Some terms defined (added to REFERENCE section)
Posted: Fri Sep 02, 2005 7:18 pm
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
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
this will be the only question posted here.