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From: djb@riccb.UUCP (Dave J. Burris )
Newsgroups: net.audio
Subject: Re: a new topic
Message-ID: <540@riccb.UUCP>
Date: Tue, 24-Sep-85 10:03:41 EDT
Article-I.D.: riccb.540
Posted: Tue Sep 24 10:03:41 1985
Date-Received: Wed, 25-Sep-85 03:45:05 EDT
References: <761@charm.UUCP>
Organization: Rockwell Telecommunications, Downers Grove,Il.
Lines: 45

> By the way, I have heard of Sonex acoustical pads.  They sound like a rip-off.
> I have spent some time surveying the market for acoustical materials,
> mostly in connection with noise control in my house.  There are several 
> companies which make acoustically absorbing foam, and it can be quite a bit
> cheaper than the amount mentioned.  There are also many other materials for
> damping, isolation, and absorption on the market.  I wouldn't go slathering 
> anything on my walls until I had a serious discussion with a technically 
> competent acoustical engineer.  I happen to know just such a person, who 
> works for a distributor of acoustical materials, and I will be glad to 
> give his name and number to anyone who is interested enough to send me mail.

While Sonex(tm) foam is a little expensive, I think if you make a comparison
of the absorbtion characteristics you will find Sonex far superior in it
absorbtion vs. frequency characteristics. Especially if you get three inch
or greater thickness. Typical sound absorbtion materials used in building have
somewhat erratic frequency responses that are usually centered in the speech
range (~300-500 Hz.). If this is where you need your absorbtion then you are
in business. If not, well...

Remember, frequency compensation through absorbtion may not even be practical.
Absorbtion is generally used only to correct for a RT60 time which is too
great (often frequency dependant) causing intelligibility loss, not for
frequency response caused by poor room dimensions and construction.
In most cases abrorbtion does NOT substitute for frequency equalization.

If you know someone who owns a real-time analyzer, you can isolated poorly
braced walls which cause dips in the low frequency response due to parasitic
oscillations. Solution: use screws rather than nails and use plenty of them.

I would highly recommend the live-end/dead-end approach for discriminating
listening. This method was documented by Don Davis and has proven to be the
most popular for studio and control room monitoring. The speakers are placed
in the dead-end which has a high absorbtion over a wide frequency range. The
opposite end of the room is reflective but also diffusive to eliminate
standing waves. The listening position is arrived at by experimentation and
somewaht by preference. Many studios even purchase expensive diffusion plates
for the live end of the room.

For home use much compromise is required but working around this concept is
an excellent starting point.

-- 
Dave Burris
..!ihnp4!ihopa!riccb!djb
Rockwell Switching Systems, Downers Grove, Il.


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