Bass Trap question

[archive]

From: GonÁalo Coelho <goncalo_coelho@x????xxx.xxxx
Date: Sat Dec 11, 1999 8:12 pm
Subject: Bass Trap question

Hello

I¥ve set up a new control room which measures about 2,3m (y) x 3m (x) x 2,6m
(z).
Right now all surfaces are still untreated but I can already tell that
theres a serious problem around the 110hz to 120hz zone.
This modal response is obvious while listening to music as it is while
playing sine waves at different keys (resonances). Theres a considerable
increase in volume at that 115hz range and all corresponding octaves.

Of all the bass trap devices I¥ve seen the RPG Bass Trap seems to be the
most efective at the lowest part of the spectrum with an absortion
coeficient of 1.12 sabins at 80hz.

Is there anyone out there with a similar problem to mine who can share some
pratical knowledge with me? Since the RPG Bass Trap is kinda expensive I
don¥t mind spending the money if its the right (and only) solution.

Let me also point that for the price of 2 RGP Bass Traps (which is as far as
I can go) I can get 4 small-sized tube traps but its peak is situated around
200hz to 500hz, an area that I¥m thinking on treating with other materials.

GonÁalo Coelho

[archive]

From: "Przemek SLUZYNSKI" <audio@x????xxx.xxx.xxx
Date: Sun Dec 12, 1999 12:22 pm
Subject: Re: Bass Trap question

>Hello
>
>I¥ve set up a new control room which measures about 2,3m (y) x 3m (x) x
2,6m
>(z).
>Right now all surfaces are still untreated but I can already tell that
>theres a serious problem around the 110hz to 120hz zone.
>This modal response is obvious while listening to music as it is while
>playing sine waves at different keys (resonances). Theres a considerable
>increase in volume at that 115hz range and all corresponding octaves.
>
Sorry, I don't have good solution _but_ I have similar problem. i have
build-up on 47Hz and 75Hz and I don't know what to do with that. Does bass
trap work on such low freq?
Help!
Thanks,
przemek.

[archive]

From: "Anthony B. Kitson" <anthony@x???????xxxxxx.xxxx
Date: Sun Dec 12, 1999 2:24 pm
Subject: Re: Bass Trap question

As I've mentioned on here before.. go for dense insulation in the corners of
your room.. the amount of bass that can be removed using this technique has
to be heard to be believed. It's more of a broadband solution though
(resonators would be need for specific frequency areas). Or you could model
a tube trap by emulating the size of them - their brochures detail the
absorption spectrum of their designs.

I would also suggest in addition to this some good diffusion seeing you are
in such a small room. This would help make the room sound larger and not so
closed in.

Best Regards,

Anthony B. Kitson BSEE AES
Pinnacle Recording Studio
www.pinnaclestudio.com

[archive]

From: SRF7@x??x.xxx
Date: Mon Dec 13, 1999 1:07 am
Subject: Re: Bass Trap question

In a message dated 12/11/99 3:19:52 PM Eastern Standard Time,
goncalo_coelho@h... writes:

Build a slat resonator... I believe there are formula on the spread sheet I
uploaded to the list. If not, I will send them to you.

Scott R. Foster

[archive]

From: Brendan Minish <bminish@x?????xxxx.xxxx
Date: Mon Dec 13, 1999 9:58 am
Subject: Re: Bass Trap question

Or a Honeycomb Port absorber, easier to build and I was able to use less
depth for the same frequency. I have a spreadsheet for making them
somewhere, if it isn't already available on the web.
If anyone want's more info please contact me via E-mail and I'll tidy up
the design info I have.

[archive]

From: SRF7@a...
Date: Mon Dec 13, 1999 8:51 pm
Subject: Re: Bass Trap question

In a message dated 12/13/99 4:58:21 AM Eastern Standard Time,
bminish@o... writes:

> From: Brendan Minish <bminish@o...>
>
> Or a Honeycomb Port absorber, easier to build and I was able to use less
> depth for the same frequency. I have a spreadsheet for making them
> somewhere, if it isn't already available on the web.
> If anyone want's more info please contact me via E-mail and I'll tidy up
> the design info I have.
>

Is a "Honeycomb Port Absorber" a box covered in masonite pegboard?

If so, its true that is pretty easy to build, but I don't see how its much
different in difficulty than a slat absorber (though pegboard does come in
handy if you are looking for a place to hang cables, and is probably a bit
cheaper too). If you don't need the hanger space, I would think a slat
structure could be made to look better with only a tiny bit of extra effort.

Assuming fer instance a concrete block wall at the back of a control room,
you could just put up some 2x4 furring and slap 1x6's horizontally across.
I'd probably pre-prime and paint the boards (or stain them), use dimes as
spacers, and mount the slats with construction adhesive and finish nails ...
you could do a large wall in a couple of hours (not including painting).
That's pretty easy and it'd have a decent finished look.

Assuming your 1x6 (nominal) slats were actually 1/2's x 5-1/2 (I don't have
one handy to measure), your center frequency would be about 120 Hz, not too
shabby considering the broad Q on such things and that therefore you probably
are effective down to about 60 Hz (not to mention panel resonances).

Of course if you need some pegboard, that's the way to go, as you get two
uses out of the structure (three if you consider the hanging coils of cable
as a form of diffuser).

