John Sayers' Recording Studio Design Forum Archive

Don't mean to be rude in any way and please pardon my hastyness i know it's a forum and you people don't get paid about what you're doing here saving our asses, but is there a way to have a comment regarding the two sketches? Workers coming back tomorrow and i am at crossroad right now..

Hey dude,

Sorry, I've been unable to get to your thread until now.

Here are my thoughts (hope it's not too late):

- you have springs hanging your ceiling. Were the spring spec'd to hold exactly the amount of weight of your ceiling including any treatment devices/lights you'll have installed on the ceiling? If these were not designed to isolate properly, I would say they are not worth keeping.

- your anti-vibrating rubber in your diagram sparks the same questions as the springs. If the rubber wasn't design specifically to hold the exact weight of your walls then they aren't doing anything short of creating an unstable footing for the wall.

If I were you, I would yank that ceiling out and build your room within a room just like everyone else on the forum does -- the ceiling joists sit on top of your inner room walls.

Greg

Hi Greg, luckily there were other tasks and i was kind of postponing for your answer. Yes both suspension and rubber bands can withhold the weight. These are the same parts that beeros used in his project here and were designed for acoustic solutions like mine.

Yes both suspension and rubber bands can withhold the weight.

Being able to hold up the weight is not all that matters here. What matters is that they actually "float" the weight. If the device is rated for more weight than you're hanging off of it, it will short circuit causing any vibrations of your drywall to transfer directly to your outer leaf. If that is the case, hanging the ceiling like that was a complete waste of time and money. If you look at Galaxy Studios and how they floated their rooms, those devices are not just holding up the rooms, they are truly floating them. The analogy is no different than floating your speakers on Sorbothane -- requiring 20% deflection.

These are the same parts that beeros used in his project here and were designed for acoustic solutions like mine.

I'm bringing this up because if you haven't used EXACT calculations for your floating ceiling, you will short circuit and lose all of your MSM isolation ultimately resulting in a room that does not work the way you need it to. Like the link you shared here, you would then maybe have to tear it all down and start again.

Greg

Adding to what Greg said (and he is right): You can't just look at what someone else did in their studio and copy it for yours. That will only work if you have the exact same situation: same dimensions for the room, same products, same weights, same thicknesses... same everything.

Floating a ceiling, floor, wall, or speaker is not simply putting in a spring or a piece of rubber: It's rather more complicated. When you mount something resiliently (on a spring or rubber pad), you create a tuned resonant system. It will resonate at that specific frequency, which is calculated from the spring constant, weight, and deflection, and at that frequency, it does NOT isolate at all! Rather, it "resonates", meaning it amplifies the frequency. You must make sure that the resonant frequency is at least one octave lower than the lowest frequency you need to isolate. You have to do the calculations and tune the system.

- Stuart -

And to add to that, if your ceiling, walls, or entire rooms are going to be experience different weights over time, like adding clouds or treatment devices or in the case of entire rooms, more or less people or equipment, the only way to ensure you maintain your proper deflection is to make those variables a very small percentage of the calculated weight. What I'm saying is that your ceiling, walls, or entire rooms must be insanely heavy so that when a 1000 pound piano enters the room with 10 occupants that ~3000 pounds goes pretty much unnoticed by the isolation system.

Greg

Just some encouragement...

You are over thinking the leaf decoupling and possibly under thinking the HVAC! If you read Greg’s replies on the first page through again it should help make more sense... also try as he suggested to do an inside out ceiling.

Actually, an inside out ceiling wasn’t mentioned, maybe as it's mainly a jamming room you don’t need to go to heavy on absorption... there’s my ignorance

I thought I had a decent first plan with my build, but with the help here I’ve re aligned my thinking process and re designing with confidence. Keep cool and positive

Tom

Gregwor wrote:

Yes both suspension and rubber bands can withhold the weight.

Being able to hold up the weight is not all that matters here. What matters is that they actually "float" the weight. If the device is rated for more weight than you're hanging off of it, it will short circuit causing any vibrations of your drywall to transfer directly to your outer leaf. If that is the case, hanging the ceiling like that was a complete waste of time and money. If you look at Galaxy Studios and how they floated their rooms, those devices are not just holding up the rooms, they are truly floating them. The analogy is no different than floating your speakers on Sorbothane -- requiring 20% deflection.

These are the same parts that beeros used in his project here and were designed for acoustic solutions like mine.

I'm bringing this up because if you haven't used EXACT calculations for your floating ceiling, you will short circuit and lose all of your MSM isolation ultimately resulting in a room that does not work the way you need it to. Like the link you shared here, you would then maybe have to tear it all down and start again.

