Soundproofing - add sheetrock or just frame another wall?

Should we assume that this is a standard uninsulated 2x4 framed wall with drywall on both sides?

If so you need to be careful of not to create the triple leaf effect by standing another wall in front of the wall by adding a "fake" wall. If you decide to do a double frame or even staggered stud wall you should pull down the drywall on the construction side of your framing, add insulation, add whisper clips and channel, add your double or triple layer of DW with GG.

Avoid any wall penetrations like outlets and lights unless you address the back of the boxes with putty pads or back boxes. Treat not only the shared walls but all paths of flanking sound. All walls, ceiling, and floor if necessary.

1) Triple leaf is 3 hard surfaces separated by two air gaps. For some reason it can create problems with certain frequencies. http://www.greengluecompany.com/unde...TripleLeaf.php

2) double frame is erecting another framed wall not touching the other wall, leaving an air gap.

3) staggered stud is using a 2x6 bottom and top plate then alternating 2x4 studs from one side to the other. It creates a mechanical break which eliminates the vibrational transfer of sound from on wall to the other side. However since they share the top and bottom plate a little vibration is transferred.

4)DW drywall, DDW double drywall

Go to Soundproofingcompany.com for articles (read before doing anything) and one good source for GG and other soundproofing products.

1) yes
2) yes but I don't know what
3) no, for GG to work it needs to be between two stiff layers. Rubber would destroy the effect of the flexible GG layer which converts vibration to heat.
4) maybe, a real expert could evaluate your house, how the rooms connect together, and determine the benefit of isolating the floor. If you can't get an expert opinion you can just do it to be safe. be sure to build a stage filled with sand that you set the speakers on and make sure the sides of the stage do not touch the walls.

http://www.soundproofingcompany.com/...e_leaf_effect/

Updated article on the Triple Leaf

Ted,

Can you explain the following:

"What are the other advantages of having a low frequency wall?

A wall that has a lower resonance point will stop low frequencies better."

I thought a resonance point meant that the wall tended to pass that information? In fact, you state the following earlier: "So things are bad when we have resonance."

So, how can a wall that has a lower resonance point, this point supposedly increasing transmission of that resonance frequency, then also "stop low frequencies better"?

Perhaps this could be clarified in the article, because right now it seems to conflict (unless I'm misreading, which is always possible).

Hi Bob,

Great question. As far as why some walls (ceilings) work better in the low frequencies (bass)? It's all about resonance. Every air cavity will resonate. Blow across the top of a soda bottle and hear the air cavity resonance. Every air cavity will resonate at a different frequency. Deeper cavities will have a lower (deeper bass) resonance point. Small cavities will have a higher resonance point (higher pitch).

The very simplified generalization is that we can deploy techniques to improve sound isolation above the resonance point, but at resonance and below resonance, our efforts are not effective. So we want to lower that resonance point of a wall through various product and construction techniques. We want the wall to have a low pitch, rather than a high pitch.

Things that lower that resonance point:

Decouple the wall or ceiling. Staggered stud framing, double stud, resilient channel and resilient clips + channel all drop that resonance point.

After decoupling the framing, we can further drop that resonance point by adding a bit of insulation, adding mass to the wall surfaces (drywall) and making the distance between the drywall layers greater.

The lower we drop that resonance point, the more low frequency bass we can contain. Using these simple principles we can contain an extraordinary amount of bass. The kind of bass created by a bank of subwoofers in a nightclub, for example.

I'm primarily a music listener and secondarily a home theater person. For me and my three subwoofers and Salk HT3 speakers (which produce an astounding amount of low bass), I'll be hearing low bass all the time. Unlike, for instance, movies, which only have low bass at very infrequent times.

Do your recommendations change for music as compared to home theater?

In terms of wall construction, does the resonance point ever get to below 20 Hz?

You won't get a wall to resonate anywhere near 20Hz. Such a wall would require a giant air cavity and a dozen or so layers of drywall.

If low frequencies alone were our only concern, we would build a solid wall (no air cavity) and use poured concrete. Such a wall would perform worse in the upper frequencies, but perform better in the extremely low frequencies.

Others here can chime in with their results, but when building walls as described earlier, generally all that is heard upstairs is a sound like distant thunder on occasion. Generally quite satisfactory.

I'm sorry, Ted, but this link simply makes no sense for my situation:

http://www.soundproofingcompany.com/...e_leaf_effect/

You state the following: "We can’t prevent resonance, but maybe we can MOVE the resonance point [at 300 Hz]. Move it to a frequency that we don’t encounter very often. Such a frequency would be low, since low frequencies are less frequently encountered. [Like the 80 or 50 Hz in your examples]"

However, music has tons, and I mean tons of information at 50 and 80 Hz.

Then you go on to say "A wall that has a lower resonance point will stop low frequencies better." That's a non sequitur, because you don't explain why and because of your previous admission in the article that resonance allows more of that frequency to travel through the wall.

It seems to me that all you've done is move the resonance point down, which for those of us who listen to music potentially could be worse than leaving the resonance where it is.

