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Using rubber to soundproof a drum room.

Posted: Sun Feb 12, 2017 10:07 pm
by Twitchy
I'm about to start building a drum room in my garage. I have decided to use rubber as I believe it has the relevant STC. I am using 10mm thick rubber mats made from recycled tyres. Yes I know rubber is expensive but I'm committed to total sound proofing. My goal is to be able to play midnight drum solos without the neighbour hearing a thing. A lofty goal.

So far I'm thinking of gluing the rubber mats onto both sides of a 16mm thick sheet of MDF. That will mean 10mm of rubber on each side, 20mm all up. My friend believes this is overkill and that I may only need a single layer of rubber.

This will be a free standing room within a room. Please note that I ask about sound proofing advise relating to the use of rubber. This is not a question of sound treatment or structure.

So does anyone have any scientific knowledge that could enlighten me as to how much rubber I would need to stop the sound of drums or a band jamming?

Re: Using rubber to soundproof a drum room.

Posted: Mon Feb 13, 2017 1:58 am
by Soundman2020
Hi "Twitchy". Please read the forum rules for posting (click here). You seem to be missing a couple of things! :)
I have decided to use rubber as I believe it has the relevant STC.
Believing something be true, and that it really is true, are often two very different things. As is the case here....
... it has the relevant STC.
Forget STC. It is no use at all for telling you how well your studio will be isolated. STC was never meant to measure such things. Here's an excerpt from the actual ASTM test procedure (E413) that explains the use of STC.

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

It's a common misconception that you can use STC ratings to decide if a particular wall, window, door, or building material will be of any use in a studio. As you can see above, in the statement from the people who designed the STC rating system and the method for calculating it, STC is simply not applicable.

Here's how it works:

To determine the STC rating for a wall, door, window, or whatever, you start by measuring the actual transmission loss at 16 specific frequencies between 125 Hz and 4kHz. You do not measure anything above or below that range, and you do not measure anything in between those 16 points. Just those 16, and nothing else. Then you plot those 16 points on a graph, and do some fudging and nudging with the numbers and the curve, until it fits in below one of the standard STC curves. Then you read off the number of that specific curve, and that number is your STC rating. There is no relationship to real-world decibels: it is just the index number of the reference curve that is closest to your curve.

When you measure the isolation of a studio wall, you want to be sure that it is isolating ALL frequencies, across the entire spectrum from 20 Hz up to 20,000 Hz, not just 16 specific points that somebody chose 50 years ago, because he thought they were a good representation of human speech. STC does not take into account the bottom two and a half octaves of the musical spectrum (nothing below 125Hz), nor does it take into account the top two and a quarter octaves (nothing above 4k). Of the ten octaves that our hearing range covers, STC ignores five of them (or nearly five). So STC tells you nothing useful about how well a wall, door or window will work in a studio. The ONLY way to determine that, is by look at the Transmission Loss curve for it, or by estimating with a sound level meter set to "C" weighting (or even "Z"), and slow response, then measuring the levels on each side. That will give you a true indication of the number of decibels that the wall/door/window is blocking, across the full audible range.

Consider this: It is quite possible to have a door rated at STC-30 that does not provide even 20 decibels of actual isolation, and I can build you a wall rated at STC-20 that provides much better than 30 dB of isolation. There simply is no relationship between STC rating and the ability of a barrier to stop full-spectrum sound, such as music. STC was never designed for that, and cannot be used for that.

Then there's the issue of installation. You can buy a door that really does provide 40 dB of isolation, but unless you install it correctly, it will not provide that level! If you install it in a wall that provides only 20 dB, then the total isolation of that wall+door is 20 dB: isolation is only as good as the worst part. Even if you put a door rated at 90 dB in that wall, it would STILL only give you 20 dB. The total is only as good as the weakest part of the system.

So forget STC as a useful indicator, and just use the actual TL graphs to judge if a wall, door, window, floor, roof, or whatever will meet your needs.

The fact that you are starting out by believing and by using STC is an indicator that there's more research ahead of you to discover how acoustic isolation actually works. Fortunately, that's what the forum is all about! :)
I am using 10mm thick rubber mats made from recycled tyres.
That's not very much isolation. The mass of rubber is around 900 to 1200 kg/m3, so the surface density of your wall will be around 10 kg/m2. Mass law says that you'll get isolation of about 27 dB. That's even less than a typical house wall, which will get you around 30 B.
Yes I know rubber is expensive but I'm committed to total sound proofing.
There is no such things as "total sound proofing". Any sufficiently loud sound will get through any conceivable barrier. It is impossible to completely stop sound. Even the best isolated acoustic laboratory on the planet still has detectable sound inside.

