From: kmat@vnet.ibm.com (Keith Matthews)
Date: Tue, 28 Jul 92 10:28:42 EST
Newsgroups: rec.audio.pro
Subject: Re: Soundproofing
Reply-To: kmat@vnet.ibm.com
Organization: I.B.M. Australia Ltd. Canberra M.P.C.
Disclaimer: This posting represents the poster's views, not those of IBM
News-Software: UReply 3.0

In <1520sdINNb2@network.ucsd.edu> Michael Breen writes:
->
->I've got a corner of my rented garage I want to put a band in.  Pretty
->good size PA, guitar, bass (electric), and drums.  I will probably allow
->for some 'comfort' room, like a sofa, and/or some bookcases, etc.  The
->room will be mostly for rehearsal, occasionally to record (roughly) to
->a 4-track.  The space is about 10'x15' (I can get up to 15'x20', if I can
->get enough material to 'soundproof' it).
You must be kidding!! 8-)
You wiil be lucky to fit the Drum kit in that much space.
I should know I just completed a project the same as what you want to do
Sorry, I shouldn't be so negative. You can probably make this work BUT
Sound Proofing is a great deal harder than you would imagine.
As you are aware the BASS IS THE MAIN PROBLEM as its wavelenths are large
enough to consider ANY Pineboard wall to be like rice paper.

->it's two walls, one with a window, a concrete floor, and a slanted roof
->with rafters.  The 'box' is completed by two 'imaginary' walls.  I have
->a bunch of 'foam', stuff from hospital beds, about 4" thick with 'cones'
->on one side. flat on the other. I also have a bit of 'professional'
->acoustic-tile-stuff.  All told, it *might* cover two walls.  I can get to a
->bunch of plywood, and will spend a little if I have too.
->
You will HAVE TO cover all surfaces not just those 2 walls. YES! including
the roof & Floor.
The materials you have will be ok at stoping most 500hz and above but they will
be useless for stopping the bass. So really the whole thing could be a waste of
time.

My room although no where near perfect took a lot more material than you have
mentioned above and cost about $2000 to build. Pretty Cheap really.
It works quite well, with an SPL of 115db at 1m in front of the Amp (ie. just
in front of the wall) I get an SPL of 55db on the other side of the wall.
(about 1.4m from the amp.) The background noise is generally about
45-50db which puts me right on the State legal limit of 5db above the
nominal background noise.
->
->1) what are my biggest 'sound leak' problems?  I assume closed
->windows made pretty good 'speakers' to the outside world.
->
You should forget the window Unless you want to go to some trouble over
it. I put a small 600mm * 300mm window from the sound room into the
Control room behind. It to 2 sheets of 10mm thick glass ofset from parrallel
and separated by a slight vacuum And that works well. In fact my preliminary
Measurments suggest it was more effective than the rest of the wall??
Remember ANY SLIGHTEST GAP or HOLE is all that is required to transmit THE
FULL sound. Try the door test. Put a stereo on full in a room & close all
openings. Its muffled right?. Now open the door to the room up just a little
so a small free air gap exists, and BANG its LOUD & CLEAR!!!!
P.S. The door has been My MAIN problem.

->2) where can I best utilize the foam/plywood/other materials?  One
->of the existing walls faces my house, so it will be my last 'sound leak'
->worry.  I thought of hanging plywood perpendicular off the rafters to
->create the two non-existing walls, then covering them with foam.
->
I swear its Not that easy!!!

->3) How can I cut corners?  I'll probably get an old sofa, and I
->understand that can act as a great bass sink.  I could also try to get
->some thick curtains.  I have lots of books and mags.  I hear carpet
->don't do squat (as with egg-cartons).
->
You CAN'T. And I don't care who told you carpet was no good, they are wrong.
Its just that you need lots of it, and its HEAVY......
The old Cotton based HEAVY underlay is VERY GOOD.

->4) Is there any advantage to 'baffles' (panels covered with foam)
->situated in front of bass sources, like the kick drum or bass amp?
->Will this dampen the sound inside more than it's worth?  Is there a
->better way?  I understand they are good for 'isolation' when you're
->recording a bunch of musicians in the same room.
->
This an internal acoustic thing, it does didly squat for sound proofing.
The Baffles are to control the room acoustics and help stop microphone
spill.

The main thing to remember is DENSITY.....
I used a separate frame, and 35mm thick boards of heavily compacted
Pine material coated in a plastic laminate(which sealed the wood).
1 sheet on each sid of the frame and the gap filled with fiberglass batts (High
 freq stopper) and several layers of heavy underlay. Some foam was used around
corners and around the outside walls.
Inside the walls have 2 layers of underlay and then Carpet.
The floor in a slab with 3 Layeres of underlay and 2 layers of carpet (bouncy
but effective) The roof is the 35mm sheets again with Omarlay underlay (for
weight reasons and a layer of carpet. All spare foam and Underlay is layed on
the roof. The contol room is a similar set up only I concentrated on internal
acoustics rather than proofing for that room.
hope this helps......
Go ahead but IT WILL COST...... a little
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