Basement practice space for drummer

[snootnose]

Hello Group,
I'm a drummer who owns a house in Massachusetts, USA, and I am building a small practice space in my basement which will hopefully isolate my from all living matter. The basement is partially submerged in the ground, on a poured slab of concrete with concrete walls. I am using one of those walls and building three more before constructing another room inside that one (room within a room). Right now I am working on the walls of the outer room. Since I have the opportunity of starting from an open space I'm using this outer shell to try to understand sound isolation techniques. So I have set the wall heel on the cement,over a layer of isolating foam and secured to the floor using anchors in an oversized hole which is filled with silicone. The anchor heads are isoltated from the heel using 3/16" rubber washers and a fender washer as a cap.
The slab floor is thin, probably has voids beneath it, and I'm sure acts like a big drumhead so I'm isolating the outer room walls from the floor just for added sound-transmission loss. My goal is to make this outer room airtight so I'm observing some of the techniques I have read about. I have Rod Gervais' great book on building studios, and I'm learning as much as I can about the principles.

I have written this brief overview because I'm sure to have many questions along the way. My first question is: is there a preference as to build the wall studs 24" o/c or 16" o/c?

Thanks,
Peter Elwyn

[Soundman2020]

Hi Peter, and Welcome!

Congratulations on your plans to build a drum room! There have been quite a few projects like that here on the forum. Have you taken a look at those?

I'm using this outer shell to try to understand sound isolation techniques.

Well, this is probably not what you want to hear, but isolation is not something you can understand from building a single wall. What you want to do is about the hardest possible thing in acoustics: isolating drums is a tough proposition in tow main ways: First, drums are loud, so you need a lot of isolation; second they put out a large portion of their energy in very low frequencies, and very low frequencies are the hardest to isolate; and a few other things too, but those are the biggies. Isolating high levels at low frequencies cannot be accomplished with a single-leaf wall, at reasonable cost. It requires a proper fully-decoupled two-leaf MSM wall, which is a tuned system. So building a single wall won't tell you anything about how to isolate a room, except that after you have built that wall, it won't work, and your drums will still be clearly audible in the rest of the house.

Rather than trying to experiment on your own, it would probably be better to first learn the theory and principles of acoustics, and then use the equations and empirical information to plan how to achieve the isolation that you want.

So I have set the wall heel

I think you mean "sole plate"? That's the bottom horizontal member of the wall that sits directly on the floor, and the studs stand on top of it.

I have set the wall heel on the cement,over a layer of isolating foam

What are the properties of that foam? Is it specifically meant to be used to float a wall acoustically? What deflection do you need to get from it in order for it to isolate? What is the loading that you need on it in order to get that deflection? What is the hardness of the foam (durometer and Shore scale)? Is it open cell or closed cell? What is the resilience?

Floating a wall is not an easy task at all. There are many calculations you need to do in order to make sure that you are placing the correct loading on the isolator, in order to produce the correct deflection at full loading, such that the resulting resonant frequency is at least an octave lower than the lowest frequency you need to isolate.

over a layer of isolating foam and secured to the floor using anchors in an oversized hole which is filled with silicone.

That probably isn't even legal. Did you check your local building code to find out if that is permitted? As far as I'm aware, structural anchors can't be set in arbitrary compounds. Wall anchors should be firmly set in the concrete itself.

Even if it is legal, what is the purpose of the silicon? What are all of the above characteristics for the silicon? (required deflection, load factor, resilience, etc.) Since you have it contained inside a non-compressible solid (concrete), how will you ensure that you get the correct deflection? The load on the isolator causes deflection, but you are preventing it from deflecting by having it embedded in concrete. Therefore, you are relying on compressing the silicon in order to get it to float, instead of simply allowing it t deflect. Deflection is roughly linear over a fairly good range of values. Compression is not. What equations did you use to calculate how the resonant frequency changes non-linearly under different load conditions?

The anchor heads are isoltated from the heel using 3/16" rubber washers and a fender washer as a cap.

Same as above: what type of rubber is your washer made from, and what are it's characteristics? How much pressure does the bolt need to apply to the rubber in order to get the correction deflection to ensure that it isolates?

But there's an overriding issue here: you have three different resilient materials, and three different masses involved: you therefore have a three-leaf system, which implies that the overall resonance will occur at a higher frequency than any of the individual parts, and the overall isolation will be much less than what it would have been otherwise.

And there's one final point here, which is probably the biggest of all: you say that what you built here is the outer leaf, and you will later build the inner-leaf "room within a room" inside of this shell. So there was no need at all to isolate this wall in the first place! It is part of the outer leaf! What is the point in isolating one part of the outer leaf from the rest of the outer leaf?

