bass absorber threads from the old forum

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bass absorber threads from the old forum

Postby Dan Nelson » Mon Mar 22, 2004 4:24 am

I am going to post some old threads for the yahoo forum since restoring the archives is some ways off still

Dan
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Postby Dan Nelson » Mon Mar 22, 2004 4:28 am

Subject: [acoustics] Corner Bass traps etc.
Date: Tue, 26 Feb 2002 12:44:38 -0500
From: Dave Portocarrero <dporto@xxxxxxxxx.net>

As I near completion with the drywall phase of my studio, I'm nearing
the "treatment" phase ( I do still have to complete 3 coats of spackle
and paint ).The studio is 3 main rooms- Control rm , "live" room , and
drum room , none of which are square ( the drum room has 2 , 90 degree
corners , the control rm has 2 90 degree corners and the "live" rm has
3. Obviously , these angles prevent me from using a simple program to
calculate rm modes. Any suggestions ?
I've got 8 4X8' panels of 1" Owens Corning SelectSound Black
Acoustic board ( I'll probably cut these into 2'X4' panels ), 4
4'X8'Select Sound board and 1 roll of Select Sound Black acoustic
blanket (1"X72"X70'). I'm planning on covering the panels with fabric
and mounting them in wood frames in various parts of the studio.
Anyway , the point is this - In the 90 degree corners , I'm weighing
the idea of building bass traps. I've looked at several different
designs ( tubes , halftubes , 1/4 tubes , panel types across the corner
etc. ). The cost is what drives my thirst for information - it would
certainly be easier to just buy some LENRD BASS TRAPS and be on my way(
I'm sure Jeff would recommend these ! ) but , I'm trying to reduce the
foam look and they're not cheap ( I know - nothing good is- unless you
build it your self ) I really want to try to reduce the trial and error
quotient ( especially the error part ) involved with the process , hence
my plea for help !
Any thought's are appreciated.
Thanks
Dan Nelson
 
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Postby Dan Nelson » Mon Mar 22, 2004 4:30 am

Subject: RE: [acoustics] Corner bass traps
Date: Thu, 28 Feb 2002 12:44:13 -0800
From: Chad York <cyork@xxxxxxx.com>


Hi Dave

I recently went through this same dilemma. Driven by cost/performance, I
proceeded with 8foot traps constructed with 4" 703 in the two 90deg corners
that I had in our smallish space (27 x 20). I was blown away! Where there
once was mud... :)

Given the odd shapes of the control room and live room I could not predict
the modal problems accurately. So I thought I would start with some
absorption via bass traps in the corners for now and build a tube traps
tuned to problem modes later. But after taking an RTA to the rooms, the
only thing I plan to do is deal with a little bump at ~60 and ~120Hz. I
could not believe how much these two 8' corner traps pulled out of the
rooms! The rest of my treatment/gobos will all be mobile...built from the
remainder of the 703...With the low end problems significantly improved, I
can actually use some ambience rather than treating the room to death.

Between building the treatment myself, and faux finishing the cement floor
(rather than tile or hardwood), I saved enough to justify a TLM103.

Good luck.
Chad
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Postby Dan Nelson » Mon Mar 22, 2004 4:31 am

Subject: Re: [acoustics] Corner bass traps
Date: Fri, 01 Mar 2002 07:38:27 -0500
From: Dave Portocarrero <dporto@xxxxxxx.net>


Chad ,
Thanks for the reply. Perhaps I can pump you for a little more info ? How
wide is the front of the trap ( the long side of the triangle ) I'm thinking
about 20 - 24". The square corners in my rooms are also about 9'6" - should I go
floor to ceiling ( I would think so ). Also , what material did you use for the
front panel - I'm thinking about 5/8" sheetrock ( this is what my walls are ).
And I'm assuming that this is a sealed cavity ? Any help is appreciated.
Regards
Dan Nelson
 
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Postby Dan Nelson » Mon Mar 22, 2004 4:32 am

Subject: [acoustics] Re: Corner bass traps
Date: Fri, 01 Mar 2002 13:51:40 -0000
From: eric_desart <eric.desart@xxxxxx.net>

Hello Dave,

Just few thoughts:

--- In acoustics@y..., Dave Portocarrero <dporto@o...> wrote:
> Chad ,
> Thanks for the reply. Perhaps I can pump you for a little
more info ? How
> wide is the front of the trap ( the long side of the triangle ) I'm
thinking
> about 20 - 24".

