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From: tness@convex.COM (Thomas Ness)
Newsgroups: rec.audio.high-end
Subject: Re: room analysis software
Message-ID: <9371@uwm.edu>
Date: 6 Feb 91 13:44:40 GMT
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In article <9318@uwm.edu> nichols@vms.macc.wisc.edu (Dennis Nichols, MACC) writes:
>Now what I want to know is how do I construct devices with the same
>function as TubeTraps, that is, home-built tube traps. Any published
>references? Any of you out there tried this? I had a dealer who doesn't
>stock them suggest that I could build some but (understandably) he
>wasn't about to say more than that. 
>
>#           Dennis Nichols             1210 West Dayton St.        608-262-1936
>|  MACC     Univ of Wisconsin-Madison  Madison, WI 53706  nichols@macc.wisc.edu
>#--------#  Academic Computing Center  UNITED STATES    nichols@wiscmacc.bitnet

I have built 16 full round tubes and 4 half round tubes since I read in 
rec.audio what they are and how they are built. I use them to make a narrow room
seem wider and to approximate a live end and dead end room. I have had very
good results with them and my musician guests seem to agree.

The core of a tubular trap is made of fiber glass steam pipe insulation. This\
comes in various sizes. All are about 3' in length but inside diameters and 
wall thickness vary. I have used a 3' x 9"id x 1" wall tube. I paid about
$44.00 per box of four. These should be available from specialty insulation
suppliers. I found one in Atlanta that was called AC&S. I know that they 
were sold and I don't know what their new name is. It is possible that AC&S
is still used in many parts of the country. (They were a nation wide firm)
It is worth checking to see if the major insulation contractors in your area
are willing to provide a vector.

I also had access to a discount drapry fabric shop in Atlanta. I was able to
buy remants of good fabric for about $5/yd. If you do rough calculations
you will see that it takes about 1yd. per tube. (BTW: Forsythe Fabrics, behind
Ga. Tech is my source, for folks in the Atlanta area)

I used construction gule in a tube because it was easy to apply and had the
bulk to glue the rough fabric to the rough fiber glass. I used ordinary sewing
pins to hold the fabric while it set.

My half tubes are cut from whole tubes with a razor knife. I bought oak
finished boards from Home Depot to top the tubes. I think that they look
good.

My materials cost was about $20 each tube. The list price is $175 for these
from ASC. I think that these are called 3' x 11" in the ASC catalog since
they seem to refer to outside diameter. I could be wrong.

I removed the paper from the outside of 4 of my tubes but left it on for the
others. I have read ASC's literature and I believe that the wrapper is what
ASC calls the "Limp Mass Crossover". I think that this means that the 
fiberglass is more absorbent for high frequencies, but the paper coating
blocks these frequencies. This would not effect the low frequency response
of the tube since these frequencies rely on the RC effect of the tube more than
simple surface absorption. If I am wrong, politely let me know.

If you want to know more, let me know.


Thom Ness
tness@convex.com