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Where to get guidance for soundproofing a basement

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I have [a lot] of experience regarding residential building construction [in North America]. Though my experience isn't specific to audio rooms, I can offer plenty of suggestions regarding sound insulation/isolation given specific information about the space.

1) Of the self-installable off-the-shelf insulating materials; mineral fibre > glass fibre > solid/sprayed foam as far as sound insulation goes.
2) don't stack drywall, space it off the substrate. Wall coverings are rigid, they vibrate sound to the next layer (the joists) which vibrate the house. The best possible solution is to use a spacer so the sound waves aren't transferred to the structure.

TLDR: Stand off your finishing materials and stuff the air cavities. Best bang for your buck.
 
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Stbby

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1) If I don't care much about sound quality/dampening in the basement but only care about isolation from the 1st floor, is there any value in insulating materials?
2) If I'm aiming to keep the joist space as open as possible, what are my options for spacing it off of hte substrate?
 

eric-c

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There is a lot of good drawings for floor and ceiling (and walls) at https://www.soundproofingcompany.com/

I used the double / triple 5/8" drywall with green glue between and sealing the gaps between joist and drywall edges between the floor joist then insulation, then channel hats hanging double 5/8" drywall with green glue.

The walls, hvac, electrical outlets have similar and other methods of sound proofing. There is a 6'+ grand piano directly above my basement home theater and I can barely hear it. The sound that is sneaking in is via a "ok" rubber sweep below the theatre door and not from above. If I close the stairs doors to the basement then you can't hear the piano.

The avs building threads as mentioned are excellent for information. I put one of my build threads there a few years ago.
 

sarumbear

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Where do I find a professional consultant for this? I don’t have the budget to hire a crew to do this (I got a bid for nearly $40k), but I could hire someone to advise me on doing it on my own if I knew where to look.
$40K for consultancy (not build work, nor parts, etc.) is thievery. Report them to their association.

I do not know what country you are based and hence cannot suggest much other than telling you that the going rate for an acoustical consultant in the US is around $100/hour. They have an organisation called NCAC and on their website you can search for a consultant near you.
 
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eric-c

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two other big considerations:

1. sourcing product. I am in Canada and I had to import the Channel Hat clips and some other products like extensions for outlet boxes etc. Even the Canadian distributor didn't want to bring them in the simple channel hat clips

2. execution. if you are contracting this out. I am quite confident that 99% of the contractors have not done soundproofing and use the right techniques as doing it right is time consuming. Even with blue prints, will they follow them? if you read through the AVS threads you will see this quite common. You need to be there or hire a proxy to ensure the work is being done correctly. Or simply do the work yourself.
 

Bugal1998

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two other big considerations:

1. sourcing product. I am in Canada and I had to import the Channel Hat clips and some other products like extensions for outlet boxes etc. Even the Canadian distributor didn't want to bring them in the simple channel hat clips

2. execution. if you are contracting this out. I am quite confident that 99% of the contractors have not done soundproofing and use the right techniques as doing it right is time consuming. Even with blue prints, will they follow them? if you read through the AVS threads you will see this quite common. You need to be there or hire a proxy to ensure the work is being done correctly. Or simply do the work yourself.

Point two above is spot on.

I didn't do my own sound proofing, and the contractor assured me they had experience. Ha! They literally either did or were about to do EVERYTHING incorrectly. No exaggeration, not a single step was correct.

My contract specified not only the types and steps of soundproofing, but that it would completed according to manufacturer guidelines and industry best practices.

To their credit, when I showed them the errors of their ways, they ripped out significant portions of their work and redid it at their cost.
 
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@Stbby
Is the basement one big room?
Do you have a way to prevent sound from simply travelling up the stairs?
Do you have a budget in mind?

I don't personally think you have any options that involve leaving your joist cavities open. Insulate the available space in the joist cavities with Roxul or other mineral wool insulation and space your drywall or ceiling material off the joists with one of the many options including randomly, this one. The spacers prevent the drywall from transferring the sound to the joists and the insulation stops the sound resonating through the cavity (and thus through the floor to the rooms above).

