Acoustic panels: how far to mount from wall?

Ethan Winer · Post by **Ethan Winer** » Sat Jul 17, 2004 1:24 am

PR,

> Even a little loss will take the edge off of rings and nulls <

I agree with this. To get a deep null requires that the original and reflected waves be nearly equal in level. Even a little bit of absorption can be enough to raise a 35 dB null up to only 15 or 20 dB deep.

> If you make your present absorber effectively 4" thick ... the effect at 50-200Hz bass frequencies will be almost none. <

I have to agree with Eric here. Regardless of theory, that just isn't the case in practice. One of my first tests with fiberglass-only bass trapping (years ago) was four inches of 703 mounted flat on the walls, but near the corners. In my partner's 16x10x7.5 foot control room the improvement at all but the very lowest frequencies was substantial. Even with that small an amount of 703, and not even straddling the corners, made a big improvement to well below 100 Hz.

--Ethan

PRR · Post by **PRR** » Sat Jul 17, 2004 5:56 am

Eric-

I am sorry if I offended you.

Has Ren Man got the help he seeks?

Eric_Desart · Post by **Eric_Desart** » Sat Jul 17, 2004 6:21 pm

Hello PRR,

Your comments were not offensive, nor was I offended.
And having read several messages I know you're intelligent and are able to help lots of people.

So my response didn't meant anything else than what I wrote.

There is too much misinformation on the net, which tends to get it's own live and becomes gospel.
So a good approach is to wonder: Do I know what I think to know?
If not tell it as an assumption, leaving questions open for discussion.
Visitors seeking help mostly won't be able to distinguish this in your place and just accept what you write as fact.

Warm regards
Eric

Ren Man · Post by **Ren Man** » Sat Jul 24, 2004 8:34 am

Three or so weeks have passed since I first posted what I considered to be a relatively simple question- Will remounting my 4" thick fiberglass panels 4" (or even more than 4”) from the wall (instead of their current 1 " mounting distance) make a significant improvement in low frequency absorption?
Let me say first that I fully realize that I've made some blunders in my control room layout that have compromised the acoustics to a certain degree. I wasn't really looking to open that can of worms; but when Knightfly requested further information, I thought "I really don't want to impose on these guys, but they seem eager to address the problem in depth, so I'll give it a shot."
I provided all the requested information with an air of anticipation that somehow I might possibly end up with some real solutions to my problem.
Not to look a gift horse in the mouth, but so far not much has occurred except what I can only describe as some high level "fencing matches" between the advocates of the different schools of thought. And still my original question goes unanswered…
Jeez guys, don't be offended but why make it any more difficult that it needs to be?
I realize that I'm not surfing the crest of the cutting edge in acoustic science; that level of thinking is way out of my league. Sure' Ill study and do as much research as I can handle, but I'm more of a hands on type of person. The type of stuff I've seen on Ethan's site is what I'm talking about- "Real-world workable solutions for the working man" if you will.
I'm not a scholar by any stretch, but I've studied as much as I can get my hands on over the past 10 or so years. The conclusions I've come to are A) that there are as many opinions as there are people in the field and B) most of them are right to one degree or another, and finally C) acoustics is as much art as it is science.
So where does that leave me? To hire some high level design firm like Russ Berger to come in and tell me what I already know- my design is flawed and the only real workable solution requires more money to correct it than I can earn in a lifetime; or slog it out as I have been doing and try to make it as good as I can with what I have along the way.
You have a great forum here, with the potential to do a lot to benefit the creative community. I hope you guys don’t lose sight of that.
Again, no offense, but to me it’s about creating music worth listening to and getting it out there without having to heal-toe to the “record industry”.

Eric_Desart · Post by **Eric_Desart** » Sat Jul 24, 2004 8:55 am

Ren Man wrote:Three or so weeks have passed since I first posted what I considered to be a relatively simple question- Will remounting my 4" thick fiberglass panels 4" (or even more than 4”) from the wall (instead of their current 1 " mounting distance) make a significant improvement in low frequency absorption?.

Yes it will and the more distance the better (within reason, but for random incidence with 4" you can easyly go to 1.5' cavity, for straight incidence a bit more carefull).
I also gave 2 links. Have you looked at them? They about answer your question.

You can have a look to this link:
http://www.bobgolds.com/AbsorptionCoefficients.htm
and
http://johnlsayers.com/phpBB2/viewtopic ... highlight=

If you want to play with thickness and cavities you can use the file of ChrisW which is one of the better Excel files on the net.
http://www.rmmpnet.org/members/ChrisW/index.html
You can fill in a thickness for the wool and play with the cavity as well as with the angle of incidence. The real live truth will be an average over the angles. But the file gives you a very good principle approach.

And if you put boards in the corners they become even more effective and you can find here:
http://www.bobgolds.com/studiotips.htm
And another thread with graphs for corner absorption you can find here:
http://www.recording.org/postt20156.html
And John Sayer solutions you can find here:
http://www.johnlsayers.com/HR/index1.htm

Ethan Winer · Post by **Ethan Winer** » Sun Jul 25, 2004 1:39 am

Ren,

> Will remounting my 4" thick fiberglass panels 4" (or even more than 4”) from the wall (instead of their current 1 " mounting distance) make a significant improvement in low frequency absorption? <

It depends on how you define significant, but I'd say Yes it's worth doing.