The slab floor is thin,

You should check that. When you drilled into it to place your anchor bolts, how far down did you drill? Did you get all the way through the slab?

probably has voids beneath it,

Why? Is there something wrong with the house? Was it not built to code? Do you have a water problem in the ground below your house? Are there sinkholes in your area? What makes you think that the ground below has washed away or subsided since the house was built? If that really is the case, then you should get that examined by a qualified structural engineer, and get it fixed before you do anything else. If there are voids under your slab, then there are likely voids under your foundations too, and that's a major serious problem.

so I'm isolating the outer room walls from the floor just for added sound-transmission loss.

There is no point at all to doing that. The outer-leaf does not need to be isolated from itself, any more than the inner leaf needs to be isolated from itself. With an MSM system, you have an outer leaf which acts as one part of the resonant system, then you have the air which acts as a spring, then you have the inner leaf which acts as the final part of the resonant system. Why would you want to complicate things additionally by creating further resonant systems that can only REDUCE the overall isolation?

There's a very basic principle in isolation: a two-leaf system provides the lowest resonant frequency possible for any given combination of mass and thickness, and it does so at the lowest cost. Any time you add further leaves to a system, you automatically raise the overall resonant frequency, thus reducing the overall isolation in the lowest frequencies. A 3-leaf system will ALWAYS provide less low frequency isolation than the equivalent 2-leaf system. A 4-leaf system will provide even less low frequency isolation than the equivalent 3-leaf or 2-leaf system. A 5 leaf system provides even less low frequency isolation than any of the others. Etc. By adding additional resilient layers and solid massive couplers, you are adding additional "leaves" to the system, creating additional resonant modes, and reducing your overall isolation.

In other words, what you are doing makes no sense, acoustically. It might seem good intuitively, but one thing you will find out as you go through your design process, is that many things about acoustics are NOT intuitive: sound does not always behave the way we think it should, and especially so when resonance is involved.

My goal is to make this outer room airtight so I'm observing some of the techniques I have read about.

Making it airtight is critical. Both leaves must be totally airtight.

I have Rod Gervais' great book on building studios, and I'm learning as much as I can about the principles.

You should probably take another look at chapters 3 and 4, since it seems you missed out on some of the things he says in there. Especially the warning at the end of chapter 3 about experimenting with strange combinations of materials...

I have written this brief overview because I'm sure to have many questions along the way.

That's what the forum is here for! Questions and answers is what we are all about. Many of your questions are probably already answered in Rod's book, if you read it carefully, but there's another book that lays out the foundations of what you need to know in order to successful design and build a studio: "Master Handbook of Acoustics" by F. Alton Everest (that's sort of the Bible for acoustics). I'd really suggest that you buy that and work your way through it, so you can understand the basics of acoustics, and the principles that you'll need to know as you start designing, then later building, your studio.

My first question is: is there a preference as to build the wall studs 24" o/c or 16" o/c?

That depends on what you want to accomplish! As Rod mentioned in his book, for very low frequencies, the isolation is governed mostly by the stiffness of the wall, but that might or might not be a factor in your case. That region of the isolation spectrum occurs below the bottom end of the MSM resonance region, starting at about 0.707 times resonance. That's the area where 24" OC is mildly better than 16" OC. But at other regions of the spectrum resonance itself is the governing factor, followed by mass, then coincidence, then mass once again. All of that depends on how you build and tune your wall. With multiple resonances going on in your complex system, you'd be pretty much on your own trying to figure out all of the implications, and what type of spacing might be better or not better. Once you step outside the realm of tried and tested building methods that are fairly well understood, and have been tested and documented, and for which there are simple equations that describe the performance, then you become your very own personal acoustic test lab, since you'll be doing things that nobody has done before, nobody fully understands, and where there are no equations yet to describe what will happen. You'll have to write those equations yourself as you go along with your experimenting...

In other words, if you continue down the current path of doing multiple untested things at once in your build, then we wont be able to help you much here on the forum. Not because we don't WANT to help, but simply because you'll be in uncharted territory where nobody has done any testing before! We won't be able to tell you what the results will be, because nobody knows. Yes, we can make some educated guesses, and perhaps adapt some equations that are close to what you are trying, but there's no way that we could come up with any kind of realistic numbers that predict how your experiments will work out. We can only tell you that you will get less isolation in low frequencies than you would have gotten from a simple 2-leaf MSM system, because that much is already known. What we can't tell you is how much worse it will be, nor how much extra mass you'd need to add to your leaves in order to compensate for the lost isolation.

