# Wall panels



## jackboy (Aug 14, 2011)

This maybe a silly question but how do you mount acoustic wall panel?
Can you hang them like a picture with wire across the back ? 

Thanks 
Brent.


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## SAC (Dec 3, 2009)

Yes, you can mount them in that manner.

There are multiple ways to mount them.

Common ways range from "L" brackets mounted to the wall upon which the panels are 'hung'/hooked, to "J" hooks secured to studs attached by small chains or Large cable ties.

Common screw-in door stops can be used as panel standoffs, as can a myriad assortment of ready-made commercially available or homemade simple wood or metal brackets.




But before you go mounting them directly to the wall, please be aware that maximal effectiveness is accomplished by employing a panel with an equal thickness gap between it and the wall.

An absorptive panel is velocity based, and the velocity of the sound wave approached zero at the wall surface, thus moving it further out from the wall will move it closer to the 1/4 wavelength point where velocity of sound is maximum.

Confused?

*Here are a few simple illustrative examples:*

A 2" thick panel (assuming for a moment that it is 100% absorptive - which, in reality, it is not!) is 1/4 wavelength of 8", which corresponds to ~1688 Hz. This is far too high a frequency for the panels to be effective for anything other than _possibly_ controlling flutter echo.

A 2" thick panel mounted with a 2" gap is equivalent to a 4" thick panels mounted directly to the wall. The material nearest the wall provides little help as the velocity of the sound energy is so small. thus it is the material that is moved away from the wall hat is doing the work. 

In this case, the total distance is 4", which is a 1/4 of 16". The frequency corresponding to 16" is 844 Hz. Still too high to be effective as much of the high energy content between ~250 Hz and 844Hz is missed.

In order to be effective and cover a the required wavelengths with maximal energy content, a panels needs to be a MINIMUM of 4 inches thick mounted 4" from the boundary surface. Thus a 4" panels with a 4" gap is equivalent to an 8" thick panel. 8" is the quarter wavelength of 32 inches which corresponds to a wavelength of ~421 Hz.




Therefore, the general guidelines for panels with regard to thickness and density exhibiting the 'proper' gas flow resisteances are:

*General guidelines:*

*Broadband panel absorbers:*

For broad band absorbent panels, the best material density characteristics are either ~3lb/ft^3 Fiberglas or ~4 lb/ft^3 mineral wool.

And the minimum configuration that should be considered for a broadband panel is 4" thick with a 4" boundary gap. (Any thinner and the effective low frequency extension suffers. In other words, they are effective against high frequencies but their ability does not extend low enough to address all of the problem energy.)

This configuration effectively behaves similarly to an 8” thick panels placed flush to the wall (effective to ~420 Hz)


*Low Density Pink Fluffy Stuff for THICK Porous Bass traps:*

The light pink fluffy stuff is ONLY useful for thermal insulation and for very thick low frequency bass traps (e.g. “Superchunk” style corner traps with 2- 2 foot wall facings and a 34” front face) where it outperforms the denser more commonly suggested materials.



A bit more than that for which you asked, but I hope it helps put the topic in a slightly more complete perspective...


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## jackboy (Aug 14, 2011)

Thanks for the info. The product I am buying is called ultratel it's 48kg per cubic meter and I was going to make them only 2" thick I was placing them on screen wall with bass traps in the corners and the floor to ceiling for the first 1.5meters then the back wall with the faced product of ultratel on the whole back wall and then just some little panel placed around with some hard surface left.


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## SAC (Dec 3, 2009)

I suspect that the intended use is to control specular (broadband) reflections. , be careful to note if the Ultratel you are considering is a faced product. You would NOT want to use this (at ANY thickness!) for broadband applications as it is reflective! If for broadband absorbers, use an unfaced variant.

A 2" thickness would be literally worthless for LF applications and of extremely limited value for broadband applications. Note, use of improper thicknesses will simple "EQ" the sound and remove the high frequency component of the energy without solving ANY of the problems caused by early reflections... thus actually aggravating a problem.. Yes, it is possible to create a larger problem!


Without more detailed information, I have questions about your intended application. You do not simply want to randomly apply broadband absorbers, lest you simply render the space 'dead' without addressing the actual anomalous reflections. Not all reflections are bad! Instead you want to make measurements and apply them 'surgically' if and where needed. Have you generated ETC plots and indeed identified the need and optimal placement for said treatments? 

They are not difficult to make and interpret. If you would like help interpreting said measurements, PM me and I would be glad to walk you through it via Yahoo Msgr or Skype.

