[Michael]

I've built resonating bass traps in the past (the type that are kind
of like a picture frame sealed to the wall), but need to build traps
that are more mid range foucsed than bass. I've found the following
frequencies for 4*8 plywood traps that are 3.5 inches deep:

1/8" plywood = 150 Hz
1/4" plywood = 110 Hz
3/8" plywood = 87 Hz

If I build a 4*4 trap instead of a 8*4, I'm assuming the frequency
goes up, but I dont know how much and also wonder about 2*4?

Another way to go up in frequency would be a thinner vibrating
membrane. Is there anything thinner than 1/8 plywood that is used for
traps?

Or if I reduce the depth, would that move the frequency up? I'm
thinking this might be bad because reduced airpocket would probably
reduce the dampening and that wont help-

Any assitance deriving diminsions or forumulas would be greatly
appreciated!
Cheers

[Peter Larsen[_3_]]

Michael wrote:

I've built resonating bass traps in the past (the type that are kind
of like a picture frame sealed to the wall), but need to build traps
that are more mid range foucsed than bass. I've found the following
frequencies for 4*8 plywood traps that are 3.5 inches deep:

1/8" plywood = 150 Hz
1/4" plywood = 110 Hz
3/8" plywood = 87 Hz

If I build a 4*4 trap instead of a 8*4, I'm assuming the frequency
goes up, but I dont know how much and also wonder about 2*4?

Another way to go up in frequency would be a thinner vibrating
membrane. Is there anything thinner than 1/8 plywood that is used for
traps?

I'd use a resisistive attenuator instead, ie. a heavy carpet some inches
from the wall. Or a real oil painting. Or a bookshelf with audiophile
magazines in a disorderly stack. It IS actually OK if a listening room looks
livable, standard furniture can do almost all you need to do.

Or if I reduce the depth, would that move the frequency up? I'm
thinking this might be bad because reduced airpocket would probably
reduce the dampening and that wont help-

Any assitance deriving diminsions or forumulas would be greatly
appreciated!

A narrow band tuned trap is not in my opinion a good choice when you need to
do something about midrange, its range will be too narrow.

Cheers

Kind regards

Peter Larsen

[Michael]

On Feb 5, 12:38*pm, "Peter Larsen" wrote:
Michael wrote:
I've built resonating bass traps in the past (the type that are kind
of like a picture frame sealed to the wall), but need to build traps
that are more mid range foucsed than bass. I've found the following
frequencies for 4*8 plywood traps that are 3.5 inches deep:
1/8" plywood = 150 Hz
1/4" plywood = 110 Hz
3/8" plywood = 87 Hz
If I build a 4*4 trap instead of a 8*4, I'm assuming the frequency
goes up, but I dont know how much and also wonder about 2*4?
Another way to go up in frequency would be a thinner vibrating
membrane. Is there anything thinner than 1/8 plywood that is used for
traps?

I'd use a resisistive attenuator instead, ie. a heavy carpet some inches
from the wall. Or a real oil painting. Or a bookshelf with audiophile
magazines in a disorderly stack. It IS actually OK if a listening room looks
livable, standard furniture can do almost all you need to do.

Or if I reduce the depth, would that move the frequency up? I'm
thinking this might be bad because reduced airpocket would probably
reduce the dampening and that wont help-
Any assitance deriving diminsions or forumulas would be greatly
appreciated!

A narrow band tuned trap is not in my opinion a good choice when you need to
do something about midrange, its range will be too narrow.

Cheers

* Kind regards

* Peter Larsen

Thanks Peter-
Unfortunately, I'm stuck with traps or something that looks like them.
My client removed a stage that was absorbing nodes, so we need low
bass as well as mids- They have plenty of wall space so resonate traps
will be great for the bottom, but can we tune a trap into the 600hz
range? If not, can we make something that looks like a trap (covered
in fabric) but include carpet or something else that will get the
mids?
Cheers
Michael

[Ethan Winer]

I agree with Peter that for frequencies above 60 to 80 Hz you're much better
off with porous absorbers. The best material is 705-FRK that's 4 inches
thick. The FRK increases bass absorption, and reduces high frequency
absorption.

If I build a 4*4 trap instead of a 8*4, I'm assuming the frequency goes
up, but I dont know how much and also wonder about 2*4?

No, the frequency is a function of the panel density / weight (mass), versus
the cavity depth which determines the springiness of the trapped air.

Any assitance deriving diminsions or forumulas would be greatly
appreciated!

This acoustic calculator can help:

http://www.mh-audio.nl/user/acoustic%20calculator.asp

But again, reserve the tuned traps for very low frequencies, and use thick
FRK type rigid fiberglass for higher bass frequencies.

--Ethan

[Randy Yates]

"Ethan Winer" ethanw at ethanwiner dot com writes:
[...]
But again, reserve the tuned traps for very low frequencies, and use thick
FRK type rigid fiberglass for higher bass frequencies.

