John Sayers' Recording Studio Design Forum Archive

Hey, first off I'd like to say that I've been lurking off and on for a few months and just joined up and this is my first post. I'll try not to leave anything out but if I do just let me know.

I play in a doom band from GA, USA and we practice about 45 minutes away in a climate controlled 20ft x 10ft storage building. The rent we've paid on there could have built a nice place here so the wife and I decided to convert our patio into a place for us to practice. I live in the city with my closest neighbor's house is about 25 - 30 ft away from my patio. It is on a concrete slab that is 15ft x 23ft wide. We built on the slab with the outside walls laid in cinder blocks filled with sand. Coming in off of that 6 inches we built a 2x4 wall with 16 in studs and then came off another 6 inches with another wall. The middle wall facing the cincer block wall has a layer of 7/16 OSB with a layer of 30 lb roofing felt on it and then a layer of 1/2 in Advantech and another layer of 30 lb roofing felt. Everything else is just studs right now, but the plan is to put insulation on the inner wall, then insulation on the outer wall, same treatment with OSB, Advantech, and roofing felt on the outside wall and then 2 layers of 5/8 in fire rater drywall. I've been sealing up some gaps with OSI SC175 acoustical caulk.

The existing roof was trimmed up and sits on the innermost wooden wall, while the outer wooden wall and cinderblock wall run higher and a new roof will be built on. I hope that gives me my room within a room as much as possible. There will be a 36in solid wooden door with a door seal kit from acousticgeometry.com on the cinderblock wall (right in the middle of the 23 foot wall) with two more on the inner wooden walls coming into the room so we can load in and out from the carport. Additional door seal kits of it needs it, which I'm sure it ill being that the doors will be a big weak link.

I'm on a cell phone so I will try to get pics uploaded and anything else that might help but I have a few questions so far...

My main goal is to be able to make everything quiet enough that I don't upset the neighbors when we play, or my wife and kids inside the house. Lower end frequencies mostly since we tune down to drop A and run 2 amps from each guitar and the keyboardist uses 2 amps as well. We have a bassist who only gets to play with us here and there because he moved 3 hours away for a job. I don't have a sound meter to see how loud we actually get but plan on it. I did download an app on my phone but it said we were only 98db, but i don't think that is right because ( I work in EMS) the other day we flew a patient out and the app said that the helicopter was only 73db and I was about 10 ft away from it. So I can't go by the app on my phone. If I was to guess I'd say we are about 125db when we play. We usually practice from about 2pm - 8pm on Sundays.

Which type insulation should I go for? I hear Roxul Safe and Sound works great and then I hear that the cheaper yellow insulation does the same thing for way cheaper.

Will the triple walls (the 2 inner wooden walls are a double leaf design) help keep the low end from escaping?

Should I put 3 layers of drywall on the inside walls instead of two? How about the ceiling.

The concrete slab on the floor... Should I carpet it or leave it concrete and just put down some area rugs here and there.

I planned on using a ductless HVAC unit for the room like this one:

https://www.acwholesalers.com/LG-Air-Co ... t=&subCat=

Is this a good idea or no?

Anyway, I apologize if I left something out or If I break a rule. If so let me know and I will correct it. Lots of info to be found here but I just want to make sure I am not seriously wasting money on anything.

I look forward to your suggestions,

Thanks,

Clifton

Hi Clifton, and Welcome!!

Coming in off of that 6 inches we built a 2x4 wall with 16 in studs and then came off another 6 inches with another wall.

That's a THREE-LEAF wall!!! You could have gotten better isolation for low frequencies by NOT building the one in the middle...

The middle wall facing the cincer block wall has a layer of 7/16 OSB with a layer of 30 lb roofing felt on it and then a layer of 1/2 in Advantech and another layer of 30 lb roofing felt.

I'm just wondering why you went with that unusual sandwich of materials... What is the total surface density of that wall, in pounds per square foot? That's what matters most, for low frequency isolation.

Everything else is just studs right now, but the plan is to put insulation on the inner wall, then insulation on the outer wall, same treatment with OSB, Advantech, and roofing felt on the outside wall and then 2 layers of 5/8 in fire rater drywall

That seems like an awful lot of expense, time, effort, and materials for an untested, unproven, questionable isolation system! Who told you to build it like that?

I've been sealing up some gaps with OSI SC175 acoustical caulk.

Excellent! Sealing your leaves air-tight will always provide an excellent increase in isolation. It's one of the best "value for money" things you can do to a wall.

