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Author Topic: membrane bass traps thickness  (Read 12646 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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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!

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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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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.  

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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
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Re: membrane bass traps thickness
« Reply #15 on: February 02, 2009, 07:42:04 pm »

Very interesting! The absorption as described makes sense and it will lower the sound levels in a room, but for music rooms will it work?  

http://www.ntnu.no/gemini/2006-01e/deamp.htm I've followed this article in the press section of their site. The metal absorbers, thin as they are likely to sing like a bird, and we already know re-radiations can be very dangerous to music...

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Re: membrane bass traps thickness
« Reply #16 on: February 02, 2009, 07:51:14 pm »

Thomas Jouanjean wrote on Mon, 02 February 2009 18:32



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)





I've a friend who is a mechanical engineer and his job is to design boxes to hold electronic PCB that must endure extreme and severe conditions like a rocket launch and space. He uses a software called NASTRAN http://www.mscsoftware.com/products/msc_nastran.cfm?Q=131&am p;Z=396&Y=422 that seems really powerful in predicting vibration modes.

The other day I picked up this book http://www.amazon.com/Vibration-Analysis-Electronic-Equipmen t-Steinberg/dp/047137685X/ref=sr_1_1?ie=UTF8&s=books& ;qid=1233622036&sr=8-1  at his house and it was very well written, definitely very useful to have around for anyone deeply interested in acoustics and it had very clear concepts and I've never see described like it's author, Dave S. Steinberg

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Re: membrane bass traps thickness
« Reply #17 on: February 03, 2009, 02:59:30 am »

Bruno Gouveia wrote on Mon, 02 February 2009 18:42

Very interesting! The absorption as described makes sense and it will lower the sound levels in a room, but for music rooms will it work?  

http://www.ntnu.no/gemini/2006-01e/deamp.htm I've followed this article in the press section of their site. The metal absorbers, thin as they are likely to sing like a bird, and we already know re-radiations can be very dangerous to music...



I've considered only the ones in Acrylic for now, the transparent ones. The radio station we are designing now wants to have huge window surface in their studio (over 2/3 of all the walls) which obviously goes against the needed acoustic performance of the space. So this product in combination with more classical systems will be great!

The transparent ones are rather thick it seems (4mm to 10mm) so re-emission *should* be limited... Using them in the radio studio will work without problems I'm sure as the conditions needed are not as extreme as in a recording or mastering studio (response and SPL wise).

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

Moreover, they allow to keep the light in - which will make the client happy. If you want, I'll share the results of our first shot at them?
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Thomas Jouanjean
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Re: membrane bass traps thickness
« Reply #18 on: February 03, 2009, 03:04:34 am »

Bruno Gouveia wrote on Mon, 02 February 2009 18:51


I've a friend who is a mechanical engineer and his job is to design boxes to hold electronic PCB that must endure extreme and severe conditions like a rocket launch and space. He uses a software called NASTRAN  http://www.mscsoftware.com/products/msc_nastran.cfm?Q=131&am p;am p;Z=396&Y=422 that seems really powerful in predicting vibration modes.



NASTRAN seems very interesting, thanks for the tip. Does it work well for smaller surfaces?

I noticed that the smaller the surface, the less accurate the estimation. Did you use it yourself?


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Thomas Jouanjean
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Re: membrane bass traps thickness
« Reply #19 on: February 03, 2009, 03:48:49 am »

Thomas Jouanjean wrote on Tue, 03 February 2009 08:04



NASTRAN seems very interesting, thanks for the tip. Does it work well for smaller surfaces?

I noticed that the smaller the surface, the less accurate the estimation. Did you use it yourself?





Sure it does! The box he's currently designing is the size of a fooball ball (it will be a part of a satellite that is to travel to Jupiter!)  and the parts have resonances in the 0.7k - 3k Hz range. I've never used the software but I've seen him working and he gave me a small presentation of the capabilities of it. For instance, the possibilities to insert the variables that are used to define a material can be made to a great level of detail. But I plan to steal him more time! Wink

There's other people that are using this software to help them make carbon fiber electrical guitars  http://ideiam.com/ I've had the opportunity to met this guys and was really impressed with the prototypes!

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Re: membrane bass traps thickness
« Reply #20 on: February 03, 2009, 03:51:42 am »

Thomas Jouanjean wrote on Tue, 03 February 2009 07:59




Moreover, they allow to keep the light in - which will make the client happy. If you want, I'll share the results of our first shot at them?


Yes please, don't forget to share with us the results!!

I also love big windows. Natural light is something that I always want to preserve!

