My Experiment with a Metal Panel Absorber

[daxliniere]

Originally Posted by G. E.

there's a resulting torsional moment that will turn the lower part of the plate/foam away from the wall.

This is absolutely correct and the reason it will lose efficiency.

[G. E.]

Originally Posted by daxliniere

This is absolutely correct and the reason it will lose efficiency.

The spring-mass system will change but the plate modes (second absorption mechanism) won't change.

[scoring4films]

DIY BOTTOM PANEL MOUNT IDEA

-Meant to be used in conjunction with the top "bracket combo" mount (see http://www.gearslutz.com/board/7269616-post118.html)

-Meant to hold the bottom of the VRP snug to the wall, not meant to hold the panel up or bear significant weight

-Prob. use two of these connectors, one in each bottom corner of the panel (or would just one at the bottom/center work?)

-As with the "bracket combo" design, the goal is to come up with a DIY design that uses easily source-able parts.

-Anyone know what the connector that holds the bolt to the wall is called? Is it easily source-able?

[scoring4films]

This GS thread from 2010 has some useful information/translations...

Who knows about or has built a vpr (fraunhofer patent)

[Nuuk]

Originally Posted by scoring4films

DIY BOTTOM PANEL MOUNT IDEA

-Meant to be used in conjunction with the top "bracket combo" mount (see http://www.gearslutz.com/board/7269616-post118.html)

-Meant to hold the bottom of the VRP snug to the wall, not meant to hold the panel up or bear significant weight

-Prob. use two of these connectors, one in each bottom corner of the panel (or would just one at the bottom/center work?)

-As with the "bracket combo" design, the goal is to come up with a DIY design that uses easily source-able parts.

-Anyone know what the connector that holds the bolt to the wall is called? Is it easily source-able?

What I don't like about that design is that it will inevitably "lock" and thereby stiffen the plate. I guess at least the screws should not be tightened to allow the plate to move more freely. However, I think a part which uses an elastomer to decouple the part attached to the plate from the one attached to the wall would be good. I know there a parts like this used in cars, but I doubt that the plate would have enough weight for them to work efficient enough. There somehow has to be an easy way to efficiently mount the whole system, without stopping the plate from moving freely. It just hasn't come to my mind yet... However, I just ordered the book about absorbers from Fuchs, which also has a chapter about VPRs... maybe that will bring up some ideas...

[scoring4films]

Originally Posted by Nuuk

There somehow has to be an easy way to efficiently mount the whole system, without stopping the plate from moving freely.

From the photos of the back of the RPG unit, it looks like in their case the foam does not bear any weight at all (http://www.gearslutz.com/board/7264029-post94.html).

The plate has to be held up somehow, so the only remaining possibility is that the frame is holding it up in some way, which means some sort of plate-to-frame attachment, which means some limiting of the plate's movement.

My mounting idea proposes 3 or 4 small plate-to-wall attachments. This would seem to be the bare minimum, allowing for as much plate movement as possible (I think).

Looking forward to hearing about what you learn from your reading...

[Absorbentbobs]

As I mentioned previously and as the above referenced photos somewhat show, the plate appears to be supported on the bottom edge only.

BTW, there may be more photos. Can someone clearly articulate what additional photographic info would be helpful in advancing our collective education?!?!?!

AB

[Nuuk]

Originally Posted by scoring4films

From the photos of the back of the RPG unit, it looks like in their case the foam does not bear any weight at all (http://www.gearslutz.com/board/7264029-post94.html).

The plate has to be held up somehow, so the only remaining possibility is that the frame is holding it up in some way, which means some sort of plate-to-frame attachment, which means some limiting of the plate's movement.

My mounting idea proposes 3 or 4 small plate-to-wall attachments. This would seem to be the bare minimum, allowing for as much plate movement as possible (I think).

Looking forward to hearing about what you learn from your reading...