Greg

Hi again Greg and people,

like i said i used the same parts (because we are basically living in the same area) but that doesn't mean i didn't adjust to my area as needed. To be exact the ceiling suspension is this one https://antivibration-systems.com/product/vibro-sh/ and is working between 10-25 kp per point. I used 3 layers of gypsum board + 1 layer of mlv 2mm that equals 700kg for a total of ~20 m2. I used 36 suspensions in a grid so that means it's about ~20 kg per suspension. If the conversion is 1 kp = 1 kg i am within safe margins and my suspension is working.

For the internal walls i used this one https://antivibration-systems.com/el/product/vibro-ws/ that is rated at 80 kp per point. Two walls each one is using 8 rubber pads for a weight of ~385 kg (3 layers of gypsum board and green glue for 11 m2 ) that equals ~48 kg per rubber pad. The other two walls one is 10 m2 and has 9 rubber pads the other one is 12 m2 with 9 rubber pads that means 420kg and equals to 46 kg per rubber pad. I think i'm good, what's your opinion?

Two walls each one is using 8 rubber pads

So how are you sealing the sole plate of the wall itself to the sub-floor? You can't have any gaps there.

- Stuart -

In addition to the issue of having no air gaps under the sole plate, there's also this:

rated at 80 kp per point. Two walls each one is using 8 rubber pads for a weight of ~385 kg (3 layers of gypsum board and green glue for 11 m2 ) that equals ~48 kg per rubber pad.

Have you also allowed for the insulation in the wall cavity, electrical wiring, screws, nails, lights, decorations, paint, and all of the acoustic treatment devices that will be hanging on that wall?

How will you prevent the inner leaf ceiling from adding any load to that wall?

What about doors, windows, and HVAC?

Are you certain that none of those will be bearing on that wall?

Also, how did you physically attach the wall to the floor? It cannot just sit there with no anchor. There has to be some type of strong connection there, that holds the wall in place: bolts, nails, screws, etc. To prevent it from moving due to vibration, building movement, changes in air pressure inside the walls and rooms, doors opening and closing, earth tremors, or even just people leaning against it, kicking the sole plates accidentally, etc. What anchors are you using to keep the wall in place, and how are you preventing those from becoming flanking paths?

Did your building inspector pass that wall framed like that, with no anchors? Did you check that it meets code, and also that your home-owner's insurance covers that type of construction?

Lots of questions here.

But perhaps the biggest one of all: with the load you calculated, and the spring deflection it causes, what is the resonant frequency of that? As I mentioned before, a wall sitting on rubber pads is a Mass-Spring system: it has a resonant frequency. It does no isolate at all for that frequency, nor for a range up to 1.414 times that frequency. Did you calculate that resonance correctly, to ensure that it does not affect the isolation of your room?

The equation here is very simple. The resonant frequency of such a system is given by:

f0 = 1/2Pi * (g/d)^^0.5

Where:
d is the static deflection under load
g is the acceleration due to gravity

What frequency does that give you, for your wall, with the load you calculated? Are you sure it is OK? What isolation (in decibels) will you get from that system?

In other words, there are numerous factors here that make this not such a good idea. Likely, it is not even necessary.

You are copying a lot of what Beeros did from his thread, so I'll do the same. I'll repeat the exact same phrase I wrote in my very first response to him, before he had to tear down and re-build everything.

"To me, it looks like you are doing an awful lot of stuff wrong (or at least "questionably"). Hopefully you are still in time to stop, go back, and fix those things."


- Stuart -

Soundman2020 wrote:In addition to the issue of having no air gaps under the sole plate, there's also this:

rated at 80 kp per point. Two walls each one is using 8 rubber pads for a weight of ~385 kg (3 layers of gypsum board and green glue for 11 m2 ) that equals ~48 kg per rubber pad.

Have you also allowed for the insulation in the wall cavity, electrical wiring, screws, nails, lights, decorations, paint, and all of the acoustic treatment devices that will be hanging on that wall?

How will you prevent the inner leaf ceiling from adding any load to that wall?

What about doors, windows, and HVAC?

Are you certain that none of those will be bearing on that wall?

Also, how did you physically attach the wall to the floor? It cannot just sit there with no anchor. There has to be some type of strong connection there, that holds the wall in place: bolts, nails, screws, etc. To prevent it from moving due to vibration, building movement, changes in air pressure inside the walls and rooms, doors opening and closing, earth tremors, or even just people leaning against it, kicking the sole plates accidentally, etc. What anchors are you using to keep the wall in place, and how are you preventing those from becoming flanking paths?

Did your building inspector pass that wall framed like that, with no anchors? Did you check that it meets code, and also that your home-owner's insurance covers that type of construction?

Lots of questions here.

