Rigid vs. Fluffy

[mshilarious]

I always thought drywall WAS the wall.

So, to make a soundproofed wall, you have sheetrock, maybe another layer of sheetrock, resiliant channel, stud, NOTHING, stud, another layer of sheetrock. The sheetrock layers being varying thicknesses, the studs staggered.

This is what you're suggesting, then? Nothing in the wall cavity at all to HELP stop sound transmission?

Sorry, it's just that a lot of people come in here and say soundproofing when they really mean treatment. And those specs you listed, those are often used for analyzing treatments.

Yes, by all means, use the fluffy stuff inside walls for soundproofing. It adds a few dB of isolation.

 

[sizzlemeister]

The absorptive properties of a given material has to do with the tortuous pathways the molecules have to flow through as the wave tries to propogate through the material. It has more to do with the geometry than mass.

Question, wouldn't "tortuous pathways" be made of from a great density of air pockets? If not, then what are these "pathway" comprised of?

And if it has to do more with geometry than mass, why did you say "that requires barrier materials that are typically limp and heavy" in regards to soundproofing earlier in this thread?

Isn't it actually a combination of mass and geometry? Mass-air-density/absorption-air-mass? All of this built into a decoupled framework?

 

[sizzlemeister]

Yes, by all means, use the fluffy stuff inside walls for soundproofing. It adds a few dB of isolation.

Now we're getting somewhere; why, though, is the rigid stuff recommended over fluffy stuff for sound absorption IN SOUNDPROOFING applications? This is what I want to know. What makes the rigid better than the fluffy given that the fluffy technically can absorb more energy (hence the mention of R-value)?

 

[apl]

By geometry I mean the shapes of the paths that the air molecules are forced through.

 

[apl]

Acoustic treatments fall into three main categories, absorbers, barriers, and isolators. A material that’s good for one is lousy at the others. If you want to control reflections you use absorbers like foam or fiberglass. These tend to be light and open. If you want to keep sound from going from one place to another you use barriers which are heavy and limp. Isolation systems prevent mechanical transmission of sound from one solid to another, and can be spring systems that float an entire room or goopy stuff you put between flooring layers to keep vibration from getting to a ceiling below.

Soundproofing a room usually means that a space is desired which cannot be heard in adjacent spaces, and sound from those adjacent spaces cannot be heard in the soundproofed space. In reality, sound transmission from one space to another is not zero (or –infinity dB). One of the simplest constructions for a well isolated room is concrete blocks filled with sand and a concrete ceiling. If you get really serious, you pour a thicker than normal concrete floor with an isolation pad surrounding it.

Adding absorption to the empty spaces between wall layers does not stop the transmission of sound. It prevents reverberation of sound in those chambers, reducing the level that the next layer of barrier has to act upon. If that absorption was not there the space would be echoey and sound energy would build up in that space. That said, a construction that uses absorption in its empty spaces between barrier layers has better isolation.

 

[mshilarious]

Now we're getting somewhere; why, though, is the rigid stuff recommended over fluffy stuff for sound absorption IN SOUNDPROOFING applications? This is what I want to know. What makes the rigid better than the fluffy given that the fluffy technically can absorb more energy (hence the mention of R-value)?

Well that's a different set of stats. Read these:

http://zone.ni.com/devzone/nidzgloss.nsf/webmain/790EA2005447DD43862568DC00687382?OpenDocument

http://zone.ni.com/devzone/nidzgloss.nsf/webmain/59787FAB60ECDB6D862568C600635B93?OpenDocument

STC is rated as part of a wall assembly, and the insulation recommended by OC for a wall assembly is the pink stuff:

http://www.owenscorning.com/around/sound/commercial_acoustics/acou-batts.asp

 

[sizzlemeister]

That said, a construction that uses absorption in its empty spaces between barrier layers has better isolation.

Excellent. Which is better for absorption in that space, rigid or fluffy?

 

[mshilarious]

Excellent. Which is better for absorption in that space, rigid or fluffy?

I suspect the difference would be very small, maybe a dB.

 

[sizzlemeister]

I suspect the difference would be very small, maybe a dB.

