Trapping Traps

[MaximumAdams]

Hi guys, awesome topic! Thanks dandan for pointing me here.
Been through the thread and some of the designs reminded me of this article I found ages ago;

SAE Institute

This acoustic hanger idea looks like its working on a pretty similar principle to the "enhanced porous absorber" design. The article seems to be pretty dated, but I thought it might be of use somehow in regards to mounting options, or a different perspective.
I'm not sure if it's anything you guys haven't seen before, but I figure every little bit helps.

[latestflavor]

Originally Posted by MaximumAdams

This acoustic hanger idea looks like its working on a pretty similar principle to the "enhanced porous absorber" design.

The hangars only work in arrays and not the same in different parts of the room. Originally they were empirically developed by non-acousticians "in the wild". We shall see where they go as they become improved through reverse engineering, but they seem to take a lot of space though and work best in non-environment designs.

[MaximumAdams]

I wasn't really thinking about the acoustical application as such, I was thinking more along the lines of the mounting method. By "similar principle" I meant that they're both resonating panels, but the metal plate design is an exponentially more effective and versatile evolution of the theory.
I suppose I should have said that "by a little dated" I really meant something along the lines of how apes are related to modern humans; they both have opposable thumbs and the like, but I couldn't see an ape being able to understand modern acoustic design.

Somewhat of an understatement you could say. Sorry, my bad.

[latestflavor]

The acoustic hangar is not a resonating panel. Conversely, a metal plate resonator ideally would not hang or rest on anything either. No biggie though, i'm not trying to shoot you down. They both look similar. An acoustic hangar is a bit hard to use if you're doing something other than a non-environment type of room because its so absorptive, if somewhat unpredictably so. A metal plate resonator, however, can be made either more or less absorptive, depending on how you desire the result. Also, a single metal VPR will attenuate LF if places where it is supposed to go (area of high pressure), a single acoustic hanger will not work at all (aside from the absorption that is hanging). So the only similarity is casually optical.

I wonder where G.E. stands with his testing, i subscribed to this thread with great anticipation! Hopefully its still alive!

[NLP]

... hangers can be different by structure, some use plywood, MDF (Newell)... hard core... some use like homosote cores (Hidley, Sayers)...
Hangers works best by waveguide effect, flexural vibration measuring with accelerometers, construction: 19mm chipboard and deadsheet of 3,5kg/m2 and both sides covered with 60kg/m3 cotton waste felt...is perhaps only 0,1% (AES E-Library ).

[MaximumAdams]

Originally Posted by NLP

... hangers can be different by structure, some use plywood, MDF (Newell)... hard core... some use like homosote cores (Hidley, Sayers)...
Hangers works best by waveguide effect, flexural vibration measuring with accelerometers, construction: 19mm chipboard and deadsheet of 3,5kg/m2 and both sides covered with 60kg/m3 cotton waste felt...is perhaps only 0,1% (AES E-Library ).

Ahhh! So the boards in hangers aren't for absorption? The penny drops! I always just thought it was a mass principle that they rely on! Oh well a lesson learned the hard way is still a lesson learned. Thanks for the insight.

[NLP]

hmmm like I said:
"...hangers can be different by structure, some use plywood, MDF (Newell)... hard core... some use like homosote cores (Hidley, Sayers)..."
... softer "hard cores" can offer significant absorption and a bit of waveguide effect... and phases between...

[G. E.]

Originally Posted by G. E.

... Now that I have an empty room with different types of bass traps (see above) and a ready-to-go test setup available I kindly take your suggestions until the end of the year 2011 to compare different configurations directly for further public reference. ...

I'm giving this thread a restart: feel free to make your suggestion till April, 30th 2012.

[G. E.]

Originally Posted by latestflavor

... I wonder where G.E. stands with his testing, ...

I used the room for testing some 1 hour listening setup with a 60cm [~2'] deep trap on the front wall. Deepest modes stayed in the 400ms range.

[BriHar]

Are those styrofoam blocks?

[G. E.]

Originally Posted by BriHar

Are those styrofoam blocks?

I used Caruso Iso Bond, a kind of non-woven polyester fabric.

[G. E.]

Today I measured a control room before/after the installation of two Enhanced Porous Absorbers (both 2,8m x 1,0m [~9' x 4']) in the front corners.

Setup included an almost square control room stuffed with a 32-channel console, some outboard, B&W 801 speakers, and minimal exisiting acoustic treatment with small porous absorbers.

