Additional comments and instructions are available at:
http://www.AudioAsylum.com/audio/tweaks/messages/17498.html
on building the full-blown wire fencing versions.

2. Quick and dirty homemade tube traps

Obtain some sheets of 1" thick rigid high-density fiberglass panels, or
better yet, rock wool panels.  If the panels are only medium density,
double up on them and size accordingly for the inner/outer panels.
Determine a size based on an equilateral triangle (side panels of 24"
or smaller recommended, make them sub-multiples of the sheet width,
e.g.,24",16",12")and once size is determined, cut the panels to size
(these can be 8 feet tall if the panels come 8' by 4', but a full 8 feet
will probably be too unwieldy).  The shape can be a right triangle so
as to fit in a corner better, size the panels accordingly.  For a full
use of a 48" wide panel, 14' on the sides, and 20" across the hypotenuse.

Glue (silicone rubber or liquid nails) these together at the edges
forming an equilateral triangle or a right triangle, and cut 3/4"
wooden end caps in the appropriate size/shape to cap the ends and glue
the triangle of panels to the end caps.  To take some of the "edge" off
of the acute angles, wrap a single layer of 3/4" minimum loosely spun
bonded polyester batting around the fiberglass panels (this also aids HF
absorption), and then wrap with fire-retardant treated burlap.  If you
want some partial reflectance/diffusion, wrap a limp plastic sheet
around one corner of the triangle and half way across the two sides.

Either one of these will easily outperform the previously posted cardboard
tubes filled with fiberglass and covered with carpet, and at a lower cost,
providing a broadband absorption over a wide and extended LF range.

Recent checks on 700 series pricing and availability has lead to the
discovery that, to the consumer, the only size that is readily available
is a 2' by 4' panel, in 1", 2" or 3" thickness's.  In some area's of the
country, rock wool panels are still available, but not everywhere.
For quick and dirty DIY bass traps, the 1" thick 705 panels will work, and
a carton of 12 panels will make 4 triangular bass traps four feet high,
roughly equivalent to 12 to 14" diameter round bass traps made using
hog wire.

++++++++++++++++++++++++++++++++++++++++++++++++
Rough Costs, based on a 14" outer diameter trap:

Fiberglass, unfaced - 6 1/2" thick, 15" wide by 39 feet long approx. $13.50
(Enough for approx. 4 traps, 2 and a half once around strips stacked up)

Hog Wire, 14 gauge - 36" by 50 feet, $17  Enough for approx. 6-7 traps

Particle Board - 4'X 4' sheet 3/4" $7 (enough for approx. three 14" traps),
4'X 8' $13 enough for 6 traps

Polyester batting, bonded fluffy loose density approx. 3/4 to 1" thick,
45" wide, $2.17 a yard.

Burlap - Dyed, with minimum levels of insect and fire protection,
available from Wal-Mart, $1.48 a yard by 36" wide.

Tube Liquid Nails 29 OZ, $4

Tube RTV Silicone Rubber, 10 OZ, $4.50

Staples, 9/16", $2 for 1,000

One small can brown or black paint, $5

Alternative Approach: Owens Corning 705 semi-rigid fiberglass panels,
2' by 4', by 1", 12 to a carton for approx. $92, not including S&H.

Rough Total per trap, minimum of 4 14" diameter by 36" high traps,
some materials left over: $19 each.
Minimum investment approx. $77 for four, with materials left over.
Costs to do 6 or 8 is slightly less per, due to better materials usage.

ASC Prices:  One 11" diameter by 4 foot tall tube trap: $248 retail, four
tube traps: $992

Latest Super Quick & Dirty Recipe
    The triangular versions I outline were just a way to do a quick and dirty version for the less labor
    inclined and/or impatient amoung us. They are not quite as effective as the round animal fence
    versions, which duplicate the effects of the retail bass traps quite well.

    The middle support disc also helps reduce any tendency for an internal resonance developing, and
    while not strictly necessary for the triangular versions (the panel flexing of the OC panels was a part
    of their design), it wouldn't really help that much.

    If one wanted to use the triangular version, then if an internal divider was tacked into place leaving
    air gaps along the sides, then they would break-up any internal waves, and not keep the panels
    from flexing. A section of the fiberglass board would do nicely.

