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Old 10th December 2011, 11:17 PM   #1
dewardh is online now dewardh  United States
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Default Wanted: acoustic "noise" source

similar (in effect) to the one shown here;

McIntosh Reverberant Room

to use for measuring/calibrating "room response". Something "electrical" rather than mechanical would be fine, as long as the acoustic power remains uniform, and the directivity doesn't change too much . . .

Simple, portable and gotta be cheap . . .
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Old 10th December 2011, 11:47 PM   #2
Pano is offline Pano  United States
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That one is a squirrel cage fan. So why not do that?
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Old 10th December 2011, 11:48 PM   #3
Ron E is offline Ron E  United States
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I think a fullranger on each side of a cube would work pretty well, probably better then the fan on the high end - and EQ-able

I actually have a genrad sound and vibration analyzer
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Old 11th December 2011, 01:01 AM   #4
dewardh is online now dewardh  United States
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Quote:
Originally Posted by Pano View Post
That one is a squirrel cage fan. So why not do that?
Not all "squirrel cage" fans are created equal (I have several, and they "sound" different). Finding the "right" one (or one with a "calibration curve") would be fine with me . . .
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Old 11th December 2011, 01:08 AM   #5
dewardh is online now dewardh  United States
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Quote:
Originally Posted by Ron E View Post
I think a fullranger on each side of a cube would work pretty well,
Too many resonances, probably, and I'm not sure how one would deal with the power response irregularity when they start beaming (in other words, how would one calibrate it?). The wind turbulence noise may show more spectral uniformity?

I'd like a tool . . . not another "project" . . .
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Old 11th December 2011, 02:07 AM   #6
Pano is offline Pano  United States
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Will be interesting to see if you can find a cheap tool like this that isn't a project.
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Old 11th December 2011, 11:33 AM   #7
tvrgeek is offline tvrgeek  United States
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I have to admit, I don't quite get what they were trying to achieve with the secondary noise source. Is it a reference floor that is extracted from the DUT output? We have far better ways to understand polar radiation.

If one had the noise source, then you would need to build the room. A far harder and more costly project.
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Old 11th December 2011, 03:54 PM   #8
dewardh is online now dewardh  United States
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I have to admit, I don't quite get what they were trying to achieve
Without a more clear explanation of *what* you don't understand it's hard to help. In the McIntosh lab the noise source provided a reference standard for power response measurements. What I'm looking for is that, and a way to (easily) measure the absorbtion profile of a room. Anything with a known power output spectrum would do, but a flat spectrum makes it easier, since the room can then be read directly with a spectrum analyzer (without having to apply a correction curve).
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Old 11th December 2011, 06:58 PM   #9
tvrgeek is offline tvrgeek  United States
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So, you are looking for basically a perfect omni-directional pink source and known power. Not sure one exists. Well, a fan is pretty clever for the 50's. Probably a bit more white than pink. Might explain some of Mac's speakers I am guessing they were trying to save the absurd cost of an anoeic chamber.

I believe the current thoughts are to use very short bursts that are less that the reverb time, and to gate the measurement. This basically eliminates the room from the DUT. I have never been a fan of broadband noise testing. About as useful as pure tone. I am sure others have their views and preferred methods. I am afraid the "easy" way we are all searching for still eludes us. It might be worthwhile to note, Joe D'Appolito gets buy with his basement and a few old surplus cotton mattresses.
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Old 11th December 2011, 08:44 PM   #10
dewardh is online now dewardh  United States
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Originally Posted by tvrgeek View Post
So, you are looking for basically a perfect omni-directional pink source and known power. Not sure one exists.
Doesn't have to be "perfect" . . . that makes it a quest for the Holy Grail. "Known power" is more important that directionality (within reason, of course).

Quote:
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I am guessing they were trying to save the absurd cost of an anoeic chamber.
No, they were looking to directly measure power response, since "guestimating" it from averaging multi-axis measurements was even more tedious then than it is now.

Quote:
Originally Posted by tvrgeek View Post
I believe the current thoughts are to use very short bursts that are less that the reverb time, and to gate the measurement. This basically eliminates the room from the DUT.
That's fine for single axis measurement of loudspeakers, not so fine for power response measurement, and all but useless for measuring a room's absorbtion spectrum.
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