So you can't stop sound, but you can attenuate it. That's why acousticians prefer not to use the term "soundproof", and rather go with "isolation". It is possible to achieve various levels of isolation, using various techniques and materials. The amount of isolation is refereed to as "transmission loss", and is measured in decibels. So the question is: How many decibels of isolation do you need? Drums can hit around 115 dBC, and more, so let's call that the high level that you need to reduce. Most people would consider 30 dbC to be "silent", and that's often the level set by noise laws. The difference, of course, is 85 dB, so in theory you need 85 dB of isolation. As you can see, your 27 dB rubber is not going to do much at all!
My goal is to be able to play midnight drum solos without the neighbour hearing a thing. A lofty goal.
Indeed. No doubt about that. 85 dB of isolation is, indeed, lofty. If that's what you want, then it cam be done, but the cost is very high. To get that type of isolation, we are talking six digits at least, perhaps seven. The very best isolated studio on the planet gets just a little over 100 dB isolation, and needed an investment of millions of dollars, and the best acoustic engineering available.

Perspective: A house wall gets you about 30 dB. The decibel scale is logarithmic. Each time you go up ten decibels, that implies an increase of ten times the intensity. So a wall that gets 40 dB needs to block ten times more sound than a house wall. One that gets 50 db must block 100 times the intensity. 60 db needs to block 1000 times the intensity. 70 dB is 10,000 times, and 80 dB is 100,000 times. So you need to block roughly one hundred thousand times more sound than a typical house wall. 10 mm of recycled rubber is not going to do anything at all for that.
So far I'm thinking of gluing the rubber mats onto both sides of a 16mm thick sheet of MDF. That will mean 10mm of rubber on each side, 20mm all up.
The math doesn't add up. 10mm rubber + 16mm MDF + 10mm rubber is 36 mm, not 20mm.

You have also increased the mass quite a bit like that, so let's check the math... We already know about the rubber, so we need to account for the MDF, which has a density of around 750 kg/m3. 16mm implies surface density of 12 kg/m2. +10 for the first layer of rubber, + another 10 for the second layer, total mass = 32 kg/m2. Wow! That's MUCH more! So it must get MUCH higher isolation, right? Nope. Instead of 27 dB from a single layer of rubber, you will now get 35 dB. Just a bit better than an average house wall.

The problem is a principle of physics called "Mass Law". It goes like this:

TL = 14.5 log (Ms * 0.205) + 23 dB

Where: Ms = Surface Mass in kg/m2.

That tells you roughly how much isolation you will get from any single-leaf wall. It's not a very heartening principle. If you want to build your studio based on single-leaf mass law, you are going to need an enormous amount of mass. Several meters of reinforced concrete should do the trick....

Fortunately, there's a better way than mass law. There are other principles of physics that apply to walls that are not single-leaf mass.
My friend believes this is overkill and that I may only need a single layer of rubber.
Both you and your friend are wrong: That is "under-kill". Extreme under-kill. It won't even get you one one-thousandth of what you need.
This will be a free standing room within a room.
Fine! That is, indeed, the way to obtain high levels of isolation at reasonable cost, and without being subject to mass law. But you can't guess and "believe" how it should work! You need to calculate it.

Here's the equations you need. First, the equation for MSM resonant frequency:
MSM-resonance-equation.jpg
Then you need to figure out the isolation for each region of the spectrum, using these equations:
Full-spectrum-TL-isoaltion-equations.jpg
With that, you can predict what the isolation of your wall system will be.
Please note that I ask about sound proofing advise relating to the use of rubber.
Sound waves are stopped by mass. Rubber is mass. It stops sound in the same way as any other mass.
So does anyone have any scientific knowledge that could enlighten me as to how much rubber I would need to stop the sound of drums or a band jamming?
According to mass law, and assuming that you want 80 dB of isolation, you would need about 180 cm thickness. Yes, that's right: a bit less than 2m. 2m will give you 81.7 dB....