But perhaps the biggest one of all: with the load you calculated, and the spring deflection it causes, what is the resonant frequency of that? As I mentioned before, a wall sitting on rubber pads is a Mass-Spring system: it has a resonant frequency. It does no isolate at all for that frequency, nor for a range up to 1.414 times that frequency. Did you calculate that resonance correctly, to ensure that it does not affect the isolation of your room?

The equation here is very simple. The resonant frequency of such a system is given by:

f0 = 1/2Pi * (g/d)^^0.5

Where:
d is the static deflection under load
g is the acceleration due to gravity

What frequency does that give you, for your wall, with the load you calculated? Are you sure it is OK? What isolation (in decibels) will you get from that system?

In other words, there are numerous factors here that make this not such a good idea. Likely, it is not even necessary.

You are copying a lot of what Beeros did from his thread, so I'll do the same. I'll repeat the exact same phrase I wrote in my very first response to him, before he had to tear down and re-build everything.

"To me, it looks like you are doing an awful lot of stuff wrong (or at least "questionably"). Hopefully you are still in time to stop, go back, and fix those things."


- Stuart -

Stuart you're asking questions i'm afraid i cannot answer. First of all i didn't pay for an engineer to design and construct what i call a home studio. Too much money for my humble need not to leave my house when i want to play the drums without neighbors get agitated. If that helps for the ceiling suspension natural frequency is 3hz at maximum load. Beyond that i don't know what you're asking me nor what i need to answer.
Yes you're right about the copy thing, not only from Beeros but a lot others guys that i have studied to come to this point to draw a plan of all actions and tasks i need do to have a basic insulation. I am not suggesting my construction to somebody else nor i intend to earn a living from building rooms like that. I try to built something myself with cost in mind.

About the walls those rubber bands are sitting on are connected with screws either to the floating ceiling and to the floor. There are rubber flap on top that cover the screws so as not to come to direct contact with the metal wall skeleton.

The ceiling was finished by the time i started with the inner walls, so i didn't put any more weight in the walls or in the ceiling. Any additional sound treatment that will need to go on the ceiling or walls i intend to keep it lightweight (just rockwool on wood frames). I am not planning on recording symphonic orchestras or anything like that so i am not asking for perfection.

HVAC will run insulated ducts just as Gregwor suggested. With silencer baffles inside and outside and wrapped in mlv and wood when running between inner and outer wall. One motor will be used in the outlet. About a/c i will run a pvc pipe for now waiting for a/c pipes to be installed by a technician. Afterwards it will be sealed.

you're asking questions i'm afraid i cannot answer.

Exactly. That's the point I was trying to make.

Let me put it in very simple terms: If you did not do all those calculations, and take all of those issues into account, then your walls are not floating. It's that simple. Or they might be floating now, but they won't be once you put up the acoustic treatment. Because the extra weight of the acoustic treatment would squash the pads too much, and then they won't isolate any more. Rubber will only isolate over a limited range of "compression", from about 5% to maybe 15%. If you compress it LESS than 5% or MORE than 15%, then it does not isolate any more. So if you did not take into account all those other things I mentioned, then it is probably being compressed too much, or it will be one you finish the wall completely.

But even if you did get lucky, and it is compressing just right, that still does not mean that it will isolate. Because isolation depends on the resonant frequency of the wall on its rubber pads. For example, if the resonant frequency of your wall is 40 Hz, then it does not isolate at 40 Hz, and in fact it does not isolate all the way up to 57 Hz. It only isolates well from about 80 Hz upwards. If you do not know what the frequency is, then you have a problem: You have no idea if the wall will isolate or not. That's a very large investment in time and money that you made, and you don't even know if it will work. The thing is, if you would have just put the wall directly on the floor, with no rubber pads, then it is guaranteed to work! No calculations required, no risk, no problems. The fact that you put it on pads creates the very real risk that it will resonate at the wrong frequency, and therefor it's not just that it won't isolate, but rather that it can actually AMPLIFY some frequencies. Right now, you have no idea if it will isolate, amplify, or do nothing at all.

Then there's the problem with the air gaps: you have just a few rubber pads under the wall, with large empty air gaps between them. That means that your wall DEFINITELY will not isolate! Because you have air gaps! Air can get under your wall, which means that SOUND can get under your wall.

The even worse problem here is that there is nothing you can do about it! If you try to fill in that gap with something to block the air, that will also change the resonant frequency of the wall, ... even if it is floating now, if you then put expanding foam into those gaps, it will not float any more. And you will have wasted all that money on those rubber pads...

