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-   -   airspace behind absorption panel (https://www.gearslutz.com/board/studio-building-acoustics/1311829-airspace-behind-absorption-panel.html)

gearstudent 22nd May 2020 10:40 PM

airspace behind absorption panel
 
Hello,

I am in the process of making some acoustic panels. They have 2" wedge foam on the exteriors and cardboard backing. I am going to hang them on the walls like lightweight pictures.

I also placed 1" foamular (lightweight rigid building foam) behind the cardboard. I read that if you create an airspace behind the panel, it extends the bass absorption by a little bit. It also allows for the addition of 1" 703 paneling behind the main panel in the future. So my panels have a 1" airspace behind them. It's not solid foamular. I cut it out like a picture frame, so it's like a rectangle picture frame made out of foamular.

Is there a lot of real-world gain by creating a 1" airspace behind the panel? I read something like "acoustic energy" or "acoustic velocity" is greatest at the boundary. So maybe my 2" foam is acting sub-optimally if it is not flush against the wall. I could actually be making my panels less effective. But I don't know.

It's quite time consuming creating the 1" airspace backing. So I could be talked out of it, even though it allows for nice backlighting effects.

Starlight 23rd May 2020 04:59 PM

Can I just stop you for a minute?

You asked (here) about foam before and avare said it without mincing words:
Quote:

Originally Posted by avare (Post 14704436)
You have so many misconceptions.

Rather than continue that discussion you started another about foam and fabric (here) about which I asked you:
Quote:

Originally Posted by Starlight (Post 14740324)
Why foam?

Rather than answer that question you are now starting another new topic about foam, cardboard and foamular. Maybe by now you can see the pattern of advice you are getting and can predict what the advice will be regarding these materials.

If your intention is to keep starting new topics until you hear what you want to hear - that foam, cardboar and foamular are ideal for acoustics - then I fear you will be dissapointed. If, on other hand, you are open to hearing what works best and what is the best value for money then here is one of the right places.

I am sorry to be the bearer of unwanted news. Hopefully you will heed the warnings before you spend your budget on expensive or ineffective products.

FreakinPavel 24th May 2020 06:45 PM

If you will make panels from mineral or glass wool later, AcousticInsider says, that air gap between a panel and a wall shouldn't be bigger than thickness of wool layer itself.

p.s. so much videos on youtube about it, f.e. Bobby Owinski 2-hours lecture.
Foam is useless

Kyle P. Gushue 24th May 2020 08:22 PM

Quote:

Originally Posted by FreakinPavel (Post 14758788)
If you will make panels from mineral or glass wool later, AcousticInsider says, that air gap between a panel and a wall shouldn't be bigger than thickness of wool layer itself.

p.s. so much videos on youtube about it, f.e. Bobby Owinski 2-hours lecture.
Foam is useless

There's no rule about the gap. In fact common test data for 2" rigid fiberglass includes mounting which is 16" away from the boundary.

Foam is not useless when used properly, where it is effective.

avare 24th May 2020 09:44 PM

Quote:

Originally Posted by FreakinPavel (Post 14758788)
If you will make panels from mineral or glass wool later, AcousticInsider says, that air gap between a panel and a wall shouldn't be bigger than thickness of wool layer itself.

p.s. so much videos on youtube about it, f.e. Bobby Owinski 2-hours lecture.
Foam is useless

If you want the short answer about gaps read post 5 in Q 4 Avare if you want a more complete answer read the entire thread.

Note it is over a decade old and still unknown for most part here.

gearstudent 24th May 2020 10:20 PM

Quote:

Originally Posted by Starlight (Post 14756282)
Can I just stop you for a minute?

You asked (here) about foam before and avare said it without mincing words:

Rather than continue that discussion

There was no discussion to continue. The advice given was "go read a book", and was done so in a dismissive way. The actual question was not answered.

Quote:

you started another about foam and fabric (here) about which I asked you:
The question was not about foam. It was about fabric... completely different topic.

Quote:

Rather than answer that question...
I didn't see the point in answering a deflective question. My question was about fabric, not about justifying the use of foam. But if it humours you, I went back and answered the deflective question.

Quote:

If your intention is to keep starting new topics until you hear what you want to hear
My goal is to fit my understanding to known data, not the other way around. Misses in acoustics are expensive in time, money, environmental waste, and space. Acoustics is mathematical and doesn't care about my opinion or anyone else's. I'm seeking the science.

Quote:

- that foam, cardboar and foamular are ideal for acoustics - then I fear you will be dissapointed. If, on other hand, you are open to hearing what works best and what is the best value for money then here is one of the right places.
My two questions on this topic (never actually answered on the forum at the time of this writing, which is o.k.) have always been about *airspace*... not the materials comprising the panels.

Quote:

I am sorry to be the bearer of unwanted news.
There is no need to say you are sorry, and there is no possibility for unwanted news, unless the news is inaccurate. This is because, as explained earlier, I don't seek a pre-desired answer to my question... only accurate news is desired. And that news was never given at the time of this writing (i.e. the question was never answered).

I found this in the Alton Everest book:
"The mounting method has a major effect on the absorption characteristics of the material. For example, the absorption of porous materials is much greater with an airspace between the material and the wall."

Also from the Alton Everest book:
"Effective low-frequency absorption can also be achieved by spacing the porous absorbent out from the wall. A spaced porous absorber can be as effective as a non-spaced absorber of the same thickness. This is an inexpensive way to get improved performance—within limits."

I saw corresponding airspsace-is-good statements repeated among several acoustics materials companies, and did not find any other academics or industrial entities with contrasting statements. So my conclusion, based on statements of multiple professional sources, is that a reasonable amount of airspace behind an absorber panel is not harmful, and is even helpful.

avare 24th May 2020 10:46 PM

You are to funny.
Quote:

Originally Posted by gearstudent (Post 14759209)
There was no discussion to continue. The advice given was "go read a book", and was done so in a dismissive way. The actual question was not answered.

My reply was "You have so many misconceptions. Read the chapter Absorption in MHoA." You obviously did that from the following

Quote:

I found this in the Alton Everest book:
"The mounting method has a major effect on the absorption characteristics of the material. For example, the absorption of porous materials is much greater with an airspace between the material and the wall."

Also from the Alton Everest book:
"Effective low-frequency absorption can also be achieved by spacing the porous absorbent out from the wall. A spaced porous absorber can be as effective as a non-spaced absorber of the same thickness. This is an inexpensive way to get improved performance—within limits."

I saw corresponding airspsace-is-good statements repeated among several acoustics materials companies, and did not find any other academics or industrial entities with contrasting statements. So my conclusion, based on statements of multiple professional sources, is that a reasonable amount of airspace behind an absorber panel is not harmful, and is even helpful.
For people not familiar with all of Everest's writings that is like from the chapter on absorption in Master Handbook of Acoustics (MHoA).

bert stoltenborg 25th May 2020 08:24 AM

Quote:

Originally Posted by avare (Post 14759154)

Wow, thanks! heppy