Sound in but not out.

[Charles Dayton]

I hope I'm right in creating a new thread with this.
I had an interesting thing happen in my "sound proofed" studio. I was in during the day, while my next door neighbors backyard was being dug out for a swimming pool. I think they had one of those Bobcat mini dozers pulling a tree stump about 30' from the back of my studio. Oh, my studio is in what was formerly my garage, in case you were wondering what this had to do with my nextdoor neighbor. Anyhow, boy did I hear that low freq rumble. It almost made me cry. I thought I had done everything right. Staggered studs, floating floor, double layers of sheet rock, and a 3' thick slab of concrete under the portion of the studio closest to the neighbor. The exterior is a nice thick coat of stucco. Here is where it gets interesting to me. I had my first band in that night. I had a drummer in there wailing away, closed up the studio tight, and went outside. Nothing. Not a thud or bang! Thus the title, "sound in but not out.". My main concern is, the recording space is also a foley stage, and some foley, Ie; cloth movement or footsteps, require a really quiet stage. Am I looking at another layer of drywall, or is there no way to soundproof against heavy equipment?

[giles117]

I am sure the guys here have better answers, but in my days of working in idustrial facilities, they floated the concrete floor as well to isolate from LF vibrations from other parts of the plant.

I essence you could stand on one slab of concrete and NEVER feel those stamping plants working.

Also keep in my that this was an earth mover working... I would assum it is similar to vibration transmission during an earthquake (of course at a smaller scale.)

[knightfly]

Charles, I'm kinda short on time right now, heading off to the dreaded "day job", but Giles is right - hopefully, you won't have heavy equipment working around very much of the time - drums are NOTHING compared to the seismic crap a close-working earth mover (even a small one like a Bobcat) can do. And if that's going to be a regular occurence he's also right - Foley work in those conditions would require a pro floated concrete floor, with a complete floated room on top and all the trimmings.

At least, you don't live next to busy railroad tracks (I hope...)

I'll check back on this tonight late, sorry for the short answer... Steve

[knightfly]

OK, still short on time (what's new) but a little more - You mentioned a concrete slab closest to the neighbors - while concrete is good for isolating AIRBORNE sound, even to very low frequencies, because of its MASS, it also CONDUCTS sound at approximately 10 times the speed of sound in air. When you have earth-borne vibrations under a concrete slab, they will go right through it into the room and vibrate anything in contact with the floor, which in turn those objects will emanate AIRBORNE sound into the room, and voila - noise...

In the case of a full floated room, there is a SECOND concrete slab that is floated, usually on springs, sometimes on composite spring/compressed fiberglas or rubber, complete with little "access hatches" distributed across the floor, so that each isolator can be individually adjusted for tension as things sag - such supports are placed on specifically designed centers according to TOTAL LOAD on the suspension, so that the correct amount of compression is achieved in the static condition. Such floors should be periodically "tuned up" to maintain the proper amount of tension on each isolator, for maximum isolation.

The rubber, or compressed fiberglas, is what isolates against higher frequency sound conduction - the springs are what takes care of the lower frequencies. If these isolators are either not compressed at all, or are compressed TOO much, they don't work because in EITHER case, they act as a SOLID connection between the "floated" slab and the "fixed" slab.

In your case, Charles, as far as Foley work is concerned there are a number of "band-aids" that can be used in various circumstances.

One is, don't record foley when they're digging swimming pools :=)

Two is, if it isn't part of the desired sound, don't record it at all. (Meaning, if you're recording the sound of leaves underfoot, and there isn't any USEFUL information below 100 hZ, roll it off or use a mic with weak low end response, or both. I'm not very familiar with most of the offerings for Mac recording software, but I would think that you'd have the option of using a high pass filter set at about 100 hZ with a fairly steep Q, to get rid of LF information. (Generally, you can CUT more with EQ without artifacts than you can BOOST.)

I use Samplitude on the PC myself, and it has a very workable noise reduction module included - you can hilight a portion of the waveform (not the stuff you WANT), get a "noise sample", then open a quite comprehensive dialog box that, given a fair degree of experimentation, will let you "subtract" JUST THAT NOISE SAMPLE from the overall wave file -

I once recorded a chord progression with a Takamine cedar-topped acoustic electric steel string, thinking I wasn't going to keep it - because of that, I recorded it with the nearfields on (direct, no mic), listening to a very strident click track - scratch track, no big deal; then, I decided I wanted to KEEP it - the track "rang out" on the last chord, and I decided that's what I wanted for the song ending - surprise, there was this very noticeable "TICK tock tock tock TICK tock tock tock... After about 3-4 tries of changing (several) settings on Samp's NR module, I was able to "subtract" the click track - to my surprise, it didn't affect anything else I could tell - string/finger noise still there, no discernible change in timber, etc...

Just some thoughts, if you use them the address for sending royalty payments is... :=)