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My Experiment with a Metal Panel Absorber
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#241
23rd December 2011
Old 23rd December 2011
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I find this amusing but the choice of Baso foam has probably not much related to acoustics

1 - it is a german product
2 - it is anti-fire class rated B1
3 - does not disintegrate such as light density rockwool
4- it is a white color product

It is not that pricey around 20-30 euros/sqm when compared to the cost of the entire product
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#242
23rd December 2011
Old 23rd December 2011
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Quote:
Originally Posted by andrebrito View Post
I find this amusing but the choice of Baso foam has probably not much related to acoustics
No, but not because of the reasons you are suspecting..

The VPR uses Basotect not because it's acoustics properties, but due to it's ability to dampen the MECHANICAL vibration produced by the steel. How much basotect surface is exposed to free air anyway? Next to nothing..Why would acoustic absortion matter? The fact Basotect absobs acoustic energy quite well is coincidental but not relevant in this specific application. And the fact that iso bond has better acoustic absorption has nothing to do with the VPR working principle, which is more mechanical than acoustic.

cheers
#243
23rd December 2011
Old 23rd December 2011
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Quote:
Originally Posted by boggy View Post
Why you don't glue IsoBond with steel plate directly to the wall (like it is described in patent document). If you hang panels with glued IsoBond, freely in air, it will have totally different working conditions, and steel plate wouldn't have mass-spring composition with IsoBond, which is glued to heavy anchor (wall), that is needed for absorption below 100Hz. I'm afraid that you heard only a part of performances you can possibly reach with your investment.
It was a practical thing.. and an experiment.. We have glued many many stones to the walls for random diffusion.. ( that was version 1.0 when we didn't know better back then..) So it would have been a pita to remove all of them..and provide a plain surface ;-)

So I thought lets try the easy way first since I read a comment from Fuchs which was also mentioned here that "some" space between the wall and the device is ok.. And I thought if it doesnt work Ill do it the hard way.. and it worked.

much better than all soft materials and /wooden) plate resonators we tried before.. And I didn't mesure it, but my ears and my recordings told me immediately that they work great way under 100hz.. so Im happy at the moment.. (no more (ok ok , much less, stays in the 3 db range.. ;-)) murky lowend and lowmids I had to eq out before.. sometimes I had to cut resonances over 10-15db..)

I will do the recording room the "right" way (+more vprs ) when I do the control room.. Till then it was the best 1 day investment I ever made.. ;-D

I thought about the metal rails from ceiling to bottom. If they have holes you may just hang the vprs in there checkerboardstyle (with some sort of screws and elastomere). So I can get maybe 20-30 pieces in the room... :-) Then put some diffusors in front of them. Theres some work to do... :-D
Have fun!

Cheers, Jens
#244
24th December 2011
Old 24th December 2011
  #244
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Quote:
Originally Posted by G. E. View Post
It's not a suggestion but a patent. The exclusive license on VPRs for Europe is held by the German company RENZ. They may give sub-licenses because other companies like FAIST in Germany sell them, too.

I think it's a question of efficiency at different frequencies. Below 100Hz VPRs are a welcome option.
Ok ok, its a patent...:-) But Im just inspired by that and build them just for our little rockn roll cellar studio.. I won't sell or market them.. so I'm not illegal, am I???

Yes and in terms of efficiancy:.. The Vprs are Broadband devices, which start very low but are efficiant till 1k.. Thats exactly what everybody in the world with a small room wants (and not only with a small room..). The room looses its murkyness and resonances in the lows and mids but stays open on top.. thats how my room sounds now.. I mean: remember its a 5m*5m*4.5m box!!!! Thats terrible dimensions..!! It sounded like as. before!! and It sounded like ass with tons (and I mean it..!!!) of porous material in it (got dull and still murky resonances in the lows..) I have to laugh when I see suggestions about the common 4` roockwool traps now..

Enough for now... ;-)

Merry Christmas, hope you get some VPR presents soon!!

