry the additional weight. He gave me green lights. But as he is no acoustic specialist, I would like to aks you if that (quite expensive) procedure would be worth the effort. I would think, the additional weight on the gypsum (hence, I would take the heaviest insulation available) must tame that resonance at least a little ...

What du you think? What is worth the effort? Again: It is not about insulation of sound coming in or out. It is just that resonance I want to dampen.

The other thing would be the separation wall, however, this time from the mixing room perspective (see pictures). As many of you suggested (and I meanwhile learned by reading), symmetry is essential for the control room. Since I got the skewed wall and the whole studio build has already exceeded my initial time frame by far (yes, I had to painfully learn that!!!), I thought about doing that properly again:
The other side of the wall is fixed, as everything had to be ready there quickly (I earn half of my income by teaching and simply couldn't dispense of using it any longer). So I came up with this symmetrical shape with the least loss of space (which is quite essential for me:
I am aware, the "arrow pointing the other way" would be better. But I would just loose so much more space this way and cannot afford to. And the tilt is only 7 - 8°. So I guess, with adding a lot of treatment to this wall (corner traps and absorbers or more slot resonators), it would be much better than the original wall, that I would otherwise just reinforce with heavier and thicker gypsum. What do you think? Worth it? Better ideas?

I think this is no problem. Germany is not known for heavy earthquakes

That doesn't matter. You still cannot leave a wall unattached to the floor. Earthquakes are just an extreme example, but ANY type of vibration can cause the wall to move, even the vibration from opening and closing the doors. Since both leaves are sealed air-tight, opening and closing doors creates large changes in pressure inside the rooms and the walls, and even that could be enough to do damage, if the walls are not anchored into the floor.

Also, the original wall (which stands since 5 years like an oak) is completely non-structural.

That also does not matter. ALL walls need to be attached to the floor, regardless of whether or not they are load-bearing (structural) or not.

However, I already had a friend over who really knows this stuff and he didn't have any complains towards me.

Is he a qualified structural engineer? Is he legally permitted to sign the documents that state that your structure is safe, and meets all legal building code requirements? If not, then his opinion does not count. sorry.

there was no inspector visiting. I just asked the owner, if I may do this and he was fine with it.

Big red flag! You really, really REALLY need to call in a professional, qualified structural engineer, and ask for his signed, written report that says your structure is legal and safe. What ANYBODY else says is simply not valid. The ONLY person who can give you the correct advice, is the person who is technically and professionally trained to do so, and legally qualified to sign the documents you need.

If you do this without making certain that you are doing it legally, then YOU are responsible for what happens, and YOU are liable for all costs, expenses, injuries, damages, fines, and jail time. Not your friend who "said it was OK", and not the owner "who was fine with it". You and you alone are responsible.

My floor consists of heavy Tiles on concrete. While I assume, the tiles will transmit some low end, my situation is probably closer to concrete slab (I am in the basement) than anything else. I will probably not be able to really calculate the needed rubber deflection and area to get it floating. There are simply to many unknowns

Exactly, and since you have a "slab on grade" floor, then it is extremely unlikely that you will need to float the floor.

Regarding the ceiling and the stuffing material: Isolation is not important here. The only isolation I need is between the tracking room and the mixing room.

That also does not matter. Isolation is a "shell" or an "envelope". You cannot only isolate in one direction, because sound travels in ALL directions. sound will not just go the way you want, and the stop when it runs into a strong barrier. It will go in ALL directions at once, and if it finds a way where there is a weak barrier, then it will go through that, and still get around to the other side of the strong barrier, just as though it was not there. So you HAVE to isolate to the same level on all sides, in all directions.

Regarding the ceiling and the stuffing material: Isolation is not important here.

Yes it is. As I said before, "The insulation is there for one purpose only: to damp resonance inside the cavity." If you do not put insulation in there, then those resonance are NOT damped, and that WILL affect not just isolation but also the acoustics of the room.

