Some terms defined (added to REFERENCE section)

[knightfly]

Wall - everything between one space and another space, preferably that sound cannot pass thru :=)

Frame - the studs, etc, that wall materials are mounted to - there are a few standard types - they are single frame, just like nearly all houses use; then, about equal performance upgrades would be a single frame with some sort of resilient mount under the wallboard on one side only, OR a "staggered stud" single frame, where you use wider cap and sole plates with 2x4 studs, typically 24" centers aligned with one edge of the plates and then 24" centered 2x4's aligned with the OPPOSITE edge of the plates and OFFSET by 12"; then, about equal to those, a single frame with light gauge (non-loadbearing) steel studs; then, a double frame wall, which is two separate frames of either wood or steel studs. For this part of the discussion I'm ignoring all the various masonry and hybrid walls.

Leaf - this is ALL the layers of various wallboard (or other mass) ON THE SAME SIDE of a frame; if you put a layer of plywood, then Durock, then gypsum wallboard, one after the other, with NO AIR SPACE, on the same side of a frame, that is a LEAF.

A solid concrete or brick wall is one leaf - a hollow block wall will act as TWO leaves, unless the hollow spaces are filled with mortar, grout, concrete or sand - in that case, it's ONE leaf again and will be governed by mass law for TL at various frequencies.

Layer - one course of any wallboard material. There can be several layers in a leaf.

Air space - the area between leaves in a total wall - if insulation is used it must be open-celled or it will act as an additional leaf, which can hurt the LF isolation of the wall. Adding insulation can make a difference of up to about 10 STC points to a wall.

Air space is defined as the distance between wall leaves, NOT the frames but the inner surface of the wallboard on one side of the frame to the inner surface of the wallboard on the opposite side of the frame.

IF you build a standard house type stud wall with gypsum or other cladding on each side of the studs, that is a 2-leaf wall, whether you put one layer of wallboard on each side or 5 layers, and whether those layers are plywood, MDF, celotex, duroc, gypsum, or whatever.

If you then build a SECOND wall identical to the first one, spaced (for example) 3" away from the first wall, and these two walls are all that's between you and the space you don't want to hear, that is considered a QUAD-leaf wall and is NOT the most efficient use of materials by far - see this for more

http://www.audio-muziek.nl/audiotechniek/acoustics.pdf

If you were to then REMOVE all the wallboard layers except the ones on the OUTSIDE of each frame, the TL (Transmission Loss) would actually IMPROVE; this is because air is a spring; the longer the spring, the softer. A softer spring will couple LESS between the two objects it separates.

If you were to then REPLACE the layers of wallboard that were removed from the inner surfaces of each frame, and ADD them to the OUTER leaf on each frame, you would then have two layers of wallboard, stud frame, space, second stud frame, then two layers of wallboard; this combination would have roughly 23 dB MORE STC than the EXACT SAME amount of material yielded when the air space was "chopped up" into 3 smaller "springs" -

If, within this double framed wall (wallboard layers ONLY on the outer surface of each frame, with a single air gap of (say) 8" (3.5" per stud frame, plus 1" separation between frames) you were to put insulation that had a paper backing, and you placed that backing ANYWHERE but against one of the wallboard surfaces, that would actually HURT the TL through the wall by acting as a third leaf between the other two; so, from an acoustic standpoint, the backing either needs to go against one or the other wallboard surfaces or be REMOVED, or use UN-FACED insulation.

The basic principle of all this is what's called a mass-spring-mass model; each "mass" is a leaf of your wall, and the air/insulation between them is the "spring". Also referred to around here and other acoustics BBS's as m-a-m, for mass-air-mass, whether there is only air between the leaves or if it's insulation.

Things that improve walls -

more mass in each leaf, either thru adding layers of same or different material, or thickening those layers.

Wider air gap = softer spring, less coupling from side to side, so less sound transmitted.

Dissimilar materials as layers in a leaf - each material (and thickness of the SAME material) has a different "coincidence frequency" (individual resonance), so different materials or thicknesses will have different coincidence frequency, therefore different weak spots.

Gluing two sheets together will cause them to act as ONE layer, with ONE coincidence frequency, therefore weaker than two UN-glued layers. One recent exception to this is Green Glue, a product of Audio Alloy. GG forms a Constrained Layer Damping bond between layers. More on this later.

Different masses in each leaf; if the two leaves aren't the same mass, they will have different weaknesses so again, whatever frequency gets thru ONE side easiest will have a tougher time making it thru a DIFFERENT mass with it's different weak frequency.