    New Quick & Dirty Recipe

    Thanks to my less motivated friends, I have a new recipe:
    buy three rolls of 15" wide fiberglass (virtually any thickness, as the rolls are longer for the thinner
    stuff, and the total diameter ends up about the same, it can be faced or unfaced) insulation, stack
    them on top of one another, leaving them in the plastic bags, and wrap burlap or grill cloth around
    them. For better HF absorption, wrap polyester batting around one side or the entire sides. You can
    use something like duct tape to hold the three bags of fiberglass together, and to tape the polyester
    batting into place, etc. How involved you wish to get is up to you. They should be placed in the
    corners, as for all bass traps.

    This will work almost as well as the wire fence version in my recipe, at perhaps 70-80% of the bass
    absortion, with no resonances, or problems.   The cost is greater, at about $50 each, if you wrap them
    in polyester batting, and cover in burlap.  However, they can be in the corners in a matter of minutes
    instead of hours/days, and for a lot less labor.  If you only get enough for two in the front corners to start,
    then you can later use these same rolls to make up wallpanels and the full blown bass traps using the
    wire animal fencing cylinder versions.  If you plan to do this, make sure you get the appropriate number
    of faced and unfaced rolls, and mix them symmetrically on each side of the room.

Additional information on the Super Quick & Dirty versions are available at:
http://www.AudioAsylum.com/audio/general/messages/70817.html

-Fire-Proofing-
Burlap, or virtually any other cloth can be made fire-retardant by soaking
it in a commercial fire retardant sold for the purpose.   For those who
are using burlap and wish to fireproof it there is a company called
Flameseal (http://www.flameseal.com) in Texas which makes a
spray-on product to fireproof fabrics, its approx. $30.00 per gallon.

If you are interested in a DIY treatment, there are two possible
alternatives:  borax and calcium carbonate.  Borax (get the pure stuff,
not with soap) is readily available, and calcium carbonate is the super
ice melting salt that comes as little white round balls of salt.
The only problem with these is that on dark colored fabrics, they will
leave white streaks/residue that is visible in the concentrations needed
to be effective.  If light colors of burlap are involved, then it is
not nearly as much of a problem.

Or, you can just use the Guileford fabric, but be aware that it is VERY
expensive!

A NOTE ON ROCK WOOL (Mineral Fiber)
Apparently, rock wool is no longer readily available throughout the
country, as the primary manufacturer has quit making it.  A near
equivalent would be an Owen Corning 706 or 705 panel, which
should work almost as well.  Owen Corning 700 series panels are
now readily available to the consumer only in 2' by 4' size.
Cartons of 12 panels in the 1" size.

More Details on Taming Room Acoustics
----------------------------------------------------------------
Q:  I visualize them as similar to rather thick Roomtunes panels
that looks like Vandersteen speakers! Am I right or wrong?

A: Essentially.  The looks can vary a little, depending on the type
of burlap, the colors, the tacks/nails/studs used to tack down
the burlap, etc.  Other cloth than burlap can be used, but at a
possible (very likely) performance penalty.  Speaker grille cloth
probably wouldn't be too bad, and would allow some choice in weave
and colors over the burlap.

Q: How tall should the panels ideally be? I understand that the
width is about 15" w/c corresponds to the width of the fiberglass.

A: For use as spot absorbers, the panels can run the height of the
wall, or as a minimum, only the middle 4 feet.  I would recommend
a minimum of two widths, or about 30" wide to be as effective as
possible.

Q: Is cotton batting a good replacement for polyester?

A:  No.  Cotton batting is usually too dense, and will cause excessive
reflectance. It also tends to settle, lump up and in general,
become a pain to deal with.

Q: How many panels are needed to effectively treat the whole
room? Is it necessary to fill the entire backwall with them?
I certainly hope not!

A:  It is not necessary to fill the room with them, or even the back
wall.  Look at ads for Roomtunes, ASC tubetraps, etc. or contact
these companies and request their literature, being sure to ask
about actual use of the product in a room and placement details.

Q: How should these panels be placed? I know they should be
at least 6-8" away from the wall but where behind the speakers?
On the space between the speakers? On or near the corners?

A: The usual minimum game plan is to use a 30" wide by 48" tall by
4" deep or more panel directly behind each loudspeaker (all panels
spaced from 2" to 6" off the walls), then one each on the mirror
points on the side walls.  The mirror point on the side walls is
the point where a mirror flat against the wall reflects the
speakers image to you at your normal seating location.  Two
panels for the rear wall IN THE CORNERS if not using tube trap
type bass absorbers, angled at 45 degrees.  These rear corner
panels would be most effective if they were floor to ceiling,
and they could be only 15" or so wide, instead of 30".

