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Author Topic: membrane bass traps thickness  (Read 13443 times)

brett

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membrane bass traps thickness
« on: December 18, 2008, 08:08:46 pm »

I have printed out the plans from ethans site. The membrane for "deep bass" is 1/4 and for mid bass is 1/8 plywood. I have a ceiling mode of 70hz and 140hz. Will the 1/4 plywood work. I am not sure what freq are considered "deep bass " vs "mid bass"?

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andrebrito

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Re: membrane bass traps thickness
« Reply #1 on: December 19, 2008, 05:59:33 am »

This is highly subjective but in large room acoustics mid freq are usually the octave bands of 500-1000 Hz

Never heard the term deep bass applied from acoustical eng but presume it is something below 100 Hz

About your questions, pick a mic and measure the room Smile
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Ethan Winer

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Re: membrane bass traps thickness
« Reply #2 on: December 19, 2008, 12:01:34 pm »

brett wrote on Thu, 18 December 2008 20:08

I have a ceiling mode of 70hz and 140hz. Will the 1/4 plywood work. I am not sure what freq are considered "deep bass " vs "mid bass"?


In the context of those traps, the low one is tuned to around 100 Hz and the high one to 180 Hz. This is mentioned in one of the notes at the bottom of the article. To target 70 Hz you'll want something closer to 3/8 inch thick, and for higher bass frequencies (an oxymoron?) I'd use traps based on rigid fiberglass rather than tuned absorbers.

What's your room dimensions? For small rooms I suggest not using tuned traps at all.

--Ethan

brett

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Re: membrane bass traps thickness
« Reply #3 on: December 30, 2008, 07:17:59 pm »

I have already applied all the broad band possible in my room. tuned is my only option to deal with this mode. room dimensions are 13x11x8. In the photos and article, the room you treat with these traps does not appear to be a large room.

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Ethan Winer

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Re: membrane bass traps thickness
« Reply #4 on: December 31, 2008, 03:17:46 pm »

The room in my wood panel bass traps article is 33 feet long, 18 feet wide, and 12 feet high at the center peak.

You could add tuned traps, and I won't say it's wrong, but they should be behind any broadband treatment so you have the benefit of both.

--Ethan

brett

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Re: membrane bass traps thickness
« Reply #5 on: January 10, 2009, 10:55:23 pm »

thanks, what about stacking them. Like having a tuned 3/8 trap against the drywall, then a higher tuned trap, then finished off with broadband?
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Ethan Winer

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Re: membrane bass traps thickness
« Reply #6 on: January 11, 2009, 02:08:17 pm »

You can't put wood panel traps in front of each other, but you could place rigid fiberglass in front of a wood panel trap. In that case the fiberglass has to "float" 1/4 inch in front of the wood, so as not to disturb the wood's vibration. I did that for four wood panels traps in my home studio. At the time I built this room 15 years ago I didn't understand the importance of absorption at the reflection points. Wouldn't you know, all four reflection points had wood panel traps there. D'oh! So I added four 2'x4'x2" 705 panels on top of the panel traps with a small space. Photos below. The first photo shows all of the added panels, which are lighter colored than the existing 8-foot tall mid/high absorbers. The other photos show close-ups so you can see the air gaps.

In your case I suggest 705 that's four inches thick to add even more bass trapping.

--Ethan

http://www.ethanwiner.com/misc-content/studio1.jpg

http://www.ethanwiner.com/misc-content/studio2.jpg

http://www.ethanwiner.com/misc-content/studio3.jpg

brett

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Re: membrane bass traps thickness
« Reply #7 on: January 12, 2009, 05:32:08 pm »

Thanks, I currently have the room treated with 4'x2'x4" panels so after the tuned panels go on the ceiling, I will add the rigid fiber ones back up.
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Greg Reierson

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Re: membrane bass traps thickness
« Reply #8 on: January 12, 2009, 06:17:52 pm »

Ethan Winer wrote on Sun, 11 January 2009 13:08

You can't put wood panel traps in front of each other ... [snip]


Ethan,

Would you say it follows that one can not place wood panel traps behind a QRD?

Thanks,


GR
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Ethan Winer

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Re: membrane bass traps thickness
« Reply #9 on: January 13, 2009, 03:28:36 pm »

It depends on what the QRD is made from. The QRD my company sells is also a bass trap, so a wood panel trap would be fine behind it for even more bass trapping. Likewise, a QRD made from thin plastic or styrofoam would be okay became bass would pass through it to the trap. But a QRD made of wood would just reflect the bass rather than pass it to the trap behind.

--Ethan

Thomas Jouanjean

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Re: membrane bass traps thickness
« Reply #10 on: January 13, 2009, 04:43:28 pm »

It happens in big studios that the huge backwall QRDs (or not QRDs type btw) are positioned in front of a big LF bass trap, a tuned Helmholtz for ex.

