How to avoid flanking in between leaves?

I have done a bunch of reading regarding construction and design in my attempts to build a drum tracking/ rehearsal room (for rock). One question I can't seem to find an answer for is what the best isolation method is for a ceiling between leaves. My gut instinct is to use use 2 layers of drywall/caulk/mineral wool in between the joists which fall in the air space between my 2 leaves. Check out my design thread to get the jist if you like: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=2580 The basic concept is to achieve isolation from the kitchen above the space keeping in mind I'd like to use this room for tracking drums (without breaking the bank). Unfortunately I must keep the load-bearing wall in the iso booth, but I plan to RC that wall/ no RC on it's leafy partner. Hey, that brings up an other question. Is it best to keep uniform mounting methods/drywall thicknesses throughout each individual room, or is safe to use RC on one wall but not an other? I understand you DO NOT want to use RC on both leaves. I guess using RC on a floating wall is okay because of different sympathetic frequencies? Thanks for following my inane ramblings- Josh

My gut instinct is to use use 2 layers of drywall/caulk/mineral wool in between the joists which fall in the air space between my 2 leaves

That is the right idea. To improve it, use RC, RSIC clips. With the RC clips you achieve an STC of around 55 with a TL of about 17dB@50 Hz. The RSIC would improve that, but I have no test data to provide. The numbers are from NRC IR-811 pdf page 72. http://irc.nrc-cnrc.gc.ca/irc/fulltext/ir811/ir811.pdf

Is it best to keep uniform mounting methods/drywall thicknesses throughout each individual room, or is safe to use RC on one wall but not an other?

It all depends on how much isoaltion you need from the space on the other side of the wall. The effects on the acoustics inside the tracking room are not significantly affected. Andre [edit] corrected typing error in page reference.

Andre- Is this what you mean? I only have a 5" airspace, so maybe 2 little strips of RC in there? I'll have to search for the RSIC clips as you mentioned. Would you use them throughout? Next question- I don't have a diagram for this one yet... Should I put the walls in the diagrams below on top of my floated floor w/ sway brackets at the top and no RC under the wall's drywall? Will I achieve the same STC with a hard connection to the floor/cieling w/ RC on the wall? Granted this is assuming that I correctly build the floor... This is what I was originally thinking: Thanks for the reply! -Josh

RISC can be found/explained here http://www.pac-intl.com/home.html They also have measurement tests there. RSIC are much better than RC. If you can afford a couple less inches of room height, consider room in a room. Then you can skip both RC and RSIC.

Okay- I get the RSIC's now. I'm still wondering about the floating wall vs RC/RSIC. If I decouple the walls from the floor and the joists using sway brackets, should I still use RC? I understand that with my cieling height (hoping for 88" finished) I don't have the room to build a complete room in a room. However, everything but the cieling will be on a separate framing structure. Thanks for your responses. --Josh

Billyboy wrote:

Okay- I get the RSIC's now.

Good move. I persoanlly do not care for RC because of it does to LF performance. There are several types of RSIC available now. I think the model for ceiling joist installation is the best for you.

I'm still wondering about the floating wall vs RC/RSIC. If I decouple the walls from the floor and the joists using sway brackets, should I still use RC? Confiming first what I think you are saying: good move to go with the decoupled wall. RSIC and RC would be of no value in this place.

Thanks for your responses.

Your welcome. Keep us posted on your progress and pictures are always appreciated! Quietly isolated; Andre

If I decouple the walls from the joists using sway brackets, should I still use RC?

If you do that then RC on the walls is less important, but RSIC on the ceiling is still recommended to decouple it a bit. (Assuming you still don't room-in-a-room the walls and ceiling).

I understand that with my cieling height (hoping for 88" finished) I don't have the room to build a complete room in a room. However, everything but the cieling will be on a separate framing structure.

In Ontario, building code requires 75% of the basement to be 6'11" or over. 88" = 7'4" In some cases people are able to put the 'room-in-a-room' joists between the existing joists, so even though the new joists are 2x8's, they only loose an inch or two of room height. (Do not remove the cross bracing if it exists)

I don't think a complete room in a room is possible unfortunately; there just isn't enough cieling height, and the cross bracing in the joists goes the full width of the joists. On the qestion of the air space cieling- What do you think? Will 2 layers on sheet rock against the sub floor with insulation below it do the trick? Maybe I should be building mini versions of the RC cieling in the airspace around the room? Thanks again.

