How much insulation in a soundproof room? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 14 Old 06-21-07, 07:03 AM Thread Starter
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How much insulation in a soundproof room?

Hi there,

I'm working on "soundproofing" my basement so that I can play guitar and drums down there with some degree of the sound not getting out to the rest of the house.

My main methods of keeping things quiet are double drywall, green glue and a staggered wall.

I'm using insulation in the ceiling joists. Initially, I've put in one layer of R-13. I was wondering if it will make much difference to sound levels going up throught the floor to put another layer of R-13. There's room and budget for it, but if it's not going to make much difference, I'm not going to waste time with it. It's just basic fiberglass insulation from Lowe's; nothing fancy.

Any opinions appreciated.

Thanks!

-- Otto
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post #2 of 14 Old 06-21-07, 07:50 AM
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Re: How much insulation in a soundproof room?

Realistically, if you want the isolation to be as good on the ceiling as it is on the walls, you either need to:

- not connect the side walls to the joists above and use PAC DC-04 clips.

In addition to the above:

- Add another set of joists between the existing ones that only sit on the walls so you have a staggered stud ceiling in effect.

- Use PAC RSIC-1 clips and hat channel.

In any case, you want the joist cavity above COMPLETELY filled with insulation. If it's 2x12's, you'll want more than even 2 layers of R13. The more the better but no need to compress it - just fill it. The additional layer of drywall and Green Glue is absolutely a help - especially for drums. Just have appropriate expectations without the ceiling isolation as I discussed above.

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post #3 of 14 Old 06-21-07, 08:04 AM Thread Starter
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Re: How much insulation in a soundproof room?

Hi Bryan,

This project was kept as simple as possible. The walls will remain concrete, so there's nothing connected to the joists. Well, the one wall that's separating the storage room from the rest of the basement is connected to the joists, but that's the way it is. I may have to address the concrete walls for their reflections, but they should not convey much sound.

I thought about using RSIC clips, but chose not to because of the cost and complication.

Really, the whole thing is a compromise, but it will be a lot better than nothing.

I will fill those joists, and all other possible spaces, with insulation. Fortunately, it's not that hard or expensive.

-- Otto
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post #4 of 14 Old 07-07-07, 08:49 AM
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Re: How much insulation in a soundproof room?

Certainly bookmark this link Otto. Even has Australian insulation coefficients!

Bryan, I notice you said not to secure the side walls to the joists above... I'm a little nervous about doing this myself, as our room needs all the structural integrity it can get (it will have a considerable IB sub system). How do you stop wall flex if you build like that?
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post #5 of 14 Old 07-07-07, 09:08 AM
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Re: How much insulation in a soundproof room?

The walls will be plenty stiff. The clips hold the tops tight but offer a shearing force form of isolation onto a rubber bushing. For the money spent, this offers a tremendous reduction in structural sound transmission.

The only thing you don't get with this setup is the walls becoming structural (holding the floor up) which you don't have now and don't need.

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post #6 of 14 Old 10-19-07, 10:02 AM
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Re: How much insulation in a soundproof room?

Using Rockwool instead of fiberglass will yield better results as it is a bit denser. Doubling up will not provide a realistic improvement.

The best soundproofing is high mass to dead air space to insulation to high mass. Double 5/8th drywall (or 5/8 and 1/2) will deaden the sound a lot but the low frequency vibrations will transfer from the drywall to the joists and up through the floor. The green glue will help with that.

You could also use the green glue on the face of the joist to help a bit. RISC clips and resilient channel are the best, but adds a lot of complexity and using 2x 5/8 drywall would add the risk of your ceiling falling down if not done properly.

Another thing you could do is to use a layer of mass loaded vinyl under the flooring above the basement and/or between the sheets of drywall. It's pretty expensive stuff but is the goto material for ultimate soundproofing.

Avoid recessed lights or any holes in the ceiling at all as well.
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post #7 of 14 Old 10-19-07, 10:52 AM
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Re: How much insulation in a soundproof room?

I would have to disagree on the airspace. You have a resonance that's set up based on cavity depth and the mass of the layers on top and bottom of that space. Air instead of insulation gains you nothing except money saved. Added insulation will absorb more of the cavity resonance.

Yes - higher density mineral wool is a better solution inch for inch. If it came down to a full cavity of fluffy stuff or 4" of mineral wool in a 12" cavity, I'll take the fluffy stuff any day.

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post #8 of 14 Old 10-19-07, 12:52 PM
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Re: How much insulation in a soundproof room?

Resonance is when the sound waves bounce around inside a cavity. A resonant frequency is one that fits into that cavity and when bounced around starts to vibrate the materials causing an amplified effect. You do want the sound waves to bounce around because every hit off of a surface reduces it's energy slightly. That's what insulation does also, makes the sound bounce around inside itself removing it's energy. If you add a layer of insulation inside the cavity you would probably abate any resonant properties.

You have probably heard that providing an inch or two of air space behind a bass trap improves it's absorption. That's because the wave takes a bounce off the wall and goes back through the absorber. Sound waves also change when they go through different materials (wood, air, water, drywall, etc).

Rockboard is not horrendously expensive but it wouldn't be cheap if you were to stuff the entire ceiling cavity (10"?) with it you would end up paying more than $10 per running foot. In a 16x12 room that would amount to almost $1500 of Rockboard in the ceiling. You would be better to add a third layer of drywall or use mass loaded vinyl, both of which would be cheaper.
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post #9 of 14 Old 10-19-07, 01:11 PM
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Re: How much insulation in a soundproof room?

You're confusing WHY a space behind an absorber against the wall works. It's not the air, it's the distance from the leading edge of the absorbtion to the boundary. If you'd ever measured this effect, you'd find that 4" of absorbtion on a wall will do a better job than 2" with a 2" air gap.

The point of eliminating a resonance in the ceiling as soon as possible is to prevent it from building on itself and propogating to the floor (membrane) above. The mass below restricts the frequencies that can enter but EVERY cavity has a resonance that needs to be tamed.

Trust me, I design rooms for a living. I've done this hundreds of times and measured the differences in the adjoining floor. I'll still take a full cavity of something half as dense any day.

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post #10 of 14 Old 10-19-07, 01:30 PM
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Re: How much insulation in a soundproof room?

Otto,
I originally used R-20 fiberglass insulation in my floor joists for an attempt at sound proofing. I added a second layer for a total of R-40. I also used plastic vapor barrier overtop of the insulation. The second layer made a difference. At "stupid levels" the only sound coming through is the low end bass, but that's unavoidable. I should mention I finished off the basement with a suspended ceiling made of compressed fibreglass panels. I imagine that helped too.



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