Slat Width 5.5 Inches 139.70 mm
Slot Width 1/32 Inches 0.79 mm
Perforation % 0.56 % 0.56 %

Cavity Depth 3 1/2 Inches 88.9 mm
Thickness of slats 1/2 Inches 12.7 mm
Center Frequency 123 Hz 123 Hz
Hiband (-3 dB) 245
LOband (-3 dB) 61

[archive]

From: Brendan Minish <bminish@x?????xxxx.xxxx
Date: Mon Dec 13, 1999 9:13 pm
Subject: Re: Bass Trap question

At 03:51 PM 12/13/99 -0500, you wrote:
>From: SRF7@a...
>
>In a message dated 12/13/99 4:58:21 AM Eastern Standard Time,
>bminish@o... writes:
>
> > From: Brendan Minish <bminish@o...>
> >
> > Or a Honeycomb Port absorber, easier to build and I was able to use less
> > depth for the same frequency. I have a spreadsheet for making them
> > somewhere, if it isn't already available on the web.
> > If anyone want's more info please contact me via E-mail and I'll tidy up
> > the design info I have.
> >
>
>Is a "Honeycomb Port Absorber" a box covered in masonite pegboard?

Not really as we are making the holes a lot deeper by using pipes (Same
principle as the tuned port you see on loudspeaker designs) also the %
perforation is much lower than with most peg board designs.
I used some honeycomb port absorbers to absorb a LF resonance of ~63 Hz and
I managed to do this in a depth of 300 mm (~1 foot.)
These absorbers work (I was making measurments with JBL Smaart Pro ) but it
is possible to build them with a far higher Q factor than is desirable, I
found a second loose sheet of rockwool resting against the backs of the
pipes inside 'Killed the Q' enough for my application.

>If so, its true that is pretty easy to build,

They are easy to build

> but I don't see how its much
>different in difficulty than a slat absorber

Try building a slat absorber with 1/10" gaps out of 2 by 4 AND the box
depth was going to be 600 mm (~2 foot) that was what was required to kill
63 Hz. 2 by 3 just isn't accurate enough for such small gaps & anyway space
is a premium in my control room

remember it's a room node that I was after, room nodes have quite High Q so
I was not after very broadband absorption.

> (though pegboard does come in
>handy if you are looking for a place to hang cables, and is probably a bit
>cheaper too). If you don't need the hanger space, I would think a slat
>structure could be made to look better with only a tiny bit of extra effort.
>
>Assuming fer instance a concrete block wall at the back of a control room,
>you could just put up some 2x4 furring and slap 1x6's horizontally across.
>I'd probably pre-prime and paint the boards (or stain them), use dimes as
>spacers, and mount the slats with construction adhesive and finish nails ...
>you could do a large wall in a couple of hours (not including painting).
>That's pretty easy and it'd have a decent finished look.
>
>Assuming your 1x6 (nominal) slats were actually 1/2's x 5-1/2 (I don't have
>one handy to measure), your center frequency would be about 120 Hz, not too
>shabby considering the broad Q on such things and that therefore you probably
>are effective down to about 60 Hz (not to mention panel resonances).
>
>Of course if you need some pegboard, that's the way to go, as you get two
>uses out of the structure (three if you consider the hanging coils of cable
>as a form of diffuser).
>
>
>Slat Width 5.5 Inches 139.70 mm
>Slot Width 1/32 Inches 0.79 mm
>Perforation % 0.56 % 0.56 %
>
>Cavity Depth 3 1/2 Inches 88.9 mm
>Thickness of slats 1/2 Inches 12.7 mm
>Center Frequency 123 Hz 123 Hz
>Hiband (-3 dB) 245
>LOband (-3 dB) 61
>
>>For more info, unsubscribe etc:
>http://www.studiotips.com

--

Brendan Minish
bminish@o...
PGP key available from key servers wwwkeys.pgp.net

[archive]

From: kevinz@x?.xxxxxxx.xxx
Date: Mon Dec 13, 1999 10:24 pm
Subject: Re: Bass Trap question


Goncalo,

The book "Master Handbook of Acoustics" written by F. Alton Everest
describes how to construct a number of different types of traps. Formulas
and/or nomographs are included to compute parameters for a particular
frequency. The traps can be constructed using readily available
construction materials and are inexpensive.

Regards,
Kevin Zwack
Aeolian Recording

[archive]

From: GonÁalo Coelho <goncalo_coelho@x????xxx.xxxx
Date: Tue Dec 14, 1999 2:31 am
Subject: Re: Bass Trap question


I¥ve looked at the formula on the site but I¥m not sure what it is and what
is made of.
Since its in the front corners (near the monitors) where the bass builds up
I was thinking on covering them (the corners) with a 1/4" thick plywood
board (layers of thin wood) angled with the two walls that made up the
corner, making a triangle shaped trap. I'm not sure about the size of the
board but if its worth it maybe something 60cm wide and 2,5m tall.

Is the slat resonator related to what I¥m planning to do at all? Do you have
any pictures/drawings?

GonÁalo Coelho

[archive]

From: SRF7@a...
Date: Tue Dec 14, 1999 5:51 pm
Subject: Re: Bass Trap question

In a message dated 12/13/99 4:31:33 PM Eastern Standard Time,
bminish@o... writes:



Sounds very useful .... do you have any specs on the design, materials,
construction methods ... a graphic would be great as well if you have one.

Thanks

Scott R. Foster