Next step up in treatment would involve a pair of panels on the
ceiling at the mirror points, possibly a center panel (normal
size) in the center of the rear wall.  If the floor is hard
with no carpeting, then removable/portable panels on the floor
at the mirror points (spaced appropriately) would help a lot.
These can be smaller sizes too, about 15" wide by 2 feet for
better portability and ease of storage when done listening.

DIY resistive bass traps would be a third step, with at least
one 3 foot tall cylinder of at least 10-12" diameter in each
corner.  Better bass smoothing and absorption can be had if they
are made 14-16" in diameter, and two are stacked in each corner,
or at least two stacked in the front.

Anything beyond this requires a true acoustic analysis of the
room as a whole, including all the surfaces, etc.

Q: Since I have small monitor type speakers that have no
deep bass to speak off (and no serious bass problems) that
means that I can get away with closer spacing of the panel
against the wall, and relatively thin panels say 3-4" thick
only for midrange/treble absorption especially at the front
wall (wall closest to listening position). Is this correct?

A:  Yes.  Use of less than full band wall absorbers will shift
the tonal balance though, and make the room/speakers sound warmer.
This may not be a bad thing in your case.
 

Q: How can a panel of this size be placed half way up the wall,
4 or so inches away from it. Special hardware?  Long,
beefy bolts with spacers?

A:  You can easily add legs to the rear of the frame, of
sufficient height to get them off the floor, some 1X1's or
1X2's, and then glue/nail some 1X2's with the desired length
for wall spacing to the back/side of the frame.
See ASCII diagram below.

Wall

|
|
|
|4"_
| |X|
|_|X|
| |X|
| |X| <Absorber Panel
| |X|
| |X|
| |X|
| |~
| |
| |
| |<2' leg
|_|____________Floor

 -About Diffusors-

Placing a diffusor array at either the speaker end, middle of
the wall, or the listening end, middle of the wall can
sometimes make a room bloom into a really great listening
environment.

For a retail solution, Auralex has the T-Fusor for about $220
(includes S&H) for four 2 foot by 2 foot panels that are 5 1/2"
deep.  This will create a 4 foot by 4 foot diffusor area on a
wall, and would be considered a minimum amount of diffusion to
provide any real improvements.  They are plastic molded sheets,
meant to have the rear filled in with fiberglass or polyester
batting to combat the hollow plastic sound that would
otherwise result from a thin sheet of plastic.  Careful use
of some of the expanding foam sold for filling/insulating gaps
and cracks would probably be superior to these loose fillings
for stiffening and damping the plastic walls of the diffusor.
For comparison, a 4X4 foot square of QRD diffusor would run
over $700, and a 45X45 inch square of Art Diffusor, Series E
runs $500.

Web Sites with Acoustics Information:
------------------------------------------------------------
The mother of all web sites for links to acoustics info sites:
http://home.att.net/~rcp-conseaco/links.htm

RPG Diffusors, QRD's, etc at:
http://www.rpginc.com/

Acoustical Sciences Corporation, tube traps, etc. at:
http://www.tubetrap.com/

Systems Development Group, Art Diffusors, etc. at:
http://www.sysdevgrp.com/products.htm

A room acoustics calculator by SysDevGrp at:
http://www.sysdevgrp.com/calc.htm
This includes a calculator for constructing Helmholtz resonators,
and other forms of frequency specific bass absorbers.
Acoustics bibliography and glossary at:
"  " /sysdevgrp/biblio.htm
An Acoustics FAQ with graphics of various acoustics techniques:
"  " /sysdevgrp/faq.htm

Auralex Acoustics, T-Fusor, MiniFusor, Lenerd, Sunburst, etc. at:
http://www.auralex.com/

A list of Acoustical Treatment Suppliere at:
http://www.musicyellowpages.com/atg.htm

Room setup info at the Cardas website:
http://www.cardas.com/insights/roomsetup.html
This uses a classical method based on mathematics to ascertain
the best place to locate your speakers.

Copyright Notice
All website content Copyright Jon M. Risch, 1997 - 2001

All applicable copyright laws apply, all rights reserved, except transmission by USENET and like facilities granted.  Any use or inclusion in print or other media are specifically prohibited.  The informational content is not warrantied in any way or form, and any use of said content are at the reader's own risk, the author shall not be held responsible in any way for any damages or injuries arising from the content of this web site.  Common safety practices are encouraged at all times.  Do not fold, spindle or mutilate.