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Re: membrane bass traps thickness
« Reply #21 on: February 03, 2009, 06:03:28 am »

This a great info exchange Bruno, we keep in touch!
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andrebrito

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Re: membrane bass traps thickness
« Reply #22 on: February 05, 2009, 06:10:18 am »

Bruno,

One thing is to predict the behavior of a box, another to predict the behavior of a box within a room and a sound field all together.

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Re: membrane bass traps thickness
« Reply #23 on: February 05, 2009, 06:12:49 am »

Meaning by that... lots of packages there for FEM but what really matters is BEM and there are no commercial packages for this yet
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Re: membrane bass traps thickness
« Reply #24 on: February 05, 2009, 06:15:15 am »

RPG has some micro-absorbing system as well. I have seen them (since I sell their products) but actually never used it in a project
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Re: membrane bass traps thickness
« Reply #25 on: February 05, 2009, 06:26:10 am »

andrebrito wrote on Thu, 05 February 2009 11:10

Bruno,

One thing is to predict the behavior of a box, another to predict the behavior of a box within a room and a sound field all together.



To have a tool that to great extent can calculate the vibration a complex structure can be a great help. Like it was said, how it couples with airborne vibration is another variable that we must have in account and likewise difficult to predict without practical experience.

For instance, in many rooms I still can't tell for sure what's causing the reverberation, is it just reflections or is it reactive energy?


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Re: membrane bass traps thickness
« Reply #26 on: February 05, 2009, 07:18:23 am »

Yes , I have used such tools a few times and you can even considered the entire room to be such a structure. The impact it is on the listener is a different stuff.

Anyway I find it too much work to do for a studio recording project and like Thomas I might use computacional acoustics if the client can afford it (usually they cannot lol).

For large room acoustics in sames cases using computacional acoustics is almost mandatory
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Re: membrane bass traps thickness
« Reply #27 on: February 05, 2009, 03:15:41 pm »

Bruno Gouveia wrote on Thu, 05 February 2009 05:26


For instance, in many rooms I still can't tell for sure what's causing the reverberation, is it just reflections or is it reactive energy?


Ah, the joys of re-emission...

Both Smile

The hardest part is when materials store energy and then re-emit periodically at their resonance frequency.

Thomas <- gets a couple aspirins.
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Re: membrane bass traps thickness
« Reply #28 on: February 05, 2009, 03:17:48 pm »

andrebrito wrote on Thu, 05 February 2009 06:18

Anyway I find it too much work to do for a studio recording project and like Thomas I might use computacional acoustics if the client can afford it (usually they cannot lol).


Hell, even the designers have a hard time affording the softwares to start with Rolling Eyes


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Re: membrane bass traps thickness
« Reply #29 on: February 05, 2009, 03:31:06 pm »

Thomas Jouanjean wrote on Thu, 05 February 2009 20:15



Ah, the joys of re-emission...

Both Smile

The hardest part is when materials store energy and then re-emit periodically at their resonance frequency.



Ehehehh! One of the most acoustical clear experiences I had was when a room that was being built, the walls were just cement blocks and the room was sounding good. When the blocks were covered with MDF, reverberation time at bass frequencies tilted up. The MDF was really loose so the it was clear where the undesired effect came.

There's another story though, that still makes me think a lot. Casa da M

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Re: membrane bass traps thickness
« Reply #30 on: February 05, 2009, 03:46:24 pm »

Bruno Gouveia wrote on Thu, 05 February 2009 14:31

 
My explanation is that as bass frequencies are more difficult to propagate through air they get trapped by the air itself and so the panels eventually absorb the energy as they vibrate, whereas in the small room we get to ear the vibration.


I'm not sure I understand you there... LF propagate very good in air, and carry a lot more energy. What you describe here is normal absorption by membrane like-panels, which take LFs 'out' of the room. Re-emission from those should fill the room with particular frequencies and up to a point (and not necessarily the ones emitted in the first place). Although I agree distance plays a role in how much you hear it (normal behaviour though).

Again, I'm not sure I fully understood your point... (Portugese -> English -> French and back can carry confusions)

EDIT: beautiful hall

EDIT 2: don't you have Helmholtz-like behaviour too in this room? If the panels are loose, it means there is a cavity...
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Re: membrane bass traps thickness
« Reply #31 on: February 05, 2009, 04:27:43 pm »

Thomas Jouanjean wrote on Thu, 05 February 2009 20:46



I'm not sure I understand you there... LF propagate very good in air, and carry a lot more energy. What you describe here is normal absorption by membrane like-panels, which take LFs 'out' of the room. Re-emission from those should fill the room with particular frequencies and up to a point (and not necessarily the ones emitted in the first place). Although I agree distance plays a role in how much you hear it (normal behaviour though).



