Room modes, calculated versus measured

Posted: Mon Mar 21, 2005 11:30 am

Franck,

I think that open office can handle most Excel files, BUT not all.
The ones with complex programming fail. But most of them will work perfectly.

And indeed open office is free.

Twisted Evil

The rest is for our Love-Cow

Posted: Mon Mar 21, 2005 11:33 am

lovecow wrote:

Franck: PM me. I am not inclined to get too deep into Walker and Bonello here. They are useful predictive measures in the right hands - 'nuff said. Pontificating further on the pros/cons here would be getting, er, "tangential" to the discussion. Can o' worms and all that... Smile

Sounds reasonable! Laughing

I'll PM you later today.

Franck

Posted: Mon Mar 21, 2005 11:38 am

Frank, you will have to use email to contact Jeff as only RO club members have access to PM functions.

Posted: Mon Mar 21, 2005 11:46 am

Thanks for the tip David! /Franck

Posted: Mon Mar 21, 2005 12:29 pm

Quote:

Now all we need is an explanation for why one type of wall versus another would shift the modes, and by what mechanism, and why they shift up rather than down.

Please read the beginning of my piost. You are looking at the ROOM, not the modes exclusivley!

Andre

{edit} Put it in engklish.

Posted: Mon Mar 21, 2005 1:23 pm

Paul,

> Out of interest what reasons did these nay-sayers put forward as to why they disagreed? <

Typical comments were unscientific and mostly along the lines of this:

"All that does is sell a few more bass traps to people who hope to remedy a bad situation."

--Ethan

Posted: Mon Mar 21, 2005 1:26 pm

Lee,

> Dennis Erskine has standardized on stiff walls precisely to minimize the discrepancy between predicted and measured results. <

Yeah, and Wes Lachot has said something similar. But I'd rather have lossy walls that reduce the need for bass trapping in the first place.

--Ethan

Posted: Mon Mar 21, 2005 1:30 pm

Ethan Winer wrote:

Yeah, and Wes Lachot has said something similar. But I'd rather have lossy walls that reduce the need for bass trapping in the first place.

One of the questions that's implied here, though, is do "lossy" walls improve a bad situation, or just create a new bad situation? Confused

Posted: Mon Mar 21, 2005 1:31 pm

Bob,

> What if the 42 hz isn't a modal peak at all. <

Sorry for the confusion. That particular graph is from a different room! (My living room.) I posted it only to prove that ETF is not in error because it gives the same results as static sine waves.

--Ethan

Posted: Mon Mar 21, 2005 1:42 pm

Jeff,

Thanks for all your excellent explanations.

> do "lossy" walls improve a bad situation, or just create a new bad situation? Confused

<

I dunno, you tell me. Very Happy

Seriously, on the surface it would seem that lossy walls are pretty valuable. But this obviously depends on how lossy, and also what's beyond the walls. If you put thin sheet rock a few inches in front of a concrete boundary, and don't fill the gap with fiberglass, there might be some very narrow band absorption that also rings. And you still have the massive wall just beyond the sheetrock, so that will reflect back anyway. Or am I missing something?

If you'd care to expound on the various pros and cons of lossy walls versus rigid, I'd love to hear it. Thumbs Up

--Ethan

Posted: Mon Mar 21, 2005 1:48 pm

Ethan

Quote:

Sorry for the confusion. That particular graph is from a different room!

Opps

Posted: Mon Mar 21, 2005 1:50 pm

Ethan Winer wrote:

If you'd care to expound on the various pros and cons of lossy walls versus rigid, I'd love to hear it. Thumbs Up

Can o' worms #739 for this thread... Confused

IMO, there are pros and cons for both.

But I'd really rather not "go there" in this thread. Smile

Posted: Mon Mar 21, 2005 1:59 pm

i don't mind going there Very Happy

but i support you acoustics combatants disregarding this poor wall mechanics dudes thoughts, lol

IMO, the only sensible comment on this topic is from Eric, when he says "check it energetically". I doubt you can build a wall with <10dB of TL EXCEPT AT SEVERE RESONANCE POINTS, and 10dB of TL means 90% of the mess remains in the room.

And furthermore, absorption of these walls is peaked AT RESONANCE POITNS, and NOT PROGRESSIVELY INCREASING AS FREQUENCY GOES DOWN. The absorption figures generated by TL tests are questionable, i know, but i'll put up every stinking figure Audio Alloy gets to back this assertion if i have to. Very Happy

for example, the TL of a panel of finite size won't steadily drop ala Mass Law, but will at some point flatten or reverse and TL will start rising due to size effects (interaction of the sound waves with things small relative to their dimension)

also for example, the TL of a normal wood stud wall will be at a minima at the resonance point, and unless it's wildly enormous in size, it won't again reach this low of a value.

finally (lol, i'm just happily ranting folks) STIFFNESS ISN'T THE OPERATIVE WORD, MASSIVE IS.

the amount of bending in a wall isn't stiffness controlled at low freqs, it's mass controlled. using some liquid nails to stiffen your wall won't cause mystic improvements in TL at 50hz, but quadrupling the mass will, etc.

all i want in life now is a Very Happy

smiley that is about 2" tall, then this post would be complete

take care everybody

Brian

Posted: Mon Mar 21, 2005 2:01 pm

Bob,

Also, while you're here, great job on the web based mode calc. I agree that avoiding having to download an .EXE program is a worthy goal. Even worse are .EXE program that must be "installed" rather than just run directly.

--Ethan

Posted: Mon Mar 21, 2005 2:04 pm

i agree, awesome, bob!

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