Wall Construction

[whatismisophonia]

The attached pic is taken from http://www.ethanwiner.com/acoustics.html , which makes me question a soundproof wall's dynamics. The picture is of a bass trap for improving interior acoustics in a room, however, was not intended for soundproofing; yet, the principles describing it seem awfully familiar.  Essentially, the wood membrane absorbs energy as it vibrates, since it takes energy to move the thing. The acoustic pad behind it slows the speed of the wave, and thus, the energy of the vibrating panel as the waves move through the pad.  The closer the pad is to the panel the better the energy is damped, though the pad should not touch the panel, as this would cause the panel to slow the pads vibration, and thus, its absorption. However, this last part is for improving the rooms' acoustics, not for soundproofing. One might think that allowing the panel to move freely would create adverse conditions for sound transmission, even as it improves interior acoustics.

Even so, proponents of mass loaded vinyl recommend using thin insulation so that it does not slow the action of the vinyl membrane. And even if mlv wasnt used, would the wallboard itself not function in place of the plyboard in the bass trap, espessially if it is decoupled on resilient channel, and facing the noise source?  So then, my question is: Even though this is what is recommended by mlv companies, doesnt such a system work more for interior acoustics than for sound proofing?   

[Randy S]

Im not sure what your question is here?

MLV is not in this base trap even though it has and is used in  bass traps.

If your thinking that this design will increase sound transmission through the wall, than that would depend on if the wall is already decoupled.

[whatismisophonia]

Not quite sure how to make the question more clear... Does this type of wall construction work more as a bass trap than for reducing noise transmission? I didnt mean to suggest that mlv was in the base trap i was showing, i was using the similar construction as a comparison for how mlv is used in soundproof walls ...you know; membrane, airspace, insulation, wall... And when you say,  "than that would depend on if the wall is already decoupled", ive no idea what you mean by that.
  I am comparing the anatomy of the base trap with the anatomy of a wall, exchanging the plywood in the base trap with the drywall on the wall, or mlv in the wall.
  If a bass trap were attached to the wall, it would surely decrease sound transmission, but what if the bass trap was the wall?

[Randy S]

When we design our best sound control systems that is what the system is.. the entire room (except floor) is all a bass trap design as the walls and ceilings.
Very expensive to do, but is truly incredible system.

[whatismisophonia]

#1)  So then, you dont fill the cavity all the way, in order that it doesnt touch the MLV?

#2)  If the wall is to be a bass trap, than im guessing it would be even more crucial to have the MLV on the side of the wall facing the noise source, so that as the compression waves hit it, it can give inward toward the interior of the wall; is this correct?

#3)  If the MLV needs room to move, it seems like it should have room on both sides of it, a small gap between it and the insulation, and a small gap beween it and the drywall; this seems like it would create a tripple leaf though, which Im guessing, is why you dont do it.  However, i think ive heard it said somewhere that if you are installing resilient channel, the MLV should go on first, then the channel, then the drywall; this would obviously be confusing for me.   

[Randy S]

Yes your on track......
The MLV is a limid product in this style of assembly therefore does not create the triple leaf...

triple leaf is 3 layers of rigid material....

[whatismisophonia]

interesting... that would also explain why another technique involving weaving the mlv in between staggered studs is effective.  Speaking of which, would you say that weaving the mlv is more effective than attaching it to the outside of the studs?  My thinking is that although the weaving technique would create more surface area to absorb sound, it may also slightly couple the studs... I'm partly asking because im thinking of doing a retro-fit staggered stud for conserving space, rather than building double walls. On one side of me i have small barking dogs and a deep bass tv, and on the other side, deep rumbling traffic.

[Randy S]

Dont do staggered studs...... either double wall or clips and channel...even RC channel would be better than staggered studs...

Think about it....are you really decoupling?? when the speed of sound through a 2x4 is 13,000 fps..?

we used to use techniques like this back in the day..not any more.. especially when dealing with LF.

