Fiberboard or Homasote as panel surface?

[jgastineau]

I have panels built with 5.5" mineral wool. In order to get a cleaner look when covering with fabric, what would be the acoustic consequences of facing the panel with 1/2" fiberboard or Homasote rather than applying the fabric directly over the framed mineral wool? Thanks in advance. Jeff

[AVare]

I have panels built with 5.5" mineral wool. In order to get a cleaner look when covering with fabric, what would be the acoustic consequences of facing the panel with 1/2" fiberboard or Homasote rather than applying the fabric directly over the framed mineral wool? Thanks in advance. Jeff

Both materials have such high resistance that it would destroy any low frequency absorption. If you want high physical protection, I suggest perforated metal. Special ordered it may be expensive, but in this application just about any perforation pattern would be good so end of runs, lft overs etc are all good.

Andre

[Soundman2020]

I suggest perforated metal. Special ordered it may be expensive,

Depending on the size of the panels, one simple source of perforated metal panels, is the metalwork made by manufacturers of standard 19" equipment racks. You can get perforated shelves, rack blanks, side panels, top panels, etc. I have used those on some studio desks where I wanted them to have as little effect as possible on the room acoustics, so instead of having solid rear surfaces on the desk, it was all perf panel, made from standard rack blanks. It's still not cheap, but as Andre mentioned, it's still cheaper than getting special order perf panel made up for you.

If you are just looking to keep the fabric taught and looking neat without the insulation making it bulge out, then what I normally do is to make the panel deeper and set the insulation back a bit form the front, and use some type of cheap plastic mesh to hold the insulation back. For example, the type of plastic mesh sold in gardening stores to control weeds, or keep insects off the plants, or even the type of mesh used to make fly-screens for windows and doors. Staple that about a half inch deep inside the front of the frame of your panel, stretched tight across, to keep the insulation in place. Then stretch your fabric across the actual frame itself.

In other words, if you want to use 4" insulation with 1x6 planks for the frame, then your frame will be 5-1/2" deep. So place the mesh 1/2" away from the front edge of the frame, put your 4" of insulation in, then more mesh an inch in from the rear of the frame (to prevent the insulation from bowing out backwards). So you have an inch air gap at the back, then mesh, then 4" of insulation, then mesh, then 1/2" of air, and finally the finish fabric across the front.

That way, neither the plastic mesh nor the insulation can touch the fabric, so it stays tight and flat across the front.

It works for ceiling clouds too. You can see how this technique gives a nice clean, crisp look to the panels, in these images from the control room at Studio Three Productions:

RDMOUS-Control-Room-Final-690x400.png

RDMOUS-M-CR-Side-.jpg

- Stuart -

[jgastineau]

I have panels built with 5.5" mineral wool. In order to get a cleaner look when covering with fabric, what would be the acoustic consequences of facing the panel with 1/2" fiberboard or Homasote rather than applying the fabric directly over the framed mineral wool? Thanks in advance. Jeff

Both materials have such high resistance that it would destroy any low frequency absorption. If you want high physical protection, I suggest perforated metal. Special ordered it may be expensive, but in this application just about any perforation pattern would be good so end of runs, lft overs etc are all good.

Andre

Thanks Andre. Your response was almost the opposite of an earlier response from knightfly to a similar question. Since his response was admittedly based on conjecture, how strong do you feel about your response?

Homasote, Celotex ...

...If I were trying for more low absorption (at the cost of mids/highs) I might consider FACING an absorbent trap with the stuff, but at the moment I have nothing beyond conjecture to back that up.

[jgastineau]

If you are just looking to keep the fabric taught and looking neat without the insulation making it bulge out, then what I normally do is to make the panel deeper and set the insulation back a bit form the front, and use some type of cheap plastic mesh to hold the insulation back. For example, the type of plastic mesh sold in gardening stores to control weeds, or keep insects off the plants, or even the type of mesh used to make fly-screens for windows and doors. Staple that about a half inch deep inside the front of the frame of your panel, stretched tight across, to keep the insulation in place. Then stretch your fabric across the actual frame itself.
- Stuart -

Thanks Stuart, good tip!. I had considered plastic mesh or chicken wire below the fabric but not recessed as you suggest.