Well, the easiest way to mount the plate to the foam would be to simply glue it. The hard part for me is mounting the foam to the wall and being able to still remove it without much hassle. As far as I understand the whole system right now, I suppose that the more you create a rigid connection between wall and plate, the more you lose the broadband characteristic in the low frequency range. That's why I think using two nuts to firmly fix the plate is not a very good idea. However, I would be glad if someone would prove me being wrong, as this would make mounting a VPR much easier to all of us

[DanDan]

it's these kind of threads that breathe new life into the forums - thanks to all for sharing / participating. Im learning a lot -

+lots

dd

[daxliniere]

Originally Posted by Nuuk

As far as I understand the whole system right now, I suppose that the more you create a rigid connection between wall and plate, the more you lose the broadband characteristic in the low frequency range.

Yes, this is absolutely correct! The wall is essentially supporting the plate, but we want the plate to move freely.

[scoring4films]

Originally Posted by Absorbentbobs

As I mentioned previously and as the above referenced photos somewhat show, the plate appears to be supported on the bottom edge only.

BTW, there may be more photos. Can someone clearly articulate what additional photographic info would be helpful in advancing our collective education?!?!?!

AB

Thanks AB!

I can't speak for everyone else, but I think it would be very helpful to see close up photos that show some detail on exactly how the steel plate connects to the frame.

You mentioned that it seems to be supported at the bottom edge only. Would it be possible to see some photos that show what that support looks like? Steel on steel? Steel plate inserted into some sort of channel on the frame? Some sort of flexible gasket involved?

How about the other three edges? Do they make contact with the frame, or are they free floating?

Any photos and/or descriptions would be much appreciated!

[daxliniere]

Okay guys,

I'm not sure how I missed this before, but this post tells us everything we need to know and can even help predict how my prototypes will perform:

http://www.gearslutz.com/board/5007476-post12.html

What materials can be used as an alternative for the steel plate and serve Isobond Basotect or Caruso? What to watch for the selection? PUR foam is equally suitable?

Foam: Actually, all materials which have a similar stiffness. Including foam or mineral wool. It must stop leaving only clog. However, one should pay attention to airborne fibers and odors. (Gerd, PUR's) In principle, the entire construct of VPR to handle very good natured.

Steel sheet: Actually, you can take each sheet, which has a similar stiffness and at least an equal mass. However, no other material really seems to make sense. Even aluminum is not. Even plastic does not.

-How should the bonding look like this (entire surface, Which Glue?)

Entire surface and with a relatively thin and uniform layer. Even double sided tape funzt. Or spray or something of the sort

-What effect does the thickness of the foam behind the metal plate?

The thicker the foam, the deeper impact of the VPR. The softer the foam, the deeper impact of the VPR. Also, you can glue several layers of foam together. (Gerd, adhesive again 4cm behind)

-What effect, except for those additional absorption at higher frequencies, an additional foam layer on the metal plate?

None

-Keep the foam consists of several individual panels to achieve the total to?

Yes, during the development phase has been partially done so even if you once had no record that was big enough.

-What to look for the attachment of the VPR?

Actually, only the fact that the plate can swing freely and that the foam flush with the wall is located. The mounting variant of Renz is probably pretty good

-What characteristics must a wall on which the VPR should be appropriate to at least meet?

It should not be too soft. So single-layer gypsum board should be enough, but 2 layers were already better.

How hard must be the connection VPR and wall?

In principle, the plate can only vibrate freely and the foam should lie flat on the wall

I also want to clear up a few things that have come up in this thread;
In the patent document, "Plate resonator" is a term referring to the entire, finished product; steel plate, foam plate and backing plate, not merely the steel sheet alone.
The reference to using Velcro to attach to the wall is referring to attaching the entire finished product to a wall, not the steel plate to the foam.

Of course, the units being built by companies other than RPG may use a different adhesion pattern such as 'dots on a grid' ("punctuated") instead of full-sheet coverage, but I personally prefer to go with the Fraunhofer/RPG method.