MLV does not cause hard connections... staggered studs are already coupled at the top plate and bottom plate.

[johnbergstromslc]

interesting... that would also explain why another technique involving weaving the mlv in between staggered studs is effective.  Speaking of which, would you say that weaving the mlv is more effective than attaching it to the outside of the studs?  My thinking is that although the weaving technique would create more surface area to absorb sound, it may also slightly couple the studs... I'm partly asking because im thinking of doing a retro-fit staggered stud for conserving space, rather than building double walls. On one side of me i have small barking dogs and a deep bass tv, and on the other side, deep rumbling traffic.

Staggered stud walls (well sealed, with insulation and double 5/8" drywall) will work just fine for this level of noise isolation.  If you're limited on space, double walls make absolutely no sense at all.

Remember to keep it in perspective - you are not building a recording studio, needing an STC 80...

Another benefit with staggered studs is that you are not limited in attaching stuff to them.  Try to put semi-heavy shelves on a wall with clips/channels and there is a good chance the drywall will come crashing down!

[whatismisophonia]

attaching pic; tell me if this is stupid... and yes, i did architectural design in college for short period, if youre wondering why i take the time to make these pics.

[johnbergstromslc]

I've thought of doing something like that; I once cut the wall plates with a jigsaw into a zig-zag pattern and separated the two sides by 1/8 of an inch to make decoupled wall panels.  But based on past constructions, I don't know that it made one bit of difference....

Honestly, I wouldn't go to all the trouble of that kind of construction.

A good, quality-built staggered stud wall (with double 5/8" drywall each side) will get you an STC of 58 and good low frequency TL.  That is more than enough to kill the types of noise you have.

Not enough?  Go with 3 layers of 5/8" drywall for an STC over 60.

Remember, you are not going for a zero decibel room, just enough for the noise not to be noticable.

[whatismisophonia]

a double wall seems to have a lot to do with the airgap; especially if the partitions are on a continuous undivided subfloor, though it still works better.  To make an intertwined double wall worth the work with it's smaller air gap, the sections would have to be almost completely divided down through the subfloor and joists to optimise decoupling at least. This may be possible for me, at least for part of the room; joists are already separated(was having a vibration issue and had enough).  Luckily, the part that is separated is right by the wall that is the worst about transmitting noise.  I of course then have to deal with the ceiling and adjacent walls.  The point is, how to build a room within a room, while still conserving space in a house that is already built.  There's always Quietrock, but it doesnt decouple, no matter how much their sales men say it does.  Eventually, you guys are just going to have to come out with a thin, super sturdy wall that floats on magnets.  Another option would be active noise canceling ear implants (not earplugs).  The way technology is advancing, that may happen sooner than we think.  I'd be happy.  Even if the CIA owned the rights to it.  They can listen to me recite my love poems at night.

[johnbergstromslc]

a double wall seems to have a lot to do with the airgap; especially if the partitions are on a continuous undivided subfloor, though it still works better.  To make an intertwined double wall worth the work with it's smaller air gap, the sections would have to be almost completely divided down through the subfloor and joists to optimise decoupling at least.

'Optimize decoupling'?

Again, not building a recording studio...  Don't overthink or overdo the solution.

[whatismisophonia]

i was only stating how to create the best solution given space restrictions; besides which, like i said, it's feasable in my bed room on one wall in particular because at is where the floor is already separated where i would need it to be for such a method to be worth following through(i wouldnt even need to add any foam, just nail the thing down).  You mentioned ripping your bottom and top plates in a zigzag pattern; that would create a double wall, though with a limited air gap, youd have to have the interior section up on foam, or have the floor cut through as well to kinda make up for lack of air gap with better decoupling.  Then again, that would also depend on whether or not you were trying to block out low frequency.   

[mike sorensen]

The graphic shown appears to be an end view of a sound absorbing device that would impact energy within the room.  It would probably impact middle and high frequencies more than low ones. I do not see how it would have much impact as  barrier technology.

Cheers,
Mike