Air Space?

Hi, I'm in the process of building a vocal booth, just a question on insulation? I'm making the walls using a layer of gyprock, insulating with rockwool and then a layer of MDF. Should I try and cram as much rockwool in as possible, or should I put in an amount that fits in easily. I read in the reference section that "if insulation is used it must be open-celled or it will act as an additional leaf" I don't know what open-celled means? Any help appreciated... Thanks Ben

benny wrote:

I'm making the walls using a layer of gyprock, insulating with rockwool and then a layer of MDF.

I think you mean leaf instead of layer. See the definitions.

Should I try and cram as much rockwool in as possible, or should I put in an amount that fits in easily.

I believe you want slight compression so that you dampen each side, and you don't compress so tightly that the assembly acts as one leaf, and you don't want less than the thickness of the cavity because there may be a "partial third leaf effect."

I read in the reference section that "if insulation is used it must be open-celled or it will act as an additional leaf" I don't know what open-celled means?

Open celled means air can pass through it. A sponge is open celled. In the mass-air-mass equation, insulation that air can flow through is considered "air." The "definitions" link above will clarify this. --Keith :mrgreen:

Thanks for the quick reply Keith... So the wall has one leaf, comprised of one layer of gyprock, the other leaf comprised of one layer of MDF, the air gap is the cavity in between which I will fill with rockwool... I'd like to be able to build a double leaf wall, but I don't have the space :( Thanks for the advice on the rockwool, we'd started on one wall and really crammed it in, so I'll take some out. I can understand how by cramming it in can make the whole wall act as 'one leaf'. Just so I understand how much I should put in, could you explain what you mean by "partial third leaf effect"??? Thanks for your advice Ben

This already is a double leaf wall. Are you sure you don't mean double framed wall?

Yeah, what he said. ;) Basically, ideally, you want enough insulation to be lightly compressed on each side of the wall. That's enough to dampen each side without it being so tight that the wall acts as one. If you do too little insulation -- meaning less than the depth of the air cavity, depending on the type of insulation you are using, you could end up with the insulation itself acting a bit like a third leaf. At least that's how I have come to understand it. If anyone is smarter than I am about this, please -- I am extending my toes and gritting my teeth! ;) --Keith :mrgreen:

Pretty much correct - for the insides of walls, using the standard "fluffy stuff" is the least expensive and (hardest to screw up) way to go, and gives as good results as the expensive rigid fiberglass, rockwool or mineral wools. For an inside construction like a vocal booth, it's best to use NON-faced batts. The "fluffy stuff", or "pink", can protrude beyond studs on one side by up to an inch or so before it will be too compressed. For ceilings, 4-6" is enough REGARDLESS of the air gap - gravity is your friend here because it will keep the insulation in contact with the inner ceiling panels for best damping. Some good general points - http://forum.studiotips.com/viewtopic.p ... 280e1d399c HTH... Steve

For maximum sound isolation you want the insulation touching one side of the wall ONLY. In other words you want a slight airgap on one side of the insulation. Andre

Interesting, Andre -- are there test results that confirm that? The wisdom I've gotten here is that you do want the insulation touching both sides. I won't even get into firestopping... That's a whole other can o' worms. :roll: --Keith :mrgreen:

sharward wrote:

Interesting, Andre -- are there test results that confirm that? The wisdom I've gotten here is that you do want the insulation touching both sides. I won't even get into firestopping... That's a whole other can o' worms. :roll:

I don't understand you. In this thead relating directly to the value of gaps. I referenced CONSTRUCTION INNOVATION Volume 3, Number 3, Spring 1998. In that document it writes

An early IRC study showed that when rigid materials, such as some of those listed in the NBC as fire stops, are placed at the wall/floor joint (see figure), the effectiveness of the sound isolation between dwelling units can be significantly reduced.

Are you now asking me find the actual test data? Confused too: :D Andre

Andre, my brain must be fried, because I nearly forgot that exchage. :oops: I stand corrected. And I stand apparently to need to rethink some of my own project plan... :? --Keith :mrgreen:

maybe my brain is fried too :) insulation is not a rigid material. quoting from the link andre cites: "Fire-stop options listed in the NBC examined in the study: gypsum board, 25 mm thick, placed vertically between joist headers (this material was not tested for fire resistance) oriented strand board (OSB) or plywood used as a continuous subfloor under the partition wall sheet steel (without profile), .38 mm thick, installed under the wall plates." none of these things sound like soft fluffy insulation to me :D maybe i need to dig deeper to figure out what andre is talking about? i see the part about how they recommend a 25 mm gap, but that is directly compared to using a rigid material like gypsum, OSB or steel as a firestop, not compared to filling the entire gap with insulation, which was not considered here as far as i can tell. andre may be right about leaving a gap, but this link doesn't seem to say that. dan

Dan Fitzpatrick wrote:

none of these things sound like soft fluffy insulation to me :D

Actually - neither is rockwool........... for the purpose of the particular wall being described however - test studies for 2 1/2" steel stud walls do indicate a slight advantage for mineral wool (rockwool) than for fluffy insulation - that being for air-borne noise only - the walls do not act as well for impact noise. However - that having been said - the particular link Andre provides relates to the installaion of a member - either drywall - steel - or a continuation of the sub-floor - that creates a rigid "bridge" between the 2 adjacent units - which then makes flanking (through this rigid material) the reason for decreased isolation. It doesn't touch at all on the issue of a flanking path being created between adjacent leafs in the wall assembly - it only centers on the floor to floor connection. Sincerely, Rod

Keith: Doing furhter research I dug up [url=http://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/02-108.html]Technical Series 02-108 [/url] AKA Noise Isolation Provided by Gypsum Board Partitions My statements were wrong. The relevant bullets from the referenced document are

Generally, at low frequencies, the increase in the transmission loss of a partition obtained by adding a sound absorptive material inside its cavity is equivalent regardless of the material used. Above 250 Hz, mineral fiber and blown cellulose give the best results; mineral fiber insulation provides slightly better transmission losses than glass fiber, especially around the critical frequency. Also, in the case of glass fiber, a greater transmission loss can be achieved by using denser batts

and

With the exception of sprayed cellulose, the best transmission losses were obtained when the entire cavity of the partitions were filled with a sound absorptive material. When the entire cavity is filled, caution must be taken not to use a material that is too dense, otherwise a mechanical coupling could occur between the two sides of the partition which could result in a degradation of the sound isolating performance of the partition, as was observed in the case of a partition whose cavity was filled with sprayedon cellulose.

We now have referenced test data for filling cavities completely. Andre

Oustanding! Clarity. References cited. Experts spoken. I love it. 8) Now all we need to do is add some "soundproofing foam"... Kidding! :lol: --Keith :mrgreen:

Thanks for the tips guys... it's now, after a bit of brain strain, a lot clearer... I'll let you know how it goes. Cheers Ben

sharward wrote:

Oustanding! Clarity. References cited. Experts spoken. I love it. 8) Now all we need to do is add some "soundproofing foam"... Kidding! :lol:

Your welcome. I didn't make it clear in my previous. The document is a summary of an analysis of IR-761, the motherlode of gypsum walls and sound isolation tests. Andre