Effective Air Lock Space ??

[Jay Hovnanian]

The walls separating my CR and Tracking Room are slated to be 2x4 wood studs, a 1" gap between, mineral wool in the pockets, and two layers of sheetrock on the outside of each wall.

The space, therefore, between the door on each wall (air lock) is about 8".

Is this amount of space enough to contribute to a proper level of isolation between the two rooms?

Jay

[knightfly]

What kind of doors/seals - is there a drawing up somewhere? Without more info, you could be looking at anywhere from STC 30 (two hollow core doors with fair seals) to STC 65 (two Overly pre-hung studio doors, their seals, about $11,000) - Steve

[Jay Hovnanian]

Steve,

I've posted a couple of times - it seems that each time (and justifiably so) you call on my lack of information provided ... then again, that's why you are the moderator here ....

See my post on page four of the Design Forum entitled "Control Room Orientation" for a general view of the floor plan.

The doors are on the rear of the double wall, just "above" the small iso booth. Each will be 1 3/4" solid core set in a solid wood jamb with Force5 weather seals (nice stuff !!) and Zero International neoprene-gasketed thresholds. I think the door systems (themselves) will be okay - short of spending the whole budget on two of the five doors.

I guess my questions really is, "Given the use of decent door systems, is there appreciable isolation to be gained or lost in the actual amount of air space between the two?"

Thanks again, Steve. These forums are SO informative.

Jay

[knightfly]

Jay, your name rang a bell but without a link it takes quite a bit of time to track down other threads, and I'm always short of that precious commodity - to answer your question, yes - the narrower your air gap, the more difference a small increase will make - a quick example; take a double framed wall, and assume that (theoretically) you can make the air gap only 2" and still have separate studs - using two layers of 5/8 wallboard on each side with standard house fiberglass batts between, estimated (calculated) STC for that wall with 2" air gap is 61 - 4" air gap, STC 66 (plus, mass-air-mass resonance drops from 84 hZ to 59 hZ - ideally, this should be below the lowest frequency you want to stop) - increasing the gap to 6" gives STC 67, and lowers m-a-m resonance to 48 hZ - it also improves 50 hZ performance by 4-5 dB over 4" gap, from 27 dB @ 50 hZ to 32 dB.

An 8" gap gives STC 67, supposedly the same as the 6" gap - but the difference in LF performance is still improving - now, we have m-a-m resonance at 42 hZ, and the TL at 50 hZ calculates to 35 dB. If you were to add an additional layer of 1/2" wallboard between the double 5/8 on ONE side only, the 8" air gap would result in a wall with STC 71, m--m resonance of 39 hZ, and a TL at 50 hZ that's around 38 dB.

You can expect similar differences with other framing methods too, but they will all be less effective than the double frame by differing amounts.

STC isn't the main criteria here, especially for music - it doesn't take into account anything below 125 hZ, which is where it's the most difficult to isolate. That area is where the extra air gap helps, along with more mass of course - doors, in addition to the problems with walls, are dependent heavily on seals - still, the more air you can get between them, the better they will work... Steve

[Jay Hovnanian]

Thanks again, Steve - more valuable information, however, giving rise to a few more questions:

1. How is the air gap measured - from the outside of each stud wall (where the drywall is attached), the gap (strictly speaking) between the interior of each stud wall, or the relative space between the batts of mineral wool? In my current plan, the respective perspectives would be 8", 1" or (roughly) 2". Naturally, I'm hoping for the first !!

2. I read your thread regarding the method of drywall attachment to wood studs ... the importance of complete isolation between the two walls (which I'll have). With the first layer of drywall screwed to the studs, is there any real advantage to a) gluing subsequent layers to the first layer, or b) gluing a layer of thermoelastic (did I get that right?) stuff between layers?

Well, my original intent was explore the notion of air space between the doors on each wall. I'll assume that the same principles (of your previous reply) apply.

With appreciation,

Jay

[knightfly]

1 - air gap is measured from the outer edge of one frame to the outer edge of the other frame, prior to placing wallboard. If you had a single frame 2x4 wall with no RC or anything, and had wallboard on both sides, the air gap would be 3-1/2" - with a double framed wall using 2x4's (3.5" each) and a 2" space between frames, the air gap would be 3.5 x 2, + the 2" between frames, for a total of 9". A single frame with RC, would be 3.5" + the .5" for RC, for air gap of 4". Placing too many studs in the framing will eventually reduce the effective air gap, but for normal framing it's pretty much ignored.

2 - gluing of layers - basically, don't. Unless you're a masochist, there is no easy way to get this right - full lamination causes the sheets to act as one, destroying any losses gotten from separately acting layers. Strip lamination using the laminating type screws is iffy at best, and can result in falling walls at worst. Rod and I discussed this at length, and the single best way is to use 1/3 the normal amount of fasteners for all but face sheet, then use full schedule fasteners through ALL layers on the face sheet. Use 1/4" spacers all around (not between panels, of course) then, once panels are in place (do this for each layer, so caulking is complete seal) pull your spacers and caulk. Do NOT omit mud and tape on inner layers, you don't want voids where the panels are tapered within 2" of the edge.

Viscoelastic stuff - really expensive, hard to get uniform, questionable benefit. I would put the money/effort into another layer of drywall, probably different in thickness from the others. Double 5/8 one side, same on other side with 1/2" sandwiched between is a good combo - for CR wall, put your heavier glass on the heavier wallboard side to match masses.

Outa time for now, post back if you need more on this... Steve