Page 11 of this document is also very useful in understanding construction; PLATE RESONATOR

[daxliniere]

Originally Posted by scoring4films

You mentioned that it seems to be supported at the bottom edge only. Would it be possible to see some photos that show what that support looks like? Steel on steel? Steel plate inserted into some sort of channel on the frame? Some sort of flexible gasket involved?

On the 1.0mm version, I am planning to make it without a frame at all, since the sheer strength of the steel-to-foam bond should easily be enough to support ~12kg.

For the 2.5mm version, I will use support brackets at the bottom with some soft silicone mounts to isolate the plate from the brackets.

[scoring4films]

Originally Posted by daxliniere

On the 1.0mm version, I am planning to make it without a frame at all, since the sheer strength of the steel-to-foam bond should easily be enough to support ~12kg.

For the 2.5mm version, I will use support brackets at the bottom with some soft silicone mounts to isolate the plate from the brackets.

Can't wait to hear about your results. How do you plan to place your VPRs in temporary locations, while testing for the most effective final installation spot?

[daxliniere]

Originally Posted by scoring4films

How do you plan to place your VPRs in temporary locations, while testing for the most effective final installation spot?

I have a set of portable acoustic treatments I made when I do location recordings. (SMW location recording 2011 | Facebook)

I welded up some telescopic stands with a heavy, X-shaped base (with one short 'foot' so you can get it close to a wall) and I plan to bolt the CBAs to those for testing.

[mhch]

The pictures shown in post http://www.gearslutz.com/board/7264029-post94.html, seem to indicate that the Renz VPR is mounted as shown in the attached sketchup diagram, i.e. in a way that does not completely
block plate movements and vibrations.

The rods on each side rest on the rack, which is itself screwed to the wall. This way the rod can rotate around their axis when the plate vibrates. They may also rotate a bit in the horizontal plane around the vertical axis going across the contact point between the rod and the rack. Rods can even move vertically a bit (I would think that not all of them do it at the same time).

These are interpretations-speculations of mine, but it is true that there are bridges anchored in a more or less similar ways into the ground so they are not firmly attached to it, so they can't break when the bridge structure expands because of heat, or vibrates under traffic weight.

[Nuuk]

Originally Posted by daxliniere

Okay guys,

I'm not sure how I missed this before, but this post tells us everything we need to know and can even help predict how my prototypes will perform:

http://www.gearslutz.com/board/5007476-post12.html

Nice.. I've spent almost all night reading that thread on that forum. There has been another interesting post containing a email from H. V. Fuchs.

Anordnung und Bau von VPR - Fragen dazu

1. The foam does not need to be directly fixed (e.g. glued) to the wall. There might be a gap up to a few mm between wall and foam.

2. The plate might be hung using wires. However, the system has to be near to the wall. (There is no hint if he means hanging the plate from the ceiling when mounting it to a wall (which I suppose), or a design what we have seen in this post http://www.gearslutz.com/board/7259233-post69.html )

3. It should be sufficient to just lean the VPR against the wall. (as long as 1. applies)

4. VPR is a combination of Mass/Spring-Resonance and flexural resonator

Concerning 2. there is a statement from Dr.Leistner from Frauenhofer: http://www.casakustik.de/forum/index...sg9860#msg9860

The plate might be hung using eyes (is this the right term in english?), as long as it doesn't degrade the ability of the plate to vibrate freely.

[G. E.]

With all due respect to the inventor and as errata to the somehow misleading (automatic?) translations:

Originally Posted by daxliniere

... this post tells us everything we need to know and can even help predict how my prototypes will perform: http://www.gearslutz.com/board/5007476-post12.html ...

• softer foam (with lower spring rate) results in a theoretically lower frequency of the spring-mass system but it may show less absorption for the modal frequencies
• experiments show that corner mounting without a rigid backing has great absorbing potential as well

Originally Posted by Nuuk

...

Anordnung und Bau von VPR - Fragen dazu

1. The foam does not need to be directly fixed (e.g. glued) to the wall. There might be a gap up to a few mm between wall and foam.

...

3. It should be sufficient to just lean the VPR against the wall. (as long as 1. applies)

...