That is why I was asking, if - in this case - tighter might be even better, because I crave absorption here, not reflection. It might still be better lighter packed.

You cannot "pack" the insulation at all. It can only be placed in the position where it needs to go, and must never be compressed or forced into a space that is too small.

The first thing would be my ceiling, which I earlier described here. It unfortunately is already a hung ceiling with just one layer of gypsum. It resonates as hell with sub woofer frequency

Exactly! That is EXACTLY what happens when you don't put damping material inside the cavity. It is also what happens when the drywall is too thin, and the air gap is too small. To fix this, that ceiling must be removed and replaced correctly. If not, you will never be able to get your room acoustics under control.

I also couldn't afford to take the hole ceiling off as to do it properly

Then, sorry to say, your room is never going to be usable acoustically. The ceiling as acting as a panel resonator (panel trap, membrane trap), since it is a tuned resonant "skin" over an undamped air space: Basically, it is a drum.

1) Are there any smaller acoustic tiles available,

Those will not be much use. They don't have much mass, and "acoustic" is just a name: they are not meant for acoustic control in studios. The real purpose of those is for offices, schools, shops and places like that, where they need mild acoustic control of speech frequencies. Not major trapping and damping of bass resonance. The damping that you need must go inside the cavity, not on the face. Damping the face will help a little bit, if you do it correctly, but you STILL need damping in the cavity.

2) To insert insulation without having to remove the gypsum there is an approved method of injecting insulation grains (different materials available) into the ceiling from just a few holes.

That probably will not work either. You would have to find out the acoustic properties of those "grains", so call the manufacturer and ask them to send you their technical reports on the acoustic testing of those products. If there is no acoustic testing information, then forget it: you cannot use materials whose acoustic properties are not known.

He gave me green lights. But as he is no acoustic specialist,

The he is probably not the right guy to do the job!

I would think, the additional weight on the gypsum (hence, I would take the heaviest insulation available) must tame that resonance at least a little

You seem to be misunderstanding the acoustic principles here: This is not about mass inside the cavity, it is about DAMPING inside the cavity, and mass on the leaf. Two very different and very necessary things. You need the extra mass, but NOT inside the cavity: the extra mass must be on the "leaf" (in this case, the drywall ceiling). And you need the damping INSIDE the cavity, not on the leaf, to damp the resonances that are going to happen inside there.

It is not about insulation of sound coming in or out. It is just that resonance I want to dampen.

Fine, but the only way to dampen that resonance is by changing the resonant frequency of the tuned system. You do that by increasing the mass of the face, and/or increasing the air gap, and/or increasing the absorption inside the cavity. Doing any of those will bring the resonance down to a lower frequency. You have to calculate what frequency you need to get to, then calculate how much extra mass, extra air gap, and damping you need. This is not about guessing: it is about measuring and calculating.

with adding a lot of treatment to this wall (corner traps and absorbers or more slot resonators), it would be much better than the original wall, that I would otherwise just reinforce with heavier and thicker gypsum. What do you think? Worth it? Better ideas?

That will work, yes. It is not ideal, but if you build that wall correctly, and treat that wall properly, then it should be OK.


- Stuart -

Thank you for your generous answer, Stuart. About the older topics: this is all good now. The separation wall is drilled to the floor with some heavy bolts.
It is more about my latest post, now:
About the wall from the control room side - that is good to know! About the ceiling - less good, but still good to know! I am not sure, if I can afford that ... and I will definitively not make that DIY. I will ask a friend, who is more experienced and call some pros for the price.

and I will definitively not make that DIY.

Replacing the ceiling is actually not that hard to do: it's just a pain in the neck! Literally: You are looking up all the time, so your neck gets tired...

Seriously, it isn't that hard to do it. And if you are going to replace the ceiling, then do yourself a big favor, and add some "resilient channel" across the joists, before you put the new drywall on: That will improve your isolation a lot, and also increases the air gap, as well as decoupling the drywall from the joists. For the extra few dollars in cost, you get some important benefits.

- Stuart -