Measured at the "client position" sofa 45cm [~1'6"] in front of the back wall window with both speakers driven, Red ... before (without EPAs), Blue ... after (with EPAs).

T60 for the lowest mode at 38Hz dropped from ~1400ms to ~600ms.

[G. E.]

Originally Posted by G. E.

... an almost square control room ... T60 for the lowest mode at 38Hz dropped from ~1400ms to ~600ms.

Here's length/width/height of this bedroom-sized studio space: 4,12m/3,96m/2,6m [~13'6"/12'12"/8'6"]

Using Bob Gold's "Room Mode calculator" gives a lowest mode at 41,8Hz. The lower measured figure of 38Hz could originate from the large window in the back or some coupling to the next room through the door. The room fails at some of the computed criteria.

[Prick Up UR Ears]

Originally Posted by G. E.

I used Caruso Iso Bond, a kind of non-woven polyester fabric.

to me those are just styrofoam blocks and those won't do a lot of trapping

[kasmira]

Holy hell GE, those results are extraordinary in that room! Superb!

Actually, I suppose its not extraordinary - that would imply that the results were unusual (but good). Instead, lets say that the results are superb.

I'm sure your client is ecstatic with the results. Why did you choose the front corner to trap?

Thanks so much for sharing this

[G. E.]

Originally Posted by kasmira

... Why did you choose the front corner to trap? ...

... in no particular order (fortunately no compromising necessary):

• there is less sound pressure in the back of this room due to a large window and a door
• the furniture left very little space in the back corners
• EPAs in the front corner tend to "fill up" holes in the bass-range of the FR

[bwo]

Great job G.E.!
May hire you one day.

[kasmira]

Originally Posted by G. E.

... some (hanging or self-standing) support from underneath:

Wow, I've read this thread multiple times, and have missed this post so many times. So simply, if you already had a cloud that, say was only hung from the sides - you could just slide a metal plate on top of it, throw some more insulation on top of it, and have an EPA? (Assuming the metal wouldn't be touching anything but the insulation above & below it)

This is really great news to some folk if so.

[G. E.]

Originally Posted by kasmira

... So simply, if you already had a cloud that, say was only hung from the sides - you could just slide a metal plate on top of it, throw some more insulation on top of it, and have an EPA? ...

I would think so (the top layer touching the ceiling?!) but I haven't tried it yet. It's not the first thing I would do in a room because typically the height-mode is substantially higher than the deepest mode and therefor easier to tame.

If you think about the ceiling in some rooms it's worth to think about the floor as well. Rooms with a height of about twice the typically listening position (lets say 1,2m [~4']) usually have a better measured frequency response if you move the mic up for 10cm-30cm [~4"-1']. One would need a platform to sit on that could incorporate a lying EPA underneath.

[kasmira]

Originally Posted by G. E.

I would think so (the top layer touching the ceiling?!) but I haven't tried it yet.

Well, what a perfect thread for this!

Could this be tested in your room? I propose checking the difference between the sandwich leaning against the wall (not corner) vs the sandwich laying on top of your cloud-box-thing.

I understand that it would mostly dampen the height mode, but considering how substantial clouds already are in a room, it may just work beautifully. Plus, there are so many studios that already have clouds (and some very large too) installed and a lot of people don't have room to put anything on the floor (or wall space may already be taken up from existing treatment), so this could be a simple addition to just beat down some modal ringing.

[G. E.]

Originally Posted by kasmira

... I propose checking the difference between the sandwich leaning against the wall (not corner) vs the sandwich laying on top of your cloud-box-thing. ...

I think results from floor testing would translate very well to the ceiling position.

[kasmira]

Originally Posted by G. E.

I think results from floor testing would translate very well to the ceiling position.

Good point. How far down does your cloud hanger sit from the ceiling? It could be nice to see the difference in effectiveness with an airgap vs filling the entire back with absorbent on something like this (be it on the wall or hanging)

I would assume airgaps with your EPA are not going to be similar to airgap on your typical bass trap, since you need the material to dampen the plate, correct? And air would not provide significant amounts of dampening..

[G. E.]

Originally Posted by kasmira

... How far down does your cloud hanger sit from the ceiling? It could be nice to see the difference in effectiveness with an airgap vs filling the entire back with absorbent on something like this (be it on the wall or hanging) ...

The cloud height is variable.

Originally Posted by kasmira

... I would assume airgaps with your EPA are not going to be similar to airgap on your typical bass trap, since you need the material to dampen the plate, correct? And air would not provide significant amounts of dampening.

