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window behind monitors.... best way to treat this??

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Re: window behind monitors.... best way to treat this??

PostPosted: Tue Jan 18, 2005 12:05 am
by bert stoltenborg
But they do have cool smileys here
:headbang:

Re: window behind monitors.... best way to treat this??

PostPosted: Tue Jan 18, 2005 1:17 pm
by Ethan Winer
Eric,

> This is not about opinions or finding but about facts, measurement techniques and acoustics. <

You are correct. It is about science. It's about finding solutions to long-standing problems. It's about getting repeatable results. It's also about cooperation and sharing resources for the mutual benefit of all.

Elsewhere you complimented acoustician Angelo Campanella for his great attitude when you wrote, "Angelo is very gentle, he encourages anyone and lots of things when he believes someone is learning and searching."

That's an admirable trait indeed, and you would do well to take a lesson from him.

--Ethan

Re: window behind monitors.... best way to treat this??

PostPosted: Tue Jan 18, 2005 1:51 pm
by Brian Ravnaas
Ethan Winer wrote:

One of these days I plan to measure the comb filtering off my large thermal-pane patio door, using ETF and my Carver Sunfire subwoofer that outputs solidly down to below 25 Hz. I think that's the best test of how much a glass door may reduce acoustic interference.

--Ethan


i think that is a marvelous idea. i wonder if you'd be able to separate the reflections/comb filtering process from the general modal behavior in the room?

i do very much think this phenomenon is worth exploring, and i'll join ethan in volunteering some time. I'll pony up a day of time in the reverb room pair in our labs to assesss the impact on modal behavior of an unimagineably bad wall - probably to be a single layer of 1/4" drywall (plasterboard).

it would be very valuable to the general goal, i think, to utilize an accelerometer and a simple impact (tap with a rubber mallet should suffice) to determine resonant points of the structure under test - then any absorption peak that may be noted could be correlated to the resonant points, etc.

Brian

PS: as i mentioned above, i also think that it is incorrect to tout poor transmission loss as beneficial to room modal behavior. Per the math and presentation above. But, then, a good unbiased test should be worht much more than a calculation or an oft-quoted, probably ancient and somewhat haphazard sentiment, no?

should be fun.

Re: window behind monitors.... best way to treat this??

PostPosted: Tue Jan 18, 2005 4:04 pm
by Eric Desart
Ethan Winer wrote: It's also about cooperation and sharing resources for the mutual benefit of all.

"Angelo is very gentle, he encourages anyone and lots of things when he believes someone is learning and searching."

That's an admirable trait indeed, and you would do well to take a lesson from him.


You're good, REALLY good...

What was the topic again????

I was involved in several topics here:

1) Minitraps and its membrane effect versus other solutions: diverted to non-related measurement techniques and suggested malice and deceit by others.

2) Validity of RAL measurements: An exact final acoustic question which could give a final answer diverted with a reference to discussions with third parties behind the scene, and reference to the distastfulness of continuing the argument in function of the "end of year" holidays.

3) The wrong use of the non-existing concept (not word or notion) "crossover frequency" (in the used context) and the energetic content of sound "outside" a room diverted to absorption in the room.
And just repeated here as if this thread never existed:
http://tinyurl.com/6wg3x

4) The current wrong misleading comparison related to density and FRK in function of corner absorption. Data published at the expense of others searching for help diverted to complete non related quotes, and advice indeed applicable to yourself.

But I agree: you're good, REALLY good.

Re: window behind monitors.... best way to treat this??

PostPosted: Tue Jan 18, 2005 4:49 pm
by Ethan Winer
Brian,

> i wonder if you'd be able to separate the reflections/comb filtering process from the general modal behavior in the room? <

I'm not so worried about that as much as assessing by how much the reflected energy is reduced. A wall that's 100 percent reflective will create a null that's infinitely deep 1/4 wavelength away from the wall. (Assuming a straight angle of incidence.) Reducing that reflection by only 1 dB raises the null from infinitely deep to only 19 dB deep. Reducing it another dB makes the null only 14 dB deep. Reduce it again to -3 dB and now the null is only 11 dB deep. Once you reduce the refection by 6 dB the null is now only 6 dB deep. So reducing the reflection even a tiny bit can make a huge response improvement in the room. This seems to me the main issue.

> utilize an accelerometer and a simple impact <

I figure that using a subwoofer with a solid output down to 20 Hz and the ETF software will show the comb filtering and the extent of the nulls. But if you know a better way that measures the same thing, go for it. I have a large glass double door to the outside, but it's 40-50 feet from my home theater receiver. My plan was to measure the comb filtering with the glass door open, with the door closed, and with the door closed and 3/4 inch sheet rock in front of the door. Besides having to find a 40+ foot RCA extension, or cobble one from a bunch of adapters, I'd also need to buy a big piece of 3/4 inch sheet rock and schlep it upstairs without getting powder all over the floor. That's why I haven't yet done this test myself. :lol:

> i also think that it is incorrect to tout poor transmission loss as beneficial to room modal behavior. <

Again, I'm not thinking in terms of modes as much as the problems caused by simple acoustic interference. Yes, I realize they are related. But as I showed above, if the reflections can be reduced even a little, the nulls (and peaks) will be greatly improved in the process.