Cheers Jens
#245
24th December 2011
Old 24th December 2011
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Quote:
Originally Posted by Jens Siefert View Post
....... So I can get maybe 20-30 pieces in the room... :-) Then put some diffusors in front of them. Theres some work to do... :-D
....
If you already finished low end absorption, there already exists something pretty compatible with "VPR-inspired" low end absorption behind.... and can be very diffuse in front!....
In other words, have you ever tried this: MyRoom Acoustic Design?
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#246
24th December 2011
Old 24th December 2011
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Quote:
Originally Posted by Jens Siefert View Post
...and It sounded like ass with tons (and I mean it..!!!) of porous material in it (got dull and still murky resonances in the lows..) I have to laugh when I see suggestions about the common 4` roockwool traps now..
I went down the same road. Packed my room full of rock wool traps (so-called Studiotips Super Chunks). By eating up all the highs, and doing nothing to the loud room modes below ~100Hz, the traps just made the LF issues worse. Oh well, I had to start somewhere and I've learned a lot since.

I'm sourcing components for VPRs right now and can't wait to start my room treatment over again. Hope I get results like Jens.
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#247
24th December 2011
Old 24th December 2011
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I am repeating myself, but I think its being ignored that according to the formula for the mass-spring absorption mechanism of the trap, the resonant frequency is dependent on only two factors with regard to the porous absorption:

1) density of the porous absorber (lower density = lower fs)
2) speed of sound in the porous absorber (lower speed = lower fs)

Its possible that Caruso and Basotect work equally well - I'm guessing that the higher density of the Caruso material is offset by the possibly lower speed of sound in the said material.

The absorption potential of Caruso v/s Basotect (independent of the metal sheet) is most likely not of any significance below 150 Hz. And there are simpler ways of absorbing above 150 Hz.

Quote:
2.5mm steel is quite stiff -- bending stiffness rises with power 4 that means 2.5 times thicker gives ~39 times higher bending stiffness
Interesting point G.E.... and looking at the coefficients for the two traps it is clear that the Type 1 is far more efficient in its frequency range than the Type 2 in its range. However, the Type 1 is totally ineffective by about 42 Hz, which is where the Type 2 has a peak in absorption.

#248
24th December 2011
Old 24th December 2011
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hey Audiothings, can you please explain what "Type 1" and "Type 2" mean on that graph. I checked out the original graph on the RPG/Modex website, but they don't really explain it in detail. Is "Type 1" supposed to be VPR that uses 1mm steel and "Type 2" the one that uses 2.5mm?

Thanks!
#249
24th December 2011
Old 24th December 2011
  #249
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Quote:
Originally Posted by audiothings View Post
I am repeating myself, but I think its being ignored that according to the formula for the mass-spring absorption mechanism of the trap, the resonant frequency is dependent on only two factors with regard to the porous absorption:

1) density of the porous absorber (lower density = lower fs)
2) speed of sound in the porous absorber (lower speed = lower fs)
As you said, only true for the mass-spring resonator aspect, which some on the thread seem to think is not a significant factor in its operation. For the plate vibration mechanism, frequencies are defined by the plate assuming the foam layer does not constrain the plate much. Therefore you'd like a material with minimal stiffness and maximum damping factor / loss tangent. Presumably if this is the major mode of effectiveness of the device, one might be able to make it thinner within the previous requirements.