That's probably the size of the slab, isn't it. Making it larger
will make the frequency range lower.
If you have a bit extra mony, you could use 1/4 duct insulation
instead, is better and looks original. Look in the bookmarks common
materials section.


The square corners in my rooms are also about 9'6" - should I go
> floor to ceiling ( I would think so ). Also , what material did you
use for the
> front panel - I'm thinking about 5/8" sheetrock ( this is what my
walls are ).
> And I'm assuming that this is a sealed cavity ?

No the cavity must, better may NOT be sealed, just wool in front of
the corner.
If you use duct insulation, it's a good basis if you want to add some
mid high frequent diffusion by lightweight foil or perforated, or.....

Regards

Eric
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Postby Dan Nelson » Mon Mar 22, 2004 4:33 am

Subject: Re: [acoustics] Re: Corner bass traps
Date: Fri, 01 Mar 2002 09:43:48 -0500
From: Dave Portocarrero <dporto@xxxxxx.net>


Eric ,
Thanks for the reply. Of course the info you've given me leads to more
questions
1) 20- 24" is the width across the front ( hypoteneuse ) of the corner trap.
9'6'' would be the height of thr corner from floor to ceiling. I'm planning
on using 1" acoustic blanket material ( made by Owens Corning - Select Sound
Black Acoustic Blanket )
behind the baffle(not touuching the baffle itself) on the two walls/short
sides of the triangle. Or transversely across the corner but behind the
baffle.
2) The major question in my mind now is this; should the openings be left
along the edges of the front baffle or at the top and bottom - or both .
Your help is greatly apreciated.
Dan Nelson
 
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Postby Dan Nelson » Mon Mar 22, 2004 4:34 am

Subject: RE: [acoustics] Re: Corner bass traps
Date: Fri, 1 Mar 2002 10:07:51 -0500
From: SFoster <Sfoster@xxxxxxx.com>


Build a 2' wide 8' tall frame, fill it with a pair of cloth covered 703
panels (2'x4") and mount the frame across the diagonal of the corner
with the top and bottom left open. If you have any batts of fiberglass
lying around tack one in the corner (tack the center of the back to the
deepest part of the corner so it gets folded almost in half). Adjust
the batt so that it doesn't stick out the top or hang out the bottom
when you cover the corner with the frame.

Voila', a very efficient broadband absorber.

Scott R. Foster
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Postby Dan Nelson » Mon Mar 22, 2004 4:34 am

Subject: Re: [acoustics] Re: Corner bass traps
Date: Fri, 01 Mar 2002 10:08:51 -0500
From: Dave Portocarrero <dporto@xxxxxxxx.net>


So Scott , what you're saying is -no hard surface across the corner - just
the 703( I'm assuming this is rigid fiberglass board ).
Thanks
Dan Nelson
 
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Postby Dan Nelson » Mon Mar 22, 2004 4:35 am

Subject: [acoustics] Re: Corner bass traps
Date: Fri, 01 Mar 2002 15:36:22 xxxxx.net>


Hi Scott

Perfect solution.

Just a question: why do you leave the top and bottom open? The 3-
corners are even more efficient than the the 2-corners, why leaving
them out?

