Something I have been thinking about?

JohnGardner · Post by **JohnGardner** » Mon Mar 13, 2006 7:19 am

Guys,
This has been bugging me for a while.
I know that triple leaf is a no-no but what about quad-leaf.
Any solid reason not to do this apart from cost?
If I was having triple leaf problems would adding another leaf fix them if this was the cheapest easiest option?
Just curious thats all.
JohnG

knightfly · Post by **knightfly** » Mon Mar 13, 2006 8:43 am

Nope; 3's bad, 4's worse - this is assuming you have the option of leaving ALL that inner air gap as ONE. Each air gap/mass combination has it's own resonant frequency, at which isolation SUCKS.

Put these together and you have SUCKY isolation at EACH resonant combination. Remove all the inner crap and you have the lowest frequency resonance you can get with the masses involved.

Isolation is worst at resonance, and only starts really improving at around an octave and a half ABOVE resonance. So you wanna get resonance as low as you can, and build as heavy as you can, and the mids/highs will basically take care of themselves... Steve

SonicClang · Post by **SonicClang** » Mon Mar 13, 2006 9:59 am

So that's why people suggest going really thick with CR window glass? (and obviously one sheet thicker than one, the thicker being on the CR side)

JohnGardner · Post by **JohnGardner** » Mon Mar 13, 2006 12:24 pm

I am actually thinking some of my problem between the rooms is the window.

I have 8mm laminated glass on both sides with a five inch airgap.

Anyone know what the specs on this window would be and how would it compare to a normal double stud wall with 1x13mm plasterboard on one side and 2x13mm plasterboard on the other side?

Maybe if I replaced the control room side glass with something thicker?

Thanks

JohnG

rod gervais · Post by **rod gervais** » Mon Mar 13, 2006 2:20 pm

SonicClang wrote:So that's why people suggest going really thick with CR window glass? (and obviously one sheet thicker than one, the thicker being on the CR side)

Sonic,

not necessarily.

If you have the same mass on both wall sides - then the mass of the thinnest piece of glass should equal the mass on one side - and you should increase the mass for the opposite side - either will work exactly the same - so where the thicker goes is irrevelant.

If you have different total mass on the sides of the walls - then you should match the mass for each side on that side of the wall (otherwise you will weaken the wall as a whole).

It makes no difference in an unbalanced mass assembly which side has the thicker treatment - because we are not building a diode here - the isolation works exactly the same from either side of the wall.

Rod

knightfly · Post by **knightfly** » Mon Mar 13, 2006 3:19 pm

Anyone know what the specs on this window would be and how would it compare to a normal double stud wall with 1x13mm plasterboard on one side and 2x13mm plasterboard on the other side?

Nearly identical, and neither being that great - about STC 45-48, with the TL @ 50 hZ being around 26-27 dB. If anything, your glass may be outdoing your wall a bit...

BTW, you didn't mention the effective air gap on the wall part; I assumed from your double frame that it'd be around 200mm/8 inches for the above calculations... Steve

TomM · Post by **TomM** » Tue Mar 14, 2006 3:54 am

I was wondering about the four leaf affect as well.... but I am also wondering how the air-space changes it?

For example, if you have a 3rd leaf 1 foot away, OR a 3rd leaf 10 feet away, will the 10 feet improve the affect caused by the 3rd leaf? by how much? and how much space does it take for the 3 leaf or 4 leaf affect to be gone completely?

knightfly · Post by **knightfly** » Tue Mar 14, 2006 5:56 am

10 feet would get the 3-leaf effect down into nearly negligible range; two single-layer, 1/2" gypsum panels 10 feet apart would have a m-a-m resonance of around 17 hZ, which would be their weakest point. Doubling those lowers m-a-m to 12 hZ. Doubling the distance to 20 feet with double drywall both sides lowers it to 8 hZ. You start getting usable isolation at just over an octave above resonance, so you can see that even 10 feet (considering most studio walls will have at LEAST two layers of drywall) becomes a "non" problem...

Now, the 1-foot thing? NOT good; resonance of two 1/2" panels 12" away is 53 hZ, so they weaken isolation up to at least twice that or more. Using 5/8" panels lowers m-a-m to 48 hZ, which would still seriously affect isolation at 100 hZ and lower, and be noticed up into mid-bass range... Steve

JohnGardner · Post by **JohnGardner** » Tue Mar 14, 2006 7:31 am

Hi Steve,

The live room wall is inside out so the airgap is about the same as the window I would guess - 5-6inches.

Wall is:

13mm plasterboard
five inch airgap with insulation
2 x 13mm plasterboard

Window is 8mm laminated glass both sides with a 5" airgap

Your figures of about STC 50 seem to be spot on for what I am seeing with a noise meter.

Thanks

JohnG

TomM · Post by **TomM** » Tue Mar 14, 2006 8:06 am

Very interesting... I have also been wondering about one other thing regarding multiple leaves (hope i'm not hijacking anything)... how does the 3 or 4-leaf change when it exists within the air-space.. For example - Say you have 2 leaves separated by 3 feet. BUT, you build a cabinet which then turns the wall (just for the size of the cabinet) into a 3 leaf. So in other words, you have an 8 foot high wall, but 2 feet horizontally and 4 feet vertically have this cabinet... will that actually lower the isolation?? Assuming that the cabinet doesn't connect both walls...since that would create a flanking path..

Or keeping the same idea, what if a small section of your wall (creating the quad-leaf) is 2 feet from the first double leaf wall, but then the remainder of the wall (say 90%) is 10 feet away. Will that 2 feet lower the isolation for the entire wall?

knightfly · Post by **knightfly** » Tue Mar 14, 2006 9:03 am

Yes, but whether it's quantifiable or obvious would be hard to say. Air is a fairly stiff spring, so any time you put mass in front of air, you create a m-a-m system. The cabinet example WOULD weaken the wall where the cabinet is.

You can do your own experiment - take a normal room, put a loud boom-box in it, then go outside and hold a 4 foot square sheet of plywood up like it's a picture you're gonna hang on the wall; walk toward the wall slowly, and listen to the changes you hear at different frequency, it's almost a mechanical wah-wah pedal... Steve