Hey again- I have an other question- this time regarding floor construction. I have read about people using 2x4's on their side to maximize cieling height. I am planning on doing this, but what insulation will be adequate for the job? The other consideration is that the floor is concrete, so I must keep some airspace in between the insulation and the cement. I have read that some compression of the insulation against the sub floor is good, but I only will have 1 1/2" to work with! Many thanks- Josh

Here's a better way for your walls/ceilng - I marked up your drawing where necessary - Be careful on your floor - narrow air gaps and light weight leaves cause higher mass-air-mass resonances, and will end up AMPLIFYING your drum kit instead of isolating it. Given your limited headroom, I would recommend forgetting the floated floor until you get everything else finished - then, if you don't get as much isolation as you need, consider floating a concrete slab on thick EPDM or better elastomeric pucks. Wider air gap and heavier floor both go toward lowering resonant frequency, which should be at least 2 octaves below the lowest frequency you hope to isolated - even lower resonant frequency is better. If you end up having to float a floor, it can be done inside the walls (after the fact) by using perimeter isolation board (Celotex) between walls and floor, then caulking thoroughly to seal... Steve

knightfly wrote:

If you end up having to float a floor, it can be done inside the walls (after the fact) by using perimeter isolation board (Celotex) between walls and floor, then caulking thoroughly to seal... Steve

Steve, I have a question in regards to this.Say the walls were floated on the slab before you went to float the floor inside them, would you still be better off using the isolator around the perimeter or wouldn't it metter. I guess my point is:If the sound travels from the floor onto the walls it's still staying in the same room because it can't go further than that since the walls are floated too. But is it better to keep sound (vibrations) on the floor only or on the wall only??I guess it would be because only one of the surfaces would resonate (at whatever frequencies).To cut my bull**** short"Should one float a wall on already floated floor"? And further...float the ceiling on those walls?? thanks :lol:

Steve thanks for taking the time to repond- I know from other posts you lead an insane schedule (and I'm sure I don't know the half of it). A couple of questions:

I marked up your drawing where necessary

I didn't see the markup- is it on the way or did I miss something? Let me know if you have trouble pulling the pic down. If I skip the floated floor as you mention- Should I float the walls and use sway brackets, or direct-connect the walls to the floor/cieling joists and use RC? I would think that the floated walls would have better low freq isolation... I think I recall Aaron (of giant Floating Floor thread fame..) had pretty low cieling height too, but he went with standard 2x4's on their 1.5" edge floated on 1/2" neoprene, no? Don't get me wrong here- if you think no floating floor will be okay, and I can do it later, it'll save me a ton of time and $$. No to mention- It will be far easier estimating the weight of what will be on the floor later (for spring sag in Neoprene) than with walls etc added to the equasion now. I guess thinking about it, if my floor is as thick as the walls are, it's got lots o' mass! BTW- anyone check out the floor plan? I'm a little curious if the splayed walls are beneficial or not. Not to mention the wierd wall intersection with the airlock wall (lower left). Thanks everybody. In no way would this be possible without y'all- Josh

Sen, for absolute MAX isolation the entire room should be floated - floated floor, inner walls resting on floated floor, inner ceiling resting ONLY on floated inner walls - this can get pretty grim in the calculation department though - best isolation is when no one wall, floor, or ceiling has any hard contact with any other. This requires some MAJOR calculations to get right, and probably only helps a couple of dB at most; it's safer to NOT float walls on top of a floated floor, but just fasten firmly; for one thing, the extra weight of the walls and ceiling will lower the resonance of the entire structure and so improve isolation, mainly through the floor, because of the improved m-a-m values. I commented about an "after the fact" floated floor mainly due to decreased ceiling height and the possibility that the floated floor may not be necessary at all; If that turns out NOT to be true, you can then build a floated floor INSIDE the walls as I outlined. This does NOT mean this is the BEST way, just a possibly more PRACTICAL way in this case. Josh, sorry for the brain fart; check that post again, the markup's there now - didn't notice if your existing floor is concrete - if so, I'd use PT lumber for bottom plates and bed in Sill Seal, or similar thin strip - then caulk after each layer of drywall, leave 1/4" gap between all perimeter edges of drywall for caulk. Leave about 1/2" gap between top of inner wall frame and ceiling joists, and use resilient sway brackets. Check Aaron's thread on about page 17-18 for ideas on this. Run your wallboard up to same height as frame, and drop your ceiling inside the side walls as I show in the markup above. I added some text to the markup too, for more explanation. I goofed on the joint between wall wallboard and ceiling wallboard though - wall should extend enough to make a full depth caulk area between wall and ceiling. HTH... Steve

