When 3 leaves aren't 3 leaves anymore

Hi there, I've been reading this board off and on for months, and I thank you all for the education. I have a question that I couldn't answer through my searches. I get the "double leaf=good" and "triple (or more) leaf=bad" concept. But how much space is required in an adjacent room before its far wall doesn't act like additional leaves of the first room? I'm not trying to solve a practical application; this is purely hypothetical so I can understand the concept a little better. (If I missed this info posted somewhere already, I apologize.) Thanks, SB

You didn't miss it as far as I know - I've been told by Eric that it's a long ways before the effect totally goes away, like many yards or something - It also isn't TOTALLY cast in stone, there are many circumstances where you simply don't have a choice - I'm looking into the chances that you could just "beef up" the two main leaves to compensate for the weakness in low end caused by the third leaf; I don't have anything at all on this yet, hope to in a week or two. I don't have anything more definite than that, although I just made the acquaintance of an MIT grad in acoustics with over 20 years experience who may be able to answer this one for me - if I don't get back to you in a week or so, please "bump" this thread and remind me until I finally get time to do it - seriously, I don't consider that "pushy" or nagging, I really need reminders for things... Steve

Interested in that one too...will be waiting for you Steve, to get back to us on that....and no worries..I'll bump it if needed :lol: :lol: very good question SB, BTW thanks

I am guessing that it is not one of those situations where it suddenly disappears but diminishes with distance. Also if I understand it the '3 leafs = bad' was more along the lines of two small air spaces are not as good as one large air space. So in reality I think the question is fairly pointless, the Architectural considerations are going to outweigh the accoustic ones.

I take the "3+=bad" concept to include that one air space is preferable to two air spaces, even if one (or both) of the two was the same size as the first. (I'm entirely open to the possibility I'm wrong about that.) In a hypothetical example, from west to east: control room -> main room -> booth -> outside When does the control room/booth or the main room/outdoors not suffer from the effects of a third (or fourth) leaf? In a practical sense, we'd probably agree that we wouldn't have control room/booth problems because of the size of a typical tracking room, but how big would the booth need to be in order to avoid weakened transmission loss from the tracking room to the outdoors? Or in another example, how about two separate studios in the same building separated by a common hallway? How wide would the hallway need to be? SB

Innovations wrote:

Also if I understand it the '3 leafs = bad' was more along the lines of two small air spaces are not as good as one large air space.

I don't think so...one 3' airspace is better than 2 3' aispaces (afa the lows are concearned

So in reality I think the question is fairly pointless, the Architectural considerations are going to outweigh the accoustic ones.

why would his question be pointless?? after all we're talking acoustics not Architecture :wink:

friendly bump :D

one more even friendlier bump! :) :D

Sorry I lost this one, don't always have time to check this forum; Innovations was as close to correct on this as I'm aware - the bottom line is, ideally you would always have mass-air-mass between you and any space you need isolation from. The reality is, this just isn't possible in many cases in a situation that's more complex than one room in the middle of nowhere. I've talked to a couple other professionals in this field in the last few months, and all agree that in cases of airlocks, for example, you still need m-a-m isolation between outside and inside when one of the airlock doors is open, so you need to maintain m-a-m construction in EACH wall of the airlock. Even though this weakens iso compared to eliminating all inside masses in the airlock, it's still enough to keep good iso; and the airlock is a necessary part of the whole when considering actual use. The British have used multi-leaf wall construction with good success in their studios, the BBC site has papers available with constructions that work; these are NOT the most efficient from a cost/construction standpoint, but they show that m-a-m isn't necessarily the ONLY game in town, just the most efficient. In cases where more than two leaves between sound isolation requirements are necessary, my take is that you just need to realize there will be compromise and build these parts heavier to compensate; In most cases this won't involve the ceiling, because it's better to do each ceiling section separately and float them inside their respective rooms when you're going for max isolation between rooms - this would allow a bit of "bleed" into the common ceiling cavity from each room's walls at the tops, but this would be minimal and would be absorbed by heavy insulation in the ceiling cavity anyway; and m-a-m would be maintained between each room and the outside world, as long as there was only the individual room's ceiling mass leaf and the outer, containment mass leaf involved. In the case of a parallel walled outer containment with splayed walls inside for acoustics, it's best to make a complete double shell outer containment with overkill, then build inner walls lighter and at needed angles, doing whatever treatment each section needs; any solid, lighter walls inside the containment will lessen the isolation given by the outer, double wall; this is why the outer shell needs to be heavier than it would if there were no trapping/acoustic control inside. Bottom line - make all walls/floors/ceilings m-a-m where it's possible, then wherever it's NOT possible increase mass in the walls that will be weakened by multi-leaf construction, and get on with it :? ... Steve

Steve, Thanks for the explanation. The soundlock example is a clear case of why I was confused -- they often seem to have double walls in a small space, which looked to me like a four-leaf system. It seemed contradictory that something serving its purpose (and actually called a "soundlock!") might really be defeating itself somehow. The idea of a lighter-mass interior wall (for acoustics) within heavier-mass separation walls is such an obvious strategy that I couldn't think of it! Thanks again, sb