I find that curious considering the parameters I initially phrased the question around earlier. R-value is the resistance-to-energy-transmission value of the material (whatever material that is), sound being energy, you'd think a greater R-value material would have better sound absorption. The rigid stuff is low in R-value compared to more common fluffy values.

A material with a R-value of 10 will absorb twice as much energy of a material with a R-value of 5.

So, what is it? The difference in energy types? What factor(s) make rigid better than fluffy for certain sound absorption applications OTHER THAN the rigidity of the material? Why is the difference in absorption very small when used in the manner we've been discussing in this thread?

For that matter, why would the OC Quiet Zone fluffy (which is R-13 IIRC) work better than standard fluffy that is R-30?

 

[HangDawg]

I find that curious considering the parameters I initially phrased the question around earlier. R-value is the resistance-to-energy-transmission value of the material (whatever material that is), sound being energy, you'd think a greater R-value material would have better sound absorption. The rigid stuff is low in R-value compared to more common fluffy values.

A material with a R-value of 10 will absorb twice as much energy of a material with a R-value of 5.

So, what is it? The difference in energy types? What factor(s) make rigid better than fluffy for certain sound absorption applications OTHER THAN the rigidity of the material? Why is the difference in absorption very small when used in the manner we've been discussing in this thread?

For that matter, why would the OC Quiet Zone fluffy (which is R-13 IIRC) work better than standard fluffy that is R-30?

I always assumed that sound transmission and heat transmission were two different animals and are measured differently. Is this not correct?

 

[mshilarious]

For that matter, why would the OC Quiet Zone fluffy (which is R-13 IIRC) work better than standard fluffy that is R-30?

The R-30 stuff is 9 1/2" thick and thus wouldn't fit in a wall cavity. The Quiet Zone is 3 1/2" thick and is designed to drop right in.

 

[scottboyher]

One thing I noticed when I was framing in my studio room was that before we put up the drywall that room was dead as a doornail. It was all insulated with R13 all the way around. I was eerily dead sounding..

 

[apl]

I suspect the difference would be very small, maybe a dB.

Or less. Note that the OC data doesn't compare different battings.

 

[apl]

One thing I noticed when I was framing in my studio room was that before we put up the drywall that room was dead as a doornail. It was all insulated with R13 all the way around. I was eerily dead sounding..

You had a hemianechoic chamber above about 250 Hz.

 

[apl]

The difference in energy types?

Thermal and acoustic energies are completely different.

 

[sizzlemeister]

One thing I noticed when I was framing in my studio room was that before we put up the drywall that room was dead as a doornail. It was all insulated with R13 all the way around. I was eerily dead sounding..

What was it like after the drywall went up?

 

[sizzlemeister]

Thermal and acoustic energies are completely different.

I can accept that. Is this why rigid has more desirable properties overall than fluffy? In layman's terms, what is the difference we're talking about?

Taking the entire thread a step further, between rigid and OC Quiet Zone fluffy, which is better for the space between walls? Will the rigid have better sound absorption than the OC QZ?

 

[scottboyher]

You had a hemianechoic chamber above about 250 Hz.

So it was not effecting the low frequency reflections?
It was just soaking everything up above 250?

 

[apl]

So it was not effecting the low frequency reflections?
It was just soaking everything up above 250?

The strict definition of hemianechoic relies on how well it resembles a free field, ie an open outside space. The measurement technique is to determine how well sound decays from a source in the center of the room toward the walls. In a free field environment, the inverse square relationship holds, that is, the level decreases inversely proportional to the square of the distance. So if you measure at some distance, doubling the distance should reduce by four, tripling should reduce by nine and so on. For a room to have that behavior, the walls have to have an absorption coeffecient in the neighborhood of one.

At 125 Hz, 3-1/2" is only .34 and .58 depending on paper, so the room is not anechoic by the time you get to 125Hz. At 250 the AC is about 1, so somewhere between 205 and 125 it loses hemianechoicness.

 

[apl]

I can accept that. Is this why rigid has more desirable properties overall than fluffy? In layman's terms, what is the difference we're talking about?

Taking the entire thread a step further, between rigid and OC Quiet Zone fluffy, which is better for the space between walls? Will the rigid have better sound absorption than the OC QZ?

The differences will be negligible, unless the rigid mechanically couples the two wall faces-- that would be a bad thing. I'd throw the cheapest stuff in there.