Different leaves thickness - A ? for knightfly

R

RaGe

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In a double wall construction:

5/8 drywall(x2)-2.5" air with insulation-5/8 drywall (x2)

Would using some 1/8" tempered hardboard on one of the leaves make enough difference on the resonant frequency and prevent that frequency to get thru the wall? Or does it have to be some pretty heavy stuff like OSB?
 
I don't have actual specs on hardboard (masonite) but it's probably close to the weight of particleboard - the thing is, any dissimilar layer will help change the characteristics of one leaf of a wall enough to lessen the two problem areas associated with identical leaves. One of those is mass, which affects lower resonant frequencies and wouldn't change as much - the other is coincidence frequency, which affects the range of 2k to about 4khZ, depending on the material. This would be improved by ANY dissimilar sandwich material.

For best results, probably using 1/2 and 5/8 on one side with the other side being two 5/8 with the thinner material sandwiched in between would be as effective as anything.

The two factors that probably help more than anything are more air space between leaves, and separate frames. If you can spare the space, going from a 3" air space to an 6" air space with two layers of wallboard on each outer side of steel studs will improve STC by 2 dB, while going from a 6" air space with 6" steel studs to the same air space with separate steel or wood studs will gain about 7 dB.

All this is farting in the wind if you don't use sound locks and double doors, different thickness double glass, and good door seals - the weakest link is what determines the whole... Steve

There's more info on wall construction here, rather than me typing it all again -

http://johnlsayers.com/phpBB2/viewtopic.php?t=598
 
Missed that you already spec'd your thickness - if you're using steel studs without Resilient channel, or wood with RC, using two layer of 5/8 wallboard each side would get you about STC 55, assuming you seal everything well.

However, your mass-spring-mass resonance would be at 73-74 hZ, so the open D string on your bass would tend to get through easier than other frequencies. In order to improve on that noticeably, you'd need to widen your air gap to maybe 6" and use separate frames for each leaf. That would lower resonance to 48 hZ.

Overall, though, double 5/8 on each side of 2-1/2" steel studs looks pretty decent, and a sandwich material on one side would improve that by a few dB. I don't have any way of calculating sandwich effects, only know that the physics improves with dissimilarity.

Hope that helped... Steve
 
You bet that helps :)

Thanks for the wise words. I am having steel studs (20ga) and judging by the weight of the hardboard it will be a decent mass addition to the internal leaf. We'll see if that 73Hz will defeat my plan.

By banging on the control room's side I can feel a little vibration on the live room's wall, so far both walls are of the same construction (ony one layer of 5/8 so far, and no, no drywall on the outside leaves!), slanted from 5" to 16" apart and they are not connected, I made sure there is no shortcut of any sort (I have floating floors on neoprene, walls built on floors).
Thinking about making the live room side a 3 layer to cure that problem.
Caulking everyting man like a freakin parano! I know the sliding doors will be my weak point though ... They are the same as Michael Jones' if this is of any indication.

Thanks again for your help Steve, you rock (as usual).
 
:=) Michael's doors are pretty heavy duty, you should be able to get pretty good isolation with a pair of those. Remember to do a breathable surround between the two doors, so that space can vent into the area between walls - that helps the overall STC a bit by lessening the transmission thru the doors (relieves pressure some) - sounds like you've got it on the run overall, but I'm not sure I understand your comment about "no drywall" - before you get any further could you "splain" exactly what your wall construction WILL be? Steve
 
Going from control room side to live room:

[2x 5/8 drywall - studs+isolation] - big space between rooms - [studs+isolation - 2x 5/8 drywall]

I have drywall only on the inner leaves of the adjacent control room and live room walls. Do i make sense?

I will probably add a 3rd layer of drywall on the live room side to make it heavier.

My CR and live room are like 2 independent boxes and I plan to staple some kind of cloth (sames as the one used for Helmoltz resonators) between each room around the sliders ... so I guess what you describe as a "breathable surround"will be achieved if that's what you're talking about.
 
So far, so good - I'd watch having identical leaves though, double 5/8 on each leaf of a wall isn't the best way, since both "halves" of the total wall will have the same flaws (probably around the open D string on a bass - your idea of adding a little "meat" to the sandwich on one side will get away from that problem... Steve
 
I'm having the sliding doors installed next week then I'll probably go rent a drumset and bang the hell out of it to test the design :) Will keep you posted.
 
One more thing .... like i mentionned before when I bang on the control room's wall I can feel the live room's wall vibrate a little, although there are no physical connection between the two. I suspect it has to do with the similar construction on each side ... hopefully a 3rd layer on the LR side will cure that problem.
 
Yeah, an extra (different) layer will definitely help.

"when I bang on the control room's wall I can feel the live room's wall vibrate a little, although there are no physical connection between the two." - Actually, there IS a physical connection - it's the AIR. Air is a much stiffer "spring" than it seems like it should be. You're coupling your "thumps" on the wall to another (still identical?) wall, so your thumps are primarily at the resonance of the first wall, which causes the air spring to move the second wall, which is at the same resonance as the first... that's what causes sounds to get through easier. Hence the extra layer on one side.

Don't expect drums to completely disappear thru a pair of sliders, especially the kick - still, it should be pretty good. There are so many variables to construction it's nearly impossible to predict results other than generally... Steve
 
It's the air stupid! ;)

Yes I still have only one layer of 5/8 on each side, we're working on AC registers right now ... Which scares me a little, I wonder how much of the sound will get thru my return ducts (they are in between the rooms, I didnt have a choice .... but the registers are offset of about 4').
What I am mostly concerned about is getting sound out of the live room into the CR thru the ducts.
 
You're probably going to be sorry from your description - AC ducts need to be run all the way from the air handler, SEPARATE ducts for each room, with at least two gradual 90 degree turns each - same with returns. NO shared ducts between rooms, period. The ducts need to be lined with absorbent (Owens Corning fiberglas duct board works, also Johns Manville "superduct" if you can find it. Flex is a last choice. Ducts need to be oversized and under velocity. Noise in ducts is roughly proportional to the 5th POWER of velocity, so a slight reduction in air velocity results in a LARGE reduction in noise.

There's a bit more to this, but it sounds like it's too late for you already. 4 feet isn't squat when it comes to sound traveling thru ducts between rooms - I don't know how to help you fix this... Steve
 
Actually there are 2 separate return ducts, but they run in between the 2 rooms. They are way oversized though ... like i said i had no other option. :( We'll see what happens.
 
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