Gypsum (most of it, anyway) has its long edges tapered for mudding and taping joints; in a multi-layer application, if these are not filled entirely so there are no VOIDS, it will weaken the wall in two ways - it creates a small air gap, which will have its own audible resonance/weakness, and it lessens the MASS of the leaf which will lower effectiveness.

HTH... Steve

[AVare]

Great stuff!

A comment and for thought, not meant to be implemented.

Some times concrete/brick are used for walls. Should the definition of leaf be revised to include those and potentially other materials?

Yes, there is the conflicting short versus complete.

Helpfully
Andre

[sharward]

Great stuff! I'd volunteer to make illustrations for each of the points, but (thankfully) I'm going to be involved in building my project in the coming weeks, so I don't think I'll have the time.

Anyone want to volunteer for that?

[knightfly]

Still working on my roof, edited first post just for you, Andre

[DreaminDrumBeats]

Thanks for the EXCELLENT resource Steve, needs to be stickied

[sharward]

It's linked from the already-stickied almighty "Reference Thread."

[nukmusic]

Thought this may be the spot to ask and maybe create an answer many also may looking for.

I was searching google for the density of different materials.
As to the thought of combining materials. What would what might work best in the event you have no room for double walls.

*RC + 5/8" drywall
*RC + 1/2" drywall + 5/8" drywall
*RC + 3/4" + 5/8" drywall
*5/8" drywall + green glue + 5/8" drywall
*3/4" MDF + green glue + 5/8" drywall
*1/2" drywall + green glue + 3/4" MDF + green glue + 5/8" drywall
*MDF + green glue + 1/2" drywall + green glue + 5/8" drywall
*5/8" drywall + green glue + 1/2" drywall + green glue + 5/8" drywall

etc etc etc Or should I have asked what combo above might work best for single stud walls and what might work best for double stud walls.

Would (3/4") plywood, OSB, Soundboard, particle board work better in place of the MDF?

The build we are about to do is a standard corner house with the inner walls totally gutted out. 2x4 framing on a cement stab. The outer wall coverings are standard plywood nailed to the studs and covered with wooden shingles.

sorry Steve....LOL this will be the only question posted here.

[knightfly]

Generally, it's mass that counts. There are a few HUNDRED walls actually built and tested here

http://irc.nrc-cnrc.gc.ca/pubs/fulltext/ir761/ir761.pdf

but nothing on GG; for either of your locations (deep south) your vapor barrier should be on the outside wall, so could make it tricky to get damping of the inner wallboard from insulation compression; for that reason, I'd probably look long and hard (for your single frame scenario) at using RSIC clips and double 5/8 gyp and GG - at full coverage, it takes 2 tubes per sheet so this will add a LOT of $$ to the cost - around $720 extra for an 8 x 12 x 18 foot room using full coverage. That's about $28 per sheet coverage, or about 3.5 TIMES the cost of another layer of drywall.

For the LOW end, there still is no real substitute for wider air gap/separate frames and higher mass; look at the graphs here

http://greengluecompany.com/greenGlue-v ... rywall.php

and note that the low end isn't all that much better with GG -

At this time, I have ZERO experience with GG so this is all conjecture; personally I'd use it for ceilings in a heartbeat, especially if there were a limitation in load bearing for the ceiling joists; in a wall, I'm not sure it's worth it - upsides are less labor, downside is cost... Steve

[nukmusic]

Thanks Steve. the plan right now is to

caulk the existing framing (1/2" wood shingles, 1/2" plywood, 2x4 studs)
add rockwool
GG on the stud edges
3/4" MDF
5/8" drywall
5/8"drywall & GG (2 tubes per per sheet)


might even put the MDF in between the the 2 sheets of drywall and GG.

[Creature82]

Hey Nuk - Hope you're doin well. I'm interested in what you finally chose for your wall construction as I'm in the same postion now... and how it worked out. I posted a topic today, but as of yet no answers.

My current plan is to add some cotton batt insulation and (2) layers of 5/8 with Green Glue between them. Lemme know. Thanks.

Creature82

[Monty_Python]

The http://www.audio-muziek.nl/audiotechniek/acoustics.pdf link is unfortunately offline, FYI.

This is a great topic and I am trying to digest it thoroughly. Thanks!!!

[Hagopm]

Any thoughts on ICF exterior walls?

[DHK]

Gypsum Board Walls: Transmission Loss Data

https://nrc-publications.canada.ca/eng/ ... 064b073e7f