In terms of the mass-spring action you also neglected that the formula contains thickness for both the pieces. Based on the relative positions of thicknesses and densities in that formula, to drive the resonance frequency low you would want a plate with high density*thickness which just means high mass per sqft of face area. Similarly a spring (the damping layer) of large depth with low density - but a ratio, so (with constant c) half thickness with half the density works same. Speed of sound in the material is the real kicker here. Since it can't be found on a material data sheet, we need to translate that into parameters that _can_ be found on a data sheet. If one of the factors to which it can be related is density, then things start to get more interesting.
#250
24th December 2011
Old 24th December 2011
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Quote:
Originally Posted by scoring4films View Post
Is "Type 1" supposed to be VPR that uses 1mm steel and "Type 2" the one that uses 2.5mm?
Yes.
#251
25th December 2011
Old 25th December 2011
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Quote:
Originally Posted by nucelar View Post
... VPR uses Basotect not because it's acoustics properties, but due to it's ability to dampen the MECHANICAL vibration produced by the steel. How much basotect surface is exposed to free air anyway? Next to nothing..Why would acoustic absortion matter? The fact Basotect absobs acoustic energy quite well is coincidental but not relevant in this specific application. And the fact that iso bond has better acoustic absorption has nothing to do with the VPR working principle, which is more mechanical than acoustic. ...
I don't agree. Basically the plate converts air pressure to air velocity at the plate's frequencies (Eigen modes). The absorbent might also dampen the plate itself (preventing unwanted ringing) but a porous absorber is needed to dissipate air motion energy. This is where absorption happens. Damping a plate without porous absorbents (foam, wool, fabric, ...) would be far less effective. For example a simple plate of hardboard (self damping) won't do the job.
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#252
25th December 2011
Old 25th December 2011
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Nuclear what damping are you talking about ?

Basotect is melanine foam, it is not a elastometer nor any kind of product for damping vibrations... I have seen Basotect, actually I sell Baso where I live.

Like G:E says, this device NEEDS an absorbent on its back. Could be Basotect or other.

I might be wrong but where does it says Basotect is used for vibrational purposes ?
#253
25th December 2011
Old 25th December 2011
  #253
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Quote:
Originally Posted by boggy View Post
If you already finished low end absorption, there already exists something pretty compatible with "VPR-inspired" low end absorption behind.... and can be very diffuse in front!....
In other words, have you ever tried this: MyRoom Acoustic Design?
Guess what!!! My Experiment with a Metal Panel Absorber-61319_115594475165049_115594128498417_112947_7852659_n.jpg

Yeah, thanks,.. Somewhat similar at least.. I see you built diffusors with airflow.. props to you, and food for thought for me... ;-)

Ahh and good luck SCORING4FILMS and everyone else!! You'll make it!!

Merry Christmas!!!
Jens
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#254
26th December 2011
Old 26th December 2011
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Excuse me for the slight OT, this is a matter of semantics rather than acoustics...

Quote:
Basotect is melanine foam, it is not a elastometer nor any kind of product for damping vibrations... I have seen Basotect, actually I sell Baso where I live.
Andre, you are the only person on this forum who has used the word 'elastometer', which is actually an instrument for measuring elasticity, primarily used in the medical industry to measure swelling of tissues etc.

An 'elastomer' however is
Quote:
'a polymer with the property of viscoelasticity (colloquially "elasticity"), generally having notably low Young's modulus and high yield strain compared with other materials.'
I doubt if Basotect can play in the same field as some other elastomers we know of, such as Sylomer, but I think Basotect will satisfy the requirements needed to be referred to as an 'elastomer'... Please correct me if I am wrong...
#255
26th December 2011
Old 26th December 2011
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RPG's explanation of how it all works:

"Technology
Sound (1) strikes the steel plate (2) which pistonically vibrates (3) against the porous absorption spring (4), mounted on a rigid backing (8). The porous absorption also damps plate bending modes (5) and absorbs higher frequencies which diffract around the plate (6) through a perforated (7) metal frame.



Surface or corner applied porous materials lose efficiency at low frequencies, because the particle velocity or air movement associated with these long wavelengths is low. In order to maintain efficiency at low frequencies, the Modex™ Plate consists of a damped metal plate system. While the velocity is low, the pressure is at a maximum near the boundary and it is this pressure that is exploited in a mass-spring manner offering absorption via three mechanisms. First, the metal plate provides pistonic absorption down to the lowest frequencies by vibrating against the “spring” of the porous backing. Second, the bending modes of the free-moving plate are heavily damped by the proprietary adhesive coupling with the porous backing which attenuates the lower mid-range frequencies. Lastly, mid-frequency sound waves diffract around the plate’s edges to be propagated and thus dissipated in the deep passive porous absorber layer. Together, these mechanisms offer the industry’s first truly efficient, broad bandwidth low frequency absorber with a shallow profile of only 4 inches."