Membrane type and resistance to flow type of treatment go well together, but there are "membranes" and... membranes Smile


LF do go through 1,25mm-1.8mm (1/2 inch) wood easier than one would think if the frequency is low enough. A lot of energy is transmitted to the wood itself as well and creates re-emission at some frequencies. What is important with membranes in studios is that the energy transmitted to that membrane is lost in heat and not re-emitted. Which type you need depends on the freq, needed width of the Q etc. So, in short, resilience of the membrane is a very important factor.

Combinations of treatment can work, but it gets really tricky to get it right.



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Thomas Jouanjean
Northward Acoustics - Engineering and Designs
http://www.northwardacoustics.com
http://www.facebook.com/pages/Northward-Acoustics/1062876633 71

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Bruno Gouveia

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Re: membrane bass traps thickness
« Reply #11 on: February 02, 2009, 08:55:27 am »

Thomas Jouanjean wrote on Tue, 13 January 2009 21:43

 What is important with membranes in studios is that the energy transmitted to that membrane is lost in heat and not re-emitted.




This is the hard part, the damping of the membrane! How can one the predict objectively the behavior of a membrane? Perhaps it'safer to put it behind something and that something will prevent the coupling of the natural vibration of the membrane with air, and that's what we want!

Thomas Jouanjean

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Re: membrane bass traps thickness
« Reply #12 on: February 02, 2009, 10:46:16 am »

Bruno Gouveia wrote on Mon, 02 February 2009 07:55


This is the hard part, the damping of the membrane! How can one the predict objectively the behavior of a membrane?


I don't dampen membranes in most cases, as they don't have to be and they work better that way. It's just a matter of working with the right material - resilience wise - and having the right data. How you design the "frame" in which it goes is very important too.

If you have proper data, you can estimate the behaviour pretty accurately Smile . Experience also helps refining techniques.

Bruno Gouveia wrote on Mon, 02 February 2009 07:55

 Perhaps it'safer to put it behind something and that something will prevent the coupling of the natural vibration of the membrane with air, and that's what we want!


Yes, membranes should be "in-between" other materials (undampened), the type depending on the design objectives and freq one is looking for. Those complex sandwiches give solid results. But they are massive!


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Thomas Jouanjean
Northward Acoustics - Engineering and Designs
http://www.northwardacoustics.com
http://www.facebook.com/pages/Northward-Acoustics/1062876633 71

Pro Audio Partners:
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Bruno Gouveia

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Re: membrane bass traps thickness
« Reply #13 on: February 02, 2009, 11:55:58 am »

Thomas Jouanjean wrote on Mon, 02 February 2009 15:46



If you have proper data, you can estimate the behaviour pretty accurately Smile . Experience also helps refining techniques.

Yes, membranes should be "in-between" other materials (undampened), the type depending on the design objectives and freq one is looking for. Those complex sandwiches give solid results. But they are massive!




What kind of software / method do you use to predict the behaviour of a panel?

If we could really achieve accurate estimates of the behavior of a membrane maybe it would be possible to have even more efficient results! For instance, using a metal membrane which exposed to sound reverbs like hell, if we get a way to stop the sound that comes in from going out, maybe we could achieve impressive absorption with a relatively smaller size in comparison from what is commonly used.  

Thomas Jouanjean

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Re: membrane bass traps thickness
« Reply #14 on: February 02, 2009, 01:32:53 pm »

Bruno Gouveia wrote on Mon, 02 February 2009 10:55


What kind of software / method do you use to predict the behaviour of a panel?


Manufacturer's data (when available) and discussion with specialists -> real-life / empirical testing -> Data to software (MATLAB etc) -> estimation within the desired confidence interval.

Then real-life test in situ. With time you build-up a database, that you refine constantly.

To design studios, I work both in B&K ODEON and AUTOCAD (to draw plans)

Bruno Gouveia wrote on Mon, 02 February 2009 10:55

If we could really achieve accurate estimates of the behavior of a membrane maybe it would be possible to have even more efficient results! For instance, using a metal membrane which exposed to sound reverbs like hell, if we get a way to stop the sound that comes in from going out, maybe we could achieve impressive absorption with a relatively smaller size in comparison from what is commonly used.  


Since we are on the subject...

Thor from SONOVO mastering introduced me to this Norwegian product:

http://www.deamp.com/?shw=PRD

Very interesting. Will use them in a Radio station we are designing now. I am eager to see how they behave!
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Thomas Jouanjean
Northward Acoustics - Engineering and Designs
http://www.northwardacoustics.com
http://www.facebook.com/pages/Northward-Acoustics/1062876633 71

Pro Audio Partners:
ATC Loudspeakers
FOCAL Professional Speakers
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