[AVare]

I have panels built with 5.5" mineral wool. In order to get a cleaner look when covering with fabric, what would be the acoustic consequences of facing the panel with 1/2" fiberboard or Homasote rather than applying the fabric directly over the framed mineral wool? Thanks in advance. Jeff

Both materials have such high resistance that it would destroy any low frequency absorption. If you want high physical protection, I suggest perforated metal. Special ordered it may be expensive, but in this application just about any perforation pattern would be good so end of runs, lft overs etc are all good.

Andre

Thanks Andre. Your response was almost the opposite of an earlier response from knightfly to a similar question. Since his response was admittedly based on conjecture, how strong do you feel about your response?

Homasote, Celotex ...

...If I were trying for more low absorption (at the cost of mids/highs) I might consider FACING an absorbent trap with the stuff, but at the moment I have nothing beyond conjecture to back that up.

Was this for 5.5" of absorbent material? Or are you quoting out of context?

Andre

[Soundman2020]

Your response was almost the opposite of an earlier response from knightfly to a similar question. Since his response was admittedly based on conjecture, how strong do you feel about your response?

Homasote, Celotex ...

...If I were trying for more low absorption (at the cost of mids/highs) I might consider FACING an absorbent trap with the stuff, but at the moment I have nothing beyond conjecture to back that up.

Link? What was the context of that comment? What was he talking about there? The identical situation you are talking about?

Facing acoustic panels with something thick, rigid and massive is going to create a whole bunch of problems for that to work as a broadband trap, as Andre said. In order for the sound to be absorbed, it has to reach the insulation. If you put a reflective surface over it, then it can't reach the insulation. I'm assuming you built 5 1/2 panels because you want broadband absorption that goes down low. If you put that thick, heavy reflective surface in front of it, it certainly won't be broadband, since it will reflect back most of the sound into the room, so it would never reach the absorption.

And if the frame is sealed to the wall, then you no liner have a simple absorber; you would turn it into a panel trap, which is very different: it is a tuned device that absorbs only one narrow range of frequencies, reflecting all others....

What do you want the panel to do? What is it's purpose?

- Stuart -


(PS. I'm pretty sure that Andre is very confidant of his answer: I am too.... )

[jgastineau]

Here is the link to knightfly's post. It was a response to someone wanting to BACK a 2" 703 panel with homasote. His comment was suggesting a homasote FACE would be what he would consider.

http://johnlsayers.com/phpBB2/viewtopic ... t=homasote

Yes, I was looking at these as broadband absorbers, and had no knowledge of what homasote would do in this context (I initially thought it might act like 1/2" of 703), so I can rule that out as a surface based on the feedback here.

Thanks

[Soundman2020]

Thanks for the link. Now that it is in the full context, it makes sense.

If I were trying for more low absorption (at the cost of mids/highs)

I think that's clear. Facing it with a panel (and assuming it is sealed to the wall) would indeed increase low frequency isolation, at a specific frequency, and would greatly reduce the id and high frequency isolation, since they would never "see" the insulation at all.

That said, I can't see Homasote making a good panel trap either! I'd have to do some math to check, but it seems to me that the density is too low, the thickness to high, and the material itself is too soft, to work well for a panel trap. Generally you want a thin, rigid, dense material for that, such as plywood or MDF. Either that, or a thin flexible dense material, such as MLV, if you wanted a limp membrane trap.


- Stuart -

[AVare]

Here is the link to knightfly's post. It was a response to someone wanting to BACK a 2" 703 panel with homasote. His comment was suggesting a homasote FACE would be what he would consider.

http://johnlsayers.com/phpBB2/viewtopic ... t=homasote

Yes, I was looking at these as broadband absorbers, and had no knowledge of what homasote would do in this context (I initially thought it might act like 1/2" of 703), so I can rule that out as a surface based on the feedback here.

Thank you for the link. He was not recommending, he was describing a direction of research.

Andre

[DanDan]

I think it was Desart who wrote of using layers of high density fibre in conjunction with light, resulting in a somewhat membrane like behaviour. I often specify a drop ceiling using Polyester Tiles with a layer of light attic insulation over them. I hope it works! High density batt traps on their own have an obvious panel trap type resonance.
I am dubious as to Homasote too but who knows. Thus conjecture.
Here's another in between behaviour. Pegboard on SoffiTraps. Very broad resonant absorption it would appear.
Thanks to our friend Jeff Hedback for the in situ measurement.

4-28-13 t60 progress.jpg

DD

[nona5000]

Truly, I was taking a gander at these as broadband safeguards, and had no information of what homasote would do in this specific situation (I at first idea it may act like 1/2" of 703), so I can decide that out as a surface dependent on the criticism here.