- Stuart -

Re: Using rubber to soundproof a drum room.

Posted: Mon Feb 13, 2017 4:00 pm
by Twitchy
Thank you so very much for your comprehensive response. You have clearly put much time into schooling me and I greatly appreciate it. I have much to digest and will do so with pleasure. My gratitude is enormous. Thank you Stuart.

I have purchased some dirt cheap MDF. 100 sheets for $800. This is enough for me to build a room within a room within a room within a room within a room.

Do you think building four shells, each decoupled is a smarter starting point?

(I promise to conform to the rules in my next post and apologise for my oversight.)

Re: Using rubber to soundproof a drum room.

Posted: Tue Feb 14, 2017 5:35 am
by Soundman2020
Thank you Stuart.
:thu: You are welcome! That's what this place is here for.
I have purchased some dirt cheap MDF. 100 sheets for $800
16mm thick, right? If so, that's a great price!
Do you think building four shells, each decoupled is a smarter starting point?
Ummm.... Nope! That would be a four leaf wall, which is even worse than a three-leaf wall in low frequencies, and the three-leaf is already worse than the two leaf, all other things being equal. This is not intuitive, because it involves the principle of resonance, which most people don't think about very much in their daily lives! People think that if one leaf is bad, and two leaves is good, then three must be even better and four must be fantastic! But that is not the case. Here's an image that illustrates what really happens:
2-leaf-3-leaf-classic-walls-diagram-MSM-walls.gif
The one on the left is a typical house wall with no insulation, and the one just next to that is the same thing but WITH insulation. The very next one shows what you propose: a pair of walls with a total of four leaves. As you can see by the STC rating, even though the wall is now more than twice as thick, and has double the mass, the isolation only increase by 4 points! Not expected at all.

The next image shows what happens if you have the exact same situation, but leave out one of the leaves: so it is a 3-leaf system. Surprisingly, the isolation jumps by a whopping ten points! That wall actually has 25% LESS mass than the one to its left, but it is twice as good (subjectively) at isolating sound.

The second last image shows what happens if you take out ANOTHER one of those leaves inside the wall: Once again, you get a whopping jump in isolation. This is nowa simple two-leaf wall, and even though it has 50% less mass than that four-leaf wall, it is 17 points more effective at isolating sound! Very much unexpected.

The last image on the right shows what would happen if you took those to sheets of drywall (or MDF) that you pulled out the middle, and instead just nailed it as a second layer on each of the leaves: Yet another very useful six-point jump.

So, a properly built 2-leaf wall is a ginormous 23 points better at isolating than the wall you propose, using the exact same mass and total thickness of the wall.

That's the power of resonance in action. Not intuitive at all, but very true, and very useful. Many aspects of acoustics are not intuitive. Sound does not actually behave the way people think it should behave!
(I promise to conform to the rules in my next post and apologise for my oversight.)
:cop: :)



- Stuart -

Re: Using rubber to soundproof a drum room.

Posted: Thu Feb 16, 2017 12:51 am
by Twitchy
Stuart, I will just assume you are a physicist. Or a very experienced studio builder. Two leaf wall it is. Each wall will be 2 layers of MDF glued together. That 32mm each wall. I also have a mountain of rock-wool. 40mm thick sheets.

Two questions.

Green glue! In your opinion, is it worth it? I'm sure it will work, but damn its expensive.

Air gap? I'm sure this is important. How big of a gap do you recommend?

You have taught me so much! My design is taking shape. I assure you that we will make amazing music once this is complete. My last studio was earning me good money recording drum tracks. Yes I'm a drummer. Upgraded to a better house. Now i'm going mental not being able to play. Maybe I will name this studio Stuart as homage to your gifts. Thanks again.

Re: Using rubber to soundproof a drum room.