> The type of stuff I've seen on Ethan's site is what I'm talking about- "Real-world workable solutions for the working man" if you will. <

Thanks. I'll also mention that this issue is explained in my Acoustics FAQ, in the section "Optimizing the Air Gap." I came to the conclusion that the optimum gap size is the same as the material thickness.

--Ethan

Sen · Post by **Sen** » Sun Jul 25, 2004 12:32 pm

Ethan Winer wrote:I came to the conclusion that the optimum gap size is the same as the material thickness.

--Ethan

Ethan, that's great news

So, if you're using 3" thick f'glass, the optimum distance to mount them from the surface is 3"?? How low down the frequency range is this theory gonna work?...actually I beteer go and read your "optimizing air gap" article...

thanks

Sen · Post by **Sen** » Sun Jul 25, 2004 12:35 pm

I couldn't get your site to open

Eric_Desart · Post by **Eric_Desart** » Sun Jul 25, 2004 7:02 pm

Edited.

I respect truth and genuineness too much.

knightfly · Post by **knightfly** » Sun Jul 25, 2004 10:04 pm

Christopher, you may have missed my announcement in the Construction forum regarding my wife's auto accident - my wife can get into and out of bed unassisted as of yesterday, and has been trying to do too much even before that.

I haven't had much time to spare or I'd have finished up our original conversation, including recommendations on the changes in absorber positioning - I hope to get this finished in the next couple of days, in between the dozens of phone calls and tons of paperwork involved in totaling a car, etc -

Ethan, Eric - my comment from the accident thread,

"As I've said before, I couldn't be more proud of a group of friends; everyone here has helped keep this board one of the friendliest, most helpful places of its kind on the internet; I can't thank you enough. "

should be indicative of what I believe a site like this should be - please keep posts to civil and accurate information, and don't even THINK of bringing your eternal feud to this board - there are a few moderator privileges I do NOT want to have to use. Personal attacks are NOT allowed; proper rebuttals and arguments ARE.

I hope I make myself perfectly clear on this - if not, please feel free to contact me privately for a clarification... Steve

Eric_Desart · Post by **Eric_Desart** » Sun Jul 25, 2004 10:18 pm

Steve,

That's an easy one.
I remove my message.

For me science is abouth truth and genuineness and responsibility.

Goodbuy.
Eric

Ethan Winer · Post by **Ethan Winer** » Sun Jul 25, 2004 10:30 pm

Sen,

> How low down the frequency range is this theory gonna work? <

"Work" is relative. It's not like rigid fiberglass absorbs 100 percent down to some cut-off frequency, and then stops absorbing completely. Rather, it absorbs completely above a certain frequency, then falls off gradually below that. Three inches of rigid fiberglass spaced three inches off the wall should absorb pretty well to 100-200 Hz anyway.

--Ethan

Ethan Winer · Post by **Ethan Winer** » Sun Jul 25, 2004 10:37 pm

Steve,

> Ethan, Eric - my comment from the accident thread ... don't even THINK of bringing your eternal feud to this board <

I'm not sure what you're referring to. I just reviewed all of my posts in this thread, and the only evidence of a feud I see is the last few posts by Eric where he apparently edited out some insults. Yawn - so what else is new?

It should be clear by now that all insults come from him, never me. This is a perpetual problem, but one I have no control over. Accordingly, you should address your warnings to Eric, not me, since he's the source of all ongoing friction.

--Ethan

Ren Man · Post by **Ren Man** » Mon Jul 26, 2004 2:43 am

Knightfly,

Please accept my apologies. Just read the other thread regarding your wife’s auto accident. I had no idea. Being a relative newcomer to this forum I really don't know you; but at the risk of sounding too familiar, my hopes and prayers are with you and your wife- for her full and speedy recovery and quick return to what you would consider normal, productive lives.
In the search for the car crash thread I came across another thread where you are describing your work schedule, construction/remodeling plans, etc. In that respect there are many parallels between our lives, and I would assume, between the lives of many others who frequent this forum. Again, at the risk of sounding too familiar, why do we do the things we do? What is it that drives us with such insatiable curiosity toward these goals and aspirations? Is it the thrill of the hunt? The desire to outwardly manifest the treasures deposited deep in the strata of our being?
I've just been through another Atril Fibrillation episode this last week. Every time this happens I search for the meaning behind it, and reevaluate my life, where I'm going and what has real meaning.
Some of the hardest things in life yield the greatest treasures.
Best wishes, Christopher

Ren Man · Post by **Ren Man** » Mon Jul 26, 2004 2:57 am

Ethan,
." I came to the conclusion that the optimum gap size is the same as the material thickness.
Thanks. Another "real world" gem.
I Appreciate your response. Obviously I need to go back to your site with my mining helmet on and do some more study.
Eric,
I did look at the links you posted. Thanks. I'm the type of person who has to pound on the nail quite a few times, frequently pulling the bent and useless nail out and starting again with a new one, before getting the pieces to stick together. One of my better (if you can call it better) attributes is that I'm too stubborn to quit. It may take me a while but I'll get it.
Christopher