Steve, That helps tremendously- thanks. I see you put 2 layers of drywall in between all of the joists- I was thinking that might help. I read in a post that you're not 100% on the RSIC. Any new opinions? I guess the $/performance ratio isn't tremendously good, but I can use every ounce (db) of isolation possible! Everything else seems pretty straight forward as far as basic construction goes. I'm sure I'll have a ton more questions as I get under way. Once again, Josh

Josh, you're right; if you want the most isolation you can get without losing any more ceiling height, then the RSIC clips are the way to go. Space them close enough, and you can put at least 3 layers of wallboard on them for more mass in the lower leaf. This will add a few dB more iso too... Steve

Just thought of an other question- Where the stringers cross the joists- I should just cut the wallboard to fit snugly, and caulk the corners? Or, should I attempt to leave an 1/8" for a bead of caulk? Or am I splitting hairs here? I have some nails protruding through the subfloor by less than 1/8". Should I trim or impale the wallboard? They won't even penetrate halfway if I impale... Thanks for your time- Josh

knightfly wrote:

Sen, for absolute MAX isolation the entire room should be floated - floated floor, inner walls resting on floated floor, inner ceiling resting ONLY on floated inner walls - this can get pretty grim in the calculation department though - best isolation is when no one wall, floor, or ceiling has any hard contact with any other.[/quote] Yep, that's what sounds logical...it's like "If one wall "gets" why should the rest of them "get" it but.....

it's safer to NOT float walls on top of a floated floor, but just fasten firmly; for one thing, the extra weight of the walls and ceiling will lower the resonance of the entire structure and so improve isolation, mainly through the floor, because of the improved m-a-m values.

EXACTLY my thoguhts!!Thank you Steve.I always thought of the first part (in bold), but the further comments are great too. Thank you sir :D cheers

Sen

it's safer to NOT float walls on top of a floated floor, but just fasten firmly; for one thing, the extra weight of the walls and ceiling will lower the resonance of the entire structure and so improve isolation, mainly through the floor, because of the improved m-a-m values.

I'm not sure about the second part of that. Sound TL is improved by forcing it all to go through mass. Just because you have a lot of weight around the edges of the floor doesn't mean that the middle 95% has mass. Imagine a drum -- lots of stiffness/weight around the edges, but the middle still bounces quite a bit.

Bob, I shoulda clarified what I meant by "safer" - I'm by no means a vibration engineer (don't even PLAY one on TV :=) so am not qualified to tell anyone how to float a wall without causing more problems than they solve - there are shear factors when resting a wall on resilient mounts, just as there are for a floor - the difference is, the wall is being bombarded with sound waves which are (kinda) perpendicular to its surface, but the resilient MOUNTS would see more of a SIDEWAYS deflection (attempting to SHEAR the mounts, instead of compressing their thickness) I've not had nearly enough study time on this subject to keep from screwing up someone's build for them, so I won't recommend they float a wall til I know a lot more. I also wouldn't recommend they "experiment" with this, unless they have more money/time than sense (or "cents" :=) - one possible outcome is that you make your wall resonant at yet another frequency different from the normal m-a-m ones, and so weaken it possibly to the point of having to tear it down and start over. I can only speak for myself, but my list of things I want to do over and over includes beer, pizza, sex, music, but NOT building my studio... Steve

Steve- I forgot to ask you about the wall detail you posted. Was the marked up drawing taking into account that I will not be floating the floor anymore? In other words, since the wall is now resting on the concrete floor (you were correct, PT is in order), should I go back to using RC, or do I not need to because of the sway brackets? Much appreciated, Josh