There's also the legal issue: if you come up with some new method for building that is not in the building code, you'd be on your own in demonstrating why it is safe, and why it should be allowed. That won't be so easy. You'd likely also find that your home-owners insurance does not cover any non-approved building methods, so you'd be liable for any and all damages that might occur if something goes wrong. For example, if the ceiling in your room collapses for whatever reason (your fault or not your fault) the fact that your walls are not anchored in an approved legal manner would exempt them from having to pay out a single cent, even if the ceiling collapse was not related in the slightest way to the wall anchors. Check the fine print in your insurance policy...

So, my suggestion would be that you undo what you already did, and just follow the normal methods that are known to work, have been thoroughly tested, and are known to work. They are also the cheapest.


- Stuart -

[snootnose]

Thank you for your kind welcome Stuart,

And I'm amazed at how much time and effort went into your reply to my first post. I greatly appreciate the interest in my project.

Yeah I know isolating drums is a monumental challenge. Personally I would like to see how much it actually works. I understand low frequencies are the hardest frequencies to absorb, so I am skeptical. I have to try though if I want to do right by my patient and suffering wife.

I guess I'll have to start over on the build. Luckily I'm not too far into it. It'll give me the opportunity to slow down as well. I'm in such a hurry to do it and get on with things, and as you said, "good enough" isn't gonna cut it. I will order the book you suggested and go thru it. I understand when you talk about uncharted land. It is very much like electricity theory. The more you understand it the more effective you will be at working with it.

A few things: my assumption about the concrete slab have voids beneath it. I have no reason to believe that it does. There is an opening that was cut into the slab, I presume when it was first set down, probably an opening for a septic pipe, that when I inspected it it seemed the gravel and dirt under it was easy to dislodge. Also the slab is roughly 4" thick - within code.(? -That's another thing I'll have to look up -so much information, so little time).

Also, the resilient materials I used were, of course, selected randomly. The foam tape I used was from an acoustics store, intended to be used for the process of isolating walls so I assured myself I was on the right track. But i did wonder if it was being compressed too much. The anchors For the walls were set directly in the concrete; it was the wood "sole plate"(thanks) that I bored oversized holes into and filled with silicone to keep the anchors shanks from touching the wood structure. These walls do not have to bear weight. They weren't here when I started, they are something I constructed so I don't think I have to be worried about how the assembly will affect the rest of the building.

I will go no further with this post until I begin to build again, although from reading what you wrote it seems I can continue with the outer room construction using conventional building technique due to the knowledge that aside from being airtight this assembly will have no further effect as far as soundproofing is concerned.

Again, thanks a lot for your time,

Sincerely,
Peter

[Soundman2020]

And I'm amazed at how much time and effort went into your reply to my first post. I greatly appreciate the interest in my project.

That often happens around here. It's what this forum is all about. New members often do get early replies like this, to help get them on track. There's a huge number of myths, mysteries, assumptions, snake-oil and magical hype out there about acoustics, and a lot of people get caught up in that without even realizing it, so we like to help get them past that and onto more solid acoustical ground.

Yeah I know isolating drums is a monumental challenge. Personally I would like to see how much it actually works. I understand low frequencies are the hardest frequencies to absorb, so I am skeptical.

Actually, isolation is not about absorption at all! That's one of those myths... People assume that the foam and panels they see on studio walls and in anechoic chambers are there to stop the sound getting out by absorbing it, but that isn't the case. It's actually pretty much impossible to isolate anything purely with porous absorption. At best, it has only a very small effect.

Rather, the only real way to isolate a room is with mass. Lots of it. "Mass" meaning thick, heavy, dense building materials, such as drywall (plasterboard), MDF, plywood, OSB, fiber-cement board, concrete, brick, glass, and suchlike. If it is thick and heavy, then the chances are it will be useful for stopping sound from getting in and out of the room. The more massive, the better. Mass is the basis for pretty much all isolation. However, mass all by itself is still not the complete solution, because of something called "Mass Law". That's an equation in physics that describes how mass affect sound, and it basically says that each time you double the mass you get an increase of 6 dB in isolation. That's in the perfect world of perfect physics with perfect mass, but that doesn't exist in real life. For actually reality, you get more like 4 to 5 dB increase in isolation for each mass doubling. It sounds good at first glance, but here's why it is actually terrible. Let's take a typical stud wall as the basic reference point. a typical stud wall in a house, built with a 2x4 frame and a sheet of drywall on each side, will get you maybe 30 dB of isolation, if you are lucky. Let's say that you need 60 dB of isolation for you drums (for example...). OK, so you double the mass of your basic wall by adding another sheet of drywall on each side, which doubles the mass, and that will increase your isolation from 30 to 35 dB. so now you double the mass again by adding TWO more sheets on each side (you now have a total of 4 sheets on each side), and you get 40 dB. So let's double the mass again, by adding 4 more sheets on each side (total of 8 each side now), and you get 45 dB. So you you double the mass one more time, by adding 8 more sheets on each side (total of 16 sheets on each side.) and you get 50 dB... I think you see where this is going! You already have 32 sheets of drywall on that wall, and you are still 10 dB short of where you need to be!