I second that, again corner mounting is another option.

[NJlo]

I'm by no means an expert on the subject, but wouldn't hanging the plate be most effective?

[johndykstra]

[audiothings]

experiments show that corner mounting without a rigid backing has great absorbing potential as well

I agree, and for no justifiable reason.

I think that the most important, most unique, and least understood mechanisms in this absorber is the pistonic vibration of the metal plate. The mass-spring resonance seems to be centered around a specific frequency... much like the panel traps that are so unpredictable... and the diffraction around the edges, effective between 150-500 Hz is not interesting enough (for me), because 4" of 705 can easily take care of it!

I am hoping that Dax was incorrect (Dax, no offense intended towards you, of course) when he said that

I think that your hanging design defeats the purpose of this device. It works on pistonic action, which is not possible in your design as there is no compression of the foam between the steel and the backing plate.

This was in reference to the hereunder pic, description (sorry for quoting myself) first:

its probably not necessary for porous insulation to be glued to the rigid wall... I am guessing that if the porous insulation is glued to the steel sheet and then suspended from the ceiling using the thinnest nylon ropes... with a ~2mm gap between the porous insulation and the ceiling, we should have equally good results... Since the wall/ceiling is supposed to be as rigid as possible, its vibration cannot be a major factor in the absorption characteristics of the system... I'm guessing that another ~2mm of spring - albeit a different kind of spring than basotect - will not destroy our absorption characteristics. Meanwhile, we are certain that the insulation is not getting compressed or stressed in any way, and, we have a relatively easy way of suspending the plate without risk...

I am under the impression that G.E.'s trap had no rigid backing, and still it worked very well...

Also, a contribution from Nuuk in this post is encouraging me to think this way:

There has been another interesting post containing a email from H. V. Fuchs.

Anordnung und Bau von VPR - Fragen dazu

1. The foam does not need to be directly fixed (e.g. glued) to the wall. There might be a gap up to a few mm between wall and foam.

Also (on a different note), there is one thing which G. E. said way back in this post, which I want to understand:

only odd modes are driven by the wavefront

[Nuuk]

Originally Posted by audiothings

Also, a contribution from Nuuk in this post is encouraging me to think this way:

Well, if I understand you correctly, this is almost the opposite of what I was trying to say. As far as I understand the system, a very important part of it is the difference in pressure between the front side and the back. If you remove the rigid backing (which I suppose is the wall you are referring to), you will prevent at least most of this difference in pressure.
If you just wanted to say, that you could mount the foam directly to a wall without any rigid backing in between - that should be no problem at all. What I mentioned in my previous post is, that it should be possible to just "lean" the foam against a wall (as long as there is no gap that is more than a few millimeters). To me that kinda makes sense as a gap that small should not affect the low frequencies.

[Nuuk]

Originally Posted by audiothings

I agree, and for no justifiable reason.
I am hoping that Dax was incorrect (Dax, no offense intended towards you, of course) when he said that

I guess that design should still work. However, I would expect it to be less efficient than a design that would only use the 4 corners to mount the plate. I don't think it is necessary that the foam is compressed. It is glued to the plate and therefore dampens the vibration of the plate. This also makes sense concerning the statement, that steel is the only material that works well (in contrary to wood or aluminium).

We didn't already have this link here, did we? http://www.rpginc.com/products/modexplate/index.htm
Definitely worth a read concerning how the system works.

[daxliniere]

Originally Posted by johndykstra

Attachment 264986

Hi John,
Since your sides are not vented, your design will not have any effect on upper-bass frequencies.

[daxliniere]

Originally Posted by Nuuk

However, I would expect it to be less efficient than a design that would only use the 4 corners to mount the plate.

If you install horizontally (suspended from ceiling) and don't support the middle, the steel sheet is likely to sag. This would result in uneven compression of the foam in the centre of the foam block, which could become an acoustic impedance.

[Nuuk]

Originally Posted by daxliniere

If you install horizontally (suspended from ceiling) and don't support the middle, the steel sheet is likely to sag. This would result in uneven compression of the foam in the centre of the foam block, which could become an acoustic impedance.