Bolding by me.
#256
26th December 2011
Old 26th December 2011
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Audiothings, ops typing error ! My mistake
#257
26th December 2011
Old 26th December 2011
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Porous Backing

Quote:
Originally Posted by Dange View Post
RPG's explanation of how it all works:... Second, the bending modes of the free-moving plate are heavily damped by the proprietary adhesive coupling with the porous backing which attenuates the lower mid-range frequencies. ...
I would like to add something to their marketing words: more mechanical damping of the plate doesn't necessarily mean more sound absorption! You may think of it this way: even lots of (probably self-damped) vibrating objects in your studio don't provide substantial absorption... because the porous backing (absorbent) is missing.
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26th December 2011
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The Basotect I know and sell is just melanine foam for absorbing airborne sound. For other typical vibrational applications such HVAV systems, machines etc the material used is quite different.

Maybe Basotect works for a metal plate due to its light weight. But it does not compare to Sylomer or other damping material for much heavier structures
#259
26th December 2011
Old 26th December 2011
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Quote:
Originally Posted by DanDan View Post
Thanks for the links guys.



Boggy, that's a quote from G.E.
His design has no rigid backing and works really well.
The OP design here has a rigid backing and works really well.
I think we are 'checked' don't you?

DD
I don't think it is that easy. The VPR is a combination of different principles, which have been outlined here a few times (see official explanation by Renz for instance). By removing the rigid backing you will decrease at least the effect of the absorbent layer. This probably will not effect the bending modes of the plate (that are still dampened by the foam), therefore it will still result in good absorption in the lowest frequency range. However, you will certainly decrease the efficiency around the 125 - 500 Hz range (Fuchs describes that absorption around this range my be achieved by using an open framing).
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27th December 2011
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It was my understanding that the plate was constrained, therefore damped, by the porous backing and adhesive and this was how the losses occurred.

Is this not the case?
#261
27th December 2011
Old 27th December 2011
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Quote:
Originally Posted by Dange View Post
It was my understanding that the plate was constrained, therefore damped, by the porous backing and adhesive and this was how the losses occurred.

Is this not the case?
Yes, the dampened bending modes of the plate is one of the principles the VPR uses. However, the quote by Renz you posted shows that this is only a part of how the VPR works. There for instance is also some edge diffraction which makes some part of the VPR work as a porous absorber. There has been a quote from Fuchs somewhere, which basically said that, if you remove the rigid backing, you create a shortcut between the back and the front of the VPR, resulting in lower efficiency. I suppose that will mainly effect the edge diffraction and the part working as a porous absorber. I suppose, but am not quite sure yet, that it also will effect some other functions of the VPR.
I am not trying to say that it will not work at all if you remove the rigid backing, but you are dealing with a different system, which behaves differently. Depending on the situation and your needs this might work perfectly or might not work at all. Therefore we need to be aware of those details.
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27th December 2011
Old 27th December 2011
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Backing

Quote:
By removing the rigid backing you will decrease at least the effect of the absorbent layer.
Hi Nuuk, this is intriguing.
How do you reckon a rigid backing or boundary increases the effect of an absorbent layer?

I would have thought the opposite is the case. i.e. Mounting the foam directly to the boundary removes the biggest exposed surface area, leaving only the edges.