Eric
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Postby Dan Nelson » Mon Mar 22, 2004 4:36 am

Subject: RE: [acoustics] Re: Corner bass traps
Date: Fri, 1 Mar 2002 08:42:50 -0800
From: Chad York <cyork@xxxxxxxx.com>


Dave,

We did most of the finishing work in the studio with rough unfinished cedar,
which is very inexpensive up here in Vancouver, Canada. Since the baseboard
was leading into the corner, we grabbed some rough cedar 4x4s and had them
ripped on a diagonal...such that they were an isosceles triangle (4 x 4 x 5
5/8). These pieces were screwed to the walls ~23" out from the corner. The
inside diagonal of the ripped 4x4 is now at a perpendicular plane to the
face of the bass trap.

4" deep frames were built for the 703 floor to ceiling, covered in a kind of
straw matting we found. We then placed the frames in between the 4x4
recessed back about 1/2" from the front plane to leave room for quarter
round trim to hold the frames in place. Behind the frames we placed
additional 4" 703 running along the wall...squashed a bit as the trap
started at ~23" out from the corner not 24".

So in the end, the traps ended up being about 32" across the front and used
six 2x4 panels of 4" fiberglass each.
If your interested in a jpeg or two I could email them to you...I know my
description of the construction looks a little cryptic on second read!

Chad
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Postby Dan Nelson » Mon Mar 22, 2004 4:37 am

Subject: RE: [acoustics] Re: Corner bass traps
Date: Fri, 1 Mar 2002 11:46:33 -0500
From: SFoster <Sfoster@xxxxxxxx.com>


No good reason - just lazy - 8' tall probably isn't enough to go floor
to ceiling and changing the height to match exactly will require
measuring and cutting (especially if the top has to be mitered to match
a sloping ceiling). I suppose, now that you mention it, it would be
easy enough raise the height to meet the ceiling (if it is flat) or add
a couple of cleats to the wall so you could drop a triangle of 703 on
top. You could do the same so a piece could fit in and close the bottom
off when the panel went up.

I think I would not go all the way to the floor in most cases, but would
instead mount it off the ground so it doesn't get kicked in / banged up.
If a piece of furniture like an end table, etc. is planned for in front
of the device, a floor to ceiling install would work without to much
concern for its durability.

Scott R. Foster
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Postby Dan Nelson » Mon Mar 22, 2004 4:38 am

Subject: RE: [acoustics] Re: Corner bass traps
Date: Fri, 1 Mar 2002 11:54:19 -0500
From: SFoster <Sfoster@xxxxxxxx.com>


None - Yes - Yes

Just cloth covered 703 fit into a light weight frame.

Take count of Eric's suggested modification and add a triangle of 703 to
the top and bottom, or make it tall enough to run from floor to ceiling.
Four such devices will have an impressive effect on any medium sized
room's RT60 and modal content.

Scott R. Foster
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Postby Dan Nelson » Mon Mar 22, 2004 4:39 am

Subject: [acoustics] Re: Corner bass traps
Date: Fri, 01 Mar 2002 17:05:06 -0000
From: eric_desart <eric.desart@xxxxxxxxx.net>


--- In acoustics@y..., "SFoster" <Sfoster@s...> wrote:

> No good reason - just lazy - 8' tall probably isn't enough to go
floor.

Thought so. :)))
It's indeed easier, when you make a nice frame, which you can
position on an ideal height. And it's indeed not important to finish
it off to the last inches.

Just an idea energetic (forgetting about superposition), just as
reminder.

Q factor free field = 1 = sphere = 10 log(1) = 0 dB
Q factor wall = 2 = 1/2 sphere = 10 log(2) = 3 dB
Q factor 2-corner = 4 = 1/4 sphere = 10 log (4) = 6 dB
Q factor 3 corner = 8 = 1/8 sphere = 10 log (8) = 9 dB = 2 times 6 dB

Trying to use 3-corners is worth a bit of trouble. (e.g. protect
bottom with slat type wooden strips, planks or other things = your
speciality)


Eric
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