Re: concrete tube subwoofer report (long)
- From: "Wecan do it" <WeCanDoit@xxxxxxxxxx>
- Date: Sat, 28 Feb 2009 09:46:01 -0500
"There's a variable frequency adjustment on the amp so I can
dial in the right sound for each CD."
Hidden in that statement is enough for any audio designer
worth a damn to know that your project is a failure. If it
were a success you would be able to find a single setting
that sounds "right" for most every CD out there. Also with a
six inch goldwood woofer the SPL you get at low frequencies
has to be very low. One thing you did not mention was how you
placed it in the room. Placement may make more difference than
any adjustment you can make on a filter.
Good luck dude. I have build speakers for 35 years and looking
back at the first 30 years they all sucked in one or more
ways. Only in the last 5 years have I been able to build
speakers that stand up. It takes time and practice to get it
right. Keep on sawing.
peace
dawg
"js" <nothing@xxxxxxxxxxx> wrote in message
news:goat7k$n4j$1@xxxxxxxxxxxxxxxxxxxxxx
I recently finished my concrete tube stereo subwoofer. Sorry,
no pics yet,
but I'm working on it. Basically, I took an 8"dia, 48"
Sonotube concrete
form and turned it into a hi fi subwoofer.
The goal for this project was to make a kickass sub as
cheaply as possible,
using up as much crap laying around my work area as
possible.
I went with a bass reflex design. For the speaker, I used a
Gold wood 6 inch
sub; the amp was a Parts Express 25W build in subwoofer amp,
and I used a 4
in flared port. Cost was less than 75 bucks.
Modeling all this in Win ISD (with a 24" tube) I got a
fairly flat response
with bump at 30hz. doubling the size took the bump down to
20. It's amazing
how many in/3 are in a cylinder, compared to the equivalent
in a box. Oh
well, math was never my strong point.
The main design problem was that space was very tight, and
neither the amp
nor the port conformed to the cylinder as I had thought they
would.
My solution was to build 2 frames out of 1 3/4" pine stock,
and sand the
backs on the concrete tube until they conformed. I used
spray adhesive to
tack down 80grit paper, cut out as much waste as I could on
the band saw,
glued the pieces into a rectangle, and went to town. THIS
was the long and
sucky part of the process. Once the conforming was done, I
sanded the tops
flat, and lamented them with some strips of oak veneer I had
lying around.
Next, I glued the port into its frame with Gorilla Glue.
This is great glue
for speaker building, because it is strong covers a large
area and creates a
foam when dry.
Next I cut the holes for the amp and port, and made two
plywood circles
using a circle cutter and a router. This was the other pain
in the ass part
of the project.
After much measuring and shaping, I had a solid 3/4" ply
top, and an open
3/4" bottom for the speaker.
I sprayed the inside with rubber car undercoating (pew!),
then attached
Velcro strips with Liquid Nails and stuck a foam mattress
lad to them. If
you ever need a killed sound absorber for cheap, "Comfort
Foam" from
Target's bedding dept. is the shit.
The covering proved to be another challenge. My initial plan
was to use
Parts Express vinyl speaker covering, as it was "catproof".
But it doesn't
stick well to anything less than perfectly even surface
like MDF. So I
wound up using standard black speaker carpet I had laying
around.
Last, I Gorilla glued the frames, and screwed them to
internal braces (also
glued in), I glued in the top and bottom, hooked up the amp
and speaker, and
made a decorative top from another plywood circle. Carpet
seams were sealed
with rubber slpine I had laying around.
I originally had intentions of building an elaborate base
and post system
with sound absorbing material on the base, but that was more
problems than I
needed. Instead, I found some 1" cylindrical drawer pulls at
the Home Depot
Design Center closeout for next to nothing, and super glued
them to the
bottom.
SOUND: As Cory pointed out, I was worried that this thing
would be a "one
noter". Nothing could be farther from the truth. It supplies
a TON of warm
bass even at low volume, with no ring or vibration. There's
a variable
frequency adjustment on the amp so I can dial in the right
sound for each
CD. I grabbed a couple long Monster RCA cables from the
Circuit City
Closeout (are recessions cool or what?) for cheap and used
them for the
hookup.
CONS: The only 2 cons I see so far are
1) There is no adjustable "Q" control, and the Frequency Q
is pretty narrow,
so the sub is in danger of being a "one noter" on certain
songs.
2) the amp controls are on the bottom rear of the sub, so I
constantly have
to bend down and adjust them. I'd probably go with an
outboard amp next
time.
Overall though, I say it's a resounding success. I'd LOVE to
try this
approach with a bass cab, or a few tubes in an array of some
sort. We'll
see. I got a LOT more stuff in the pipeline...
.
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