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#1871177 - 01/12/08 03:19 AM

calculation of pannel Bass trap 4 specific freq

killaCez
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hi Ethan,
first of all thx for the great articles you have posted, they have cleared most of my problems/questions $\:D$

I have searched everywhere for a formula to calculate the specific center freq for a given panel using width, length and density of the panel and the depth of the cavity.

i personally have two spaces of 190cm by 75cm for the deep bass traps and i could easily make them up to 20cm deep, but i'd like to take most of the guess work out of the construction and pinpoint in the design the freq that are problematic.

here is the freq responce at mixing position in my room:

for the mid/high badd traps i have more flexible space on the ceiling (not much tho)

thx a lot in advance for any suggestion u might be able to give me $\:D$

Cez

PS.: pic not showing on post $\:\($
here is a link to it http://www.rmpnet.com/roomproblems.gif

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#1871283 - 01/12/08 08:48 AM

Re: calculation of pannel Bass trap 4 specific freq [Re: killaCez]

killaCez
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yeee, managed to put the picture in the post $\:P$

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#1872391 - 01/14/08 08:15 AM

Re: calculation of pannel Bass trap 4 specific freq [Re: killaCez]

Ethan Winer
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Registered: 06/12/00
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Loc: New Milford, CT, USA

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Originally Posted By: killaCez

I have searched everywhere for a formula to calculate the specific center freq for a given panel using width, length and density of the panel and the depth of the cavity.

The formula is in Everest's book, and also linked (eventually) in the READ THIS FIRST post here in the forum. But ...

Quote:

here is the freq responce at mixing position in my room:

I really wish you stated the size of your room. Most rooms do better with broadband bass traps than tuned. Tell me the dimensions of your room and then we'll know for sure which is best.

--Ethan

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The acoustic treatment experts

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#1872433 - 01/14/08 09:45 AM

Re: calculation of pannel Bass trap 4 specific freq [Re: Ethan Winer]

killaCez
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Registered: 01/12/08
Posts: 25

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Hi Ethan,
thx a lot for the quick answer $\:D$

I'm going to look again for the formula in the READ THIS FIRST, I did read it but I probably missed it.

Here is the room:

The purple lines are the walls i created, as u can see there aren't any corners cause i had to avoid a bunch of structural columns in the room.
All the walls are made of 2 sheets of 13mm high density drywall with a layer of lead in between for insonorization (I live in a residential building).

The two blue structures on the top and bottom right corners are two closets i've built to store instruments, the computers and other stuff, they're made mostly of the same drywall i used in the walls. Pyramid foam covers the entire inside of these closets.
In the center of them i flush mounted the speakers and filled the cavities with rook wool to avoid resonance.

I had considered to use the broad band bass traps i found in your article but i have no vertical corners $\:P$

I have also placed 3 skyline panels (180cm wide and 60cm tall all together) behind the listening position, Auralex Purple LENRD Bass Traps on the corners between ceiling and side walls, Auralex Purple Venus Bass Traps on the back walls (the 2 45 degrees walls on the left) and a bunch of pyramid foam in the reflective spots on the sides and ceiling.

The frequency curve that u see on my previous post is taken after all the treatments i just described where put in place.

Since i would like to perfection the room a little more before having to use an eq i was thinking to move the venus traps elswere and place 2 deep bass traps on the inclined corners (dark blue in next pic) and 2 mid bass traps next to them on side walls (lighter blue on next pic).
The traps will be approximately 2m in length and 70 cm wide.

The deep bass i'd like to tune exactly to the offensive freq ( i think to tune it to 60Hz and the mid one to 100Hz.

What do u think of these frequencies? They seem to me like the ones creating the problems also with they're harmonics...
Or maybe i should look at the deeps intead of the peacks?

Thx so much again for the great support u guys offer in this forum $\:D$

Cez

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#1872446 - 01/14/08 10:05 AM

Re: calculation of pannel Bass trap 4 specific freq [Re: killaCez]

killaCez
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here some additional pics $\:D$

PS.: did not find the formula $\:\($

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#1873114 - 01/15/08 09:53 AM

Re: calculation of pannel Bass trap 4 specific freq [Re: killaCez]

Ethan Winer
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Registered: 06/12/00
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Loc: New Milford, CT, USA

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Originally Posted By: killaCez

PS.: did not find the formula $\:\($

Apparently the link Phil posted is now dead. So I just changed that and added a link to this calculator program:

http://www.mhsoft.nl/user/acoustic%20calculator.asp

You can download this program and use the panel absorber section.

However, I do not recommend tuned panel traps for a room that size anyway. Broadband traps made from rigid fiberglass will do a better job.

--Ethan

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The acoustic treatment experts

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#1873579 - 01/16/08 12:03 AM

Re: calculation of pannel Bass trap 4 specific freq [Re: Ethan Winer]

killaCez
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Registered: 01/12/08
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Hi Ethan,
i already had the calculator, but when doing the calculation u have no control over the size, that's why i was looking for the actual original formula.
On the book u suggested i found the formula:
freq= 170/sqr[mass (lb/sq) * d (depth of airspace)]

The curious thing is that the size of the panel is actually non influential in the equation (that sounds strange to me cause i thought the resonance had to do with the lenght of the panel in comparison to the wave lenght).

By broad band u mean the ones u put on the corners right?
If that's the case unfortunately i don't have anymore corner space in the room, all i have is lot's of flat space $;\)$ that's why i am inquiring about those membrane panels.

I also would like to ask a question that maybe u didn't see on a previous post:

I think that 60Hz and 100Hz are my problem. What do u think of these frequencies (in the freq response of room picture)? They seem to me like the ones creating the problems also with they're harmonics...
Or maybe i should look at the deeps instead of the peaks?

Thx a lot again
Cez

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#1873892 - 01/16/08 10:18 AM

Re: calculation of pannel Bass trap 4 specific freq [Re: killaCez]

Ethan Winer
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Registered: 06/12/00
Posts: 5300
Loc: New Milford, CT, USA

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The size of the panel is not part of the formula. Whatever happens with one square foot happens with 8 square feet too.

As for flat walls, I'd still use rigid fiberglass in a room that size. That will help the peaks as well as the nulls. Another choice is to move the foam you have near the corners now to other places, and use rigid fiberglass straddling the corners.

--Ethan

_________________________
www.realtraps.com
The acoustic treatment experts

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#1874393 - 01/17/08 04:57 AM

Re: calculation of pannel Bass trap 4 specific freq [Re: Ethan Winer]

killaCez
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Registered: 01/12/08
Posts: 25

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Quote:
As for flat walls, I'd still use rigid fiberglass in a room that size. That will help the peaks as well as the nulls. Another choice is to move the foam you have near the corners now to other places, and use rigid fiberglass straddling the corners.

I'll try to do that Ethan, thx a lot.

Could u hal me analyze the frequency responce of the room tho?
I'd like to learn and understand how to asses the situation also on my own for future situations $\:D$
thx again

Cez

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