Clearly, mass law isn't much use.

That's where 2-leaf MSM comes in. MSM is shorthand for "Mass - Spring - Mass", which is a totally different principle in physics, because it is a resonant phenomena. If you hold up a massive object in mid air, hang a spring from it, then hand another similar mass on the spring, you have created a resonant system. The bottom mass wants to bounce up and down at only one single frequency, and it resists "bouncing" at all other frequencies. In other words, it resonates at one frequency. It is very much like a tuned electrical circuit, known as a bandpass filter: it allows one very small range of frequencies to get through, but blocks all others. An MSM wall works on this exactly same principle: you have two leaves of "mass" (eg. drywall), and they are separated by a "spring" (=air). They two leaves are not connected in any way, mechanically: each is held up by its own independent frame. Such a wall will have a resonant frequency at which it vibrates naturally, and any time it "hears" that frequency on either side, the entire wall will resonate, and pass through that frequency to the other side. Not only does it pass it through it can actually amplify it, so it is louder on the other side than the original signal.

So the idea here is that you tune the wall such that its resonant frequency is much lower than the frequencies that you need to isolate. Mathematically, the wall does not isolate until 1.414 times the resonant frequency, but above that point the isolation increases at a rate of about 18 dB per octave (theoretically), which is way, way way superior to the measly 6dB per octave you get by mass law. Once again, that 18 dB figure is theoretical for perfect walls, perfect materials, perfectly built, etc.. Real world is more like 12 dB per octave, but that's still nearly an order of magnitude better than for mass law! So you can get much better isolation with much less mass, and much lower cost.

There's no need to be skeptical about this: There's no guess-work involved. All you need to do is to figure out what frequencies you need to isolate, then do the math to see how much mass you need on each leaf, and how big the air gap needs to be, in order to get the amount of isolation you want for your drums. If you then build your room according to the calculations, it will work. That's the nice thing about science: the equations have been tested and tested and tested, and they are know to accurately predict the outcome!

I guess I'll have to start over on the build. Luckily I'm not too far into it. It'll give me the opportunity to slow down as well.

That would be the very, very smart thing to do!
Here's the sad story with a happy ending of another forum member who tried your approach to building his own drum room, but was much further advanced in his build when he found the forum, and discovered that what he was doing would not work. He then did some testing on his partly completed room, and found out that what we were telling him was true: his room did not isolate, and would not ever isolate they way he was going. so he took the heart-wrenching decision to rip it all apart and start again, doing it the correct way as we guided him through it... and it worked! It's a fascinating read, so go make yourself some coffee, and prepare to be entertained for the next couple of hours as you ready through his fascinating tale of anguish and success.

http://www.johnlsayers.com/phpBB2/viewt ... =2&t=17363

So don't feel alone! Other people have done this before you, and succeeded (after first failing). You are nowhere near as far along as he was, so taking down what you have done then re-starting is not such a big deal.

I'm in such a hurry to do it and get on with things,

Yep! So was this guy in the thread above... I don't know if you are familiar with the saying "Haste makes waste."? Your room will be far, far better if you do slow down now, take the time to plan and design it properly, in all aspects, then build it correctly. There's a well respected acoustician who is a member of this forum, and his signatures says something like "Studio building is 80% design, 20% construction". He is dead right about that. So take your time to learn the principles of acoustics, then the principles of design, then do the actual design, then build. And post regular updates here on the forum all the way along, in all of those stages, so we can be "looking over your shoulder" so to speak, to make sure you don't make any more mistakes!

There is an opening that was cut into the slab, I presume when it was first set down, probably an opening for a septic pipe, that when I inspected it it seemed the gravel and dirt under it was easy to dislodge.

Right: That's the way slabs are usually built. The native ground is leveled, then layers of gravel and sand are poured on top, to create a stable surface, then a waterproof membrane of some type is put on top, then the slab is poured. The gravel and sand might seem loose in that hole, but as long as the earth underneath was in good condition prior to the slab being poured, and there's no issues with ground water or sinkholes in your area, then you should be OK. Tapping gently on the floor with a hammer can help to reveal if there are voids under the slab, or other issues: you'll notice a change in the sound.

