Automatic bass trapping due to spaced walls???

[666666]

I am putting together a temporary recording room in a basement. It will be a room within room construction, sitting on the basement floor. Room is small, about 12 wide by 18 feet long. The "inner" wall with be 2-layers of 5/8" sheetrock, and "outer" wall, one layer of 5/8" sheetrock.

Here's the question... this entire sheetrock recording room will be spaced 18" AWAY from the outer basement CONCRETE walls (at least on two sides). Thus, some bass frequencies will pass through the several layers of sheetrock and have to travel another 18" before hitting the solid concrete (where I'd expect the bass to then be reflected back). I am thinking / hoping that this arrangement may act as somewhat of a "built-in" bass trap. I am wondering at what frequency level the waves will actually PASS through the sheetrock and go out into the 18" gap where a lot of it will hopefully get "trapped".

Or perhaps this arrangement is very bad and will cause a lot of problems????

In any case, I'd expect this arrangement to be way better than if the actual recording room walls were sheetrock nailed up right AGAINST the basement concrete walls. In that case, the bass would truly be contained within the room. With the 18" gap around the outside of the sheetrock though, I am hoping some bass will get lost in the gap.

Comments?

[lowfreq33]

Technically, yes, but not enough to make much difference. You'll still need acoustic treatment.

And you'll want at least some r-19 in between the sheetrock and the concrete to keep the space from becoming a resonating chamber. Think of the sheetrock as a diaphragm that will vibrate at a specific frequency.

[u b k]

a 12x18' room made up of multiple layers of sheetrock is going to sound like ass; the dimensions are multiples of 6, meaning your nodes will double up for twice the misery. sheetrock is hard and cold sounding, and most of your bass is gonna stay in the room. if your ceiling is 7-8', your problems will triple thanks to head end ringing.

if making the room 11x18 or 12x17 is an option, do it.

in any case you'll need treatment, and lots of it. traps in all the corners, lots of diffusion, cloud over the mix position, rugs on the floor.


gregoire
del
ubk
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[bpape]

Well, it's not so much bass trapping as it is a benefit from NOT having a huge buildup in one frequency (and up higher in frequency) as if all walls were the same distance from the concrete wall.

2 walls being 18" and the other 2 being whatever will at least spread the resonance that's trying to build up and come back into the room from the outside.

As was said previously, you'll still need to deal with decay times and reflections inside the room with treatments. It just gives you a little better starting point.

Bryan

[666666]

Thanks for the replies so far guys.

u b k, as it turns out, the room will NOT be exactly 12'X18'... I just used those numbers as an approximation... the real numbers might be closer to 11.3'X19.5' or something like that.

This room will actually be (gulp) a drum tracking room... not a control room. I do realize that I'll need lots of treatment INSIDE the room. Fortunately, I actually prefer a more intimate, fairly dead, dry drum sound... I've been able to work wonders with top-end reverb units and compressors when a room sound is needed... or I just blast a drum submix out into a nice room over loudspeakers and mic the room, etc.

I was indeed hoping though that the fact that the concrete walls were spaced farther back from the sheetrock would help the situation so that perhaps not SO much bass trapping would be needed inside the room... because the room is quite small as it is, adding 4" thick or greater traps all over the place actually cuts down considerably on the amount of usable interior space. But I realize I WILL have to deal with some degree of this.

On a positive note, I have tracked drums in another basement room that was SMALLER than this, with an even lower ceiling, and a certain amount of foam absorption all around, and the tracks came out well. Not amazing, but more than adequate for the production that was being worked on. It came out better than you'd expect. So I have hopes that I can massage my new basement room into something that will be even better... especially if I really fine tune the inner treatments.

Yes, the concrete walls are 18" away on two sides, but then on the other two sides, there is over 15 feet before any concrete walls... so indeed that will help spread the resonance a bit.

So you guys think it would indeed be beneficial to add absorption OUTSIDE the room, against the two concrete walls that are 18" away?... such as hanging R-19 insulation on the concrete or whatever? I did think of this, but was hoping it might not be necessary because that 18" gap between the walls will actually be used as a service path to be able to access pipes and wiring. If I add insulation in there, it will just make life harder when someone needs to go in there, but it CAN be done if it is indeed worth it sonically. I just figured that a mere 5 inches of batt insulation would not do much for taming long bass waves that would actually make their way through and across the 18" gap... but maybe I'm wrong. I guess if the entire 18" gap was completely filled with insulation or whatever that would be great, but I can't completely fill the gap.

I appreciate the advise

[Glenn Kuras]

Originally Posted by 666666

Thanks for the replies so far guys.



So you guys think it would indeed be beneficial to add absorption OUTSIDE the room, against the two concrete walls that are 18" away?... such as hanging R-19 insulation on the concrete or whatever? I did think of this, but was hoping it might not be necessary because that 18" gap between the walls will actually be used as a service path to be able to access pipes and wiring. If I add insulation in there, it will just make life harder when someone needs to go in there, but it CAN be done if it is indeed worth it sonically. I just figured that a mere 5 inches of batt insulation would not do much for taming long bass waves that would actually make their way through and across the 18" gap... but maybe I'm wrong. I guess if the entire 18" gap was completely filled with insulation or whatever that would be great, but I can't completely fill the gap.

I appreciate the advise

Well adding it will help but it is not going to (as Bryan said) be the cure for bass trapping. I know you don't want to take up a lot of room inside of the room with bass traps, so why not think about straddling ceiling to wall corners or something like our Tri Trap that does not take up as much room?
Also if this is going to be a live room you may want to think about not only absorption in the room but maybe some diffusion. I am sure you don't want the room to be totally dead.

Glenn