The existing roof was trimmed up and sits on the innermost wooden wall, while the outer wooden wall and cinderblock wall run higher and a new roof will be built on.

That's an unusual way of building an isolation system, but the concept is correct. Assuming that the "inner-roof" is full sealed to the inner walls (no gaps at all), and has roughly the same surface density. Ditto for the "outer roof": it needs to match the surface density of your outer wall, and also be sealed hermetically.

There will be a 36in solid wooden door with a door seal kit from acousticgeometry.com on the cinderblock wall

That is a full-perimeter seal kit that you got, right? Meaning that there is a continuous seal that runs all around the edge of the door, including both sides, the top and the bottom? No breaks, gaps, etc?

That takes care of your first seal on that door: what is your plan for the second seal on that door? Another similar kit?

with two more on the inner wooden walls

Assuming you really do have three leaves here, and will have one door in each leaf, how do you plan to open the door in the middle leaf? It cannot swing outwards, or it will bang into the outer leaf, and it cannot swing inwards, or it will bang into the inner leaf... So what's the plan there for opening it?

I don't have a sound meter to see how loud we actually get but plan on it. I did download an app on my phone but it said we were only 98db, but i don't think that is right

definitely not! Never trust a cell phone app for measuring SPL levels. The mic on a cell phone is not an omni, so it is useless for that purpose anyway, it is only designed for voice frequencies, and the pre-amp is too. Plus, the mic and pre together probably only cost a few cents... Buy yourself a proper Sound Level Meter, of a reputable brand, such as an Extech or Galaxy. That will run you about a hundred dollars on e-bay or Amazon. Avoid the cheap Chines junk meters that cost around US$ 25-50: they are merely cute toys that are probably even worse than your cell phone.

the other day we flew a patient out and the app said that the helicopter was only 73db and I was about 10 ft away from it.

Yup. Goes to show how bad those apps can be. The only time a cell phone app is any use is if you have a proper mini-acoustic mic that plugs into the cell phone (Dayton makes some reasonable ones), and you have calibrated it against a real meter, and you have loaded the calibration file into the cell phone.

If I was to guess I'd say we are about 125db when we play.

That's probably an over-estimate: 125 dBC would be painful already to most people. 120- 125 is usually considered the threshold of pain. You guys are probably more like 115-120 dBC.

Which type insulation should I go for?

For which purpose? Different densities and impedances are good for different purposes. Assuming you are looking for stuff to damp the resonances in MSM wall cavities, then you would need something that has a density of around 30 kg/m3 if you use fiberglass insulation, or around 50 kg/m3 if you use mineral wool insulation. Those will give you about the right gas flow resistivity for that application. On the other hand, if you are looking for something for a bass trap, you'd probably need a lower density, and if you wanted something to kill high frequency reflections on a surface, you'd need a rather higher density.

Will the triple walls (the 2 inner wooden walls are a double leaf design) help keep the low end from escaping?

Nope! On the contrary, it will HELP the low frequencies to get out! Three-leaf walls will ALWAYS have a higher resonant frequency than the equivalent two-leaf wall, all other factors being equal. The reason is simple: resonance. A 2-leaf wall has only one single MSM resonant frequency, and it is low, due to the large gap size. If you put another leaf in the middle, even though you increased the mass, you split the cavity in half. So now you have two thin cavities, each of which has a much higher MSM resonant frequency, plus you have the combined resonances (f+ and f-), which all go together to trash your low frequency isolation.

Should I put 3 layers of drywall on the inside walls instead of two? How about the ceiling.

How much isolation do you want, and how much did you lose by building 3-leaf instead of 2-leaf?

The concrete slab on the floor... Should I carpet it or leave it concrete and just put down some area rugs here and there.

Definitely no carpet. It trashes the internal acoustics of the room, despite popular belief, and internet myths and legends. Carpet does the opposite of what a studio needs, acoustically. Which is why you practically never see any in high-end professional studios... and if you do see it, it is probably just hiding the REAL treatment that is on the other side...

Leave your floor as plain concrete, or if you don't like how that looks, put down laminate flooring, or ceramic tiles, or something similar... that has no air gaps under it!