I agree with you that the wall constructions shown are likely beneficial, even for those of us music listeners, but the linked page is confusing.

You may do with this info whatever you wish.

Sorry for the confusion.


Not the case at all. Again, above that resonance point we can assist with isolation. Below that resonance point, we cannot. So obviously we'd like to move that resonance point to a lower frequency.

Imaginary wall #1 has a resonance point of 100Hz. We start losing isolation performance at around 150Hz. The performance gets worse as we go to lower and lower frequencies.

Imaginary wall #2 has a resonance point of 60Hz. We start losing isolation around 90Hz and below.

A higher resonance wall will start losing isolation at a higher frequency. Make sense?

EDIT: Just to clarify, when I say lower resonance point, I mean dropping the frequency, not reducing the volume (dB).

Hi Ted,

I am building a woodworking shop underneath my patio. Unfortunately it shares two walls with the suite that I rent out. The existing walls of my house are 2x6 construction and from the outside in are hardy plank, insulation, then drywall.

I understand that a triple leaf can cause a resonance effect that can potentially make things worse and I understand that a double leaf is the better approach. However, removing the hardy plank from my house is not an option. So would building a false wall out of 2x4 and filling it with insulation (thereby creating a triple leaf) still be better than just sticking with the double leaf that is in place?

Would it make a difference if I stuffed the cavity full of insulation to eliminate the narrow air gap?

Thanks in advance for your help.

If you have to have a triple leaf, then you'll want to decouple, intruduce as much of an air cavity as practical, add as much mass (drywall) as practical, and damp that mass. Insulate with R13

So the frame of the new wall is decoupled from the walls of the house. I'm tied into the concrete floor underneath the patio and into the joist of the patio. While that is tied into the same plate as the ceiling of the suite, I have decoupled the ceilings of the suite.

And my tools transmit mainly high frequencies, so I don't think the joists will be much of a problem.

UNfortunately my space is limited, so maximizing the air space will not be possible and I had intended on sheeting the walls with plywood for functionality which isn't as heavy as drywall.

So here are my options.
1) i could just leave the frame bare, no insulation, no sheeting and just rely on the existing exterior walls of the house.

2) Or, I could not insulate and just sheet the walls. This would maximize the airspace wouldn't it?

3) Or would filling the cavity completely with insulation work better?

4) or I could fill the space with insulation and just cover it in plastic. Don't sheet it with drywall nor plywood. Should I fill the cavity in this case?

Out of these four what is my best option?

And my last question is whether to pay the extra for safe and sound or not? Or just stick with the r13 pink stuff?

For sound isolation, you need mass in the way of the sound wave. We want that mass suspended in such a way that it is independent of the original frame. To accomplish this with the most space conservation, you could apply clips and channels directly to the original wall. Obviously this results in a small air cavity. You'd want to consider a double mass layer to hang on that decoupled frame. Drywall / OSB or OSB/OSB. I'd recommend damping the mass as well. The added damped mass will offset some of the loss from the now minimal air cavity.

Ahh, unfortunately the frame's already been built and nailed to the concrete, so I won't be able to implement yours suggestion. Plus I'll be hanging hundreds of pounds of lumber on racks on the wall so those racks need to be screwed right into the joist anyways rendering the Res channel ineffective.

So my options are pretty much one out of those four.

When you say the wall is nailed to the concrete, you're meaning the slab (floor), right? Is the framed wall contacting the original wall? If not, I would add R13 fiberglass (cheapest you can find) and the double OSB, damped

Yup, nailed to the slab floor. The wall doesn't contact the original wall.
I'll do what you suggest, thanks for the help! Should I fill the cavity completely or leave and air gap? If I should leave a gap, should it be between the original wall and the new wall or should I put the insulation against the original wall and leave gap against the osb I'm putting up?

An air cavity is an air cavity whether insulated or not. When we say "air cavity," we generally assume it is insulated. There is no reason to try and leave a portion of the air cavity without insulation (presumably to attempt to reduce conduction), and similarly there is no reason to try and fill every cubic inch of cavity with insulation. You just want some insulation, as compared to none.

Other insulation thoughts would be to use the cheapest available. Nothing beats fiberglass for price / performance

You can use faced or unfaced insulation. I like faced because you can staple and it stays in place.

Generally any similar density fibrous insulation will perform similarly, so if mineral wool is on sale, feel free.

Don't compress or compact insulation, as it will start to conduct vibration.

I was following this thread as I have a triple leaf effect. I had a noise problem and the contractor, who said he had experience with noise reduction, installed sound bar on top of the existing drywall creating a small (1/2") air gap between the 2 layers of drywall. I had no idea so he installed it. After the noise problem didn't go away, I started doing research. Besides adding another layer of drywall or ripping this down, is there any way to get rid of the air gap? I see from above, Ted mentioned insulation will add some damping, but it won't be easy to get batt type insulation into the small gap. What about blow in insulation such as cellulose? Or something like sand to eliminate the air gap? Any suggestions?

You can add more drywall and look to crush the channel, eliminating much of the problematic air cavity