Like I said I'm not sure if it applies, but considering loudspeaker reproduction of low frequencies if the speaker isn't big enough it won't be able to develop LF waves that one can hear, by other words, there will be negligible radiation. Check this book   http://www.google.com/books?id=qc-mjjSFAlAC&pg=PP1&d   q=john+watkinson+sound+reproduction&ei=vViLSeTdCZb0ygS22 KG6BQ#PPA96,M1 page 96.

The point is, if the reproducing device is small and the frequency is low air itself will act like a spring and won't let the LF leave the premises. But I'm still struggling to grasp it better...

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Re: membrane bass traps thickness
« Reply #32 on: February 05, 2009, 05:14:46 pm »

No, not cavities behind wood panels in concert halls ! Laughing That is a basic mistake that reduces bass in concert halls for music purposes.

LF are not absorbed by air... air is the most important absorber in such places.

I know Casa da Musica well, was there a few times! There are some ressonators (the organs!), some diffusion as well.
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Re: membrane bass traps thickness
« Reply #33 on: February 05, 2009, 05:22:18 pm »

Yes the loudspeaker will not have enough inercia at low frequencies but not only that, since you have to consider the box the loudspeaker is in
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Re: membrane bass traps thickness
« Reply #34 on: February 08, 2009, 03:30:28 pm »

Hey Thomas and Bruno... I don't consider myself an expert by any means in large room acoustics, but I know the physics is basically the same. There are typically different goals. I'm a little confused too:

We use Membrane Traps, Helmholtz Resonators and other Broadband LF trapping to INCREASE the amount of percieved bass in a (small) room like a control room. In other words, the more we trap, the better and tighter and more detailed the Bass sounds. It is a popular misconception in control room treatment, that bass traps will "remove" bass from the room...

BUT, this seems to be what both are you are implying unless I'm not understanding correctly>>> that too many loose panels acting as membranes will take bass response away from the room.... Am I getting this right?? sorry for my confusion.... Maybe it's totally different in large performance spaces, but I know how larger recording rooms behave and we still strive to add sufficient LF trapping in these rooms to ensure the bass is tight and the decay is comparable to the rest of the spectrum... as you know it's easy to absorb too much High and Mid frequency and end up with a boomy sounding room.

Thoughts>????
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Bruno Gouveia

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Re: membrane bass traps thickness
« Reply #35 on: February 08, 2009, 04:06:52 pm »

franman wrote on Sun, 08 February 2009 20:30

Hey Thomas and Bruno... I don't consider myself an expert by any means in large room acoustics, but I know the physics is basically the same. There are typically different goals. I'm a little confused too:

We use Membrane Traps, Helmholtz Resonators and other Broadband LF trapping to INCREASE the amount of percieved bass in a (small) room like a control room. In other words, the more we trap, the better and tighter and more detailed the Bass sounds. It is a popular misconception in control room treatment, that bass traps will "remove" bass from the room...

BUT, this seems to be what both are you are implying unless I'm not understanding correctly>>> that too many loose panels acting as membranes will take bass response away from the room.... Am I getting this right?? sorry for my confusion.... Maybe it's totally different in large performance spaces, but I know how larger recording rooms behave and we still strive to add sufficient LF trapping in these rooms to ensure the bass is tight and the decay is comparable to the rest of the spectrum... as you know it's easy to absorb too much High and Mid frequency and end up with a boomy sounding room.

Thoughts>????


I'am confused too. I mean, I still have to study this subject further. The fact is, two big rooms I know of Casa da Musica and a church full of loose wood here in Porto have a lack of bass energy. For sure the wood is coupling with the sound as one can access easily with an accelerometer or a piezo pickup. What it does to the sound in the room, is what's puzzling me...

I also can add that I already spend some time in a small room 7x5x3 and is also full of loose pine wood everywhere and the ceiling has wood conglomerate panels. The acoustics are bass heavy in this case, or they are lacking treble. But overall it's a pleasant acoustic, already done good recordings there.

andrebrito

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Re: membrane bass traps thickness
« Reply #36 on: February 08, 2009, 06:49:52 pm »

Lack of bass does not mean the bass energy is less than the middle and high frequency energy in the room, it just means that for the goals of the room and the perception of the listener something is missing.

Also bass energy in a large room is basically the octaves of 125-250 Hz where in a small room bass energy is often seen as something below 100 Hz or below the Schroeder frequency.

Keep in mind that auditorium is first rather small and secondly not sure how the seat dip effect behaves in such a room.