I planned on using a ductless HVAC unit for the room like this one:

If it is ductless, then how do you plan to get air into and out of the room? People have this strange habit: we like to breathe. We love to suck in O2 and blow out CO2. A tightly sealed room that has double hermetic seals all around, twice over, only has a limited amount of O2 in it... I think you can see what the problem will be if you have a dozen people in there for six hours, jamming hard... that limited supply of O2 will be used up pretty fast, the amount of CO2 will rise, and pretty soon the people won't be breathing so well any more...

You need ducts. You need to bring in fresh air, and you need to pump out stale air. And since punching holes through your perfect isolation walls to put the ducts through, also destroys your isolation, you need properly design silencer boxes at the wall penetrations, to allow the air to get through will stopping the sound from getting through.

Lots of info to be found here but I just want to make sure I am not seriously wasting money on anything.

That middle-leaf wall probably qualifies in that category! Diagrams and photos would help to figure out how much of a problem it is...


- Stuart -

Soundman2020 wrote:Hi Clifton, and Welcome!!

That's a THREE-LEAF wall!!! You could have gotten better isolation for low frequencies by NOT building the one in the middle...

I thought a 3 leaf wall was for the same materials? So which wall should I take out The inner wall or the one between that and the cinderblock wall? Removing the middle would leave a 12 in gap between the walls, removing the innermost set of studs would still keep it at 6 inches between the studs and the cinderblock wall. Its going to be a pain in the ass to remove the OSB and Advantech off of the middle wall.

I'm just wondering why you went with that unusual sandwich of materials... What is the total surface density of that wall, in pounds per square foot? That's what matters most, for low frequency isolation.

I am not sure what the total surface density is. We recorded in a studio that had each side of the wall with a 7/16in OSB and 1/2 in quiet brace and 2 layers of sheetrock and Rockwool on the inside and i couldn't hear the drummer on the other side. Quietbrace isn't available in our area so we used the Advantech instead. We are adding on a master bedroom as well and that is what they used for the subfloor and walls. Its heavier and thicker than regular OSB so I figured it wouldn't hurt. The roofing felt was left over from that job. Figured it'd help decouple the two layers.

That seems like an awful lot of expense, time, effort, and materials for an untested, unproven, questionable isolation system! Who told you to build it like that?

Lurking on here for a little while it seems like the general consensus is to have mass and space. I figured that would do both. This is the first time ever doing this so everything is a little confusing so far. There is so much contradicting info that I have found I'm having a hard time with it.

Excellent! Sealing your leaves air-tight will always provide an excellent increase in isolation. It's one of the best "value for money" things you can do to a wall.

This would be what I need to do the double drywall layer on the inside wall too, right?

That's an unusual way of building an isolation system, but the concept is correct. Assuming that the "inner-roof" is full sealed to the inner walls (no gaps at all), and has roughly the same surface density. Ditto for the "outer roof": it needs to match the surface density of your outer wall, and also be sealed hermetically.

So I should leave this roof alone and then build the new roof on for a double leaf wall as well? Should I put insulation in between the studs and then a layer of drywall on the ceiling?

That is a full-perimeter seal kit that you got, right? Meaning that there is a continuous seal that runs all around the edge of the door, including both sides, the top and the bottom? No breaks, gaps, etc?

That takes care of your first seal on that door: what is your plan for the second seal on that door? Another similar kit?

Yes, full perimeter seal but I might have to do it on the others down the road if it goes over budget.

Assuming you really do have three leaves here, and will have one door in each leaf, how do you plan to open the door in the middle leaf? It cannot swing outwards, or it will bang into the outer leaf, and it cannot swing inwards, or it will bang into the inner leaf... So what's the plan there for opening it?

Door under the carport would swing outward, the door on the inside would swing inward, and the middle door would have the hinges on the opposite side and swing inward as well. I could leave that middle wall out though since it has not been built yet. That would be better right? by keeping that to a double leaf wall? If it goes with only two doors, the hinges should be on opposite sides right?

If I was to guess I'd say we are about 125db when we play.

That's probably an over-estimate: 125 dBC would be painful already to most people. 120- 125 is usually considered the threshold of pain. You guys are probably more like 115-120 dBC.

Yeah, I hit the wrong key. I meant 115. Sorry about that. I'm gonna see if I can find someone local who has one I can borrow. If not I'll pick one up and bring it to the next practice we have.

For which purpose? Different densities and impedances are good for different purposes. Assuming you are looking for stuff to damp the resonances in MSM wall cavities, then you would need something that has a density of around 30 kg/m3 if you use fiberglass insulation, or around 50 kg/m3 if you use mineral wool insulation. Those will give you about the right gas flow resistivity for that application. On the other hand, if you are looking for something for a bass trap, you'd probably need a lower density, and if you wanted something to kill high frequency reflections on a surface, you'd need a rather higher density.