The suggestion of "double 5/8 drywall wedged in the cavities" that was offered to you will not work. Though drywall is a better sound insulator than air, it's a pretty crappy sound insulator on its own. You'd be better off insulating the cavities half full and not finishing the ceiling.
 

eric-c

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I will beg to differ with the above post based on personal experience regarding the effectiveness of drywall vs roxul at least in my space. My basement theatre room from the previous owner had roxul between the joist ceiling cavities then 5/8" drywall directly attached to the joist (not channel hat) and it didn't do much preventing noise transmission from the living room above especially with the foot fall noise (vs airborne noise). Foot fall / floor vibration noise is much harder to soundproof vs airborne noise. When I was building my theatre in that space, I ripped everything out to the studs. By putting the mass ie double and triple drywall between the floor joist attached to the subfloor, the noise especially the foot fall noise and piano vibrations were reduced at least 5x (from memory). This was even before the insulation between the cavities were put in and before the double drywall installed on channel hat. The link to the soundproofing company I linked earlier has the STC ratings listed for each type installation. I went for the Cadillac of installation types ie Level 3 which provides a STC rating of 76. if you do not use the double drywall between the floor joist and do everything else the same you will yield a STC rating of 66.

As for the Resilmount A237R clips referenced, these were the only ones I could source in Canada. I do not recommend them.
4d8c9898b5bb88437f053c8b957f47f3_M.jpg


Instead use the standard A237 non R channel hat clips

Untitled-01.jpg


I bought a bunch of the A237R clips before I could source the A237 clips from the USA. The "R" clips are 3x-4x the price if I recall. I ended up using the A237R clips on my ceiling to exhaust them since I purchased them. I used about 4x the amount of A237 clips for the walls/

When I was building my HT and researching, I recall seeing that there really wasn't much if any difference STC difference between the clips lastly, you will lose about 1/2" -3/4" of ceiling height

Here is the thread on the quasi finished build. If I can find pictures (think I took some) of the ceiling construction


here is the before during the demo

1671755965447.png


During construction. I didn't take pictures of the drywall only in the floor joist but trust me its there.

1671756042594.png


1671756160310.png


Looking at the pictures reminded me of other things.

- I removed the X braces between the the floor joist and replaced them with solid 2 x 10 block and mounted the A237R clips to the blocking as the channel hats were going perpendicular to the drywall
- I used long 10' and 12' long drywall to minimize the seams (less gaps for sound leakage, less taping)
- the cheaper pink insulation works just as well as a space filler over roxul. You see I used roxul as I had some left from the ceiling and from other parts of the basement outside the theatre that were exposed (eg closet ceiling) where roxul worked better because it was stiffer.
 
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Stbby

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@Stbby
Is the basement one big room?
Do you have a way to prevent sound from simply travelling up the stairs?
Do you have a budget in mind?

I don't personally think you have any options that involve leaving your joist cavities open. Insulate the available space in the joist cavities with Roxul or other mineral wool insulation and space your drywall or ceiling material off the joists with one of the many options including randomly, this one. The spacers prevent the drywall from transferring the sound to the joists and the insulation stops the sound resonating through the cavity (and thus through the floor to the rooms above).

The suggestion of "double 5/8 drywall wedged in the cavities" that was offered to you will not work. Though drywall is a better sound insulator than air, it's a pretty crappy sound insulator on its own. You'd be better off insulating the cavities half full and not finishing the ceiling.

It's one big room.

I've heard that Roxul in the cavities is good for improving the acoustics of the space but would likely do next to nothing when it comes to sound transmission of voices from the floor above.
 
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Stbby

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Green glue is not meant as a sealant, it is designed to stay viscous to provide constrained layer damping. To seal small gaps, use caulking. For large gaps, closed cell expanding foam.

Yes, two layers of drywall with green glue and sealant will do a good job of blocking high frequencies. You should also place 3.5" insulation inside the wall cavity, this is extremely cheap and greatly enhances mid frequency absorption.

A relatively cheap way to boost low and mid frequency isolation is doing a staggered stud setup, where you have 2x6 top/bottom plates for the walls, and two rows of offset 2x4 studs. Any energy striking the drywall has to travel through the base plates and into the second stud row, several feet of distance, rather than directly through a single row of studs. This approach only costs you 2" of internal room volume + extra lumber, the amount of drywall and insulation used remains the same.
If I did a layer of closed cell expanding foam across the entire ceiling would that potentially give me a decent reduction in transmission of voices?

Regarding 3.5" insulation inside the wall cavity: If I'm following correctly, I don't think I have any wall cavities to seal; the basement is an open floorplan that covers the entire footprint of the house.
 
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