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Thomas Jouanjean

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Re: membrane bass traps thickness
« Reply #37 on: February 09, 2009, 03:10:37 am »

franman wrote on Sun, 08 February 2009 14:30

We use Membrane Traps, Helmholtz Resonators and other Broadband LF trapping to INCREASE the amount of percieved bass in a (small) room like a control room. In other words, the more we trap, the better and tighter and more detailed the Bass sounds. It is a popular misconception in control room treatment, that bass traps will "remove" bass from the room...


When trapping or using resonators, you are taking (LF) energy 'out' of the room, into heat. And because you do so, you even out the freq response of the room, by reducing and sometimes basically stopping any interactions between direct field energy and reflected/re-emitted energy. I don't think it is wrong to say that one takes bass out of the room - but I agree it should not be mistaken for another concept, that bass is not existing anymore in the room.

franman wrote on Sun, 08 February 2009 14:30

BUT, this seems to be what both are you are implying unless I'm not understanding correctly>>> that too many loose panels acting as membranes will take bass response away from the room.... Am I getting this right?? sorry for my confusion.... Maybe it's totally different in large performance spaces, but I know how larger recording rooms behave and we still strive to add sufficient LF trapping in these rooms to ensure the bass is tight and the decay is comparable to the rest of the spectrum... as you know it's easy to absorb too much High and Mid frequency and end up with a boomy sounding room.

Thoughts>????


What can happen in such a room, is that the decorative loose panels (which for most I suspect have the same overall size) are acting as resonators with a certain bandwidth.

Also, in these types of room, for the vast majority of the public, the ratio of (direct energy) / (reverberated energy) will be in clear favor of the reverberated field, which therefore implies the most energy perceived by the ear is from the reverberated field.

If those panels are such that they resonate and kill, say, the 100Hz / 150Hz band (because of differences of incidence), for those freq you are only left with direct energy, and none in the reverberated field. Which means that overall, this will be perceived by the public as a lack of bass, because it creates an imbalance in the reverberated field - which accounts for most of the perceived energy. Decay very is messed up freq wise.

Chances are these re-emit in the LMF band too, therefore increasing perceived energy with regards to bass, increasing the imbalance. (Those modern rooms I have visited have little to no MF treatment as well. Treating HF is no use, air does that job pretty well.)

EDIT: having a very live, but very balanced room reverb is important for those halls. They can't be deadened - or they sound dull and life less. This is an important difference with studios.
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Thomas Jouanjean
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Bruno Gouveia

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Re: membrane bass traps thickness
« Reply #38 on: February 09, 2009, 07:13:31 am »

Thomas Jouanjean wrote on Mon, 09 February 2009 08:10



Chances are these re-emit in the LMF band too, therefore increasing perceived energy with regards to bass, increasing the imbalance. (Those modern rooms I have visited have little to no MF treatment as well. Treating HF is no use, air does that job pretty well.)




Hey, this makes a lot of sense and can explain what's happening!! Very Happy

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Re: membrane bass traps thickness
« Reply #39 on: February 09, 2009, 07:21:11 am »

Yes that's what I'm talking about...air does the job if the room is large enough. But that Concert Hall is not that large. And even the MF treatment has to be carefully placed in it.

Old concert halls have lots of ornamentation in their architecture
and provide good acoustics by diffusing the sound in the room. But new concert halls don't have that and then we need to have artificial ways to provide the necessary diffusion to the room.

In fact for musical purposes, diffusion plays a much major role than absorption since the audience is indeed the major absorbent in the hall.

In Casa da Musica the chairs were designed to match human absorption so the sound does not sound that different when it is empty or at 50 % of its capacity, or people just in one side of the available seats
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Thomas Jouanjean

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Re: membrane bass traps thickness
« Reply #40 on: February 09, 2009, 11:52:53 am »

For the fun of it, a small video of a scattering in one of the "demo" rooms in ODEON...

Shows the whole shebang...

HERE
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Thomas Jouanjean
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franman

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Re: membrane bass traps thickness
« Reply #41 on: February 09, 2009, 08:20:43 pm »

Link no work??  Confused
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Thomas Jouanjean

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Re: membrane bass traps thickness
« Reply #42 on: February 10, 2009, 02:30:44 am »

Try again...
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Thomas Jouanjean
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andrebrito

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Re: membrane bass traps thickness
« Reply #43 on: February 10, 2009, 07:08:26 pm »

That is a nice picture !

I have worked with ODEON, CATT, EASE and other ray tracing image-hybrid software. ODEON is one of my favorite but $$%#$#@$@# expensive
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