--Ethan

Re: window behind monitors.... best way to treat this??

PostPosted: Tue Jan 18, 2005 10:30 pm
by Brian Ravnaas
hey again,

you could try a piece of 3/4" MDF - no powder, and at least as heavy (varies from type to type)

that tests sounds interesting. I wasn't proposing any changes - the acclerometer part would just be to identify resonant points in the glass door (and later the mdf) to correlate those to any effect that was measured.

what i propose (and this must be a long term project) is just to measure the decay time and freq response in a reverb room when one wall is varied. make the one wall 1/4" drywall, then 4 layers of damped 5/8" drywall or brick , and see how transmission loss affects things.

for the guru's, one and all: would it be wiser to render the second pair of rooms quasi-anechoic by filling it with absorbing material for this test, or to leave it empty/reverberant?

Re: window behind monitors.... best way to treat this??

PostPosted: Tue Jan 18, 2005 11:35 pm
by Ethan Winer
Brian,

> you could try a piece of 3/4" MDF <

Okay, you come over and help me carry it up the back steps. :crazy:

> the acclerometer part would just be to identify resonant points in the glass door (and later the mdf) to correlate those to any effect that was measured. <

Got it, great idea.

> measure the decay time and freq response in a reverb room when one wall is varied <

I assume you'd build a wall into the reverb room's large door? But then you have to take into account whatever is on the other side of that door, since that will reflect back into the path. That's why I like the idea of using an outside door or window - that way you're guaranteed not to have any "extra" reflections.

> would it be wiser to render the second pair of rooms quasi-anechoic <

Oh, I see. You mean build a wall that divides the reverb room in two. That would be one mighty big wall, no?

--Ethan

Re: window behind monitors.... best way to treat this??

PostPosted: Wed Jan 19, 2005 12:15 am
by bert stoltenborg
goddammit these smileys are so [ ****** ] cool! :protest:

Re: window behind monitors.... best way to treat this??

PostPosted: Wed Jan 19, 2005 12:16 am
by Scott R. Foster
Ethan:

Why bother with a reverb chamber?

Re: window behind monitors.... best way to treat this??

PostPosted: Wed Jan 19, 2005 8:25 pm
by Ethan Winer
Scott,

> Why bother with a reverb chamber? <

That was Brian's idea, not mine. The test as I described it would be easier to perform and would probably give a more direct answer. But if Brian wants to test this as he described, that will give yet another perspective.

--Ethan

Re: window behind monitors.... best way to treat this??

PostPosted: Wed Jan 19, 2005 11:13 pm
by Scottdru
bert stoltenborg wrote:goddammit these smileys are so [ ****** ] cool! :protest:

Hehe . . . Image


:D

Re: window behind monitors.... best way to treat this??

PostPosted: Thu Jan 20, 2005 9:45 am
by Scott R. Foster
Ethan?

Just to be clear... you don't think you need a reverb chamber to do those LF absorbtion tests right?

Got those figures on 701, 703, and 705 together yet?

Re: window behind monitors.... best way to treat this??

PostPosted: Thu Jan 20, 2005 10:27 am
by Hugh Robjohns
Foz wrote:Just to be clear... you don't think you need a reverb chamber to do those LF absorbtion tests right?


Er.... Are you making this up as you go along? Ethan and Brian appeared to be talking about assessing interference patterns in the room, not doing "absorbtion tests"....

One of your favourite Graemlins is called for...

:headbang:

hugh
;)

Re: window behind monitors.... best way to treat this??

PostPosted: Thu Jan 20, 2005 5:46 pm
by Scott R. Foster
Thanks for keeping us on topic Hugh

:headbang:

Re: window behind monitors.... best way to treat this??

PostPosted: Fri Jan 21, 2005 8:12 pm
by Brian Ravnaas
i should like to add that i propose nothing formal, nothing intended to replace the official standards, nothing like that.

and i happen to have a keen curiosity about this "a bad wall helps low frequency modal problems" concept since a fellow on another forum posted it a month or so back, and since it is something that gets discussed from time to time, and since i can't fathom how it could be so.

and building a very bad wall, like a single sheet of 1/4" drywaqll, and testing the in-room response, comparing that to the same with a rigid, high TL wall in place, and taking said very bad wall back out will waste a day or so... but it would be worth the time for the sake of curiosity and the general interest. I don't have an accredited reverb room ala IBM or Riverbank, etc., nor would the tests purport to be up to any official level. i just happen to have acces to two small reverb rooms with a parition/opening and a very low level of absorption / high level of modal activity.

and the test seems reasonable enough, and considering that i must have seen a dozen threads on this topic over my limited time on the web, it seems to be interesting to many. The tests would just intend to take a peek at this singular topic - can a very bad wall mitigate modal response in a room.

take care everybody

Brian