DD
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27th December 2011
Old 27th December 2011
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I assume this is referring to the panel if not mounted directly to a boundary? Yes? Perhaps it is the same principle that applies to a porous absorber in the middle of a space in which the wave would find a path of least resistance around the object.
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#264
27th December 2011
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Come to think of it, the rigid backing seems redundant other than from a manufacturing point of view.
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27th December 2011
Old 27th December 2011
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Quote:
Originally Posted by DanDan View Post
Hi Nuuk, this is intriguing.
How do you reckon a rigid backing or boundary increases the effect of an absorbent layer?

I would have thought the opposite is the case. i.e. Mounting the foam directly to the boundary removes the biggest exposed surface area, leaving only the edges.


DD
to my understanding this is not the point. You are using a metal plate in front of the foam. Therefore the plate reflecting soundwaves, the soundwaves are exciting the plate, and/or the soundwaves are just moving around the plate and the foam, if you are not (!) using a rigid backing. By using a rigid backing, the soundwaves which are moving around the plate will be caught by the foam due to edge diffractions. I am unfortunately not able to provide a scientific explanation for this right now, without doing some more research, which I can't do right now. Maybe someone else could jump in here....
However, if you are talking about soundwaves, that are moving around the plate and the foam, then are reflected by another wall and then hit the back of the foam (not using rigid backing) you might be right. But I doubt this will be more efficient than the VPR design.
Fuchs interestingly describes a few variations to the VPR design in his book: You could either way mount it to a wall, integrate it into a wall or mount it apart from a wall using another rigid backing. However, I would assume that the best way mounting a VPR is in the corners and egdes of a room.

I also read a quote form Fuchs in another forum where he described that you will be creating a shortcut between the front and the back of the VPR if you do not mount it with a rigid backing. To me that actually makes sense.
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27th December 2011
Old 27th December 2011
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Hmmm

I am afraid I can't make sense of that Nuuk. The full surface area available without the rigid backing or boundary has to absorb way more of the MF which finds its way around the plate. The thing for me is, I want to believe the device is perfectly viable without a backing. This makes DIY and Mounting etc. a whole lot easier.
G.E.'s test shows incredible performance at LF, no backing.

I don't understand the reference to short circuiting the front to back. Presumably a translation loss!

Given G.E.'s result, (albeit in a corner) I am inclined to think that the design team did not explore all options here.
I am further inclined to think this way, due to the later discovery that Caruso Isobond performs better than Basotect, plus the very varied density recommendations.

With no disrespect whatsoever intended, I rate the work here by G.E. and the OP higher than the information in the patent.

DD
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27th December 2011
Old 27th December 2011
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Quote:
Originally Posted by DanDan View Post
I am afraid I can't make sense of that Nuuk. The full surface area available without the rigid backing or boundary has to absorb way more of the MF which finds its way around the plate. The thing for me is, I want to believe the device is perfectly viable without a backing. This makes DIY and Mounting etc. a whole lot easier.
G.E.'s test shows incredible performance at LF, no backing.

I don't understand the reference to short circuiting the front to back. Presumably a translation loss!

Given G.E.'s result, (albeit in a corner) I am inclined to think that the design team did not explore all options here.
I am further inclined to think this way, due to the later discovery that Caruso Isobond performs better than Basotect, plus the very varied density recommendations.

With no disrespect whatsoever intended, I rate the work here by G.E. and the OP higher than the information in the patent.

DD
Hmm, I think our main problem here is how and where to use a VPR without a backing. Depending on that and the frequency range you are targeting an additional absorptive area on the backing might make more sense. I believe a VPR without a backing would still give sufficient absorption in the low frequency range, even though I think it will result in lower efficiency in the lower midrange. However, this still is very hypothetical and theoretical as I haven't done any measurements nor have the equipment to do reliable measurements in the low frequency range nor am I a professional acoustics expert.
As you mentioned the patent as resource of information, I think the comparison between different lab measurements is much more important and gives more accurate results.
However, besides all theoretical discussion I will be more than happy to see any measured improvement to the patented VPR design, as we all would benefit from that
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27th December 2011
Old 27th December 2011
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Quote:
Originally Posted by Nuuk View Post
.......
However, besides all theoretical discussion I will be more than happy to see any measured improvement to the patented VPR design, as we all would benefit from that
I will try to explain in short... G. E. will help me...