That's the walls. You also have a problem with your ceiling: it is suspended on springs, and therefore it CANNOT be allowed to touch the walls. Because if it touches the walls, that changes the resonant frequency. If you do as you showed in your diagram, the ceiling would be resting on top of the walls, and connected to it through the caulk. Thus, the ceiling would not be floating, and neither would the walls. You also have yet another problem: the ceiling has no lateral bracing right now: with an earthquake it can swing from side to side, because you did not install sway braces to allow for that. That's many hundreds of kg up there, and in a quake that can move a LOT. Serious inertia! It's going to do some serious damage.

Those are just a few of the problems I see. This is not a good situation. There are many questionable things in what you have done, and are planning to do. Some of them will trash your isolation, and some of them are dangerous. Some of them won't do any harm, but they are just a waste of money.

You really probably should do what Beeros did: take it all down, and rebuild it properly. When we originally told him that, he got upset, and angry even... but if you read his first post, you can see that he soon realized that we were right. So he took it down, rebuilt it properly, and it worked out GREAT.


- Stuart -

There hasn't been a design especially for my room but i am following a design that a friend of mine had from the same company Beeros had used. It's obvious since i am using the same meterial and parts and the only alteration is the ceiling design (over the wall instead of next to the walls). But this came too from analysis that this company made.

So to answer your question i am following a general design but the resonant point for both ceiling, walls and floor isn't made for me. I have adapt the analogy of suspension and the rubber bands according to my space though. Still the design i am following says that resonant point for the whole room is 6-7hz in full load.

So yes perhaps i am hoping more than expecting for a good result (but i'm strongly hoping)

Beneath and over the walls between the metal skeleton and the floor/ceiling there will be rockwool and in between those layers of gypsum boards i will seal with polyethylene cord and elastic caulk.

Aside from main work i am building baffles for my hvac. I bought a roll of duct liner (only one supplier here in Athens that charged me a whole roll of 24 m2 when i only need just a little). I am thinking that i will cut stripes and putting them inside the baffles. I am supposed to put some kind of glue or fixing it with screws instead? When i cut it to stripes is there a way to restrict fibers coming loose inside the baffle? Should i put caulk on the edges?

that charged me a whole roll of 24 m2 when i only need just a little)

A typical silencer box for a studio can easily use up 4, 5 or 6 m2, and a big one could use 7 or even 8. Assuming you only use 6m2 per silencer, you will use up every bit of that 24 m2 for your four silencer boxes...

I am thinking that i will cut stripes and putting them inside the baffles. I am supposed to put some kind of glue or fixing it with screws instead?

It's not just "strips" that you need to cut: You need to cut each piece carefully to properly fit the surface that it has to cover. ALL of the interior surfaces must be fully covered with duct liner, not just the baffles!

Yes, you can use an approve spray-glue to attach the duct liner to the wood. Check with the manufacturer to find out what glues they recommend.

When i cut it to stripes is there a way to restrict fibers coming loose inside the baffle? Should i put caulk on the edges?

If you have proper duct liner, then there should be no fibers! That's the entire purpose of duct liner: the surface is treated in such a way that all fibers are bonded and cannot come loose. Yes you should caulk the joints between the wood, no it is not necessary to caulk the duct liner. Just glue it.

Here's what a typical duct liner looks like:

the design i am following says that resonant point for the whole room is 6-7hz in full load.

Are you sure about that? Are the rubber pads compressing by about 8mm when the full load is on them? If not, then it is not floating and/or not tuned to 6 Hz... Here's why:
To get a frequency of 6 Hz, you would need a static deflection of about 1/3 inch, or about 8mm. In other words, each spring, each rubber pad, and every other piece of resilient materials, must be compressed by 8mm when the full load is on it. And considering that rubber only isolates when it is compressed in the range of around 10% to 20%, that means that your rubber pads must be about 40mm to 80mm thick originally, and compressed down to a thickness of 32mm (if they were 40 originally and can handle 20% compression), or 72mm (if they were 80mm originally, and can handle only 10% compression). Is that the case? Did you check? All of them must be compressed to the exact same degree. If one of them is compressed too much, or too little, compared to the others, then that one has a different frequency...

Also, have you considered that the compression on the rubber pads under the floor will CHANGE all the time, as you change the load? As you walk on the floor, different parts of the floor will experience different compression: More at the point where your foot is pressing down, and less where it is not pressing down. And it will also change as you put equipment in there, or take it out, or as you put instruments in there, and take them out, or as you put furniture in there, or take it out, or as other people come in, or go out... So which of those scenarios did you calculate the load for, and the 6 Hz resonance? That will only happen for the one specific situation where all of the pads are compressed by 8mm: for any other situation, where some pads are compressed more than 8mm, or less than 8mm, the resonant frequency will be different.... Did you consider that in your floor design?


- Stuart -