Also, why would you want to apply a material whose character and manner of application would only (possibly if thicker!) be effective for broadband applications and then use a faced material that is reflective? This application is at crossed purposes...despite gaining a bit of thermal insulation! Simply leave the wall plain and you have the same performance and you will have saved yourself time and money! 

Again, I would seriously suggest a few measurements that will allow you to surgically apply the proper treatment in the correct placed as Needed! Broadband treatment is not to be used as a 'general' treatment, contrary to some impressions you might have gathered from too many places on the web.


Again, see the above suggestions for thicknesses for broadband absorbers.


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## bpape (Sep 14, 2006)

Just for clarity and accuracy - the specs you are stating SAC are correct in terms of direct absorption. For random angles of incidence, the 2" and 4" panels with or without spacing will reach MUCH lower than the 1/4 wavelength related to that particular thickness. A 2-3" thick panel in terms of a reflection panel will function just fine considerably lower. 

I do agree with the air gap being equal to the thickness being optimal while not inducing a hump in the curve. That said, this is not always practical in a non purpose built space, someone's living room, etc.

Bryan


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## SAC (Dec 3, 2009)

The figures cited above were for normal incidence.

At greater incidence we encounter a _*mixed*_ result.

Figuring a 45 degree angle of incidence the effective thickness of a 2" thick panels is now ~2.83", giving a 1/4 wavelength of ~11.3" and an effective frequency of ~1195 Hz. Slightly lower, but not significantly so, and certainly not broadband...especially on a back wall.

Note, with an increase in the angle of incidence, the reactive component of the acoustical impedance of the absorptive material (and its covering!) will increasingly REFLECT energy, thus decreasing the overall effectiveness of the absorptive material.

We could model this is Soundflow or Zorba, but the results are consistent.


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## bpape (Sep 14, 2006)

Agreed on the rear wall if trying to address length modes. For reflections, you're still looking and posting numbers relating to the OPTIMAL absorption, not a lower limit where it falls off to no absorption. Even so, you are still looking at approx 30% change in the optimal lower frequency limit based on thickness vs. wavelength. That's hardly a trivial change.

Also agree on the reflection as the angle gets shallower which is why lighter density materials can actually perform better in this type of application.


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## SAC (Dec 3, 2009)

I am not worried about what constitutes a "significant change" if that change does not result in a significant improvement in performance in the range required! 

That is rather like someone noting that the fire department arrived with all the resources required to extinguish a fire 3 hours after the structure burned to the ground! The resources may indeed be 'significant', but I would hesitate to say hat they were effective...

And per both Ingard and D'Antonio & Cox, the thickness must be _at least_ 1/10 of a wavelength to absorb a significant amount of energy. At a thickness of 2.8" of linear travel still only 2" from a boundary, that puts the low frequency cutoff below which it it utterly ineffective at almost 500 Hz - and that simplified reasoning ignores the fact of the limitation imposed by the boundary to surface spacing and the velocity propagation models. Note, we are not talking of substantial absorptive losses in the region above 500 Hz.

I will even note that even Toole (ironic for a few reasons I won't expound upon here) states in his _Sound Reproduction and Auditory Perception_ that the "typical 1" or 2" sound panel most often affixed to walls works only at relatively high frequencies, and acts to effectively turn down the tweeter with no effect on the mid-range or upper bass, thus unbalancing the sound."

I would be the first to celebrate were such limitations not indeed a fact,and as such I would hesitate to recommend one proceed in spending the money, time and effort in applying treatment with only limited, or worse, an exacerbating effect on the behavior.

ESPECIALLY if one is considering using a _faced_ substrate which will negate just about ANY beneficial behavior at the frequencies of interest - regardless of thickness.

But with this I think we have made our derivative points, and I will leave it at that... Just LOSE the faced broadband material, whatever else you choose to do!! :yikes:


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## jackboy (Aug 14, 2011)

Oh ok I am lost now?


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## SAC (Dec 3, 2009)

Relax, all is OK and easily sorted out! PM me!


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## Prof. (Oct 20, 2006)

jackboy said:


> Oh ok I am lost now?


Ultratel is not faced and has been used very effectively in both bass traps and wall panels..


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## SAC (Dec 3, 2009)

Just a bit more info regarding the available material formats...

Ultratel is available un-faced or with a variety of facings. 

If sourced from a distributor whose most common commercial client uses the material for its intended primary use, duct lining, then the most commonly available form will most likely have some type of facing - as this was developed specifically to minimize the accumulation of detritus in ducts. 

Make sure you do not get the faced variant.
The faced varieties are not appropriate for broadband absorption.


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## jackboy (Aug 14, 2011)

Hey Mark,
Did you get that lay out?


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