Also, the resilient materials I used were, of course, selected randomly. The foam tape I used was from an acoustics store, intended to be used for the process of isolating walls so I assured myself I was on the right track. But i did wonder if it was being compressed too much

Yep. That often happens. Resilient materials are very, very useful in acoustic isolation, but the properties need to be known and understood, and the correct materials need to be used in the correct places with the correct load on them, or they don't work. That's why I have to laugh at the vast majority of "how I built my studio" videos on YouTube, where the builder proudly shows how he put down a bunch of rubber pads, puts some 2x4s on top, then a piece of plywood, and tells you how he has done an amazingly good thing in "floating his floor". In reality, he just trashed his isolation, and also screwed up his acoustic response in the room. But at least he's happy!

Here's a very interesting thread about floating your floor, which also applies to floating your walls (same concept):

http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8173

The anchors For the walls were set directly in the concrete; it was the wood "sole plate"(thanks) that I bored oversized holes into and filled with silicone to keep the anchors shanks from touching the wood structure. These walls do not have to bear weight.

Ummm... actually, they DO have to bear weight! They have to hold up your inner-leaf ceiling, which will be quite heavy... You did say you plan to build a proper "room in a room" for your studio (and yes, you really do need to do that; you are totally correct there), but building the inner "room" implies four new walls plus a new ceiling ... That's what a "room" is! Your inner-leaf is a complete shell, just like your outer-leaf. The inner leaf has four walls, and it also has a ceiling across the top. The full weight of the ceiling rests on those walls. The ceiling is not attached to the outer leaf in any way.

So your walls are load-bearing, in the sense that the support a heavy ceiling.

Apart from that, they are also rather heavy themselves: you want to isolate drums, so you'll be putting a lot of mass on each leaf, as well as leaving a large gap between them. Your walls and ceiling are going to weigh thousands of pounds...

They weren't here when I started, they are something I constructed so I don't think I have to be worried about how the assembly will affect the rest of the building.

You do need to be worried about that, in all senses: the legal sense, the safety sense, and also the acoustical sense. Take a look at your home-owner's policy, and buried in all the legal-speak somewhere there is very likely a phrase that says pretty much that if yo modify the building in any way that does not meet code and is not approved, inspected and passed, then they insurance company is not liable for ANY damages in the event of a catastrophe. So let's say your house burned down because of an electrical fault in the kitchen, but you had also done electrical work in your studio that was not signed off, inspected, approved, stamped, etc. by the relevant authorities... you can bet the insurance company would say that the electrical system had been modified illegally, and therefore they were do not have to pay for the damages. Even worse, if somebody died in that fire, you could be held criminally responsible, and if the fire also damaged your neighbor's house, you would be responsible for his damages too. Legal liability is a bitch. Please make sure that everything you do in building your studio is approved, meets code, has all the applicable permits, and is fully inspected at every stage.

I will go no further with this post until I begin to build again, although from reading what you wrote it seems I can continue with the outer room construction using conventional building technique due to the knowledge that aside from being airtight this assembly will have no further effect as far as soundproofing is concerned.

I guess I didn't explain that very well, because your outer leaf WILL have a major effect on your sound isolation: the outer-leaf is part of your TWO-LEAF system. It is the first "M" in "MSM". The entire wall, including both leaves, is a system: it all works together. It is "greater than the sum if its parts", since it is a resonant system. resonance adds a whole new dimension to things. Many people make the mistake of assuming that a two-leaf wall is just like two single leaf walls next to each other, that each walls provides some isolation, and you just add up the bis provided by each. totally wrong. A two-leaf wall is nothing at all like a single leaf wall, and does not behave like one acoustically. You cannot just add up the isolation numbers from each part to get the total. Resonance changes all of that, in many ways.

So your outer-leaf is an integral part of the isolation system that you will be building. It needs to be considered in the design and calculations for your entire isolation plan. What you do to your outer-leaf has implications that affect the amount of isolation you will get when you build your inner-leaf, since they act together, in harmony, as a complete system, to provide isolation. Change any one factor on either leaf, and you change the total isolation, sometimes in ways that are non-intuitive, and even counter-intuitive. For example, it is possible to add mass on a wall in such a way that you get LESS isolation after you do that... and the reverse is also true: it is possible to remove mass from a wall in such a way that the result provides BETTER isolation.

Resonant systems are weird and wonderful things...

Here's one of the best documents that describes this whole issue of single-leaf, two-leaf, and three-leaf partitions:

https://app.box.com/shared/jcaoavdc8g

It's pretty old, but it lays out the basic principles for understanding all of this. Very much worthwhile reading.

- Stuart -