I'm looking to keep the sound from escaping outside and pissing off my wife and neighbors. Mainly more concerned about the lower end than anything else.

How much isolation do you want, and how much did you lose by building 3-leaf instead of 2-leaf?

I'd like as much as I can afford to get. This room is in the middle of being built so I'm not sure on how much is lost gained yet.

Definitely no carpet. It trashes the internal acoustics of the room, despite popular belief, and internet myths and legends. Carpet does the opposite of what a studio needs, acoustically. Which is why you practically never see any in high-end professional studios... and if you do see it, it is probably just hiding the REAL treatment that is on the other side...

Leave your floor as plain concrete, or if you don't like how that looks, put down laminate flooring, or ceramic tiles, or something similar... that has no air gaps under it!

Laminate flooring will be no problem. After the room is built the next project will be to treat the room to get it sounding better inside there. For now I just wanna keep it as quiet on the outside as I can.

If it is ductless, then how do you plan to get air into and out of the room? People have this strange habit: we like to breathe. We love to suck in O2 and blow out CO2. A tightly sealed room that has double hermetic seals all around, twice over, only has a limited amount of O2 in it... I think you can see what the problem will be if you have a dozen people in there for six hours, jamming hard... that limited supply of O2 will be used up pretty fast, the amount of CO2 will rise, and pretty soon the people won't be breathing so well any more...

You need ducts. You need to bring in fresh air, and you need to pump out stale air. And since punching holes through your perfect isolation walls to put the ducts through, also destroys your isolation, you need properly design silencer boxes at the wall penetrations, to allow the air to get through will stopping the sound from getting through.

The unit is a split system and has a send/ return through a 1/2 in pipe through the wall. It allows air exchange. I can't run ductwork through the house because everything is on a slab. If I could have gone that route I would have.

That middle-leaf wall probably qualifies in that category! Diagrams and photos would help to figure out how much of a problem it is...
- Stuart -

Forgive me for a bit, my computer is down so I'm doing all of this on my phone and uploading pics is quite a pain. The outside wall is complete already. It is cinder block filled with sound. The two inner wooden walls are built like this:


but with only one side (the side closest to the blocks) having the 7/16 OSB and 1/2 in Advantech on it. The other is just studs for now.

Thanks for your helpso far. I really appreciate it.

I thought a 3 leaf wall was for the same materials?

A 3-leaf wall has multiple resonances, and will always, always isolate WORSE than the equivalent 2-leaf wall, in low frequencies. The math is fairly simple. It does better in high frequencies, but worse in low frequencies.
As you can see, the 2-leaf wall is about 13 dB better than the three leaf wall of the same total mass and thickness. And that's measured with STC, which is a notoriously terrible way of measuring isolation at low frequencies.

Here's the direct graphs of the two types:
Better for high frequency isolation, but worse for low. And low is where you need it most! A wall that isolates well for low frequencies will pretty much always isolate much better for highs, but the inverse is not true.

So which wall should I take out The inner wall or the one between that and the cinderblock wall?

Once again, it boils down to how much isolation you need, in decibels. There are equations for calculating how well a wall will perform for each frequency band, but you need to plug in real-world numbers, in decibels, not "enough to not annoy my wife". You can't do math on subjective phrases! You need actual numbers.

That said, most likely you would be fine if you take down the "inner-leaf" framing, and leave what is now the "middle" leaf in place, becoming your new "inner" leaf. You might need to put more mass on it, but first you'll need to figure out how much mass you already have there, so you can do the math based on facts, not guesses.

removing the innermost set of studs would still keep it at 6 inches between the studs and the cinderblock wall.

That would probably be fine. Is that "middle" leaf built conventionally (sheathing facing the room) or "inside out" (sheathing facing the cavity)?

We recorded in a studio that had each side of the wall with a 7/16in OSB and 1/2 in quiet brace and 2 layers of sheetrock and ...

