Drwall on both sides or two sheets on one side of wall?

[Ethan Winer]

A knee wall won't give much isolation because sound just goes right over it. Or am I missing something in your question?

--Ethan

The Acoustic Treatment Experts

[PaulInTheSticks]

Originally Posted by Ethan Winer

\Or am I missing something in your question?

Yea, its a loft. The knee wall is connected to a pitched roof. That's why there is little room behind the knee wall.

Also, from an isolation perspective, I understand that filling the spaces between studs with mass such as drywall and wood scraps and filling the rest of the space with loose insulation is preferable to filling the entire space with insulation. Am I understanding correctly.

Thanks.

[ejbragg]

This is quite correct. The space within the wall is what helps stop the low frequencies. Without depth, you have no armor against anything but high and (to some degree) mid freqs.

So if the knee wall comes all the way up to the roof, then there's no gap for air to flow over or around the wall? (I suspect this was Ethan's concern, and rightly so, since in the case of an open wall, you wouldn't gain anything by making the wall beefy.)

But then there's the roof problem, as well. Is the roof surface only one layer? If so, then you're kind of back to the same problem. Unless all surfaces within the area are "double-skinned", then making only one of them double sided probably won't help.
But if you have a ceiling plus a roof, you may be okay... well, better, at least! Best if everything is airtight.

Here's the best explanation. Theoretically, if you poured water inside your wall, you should be able to fill it up to the top between the layers without any leaks. If your roof is low, then you'd have to envision filling that barrier as well. It should all be that airtight, if you want it to work correctly. Then of course, fill the gap with insulation rather than water, caulking everything so that it really is airtight.

One hole the size of a quarter will let 85% sound penetration, as perceived by the listener at most frequencies. A much smaller hole may block more, but low freqs will still penetrate.

[Rod Gervais]

Originally Posted by ejbragg

One hole the size of a quarter will let 85% sound penetration, as perceived by the listener at most frequencies. A much smaller hole may block more, but low freqs will still penetrate.

EJ,

not meaning to pick nits here - but where in the world did you come up with that?

Blanket statements like that without qualifying data to back them up simply make no sense.....

Think about it this way - do you seriously believe that the loss in TL value of a wall 100' in length - 50' in height - with a hole in the skin the size of a quarter is going to experience the same loss of TL value as an 8' x 8' wall section would with that same size penetration? (let's assume the same construction for the purpose of this exercise.)

It simply is not correct.....

Rod

[Rod Gervais]

Originally Posted by PaulInTheSticks

Also, from an isolation perspective, I understand that filling the spaces between studs with mass such as drywall and wood scraps and filling the rest of the space with loose insulation is preferable to filling the entire space with insulation. Am I understanding correctly.

Paul,

You are not understanding correctly - as has been pointed out to you in a different thread....



Rod

[PaulInTheSticks]

Thanks Rod. Sorry to duplicate the post but I'm in the middle of building and sometimes my posts don't get any responses.

Can anyone tell me if doubling the drywall on the room side and leaving the back open is as effective as single drywall on both sides of an insulated wall?

Thanks.

[Rod Gervais]

Paul,

It all depends on a lot of things........

If you could give us a sketch of what you have/propose we could better answer your question.

[ejbragg]

Originally Posted by Rod Gervais

EJ,

not meaning to pick nits here - but where in the world did you come up with that?

Blanket statements like that without qualifying data to back them up simply make no sense.....

Think about it this way - do you seriously believe that the loss in TL value of a wall 100' in length - 50' in height - with a hole in the skin the size of a quarter is going to experience the same loss of TL value as an 8' x 8' wall section would with that same size penetration? (let's assume the same construction for the purpose of this exercise.)

It simply is not correct.....

Rod

Rod, I understand the statement was not concise, due to the ambiguity of unknowns. The more accurate comparison was described more along these lines...

An infinite, perfect wall (assuming infinite mass, of course) separates a listener from an orchestral performance. The sound perceived by the listener from the other side of the wall is zero (complete silence). If the listener stands approximately arm's length from the wall, and opens a quarter-sized hole, the perceived sound will be approximately 85% of the SPL, compared to the wall being removed. Mind you, this is not an exact quote; it is a ball-park figure from my cobweb-filled brain; memories of a required-reading text book in a mechanical engineering class I took at Purdue University - engineering acoustics. Specifically, the control of sound in buildings. I still have the book.... somewhere....

Anyway, perhaps that removes the ambiguity of the "blanket statement".

[Rod Gervais]

Originally Posted by ejbragg

An infinite, perfect wall (assuming infinite mass, of course) separates a listener from an orchestral performance. The sound perceived by the listener from the other side of the wall is zero (complete silence). If the listener stands approximately arm's length from the wall, and opens a quarter-sized hole, the perceived sound will be approximately 85% of the SPL, compared to the wall being removed. Mind you, this is not an exact quote; it is a ball-park figure from my cobweb-filled brain; memories of a required-reading text book in a mechanical engineering class I took at Purdue University - engineering acoustics. Specifically, the control of sound in buildings. I still have the book.... somewhere....

Perhaps if the opened hole just happens to be at ears height directly in front of the listener - however - if an author put that in a college level text - even for Acoustics 101 - it's a pretty lame method of trying to make a point........ not everything that goes into even college texts is necessarily correct.

Rod

[Rod Gervais]

Paul,

we need a section through the building - floor plan gives us no more then we had to begin.

Rod

[PaulInTheSticks]

Originally Posted by Rod Gervais

Paul,

we need a section through the building - floor plan gives us no more then we had to begin.

Rod

Rod, I have no ability or idea how to do a section. AAMOF, I spent about 2 hours messing with some archaic software just to get that floor plan. Thanks any way.

[Rod Gervais]

Paul,

A building section is simply a cut away of the building - picture if you took a knife and cut through the middle of your space - parallel with the rafters....... and then looked at it from the side.

Try it with a paper sketch and then scan it in high resolution.

Rod

[PaulInTheSticks]

Rod,

Drawing a perspective of a 3d object that has any significant detail is something I've always found mind boggling and I'm amazed at people who can do it well. Kind of the same way I feel about advanced math.

But I tried again this morning and didn't come up with anything that would be at all helpful. I can draw a pretty mean box though.