Covering Superchunks & Linacoustic

[Vinculum]

Hi,

I have a few questions for the experts if you don't mind!

I'm installing superchunk basstraps in the front corners of my home theater. I am also using OC's version of Linacoustic to cover the front wall, and a few feet up the sides. This of course is going to be behind an acoustically transparent projector screen.

My main question is can I just overlap the Linacoustic over the superchunks to hold them in place and maintain a dark color without loosing the benefit of the bass traps?

Next is, I have 1" thick Linacoustic. One side of it has a thin dense layer on it. I assume this is the side I place against the wall and leave the fluffy side towards the listening area?

Am I ok to put 2 layers of this up for a total of 2", or will the thin dense part on the second layer have a detrimental effect on the functionality of the first piece?

Many thanks!
Dr Vinculum

[DanDan]

I googled Linacoustic, seems there are a few...
If you can breathe or blow through the stuff it will be fine fronting any traps.
I would assume the dense layer is meant to face the world, to keep the fluffy stuff in. If you can breathe through the dense side, it is fine to use it as a facing or inside a sandwich. However if it is an impermeable backing/mounting layer, the opposite applies.
I am not sure that you need to cover the front wall. Take a look at the article on Front wall absorption at RealTraps.com
DD

[Vinculum]

I haven't yet tried blowing through the treated side. I did some searching around and it seems most put this side towards the room (but some dont!) More searching...

Ethan's article on front wall absorption doesn't mention the fact that some sound bounces off an acoustically transparent screen right back at the front wall. Perhaps he didn't have this type of setup in mind when he wrote the article?

Thanx,
Dr Vinculum

[DanDan]

Doctor, the screen cannot simultaneously be acoustically transparent and bounce sound. Also, what sound is there to bounce back there?
DD

[Vinculum]

Originally Posted by DanDan

Doctor, the screen cannot simultaneously be acoustically transparent and bounce sound. Also, what sound is there to bounce back there?
DD

Sure it can. It is not 100% acoustically transparent. Play pink noise and vary the distance of a swatch of any "acoustically transparent" material and you'll hear combing from from the sound bouncing around exactly like in Ethan's comb filtering video. The trick is to make the distance large enough to move the notches out of band, or to a least destructive region.

Dr V

[DanDan]

Indeed nothing is perfect. You have things on your mind I cannot telepathically read, although I try :-)

Would I be right in guessing this screen is probably quite a ways from acoustically transparent? Do you have a speaker in the void between the wall and the screen? If so then I can see your ambition. Kill any flutter between screen and wall.
I would point out though, that the screen can only be reflective at HF. The speaker's output at HF is quite directional. Thus a fairly small patch of absorbent material behind the speaker or perhaps even in front it should kill any splatter.

Back to the question. Apart from dubious benefit, as in Ethan's article, there is also little or no harm in covering the front wall. Maybe it's a 'look'. If you wish to link me to whatever version of Linacoustic you are using, I am willing to read the specs and so on to determine which side to face out.
DD

[Vinculum]

DD,

Correct, the speakers will be in the void between the screen and the wall. Here is a link to the screen material if you are curious of its properties. It is probably not much more restrictive than a "speaker grill".

Seymour AV | Center Stage screens


I'm actually going to use the Owens Corning equivalent that a friend has left over from a project. I also have a little bit of the Linacoustic, which is a Johns Manville brand name. Same stuff. Here is a link to the Linacoustic RC.

http://www.jm.com/insulation/perform...coustic_rc.pdf

I can blow through the coated side, and from my deep google searches It appears most people are putting the coated side towards the listening area. I just haven't read any acoustics professional directly say this is the correct way to do it. (yet?)

Just finished my superchunk bass traps, next up is putting this stuff up on the wall.

I probably should have just went to a home theater oriented forum to ask, but I like to take different avenues every so often. Thanks for your interest!
Dr V

[SAC]

If the Linacoustic stuff is faced with FRK/FSK (I know that's a product specific nomenclature, but I am using it generically), you will apply it facing out on the surface, but you do not want such layers interspersed/layered internally inside the trap.

As far as sound reflecting off an 'acoustically transparent' surface, it happens normally with all such applications; with the degree of reflection increasing with the incident angle. This happens with 'all' such facing materials and is an all too commonly ignored aspect of panel 'absorbers'. Hence a reason to not only measure sound pressure levels with respect to amplitude reduction, but to look at iterative ETCs during the application of treatment to ascertain the actual amount of energy being reflected that is often neglected but which may be detrimental (depending upon orientation to the listening position).

(Pardon me if I don't have the specific configuration down, but the solution will be essentially the same regardless...) If sound sources are placed behind the screen, and the concern is energy reflecting off the screen back towards the wall... And it then goes where? Back towards the screen? Basic ray tracing models can anticipate this. I guess my concern is not so much that it may be reflected back to the wall, but what happens afterward. If the reflections are then able to reach a listening position, then there is a problem. If the partially damped lower level reflections are simply returned to the wall and then impinge upon the screen once more at a low enough level that they are not destructive to intelligibility and imaging (10 - 20 dB down), then there really isn't much of a 'real' problem.

Again, an ETC response provides information about the reflections and would indicate the delayed arrival time as well as if they are of sufficient amplitude to be a real issue requiring mitigation, or simply a 'conceptual' problem that we can debate here.

[DanDan]

In the picture fully now :-)
Those duct liners have that coating to keep loose fibres out of our air stream. Thus the 'coated' layer should be the exposed one. If it suits you visually and financially, a decent choice. Although, I am still pretty sure it is not necessary acoustically.
A layer of it or other absorbent on the screen in front of the speaker, should prevent any back scatter, with only minimal HF attenuation. This would have the added effect of preventing HF flutter between the screen and the speaker front panel.

DD