Yes, it's different from a standard porous absorber. Nevertheless the absorption (energy dissipation) comes from the porous absorber and it still needs (relative) velocity between air and absorber.

Therefor I think from all the mounting options so far the distant ceiling mounting is the most unpredictable so testing makes sense.

[gullfo]

o.t. - interesting page with calculators for various DOF for plates - mainly displacement but interesting...
eFunda: Classical Plate Equation

[G. E.]

Originally Posted by gullfo

... calculators for various DOF for plates - mainly displacement but interesting...
eFunda: Classical Plate Equation

... helpful resource though the link does not cover the rectangular plate under free boundary condition (in a mechanical sense, as is the case here).

[kasmira]

Originally Posted by G. E.

I'm giving this thread a restart: feel free to make your suggestion till April, 30th 2012.

Any updates / testing done, good sir?

[Mctwins]

Originally Posted by G. E.

Today I measured a control room before/after the installation of two Enhanced Porous Absorbers (both 2,8m x 1,0m [~9' x 4']) in the front corners.

Setup included an almost square control room stuffed with a 32-channel console, some outboard, B&W 801 speakers, and minimal exisiting acoustic treatment with small porous absorbers.

Measured at the "client position" sofa 45cm [~1'6"] in front of the back wall window with both speakers driven, Red ... before (without EPAs), Blue ... after (with EPAs).

T60 for the lowest mode at 38Hz dropped from ~1400ms to ~600ms.

The yellow line from 20-50Hz schoulden't be there, if you have this and according to ARTA "denotes frequency region where the time-bandwith requirement is not fulfilled", read "System Analysis from Impulse Response"

and

The burst decay graph, is it mesured in sweep, sequence lenght 256 or what?
Can you show? Burstdecay, Mode Waterfall_F

Nevertheless, there is a huge suckout and there is no changes before and after. Just saying.

[G. E.]

Originally Posted by kasmira

Any updates / testing done, good sir?

I'm more into control room setups the last weeks, looking if the test results translate to this situation. Latest result shows that the 42Hz mode is totally gone.

[G. E.]

Originally Posted by Mctwins

The yellow line from 20-50Hz schoulden't be there, if you have this and according to ARTA "denotes frequency region where the time-bandwith requirement is not fulfilled", read "System Analysis from Impulse Response"

and

The burst decay graph, is it mesured in sweep, sequence lenght 256 or what?
Can you show? Burstdecay, Mode Waterfall_F

Nevertheless, there is a huge suckout and there is no changes before and after. Just saying.

Thanks for pointing me to the yellow line, I've never noticed that before.

I can't remember if the measurement was made with ARTA's sweep or periodic noise but I'm quite sure that I've used maximum (256k) sequence length.

Feel free to make your own conclusions with the attached PIR-files (before/after).

The measurement was made to show the reduced decay time of the lowest mode. I agree with you that the FR at this position has major flaws.

[Mctwins]

Originally Posted by G. E.

Thanks for pointing me to the yellow line, I've never noticed that before.

I can't remember if the measurement was made with ARTA's sweep or periodic noise but I'm quite sure that I've used maximum (256k) sequence length.

Feel free to make your own conclusions with the attached PIR-files (before/after).

The measurement was made to show the reduced decay time of the lowest mode. I agree with you that the FR at this position has major flaws.

Hi
Thanks for the file...

About the yellow line, it depends if you push the button Smoothed FR or Dual-gate Smoothed FR. In Dual-gate Smoothed FR the yellow line comes up but not in Smoothed FR if you have the Gate1 and Gate2 set in the default value (20ms and 200ms). The Y line can accure in Smoothed FR if you set the yellow curser line and red marker line in the Impulse Response Envelope.

Via Setup and Analysis parameters one can set a fix value or default value for the Y-line only for Dual-gate Smoothed FR but if you use yellow curser line and red marker line in the Impulse Response Envelope you are changing both Smoothed FR and in Dual-gate Smoothed FR despite the fixed or the default value.

I am always lokking at Smoothed FR or Unsmoothed FR(DFT)

The only thing I can see from your before and after measurements in ARTA's Burst decay is a slight differense in the resonance but it is not as effective as it schould be, maybe you need alot of your basstrapps to be effective. There schould also be a pressure change in that region as well. According to Smoothed FR there is no changes before and after.

Could you tell me where your mic was when these measurements was done. It is also important that the mic is not moved from it's position when doing before and after measurements, but I think you know this.

I have one Q?? Why the REW waterfall when you have ARTA, it has to come from the same impulse response envelope to be able to see some difference.