At my age, 650 Hz is damn-near treble!
--
% Randy Yates % "And all that I can do
%% Fuquay-Varina, NC % is say I'm sorry,
%%% 919-577-9882 % that's the way it goes..."
%%%% % Getting To The Point', *Balance of Power*, ELO
http://www.digitalsignallabs.com

[Michael]

On Feb 6, 9:50*am, Randy Yates wrote:
"Ethan Winer" ethanw at ethanwiner dot com writes:

[...]
But again, reserve the tuned traps for very low frequencies, and use thick
FRK type rigid fiberglass for higher bass frequencies.

At my age, 650 Hz is damn-near treble!
--
% *Randy Yates * * * * * * * * *% "And all that I can do
%% Fuquay-Varina, NC * * * * * *% *is say I'm sorry,
%%% 919-577-9882 * * * * * * * *% *that's the way it goes..."
%%%% * * * * * % Getting To The Point', *Balance of Power*, ELOhttp://www.digitalsignallabs.com

Thanks all! This is extremely useful- If the foam prices well, that
will be the answer!

One last issue since you nailed the first- This same room has
developed severe highend flutter for entirely different reasons (yes
the room really should be analyized, but see my earlier post I've
suggested tradiation absorbtion and difusion, but the price is too
steep and they want to build whatever they go with to save $. As I
mentioned, there are a lot of opinions floating around and one of them
is that regluar old cheap, drop ceiling tiles are good for high end
aborption. They are thinking about gluing them to the walls and
painting them, and I have absolutly no idea what they are likely to
do.

Can anyone point to anything on the web that would help me understand
if this could work? And if it's a bad idea, does anyone have ideas on
inexpesive high freq absorbtion? They had a tremendous floor to
ceiling curtain in the room before that sucked up all the highs, but
we can't convince them to put it back

Cheers
Michael

[Scott Dorsey]

Michael wrote:

One last issue since you nailed the first- This same room has
developed severe highend flutter for entirely different reasons (yes
the room really should be analyized, but see my earlier post I've
suggested tradiation absorbtion and difusion, but the price is too
steep and they want to build whatever they go with to save $. As I
mentioned, there are a lot of opinions floating around and one of them
is that regluar old cheap, drop ceiling tiles are good for high end
aborption. They are thinking about gluing them to the walls and
painting them, and I have absolutly no idea what they are likely to
do.

They will cause a disaster, because you will get low end absorption
which will if anything emphasize the midrange frequencies where the
flutter is a problem. Try random diffusion. Bookcases or stacks of
junk will help if you can't afford fancy diffusers. Carved wood
wall hangings are nice too.

Can anyone point to anything on the web that would help me understand
if this could work? And if it's a bad idea, does anyone have ideas on
inexpesive high freq absorbtion? They had a tremendous floor to
ceiling curtain in the room before that sucked up all the highs, but
we can't convince them to put it back

High frequency absorption is easy. The cheapest thing to do is use
fibreglass banners. The problem is that absorption on the top end will
tend to emphasize midrange and bass problems.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

Scott Dorsey wrote:
Michael wrote:

One last issue since you nailed the first- This same room has
developed severe highend flutter for entirely different reasons (yes
the room really should be analyized, but see my earlier post I've
suggested tradiation absorbtion and difusion, but the price is too
steep and they want to build whatever they go with to save $. As I
mentioned, there are a lot of opinions floating around and one of them
is that regluar old cheap, drop ceiling tiles are good for high end
aborption. They are thinking about gluing them to the walls and
painting them, and I have absolutly no idea what they are likely to
do.

They will cause a disaster, because you will get low end absorption

err... high end absorption.

Get one of the data sheets from the tile manufacturer and look at the
plot.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Chris Hornbeck]

On Fri, 6 Feb 2009 11:44:24 -0800 (PST), Michael
wrote:

Can anyone point to anything on the web that would help me understand
if this could work?

My strongest recommendation is to start by looking on Ethan
Winer's websites, his personal site and RealTraps. They're
practical, no-BS, and give a solid fundamental grasp on the
issues that really matter (which *aren't* what we think
they are, on first blush and based on street lore!) Highly
recommended.

In one of the tutorials, you'll find an end-of-clip credit
to on-camera mic that will amaze anyone who's ever tried
to do something similar. The difference is in room treatment.
Truly breathtaking if yer of such a mind.

All the best fortune,
Chris Hornbeck

[Michael]

On Feb 6, 8:34*pm, Chris Hornbeck
wrote:
On Fri, 6 Feb 2009 11:44:24 -0800 (PST), Michael

wrote:
Can anyone point to anything on the web that would help me understand
if this could work?

My strongest recommendation is to start by looking on Ethan
Winer's websites, his personal site and RealTraps. They're
practical, no-BS, and give a solid fundamental grasp on the
issues that really matter (which *aren't* what we think
they are, on first blush and based on street lore!) Highly
recommended.

In one of the tutorials, you'll find an end-of-clip credit
to on-camera mic that will amaze anyone who's ever tried
to do something similar. The difference is in room treatment.
Truly breathtaking if yer of such a mind.

All the best fortune,
Chris Hornbeck

Thanks guys- RealTraps is a great site! Thanks for everything.
Michael