Josh, with or without a floated floor if you're using separate frames you wouldn't see much difference in performance between RC and no RC - If anything, you'd probably see a bit worse bass isolation and a bit better mid-high isolation. Generally this is NOT what you want to do for music isolation. I personally would bed your inner wall plate in either sill seal or a double layer of 30# roofing felt, lag it to the floor, space/sway bracket it to the ceilng joists, and mount your wallboard using 1/4" spacers around the perimeter of the wall, do each layer, pull the spacers and caulk; use half the screws on all but the final layer of wallboard - be sure to find a way to keep the insulation batts in snug contact with the first layer of wallboard in the inner frame, to help damp these layers so ringing isn't a problem. Your ceilings should be each separate from the other room's wallboard layers, and dropped inside the walls (1/4" spacers, then pull the spacers after fastening and caulk at each layer) - insulation fill should be snug at most; gravity will keep the insulation against the wallboard on the ceiling, which is good. For best isolation, insulation in walls should be at least 2.5 PCF, up to about 4 PCF. Hope this helps... Steve

Steve- Thanks! That's exactly the info I was looking for. Good info on the lag bolting- I hadn't considered means of attatching the lower part of the walls. I truly appreciate all of the help you, John and the rest of this forum has to offer. The fact that you guys spend time out of your busy days to share your hard-earned knowledge is a testament to humanity. Cheers, Josh

Josh, it's always nice to be appreciated - thanks for your kind words. I'm not clear on your question earlier - "Where the stringers cross the joists- I should just cut the wallboard to fit snugly, and caulk the corners? Or, should I attempt to leave an 1/8" for a bead of caulk? Or am I splitting hairs here? I have some nails protruding through the subfloor by less than 1/8". Should I trim or impale the wallboard? They won't even penetrate halfway if I impale..." If you're talking about the extra layers of wallboard up against the subfloor between joists, these should have ZERO air gap between subfloor and each layer - so unless you can use some sort of hydraulic jack to impale them FIRMLY against the subfloor, I'd find a different way. Maybe clip each nail and grind it flush with a small hand grinder, or grind a sharper point on each nail so it "impales" easier? Air gaps here are NOT your friend - Fastening these inserts - if the subfloor is separate planks and has any irregularity (like grooves) I would first smooth this using drywall joint compound - once the compound is in place, you can put up the first layer using the compound as glue - then do a stripe along each joist (but NOT in the rest of the area) of joint compound, and immediately press the second sheet firmly upward and fasten using a cleat attached to the vertical side of each joist - this will keep the pieces of drywall from sagging or falling down later. Once this is all in place, you can caulk along the edges of the cleats and where cleat meets drywall insert for a hermetic seal. After all that, did I misunderstand your question? :? Steve

After all that, did I misunderstand your question?

No- I think you covered it. I was specifically trying to get an answer on how to interface the wallboard and joists/stringers. I.E. should they butt up against the joists/stringers, or should there be a gap a la wall construction for caulk to fit inbetween the wallboard and joists? It will be quite a bit of work, but worth it I'm sure. The subfloor is planking, and there appears to be lots of nails protruding, again only 1/16" to 1/8". I'll just have to perform a test to see if I can get things flush via impaling...

immediately press the second sheet firmly upward and fasten using a cleat attached to the vertical side of each joist - this will keep the pieces of drywall from sagging or falling down later

Can you describe this "cleat" to me? Do you mean a small strip of wood which I'd tack to the joist (parallel to it) to hold the edge of the wallboard? Or am I misunderstanding. Don't mention the kind words- you're more than deserving. :D Thanks yet again, Josh

You're correct in what you think a cleat is - just a long strip of wood, typically 3/4 x 1 - can be ripped from 2x stock, set rip to 3/4" and you'll end up with 3/4 x 1-1/2 stock. A gap is fine, hard to get perfect; then caulk or mud before next layer; main thing is keeping that area from becoming a void, so mud or caulk but NOT air. Fastening full length cleats while putting up the last layer will keep air gaps from developing between layers, and also keep the layers from falling down should any adhesive fail. Cleats should be left in place even after glue/caulk/mud dries, so that any later failure of adhesives won't cause the inserts to fall down and create a triple leaf system. If you decide to screw the cleats in place instead of nailing them, you'd need to countersink and drill for each screw - not really necessary, I'd just lay a bead of caulk before nailing the cleat, then push hard and nail. A small finish nailer works well for this if you have compressed air available - other wise you may need a helper to hold the cleats FIRMLY in place while nailing them... Steve