Yup, but you have no idea how that wall was tuned, or what else went into it. How big was the air gap? What insulation was used? How thick? What characteristics? You also don't know how the rest of the facility was built... You can't simply copy part of a studio and expect it to perform the same in your place. Most things in acoustics are not scalable, or "copyable". It's like someone watching Formula 1 racing on TV, and seeing that the cars have spoilers on the back, so he makes a spoiler out of wood and puts it on the back of his 1970 Toyota, hoping that will somehow make it go faster... (OK, I exaggerate, but you get the picture...) Acoustics is a science, and there are equations and even rules of thumb for figuring all this out. Copying what someone else did is unlikely to work the same, unless you actually do the math to check, and adjust the build parameters to make sure it will work. Guessing is not a good way to build a studio.

Quietbrace isn't available in our area so we used the Advantech instead.

So you already did something different, and therefore your wall will NOT perform the same as the other one...

The roofing felt was left over from that job. Figured it'd help decouple the two layers.

Nope. Decoupling requires the correct resilience for the mass and frequency range. Roofing felt USED to be used as a poor-mans constrained layer damping compound, and even as limp mass membrane, but not any more. The results were too random and not repeatable, due to manufacturing differences. Modern materials and techniques are much more consistent and predictable..

it seems like the general consensus is to have mass and space.

It's not just a consensus: It's a set of mathematical equations that define how it works! You can calculate it yourself. You don't need to go on hearsay, and rumors, and myth. Numerous scientists and laboratories have tested numerous materials and techniques over the years, and figured out the equations that define how walls isolate. You can use those equations yourself. That's a far better option than listening to some guy on YouTube who waffles on about the mystical properties of his special method and materials...

This is the first time ever doing this so everything is a little confusing so far.

It is confusing at first, yes. It takes time to learn the basics of acoustics, and the basics of studio construction. I'd suggest two books: "Master Handbook of Acoustics" by F. Alton Everest (that's sort of the Bible for acoustics), and "Home Recording Studio: Build it Like the Pros", by Rod Gervais.

There is so much contradicting info that I have found I'm having a hard time with it.

You can ignore most of it. If there is no math or laboratory test results to back up a claim, then forget it. Acoustics is a science, not a religion. You don't need faith in some esoteric materials or techniques to figure it out. You just need to do the math.

This would be what I need to do the double drywall layer on the inside wall too, right?

Right. EVERYTHING must be sealed. If air can get through a gap or crack, then so can sound.

the door on the inside would swing inward,

... and would crash into the inner-leaf! Regardless of how you set up the hinges... Think about it... the inner-leaf would be six inches away, and it would have a door FRAME with a door jamb on it: Your middle-leaf door would not be able to get past the inner-leaf jamb. You would have to make that door several inches shorter and several inches narrower, and leave a gap several inches high at the bottom, in order for it to be able to PARTIALLY open... before it still hits the other jamb on the inner leaf. It will never open more than about 60°, max.... hard to get a kick drum through there!

This is why you need to plan out your entire design in 3D, in SketchUp, before you start building anything, so you can make sure that all the various parts of your studio work together properly, with no clashes.

I'm looking to keep the sound from escaping outside and pissing off my wife and neighbors. Mainly more concerned about the lower end than anything else.

Right, but you need to put that in numbers: decibels and frequencies. You can't plug in words to the equations!! Only numbers.

This room is in the middle of being built so I'm not sure on how much is lost gained yet.

You could calculate it...

The unit is a split system and has a send/ return through a 1/2 in pipe through the wall. It allows air exchange.

Ummmm... Nope! Those are the COOLANT pipes: They carry high-pressure refrigerant gas, which circulates in a close loop between the indoor unit (evaporator) and the outdoor unit (compressor / condenser). Those pipes do NOT bring in air for you to breathe. Even if they did, 1/2" is hugely, enormously, insufficient for the amount of air a dozen people need. HVAC specs generally call for at least 6 room changes per hour: In other words, the entire volume of air inside your room needs to be replaced every ten minutes. Can you imagine how fast you'd have to pump air through a tiny 1/2" pipe to accomplish that? The correct size duct for your room is probably at least 6", maybe 8"...

You need to do some research on HVAC systems for studios. There's an entire chapter on that in Rod's book.

I can't run ductwork through the house because everything is on a slab.

The ducts don't go through the floor: they go through the ceiling....

If I could have gone that route I would have.

You don't have a lot of choice here, if you like breathing...

The two inner wooden walls are built like this:

That's not how you described them! You described yours very differently, with different materials, different thicknesses, and different arrangements. That wall is not comparable to your wall. Even a slight change in materials or dimensions can have a large change in isolation.

Thanks for your helpso far. I really appreciate it.

That's what we are here for!


- Stuart -