Posted: Thu Feb 16, 2017 4:56 am
by Soundman2020
Stuart, I will just assume you are a physicist. Or a very experienced studio builder.
Well, you DID ask for " anyone have any scientific knowledge that could enlighten me"! :)
Each wall will be 2 layers of MDF glued together.
Nope! Don't glue your layers together. They need to act independently, as well as together. There's a penalty for gluing panels together... Just nail up the first layer, then nail the second layer on top of it, with Green Glue in between, if you decide to go that way (but Green Glue is not glue....). You could also use drywall for the second layer, if you prefer. And either way, stagger the joints between panels with the second layer, making sure that no joint in layer #2 lines up with a joint in layer #1.
I also have a mountain of rock-wool. 40mm thick sheets.
:thu:
Green glue! In your opinion, is it worth it? I'm sure it will work, but damn its expensive.
Depends on what you are trying to accomplish: If you want the best possible isolation in low frequencies, then yes, it is worth it. If you just want average isolation, then you can get by without it.
Air gap? I'm sure this is important. How big of a gap do you recommend?
Check the equations.... :) You can figure it out from there. The depth of the air gap is part of what tunes the resonant frequency of the wall, so you adjust your air gap in order to get the resonance down to one octave below the lowest frequency that YOU need to isolate, for YOUR studio. That might be different from what other people do. But the minimum air gap is about 4": if you go much less than that, then you need to pile on too much mass to keep the resonance low. Both air gap AND mass are factors in the equations...
Maybe I will name this studio Stuart as homage to your gifts.
:oops: Wow! That's the first time anyone has said that! :oops: As long as it's not a "little" studio, and you call it "Stuart Little's Studio", that would be cool! :)

- Stuart -

Re: Using rubber to soundproof a drum room.

Posted: Thu Feb 16, 2017 2:16 pm
by AVare
Twitchy wrote:Stuart, I will just assume you are a physicist. Or a very experienced studio builder.
Stuart is many things. Among the most important is a great person!

Andre

Re: Using rubber to soundproof a drum room.

Posted: Thu Feb 16, 2017 5:30 pm
by Soundman2020
Andre! You are back! Wohhoooo!!!!!! :yahoo: :) :) :) :) :yahoo:

This is, indeed, a pleasant surprise. VERY pleasant! (and thank you for the very kind words: High praise indeed, coming from you).

I sure have missed your sharp, concise, accurate, and amazingly knowledgeable posts! And I really, REALLY hope you'll be sticking around, to correct me and keep me in line.

You are Yoda to my young Skywalker... The Master has returned.


Ecstatically,

- Stuart -

Re: Using rubber to soundproof a drum room.

Posted: Thu Feb 16, 2017 10:29 pm
by Twitchy
Then I must be Jah Jah Binks! Glad to have two masters on board. If only one of you was a Q who could magically make this studio appear. But there would be a catch of course.

Ok, Green glue was beyond my budget, but to hell with the budget. I asked the boss and she says go for it!

Calculating the gap. Ok, I'm no mathematician. But my nephew is. Well physicist/mathematician. I will get him onto it. I have room for up to 6 inches.

Thanks again. Stay tuned for an update.

Re: Using rubber to soundproof a drum room.

Posted: Fri Feb 17, 2017 12:56 am
by Soundman2020
Calculating the gap. Ok, I'm no mathematician. But my nephew is. Well physicist/mathematician. I will get him onto it. I have room for up to 6 inches.
Just to clarify, since some people get confused about what the "air gap" actually is: It's the distance across the cavity from leaf to leaf, regardless of any insulation that might be in there. In other words, if you could get your hands inside the wall cavity with a tape measure, it's the distance from the face of the MDF on the one set of studs, to the face of the MDF on the other set of studs. Putting insulation in there does not change that. It's also not the distance between the stud frames.

So, assuming that your existing garage is unfinished (no drywall on the inside, just studs), and that you build your new inner-leaf wall conventionally, one inch away from the existing wall, then your air gap will be the depth of the existing studs (3 1/2") plus the depth of the gap between frames (1"), plus the depth of the studs in the new inner-leaf frame (3 1/2"), so a total of 8 inches, in this example.

However, that could change: Since you are doing a drum room (VERY LOUD THINGS!!!), you need high isolation, which suggest that you would need to "beef up" your existing garage wall by adding more mass to it. You can't to that on the outside, of course (unless you take the whole wall apart....), but you can do it on the inside: You can cut strips of MDF, drywall, OSB, or whatever to fit in between the existing studs, and press them up against the existing outer-leaf, then caulk around the edges to seal them in air-tight, then add small cleats, nailed sideways into the studs, to hold them firmly in place. If you need LOTS of isolation, you could put two layers of "beef" in there. ... and of course, that now means that your air gap has shrunk by the thickness of the "beef". So if you put in two layers of 3/4" MDF, for example, you now have 1 1/2" less air gap.... so it is down to 6 1/2" inches now. So be careful to take into account things like that when you figure out your isolation: You do need to have a reasonably accurate measurement for your air gap, and also for your mass (surface density) of each leaf.