G. E. made a measurements of this construction:
Perforated Panel with Porous Absorber trap

... as something that may be called "before and after burst decay analysis":
Perforated Panel with Porous Absorber trap

Absorber is built with IsoBond and steel sheet (G. E. may correct me if I'm wrong), and mounted in corner(!), then he improve response in room as you can see in measurement results. Absorber isn't mounted glued to the heavy back wall, it is free standing (G. E.?), and it is even supported (at side of steel plate?) with couple of batons.

Probably the best damping results of lowest resonant frequencies I ever see in a small room with only two 1m x 1m absorbers mounted in one corner of the room.

This is possibly a reason why we (still) discuss topic about metal panel absorbers in a way you can notice. I'm aware that this type of mounting isn't as patent recommendation,... but it seems that this works...question is, is this will work in every room? and how to recreate same or similar results in different rooms?

Hope this helps.
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27th December 2011
Old 27th December 2011
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Quote:
Originally Posted by boggy View Post
I will try to explain in short... G. E. will help me...

G. E. made a measurements of this construction:
Perforated Panel with Porous Absorber trap

... as something that may be called "before and after burst decay analysis":
Perforated Panel with Porous Absorber trap

Absorber is built with IsoBond and steel sheet (G. E. may correct me if I'm wrong), and mounted in corner(!), then he improve response in room as you can see in measurement results. Absorber isn't mounted glued to the heavy back wall, it is free standing (G. E.?), and it is even supported (at side of steel plate?) with couple of batons.

Probably the best damping results of lowest resonant frequencies I ever see in a small room with only two 1m x 1m absorbers mounted in one corner of the room.

This is possibly a reason why we (still) discuss topic about metal panel absorbers in a way you can notice. I'm aware that this type of mounting isn't as patent recommendation,... but it seems that this works...question is, is this will work in every room? and how to recreate same or similar results in different rooms?

Hope this helps.
Well, I still think this is just some kind of misunderstanding. I never neglected a VPR-style absorber without a backing having a significant impact to the low frequencies. I just stated that you most likely would lose some low mid absorption compared to a VPR. I know G.E.s postings. I think I read them several times the last months, since I find them very interesting and inspiring. (Keep up the good work G.E.)
However, there is neither a direct comparison to a VPR nor data that is directly comparable to measurements we have about VPRs. Therefore I still don't think there is any reason to state that it doesn't matter if you mount a VPR against a wall or use a rigid backing etc... not even talking about where you place it in a room. I actually do not see any reason why a VPR without rigid backing should work better than one with rigid backing. G.E. seems to had great results, but I don't think that should give any reason for generalizing things. We simply don't have enough data for that.
However, in the end we are asking the same questions. Is it repeatable..? If so, under which conditions? Probably I should also add: Due to which conditions would it work better in the lowest frequency range than a standard VPR? I guess if you could answer that last question to me in terms of physics, we would all be good
#270
27th December 2011
Old 27th December 2011
  #270
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Quote:
Originally Posted by Nuuk View Post
Well, I still think this is just some kind of misunderstanding. I never neglected a VPR-style absorber without a backing having a significant impact to the low frequencies. I just stated that you most likely would lose some low mid absorption compared to a VPR........
I agree with you.
We don't have measurements of all possible combinations in small rooms, only manufacturers measurement data, and G. E. measurements. If VPR-style absorber isn't mounted on a (heavy) back wall, resonant structure can't be as defined by inventors, measured data isn't applicable. If we hang this absorber with ropes using holes through resonant membrane, this will be, again, different resonant structure. If we hang VPR for a new back "plate" built from thick MDF (heavy wall simulation), this resonant structure will be... different... free standing will be also different etc. and working range will be different for all that four absorbers even if they are very "similar"... and if we only change type of mounting.
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