Hmm, you're probably right about that one. However, I find it hard to judge without even having seen the used foam at all. At least that should be a problem the commercial solutions would have as well, as they are not glued to the wall.
That whole system looks so simple, but it seems to be so hard to install it properly...

[daxliniere]

Originally Posted by audiothings

I am hoping that Dax was incorrect (Dax, no offense intended towards you, of course) when he said that...

No, I'm not offended. In fact, I'm happy to be proven wrong, if it means we come up with a better design outcome!

So I guess my big question now is about an apparent contradiction;
Somewhere I read that a rigid backing is important (something like "one layer of plasterboard is okay, 2 layers is much better") and the new consensus (which I am very happy about) that the CBA/VPR is simply 'a steel plate with attached damping foam'. The latter would make designing a working module much easier (and cheaper).


I went to the foam supplier yesterday and have some information that may be of interest.

First of all, the Basotect sample that I showed to the shop keeper.
"Wow, I've never seen a foam like this before. It's really interesting!"


The low density 15/70 foam is only available in low quality, since it's designed for packaging/protection uses, not long-term use.
Yesterday, I thought this would be a problem since it even though it might support the weight of a 12kg sheet now, it will deteriorate over time and start to sag, however...
Now that we know that we can suspend the sheet via eyelets, we don't have to worry that the foam is strong enough to prevent sheering. It also means that 'regular' spray-on adhesives can be used, as opposed to high-strength (and high cost) PU adhesives.

For those wondering, this is the hardware I'll be using with my frameless solution:
Stainless Fork Terminals
For those who don't recognise them, see here: Hydraulic Swaged Balustrading - YouTube

There is a 28/80 foam which seems quite good too. Feels more similar to Basotect than the 15/70, but is also twice as dense.

38/200 still seems like a good foam to test.



All the best,

[johndykstra]

Originally Posted by daxliniere

Hi John,
Since your sides are not vented, your design will not have any effect on upper-bass frequencies.

Simple enough to route out some venting in the sides of both the finish and interior frames. However....


I'm guessing a few inches of side frames will not be a sufficient amount to tame this 150-500hz area of a room. Some fiber broadband in combination with vprs will likely be needed regardless. In sight of that, I would imagine a number of these on a wall, with broadband filling the space between vprs.

Not saying my stab at a design should be the end all be all... or that it would even work at all, but I wouldn't pass or fail a design concept on it's incorporation of the 'free meal' high bass absorption via diffraction.

[audiothings]

Somewhere I read that a rigid backing is important (something like "one layer of plasterboard is okay, 2 layers is much better")

Exactly... which is why I put two layers of 19mm plywood (5/8" sheetrock is not available here).

and the new consensus (which I am very happy about) that the CBA/VPR is simply 'a steel plate with attached damping foam'. The latter would make designing a working module much easier (and cheaper).

Not sure we have a consensus here, and absolutely no proof of concept, but this is exactly where we want to be.

Somehow I am reminded of an old folk tale which everyone in India knows, I'll take a short entertainment break, if I may

Six blind men were asked to determine what an elephant looked like by feeling different parts of the elephant's body. The blind man who feels a leg says the elephant is like a pillar; the one who feels the tail says the elephant is like a rope; the one who feels the trunk says the elephant is like a tree branch; the one who feels the ear says the elephant is like a hand fan; the one who feels the belly says the elephant is like a wall; and the one who feels the tusk says the elephant is like a solid pipe.
The king explains to them:
"All of you are right. The reason every one of you is telling it differently is because each one of you touched a different part of the elephant. So, actually the elephant has all the features you mentioned."

[daxliniere]

Nice tale!

Originally Posted by audiothings

we have...absolutely no proof of concept

We have information from 2 or 3 of the people involved in the design of these devices (H. V. Fuchs and one or 2 from Fraunhofer), saying the backboard should be firm, but not necessarily attached to the foam. I thought that was good enough for me.