And there's another curve ball: You could also build your inner-leaf walls "inside out", instead of "conventionally". With inside-out walls, you build them the other way around: The sheathing (MDF, drywall, etc.) faces the cavity, and the studs face the room. That has certain advantages, but it does mean that your air cavity inside the wall is now smaller again, so you'd probably want to move the wall in a bit, to increase that again.

Lots of things to take into account!

Also: Insulation is important. Fill your entire wall with it, if your local building code allows that. The difference in isolation between "no insulation" and "full of insulation" can be as much as 16 dB, but likely at least 8 or 10 dB, which is a big deal. So do plan to put insulation in your walls. If you use mineral wool, then the density should be around 50 kg/m3. If you use fiberglass then it should be around 30 kg/m3. And if you use something else, then all bets are off.... :) (OK, so there are a couple of other possibilities, but since mineral wool and fiberglass are so abundantly available everywhere, and relative inexpensive, and really excellent for this, there's no need to look at "other stuff").

So make sure your nephew is well aware of all this stuff when he does your calculations! There's a lot of variables in those equations.... He'll need to do some research to find the values of some of them... or he could ask here! :) There are also simplified versions of those equations, that can give you a "ball-park" estimate....


- Stuart -

Re: Using rubber to soundproof a drum room.

Posted: Fri Feb 17, 2017 9:53 am
by Twitchy
quick note as I dash out the door. I'm in a rental so I am building a free standing structure. My studio will not touch the garage walls as its not my house. (Average house price in inner Melbourne is over 1 million.) Its to be portable in case the land lady kicks us out.

Re: Using rubber to soundproof a drum room.

Posted: Mon Feb 27, 2017 10:50 pm
by Twitchy
My apologies for my absence. There was this party you see.......... Then bad news from my mechanic resulting in some studio funds being reallocated to getting on the road again. The silver lining is that I have more time to design.

My garage is solid brick which is a huge advantage. I will have to cover the roller door and the roof. I will do that externally. That's easy.

So far Stuart, my design meets your specs. Two leafs with their own exclusive frame. Each leaf will be 2 sheets of 16mm MDF with green glue in between.
Also: Insulation is important. Fill your entire wall with it,
So the gap is most important. But are saying that there is no need for a gap between the insulation? I should just fill the cavity completely?

Re: Using rubber to soundproof a drum room.

Posted: Tue Feb 28, 2017 10:03 am
by Soundman2020
Two leafs with their own exclusive frame. Each leaf will be 2 sheets of 16mm MDF with green glue in between.
Nope. You are still missing the point: YOU ALREADY HAVE ONE LEAF! The garage ITSELF is the outer leaf. If you add two more leaves to that, then you have THREE LEAVES.

There is an announcement at the top of the forum about what to do to assure getting as many responses as possible.
The announcement leads to this post (click here). Actually, several people on this forum who are experts will most likely not reply if you don't do what is written in that post. Many others who are very helpful, will probably not reply out of respect for the moderators' wishes.

- Stuart -

Re: Using rubber to soundproof a drum room.

Posted: Tue Feb 28, 2017 3:27 pm
by Twitchy
I see that I am still not being clear. I apologies again.

As I am renting a home, it is illegal for me to alter the garage structure in any way. This will result in the termination of my lease. Australian housing is in a really bad way. Renters have few rights if any. I cannot alter the garage in any way. If i build on the existing structure my family will be forced to leave.

This will not be a permanent structure. It will be disassembled once the lease is up in 2 years time and reassembled in which ever garage I relocate to.

The room is probably better described as a large booth that will be in the centre of the garage with it coming within 600mm of any wall.

I hope this clarifies things although I feel that I'm still missing the point.

Tim

Re: Using rubber to soundproof a drum room.

Posted: Tue Feb 28, 2017 11:26 pm
by Soundman2020
The point is that you keep on talking about adding two leaves (frame with drywall on both sides). You do not need to add two leaves, because you already have one leaf. If you add another two leaves then you will have three leaves. You only need to add one leaf: frame with drywall on just one side. I don't now how ot explain it any more clearly than that.