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Old 5th November 2012, 08:34 PM   #28921
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Quote:
Originally Posted by scott wurcer View Post
There are 7.9 mW/square meter at 99dB SPL. Integrated over a 1 meter radius sphere (maybe hemishere is closer), you got about 50mW acoustic power at 1W (500W). Your maths aren't too bad.
Yah, but now I have a headache..

jn

ps..99 dB spl 1W/1M is pretty much the highest I've dealt with in dynamic drivers. Horns go better, I think the K's were 103.

Last edited by jneutron; 5th November 2012 at 08:37 PM.
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Old 5th November 2012, 08:45 PM   #28922
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Big magnet compression drivers have a conversion efficiency of about 30%, which isn't too shabby considering that half of everything is lost (from the non-radiating side of the diaphragm). Pretty hard to get there for bass drum sizes though.

Thanks,
Chris
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Old 5th November 2012, 09:26 PM   #28923
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Originally Posted by Chris Hornbeck View Post
And drop trou to get to 21!
But of course women are smarter and can get to 22.

se
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Old 5th November 2012, 09:53 PM   #28924
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Quote:
Originally Posted by jneutron View Post
Aha, what appears to be a mistake!!!

The velocity of sound is pretty much independent of pressure. However, I forgot to mention that the air, when pressurized, increases it's temperature (pv=nrt). My pondering involves the effect the acoustic power has on the gas as it traverses it. 4 watts going through a tube of roughly a square inch..

Perhaps somebody can do the math?? Heat capacity of Nitrogen is 1.040 kj/kgK.

Once I get past 10, my math skills slow down..have to unlace my shoes to get to 20..

jn


When spot local temp. varies as in places inside the throat close to the compression driver at mid to high freq.(PA?), things may be not so clear, even if γ remains constant.

Theory of Nonlinear Acoustics in Fluids - B.O. Enflo, C.M. Hedberg - ?????? Google

When air is stressed, it becomes non linear.

At freq. above ~25kHz this becomes very evident and it has been exploited.

http://www.akoustic-arts.fr/wp-conte.../article_1.pdf
http://ew3.ee.uec.ac.jp/e/wespac9.pdf

There are some products making use of the theory and the developed technology

LRAD Corporation - OVERVIEW
Audio Spotlight - Add sound and preserve the quiet.
Soundlazer

In industry, Air-coupled Ultrasound inspection of materials (f: 50kHz-1 MHz) is utilized for ~10 years now.

George
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Old 5th November 2012, 09:59 PM   #28925
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Originally Posted by RNMarsh View Post
If you are playing at moderate-high levels in a large living room at listening distance, then up close to driver the spl is huge! As is distortion.
This touches on a "fetish", , of mine: eons ago I realised there is an excellent subjective marker of a system working well enough, way superior to the normal test instrument procedures. And this is that one is never aware of distortion coming from a speaker driver, no matter how close the ear is to the driver. Obviously there still is distortion emerging, if one applied a measuring mic, etc, it would still register; but, because the ear/brain automatically turns down the gain when subjected to loud sound and psychoacoustic masking comes into the picture, the distortion subjectively never registers as being present, in your mind the sound is clean.

This is what people are experiencing when they say the system sound is at a "magic" level, that they can't imagine it getting better. In essence it is optimisation, lifting every aspect of the system to a very high state of tune that gets you there; it's also very fragile, typically; the slightest maladjustment or deficiency can be sufficient to knock the SQ off that pedestal ...

Frank

Last edited by fas42; 5th November 2012 at 10:02 PM.
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Old 5th November 2012, 10:04 PM   #28926
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Originally Posted by scott wurcer View Post
I was more interested in the "discovery" that odd functions can only make odd harmonics.
Fair enough, ...

Frank
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Old 5th November 2012, 10:36 PM   #28927
gpapag is offline gpapag  Greece
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Originally Posted by jneutron View Post
The guys here seem to consider mu zero constant even in the megatesla range. I'll ask one of the carpool guys about the 7 TEV collisions. (chances are, I will not understand the answer. )
jn
If you will not, chances are that what happens is worse than (or at least, different from) what you could think of.

Relay here the un-understandable please

George
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Old 5th November 2012, 10:44 PM   #28928
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Default Speaker Distortion

2 points

Horn Distortion

Olson, in his comprehensive treatment quotes studies going back to 1933. Basically, the smaller the throat and greater the compression ratio, the higher the distortion. Hence my advice to use the least compression ratio to achieve your desired efficiency. Less drastic flares help too.

Loudspeaker Distortions: can we hear them?

The Fryer et al papers I mention investigates the audibility of various distortions. I extended that work in nearly 2 decades of Blind Listening Tests.

One of the most interesting findings is that it is possible to have a speaker with poor measured harmonic distortion at modest levels sound 'less distorted' than one which measured a lot better.

The speakers involved would all be considered good speakers today and the panel were all experienced listeners with proven better than average aural discrimination.
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Old 5th November 2012, 11:01 PM   #28929
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Originally Posted by kgrlee View Post
Loudspeaker Distortions: can we hear them?

The Fryer et al papers I mention investigates the audibility of various distortions. I extended that work in nearly 2 decades of Blind Listening Tests.

One of the most interesting findings is that it is possible to have a speaker with poor measured harmonic distortion at modest levels sound 'less distorted' than one which measured a lot better.
Richard, there is indeed a clash between science and the mind in this area, in part because science always wants to separate out one part, concentrate on one aspect, consider just the black box. Trouble is, in audio the black box extends beyond the element that supposedly is solely being "tested", all the ancilliary equipment comes into play, the level of electrical interference from the various sources, etc. And the ear/brain, of course, the most important component of all.

In another post I mentioned in some tertiary coursework being lectured on the need for extreme care in the experimental setup, for the final measurements to have any meaning. In audio the same sort of rigour needs to be applied, and sadly, this seems to be a very rare occurence ...

Frank
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Old 6th November 2012, 12:06 AM   #28930
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Originally Posted by fas42 View Post
Richard, there is indeed a clash between science and the mind in this area, in part because science always wants to separate out one part, concentrate on one aspect, consider just the black box. Trouble is, in audio the black box extends beyond the element that supposedly is solely being "tested", all the ancilliary equipment comes into play, the level of electrical interference from the various sources, etc. And the ear/brain, of course, the most important component of all.

In another post I mentioned in some tertiary coursework being lectured on the need for extreme care in the experimental setup, for the final measurements to have any meaning. In audio the same sort of rigour needs to be applied, and sadly, this seems to be a very rare occurence ...
Frank, you are perfectly right about this. The measures you need to take to ensure a Blind Listening Test (especially with speakers) is both not biased as well as comfortable to the panel are immense. We pontificate on the details in at least 3 of our papers.

Doing these tests costs a great deal of time and money. Each member of the panel is tested separately and may take up to half a day for a single test. Ideally, the test needs to be repeated at least once. It tied up one of our most important tools, the Listening Room and its gear and several highly trained (expensive) people for long periods.

But IMHO, as listening is the ultimate purpose of all our efforts, we need to extend at least as much rigour in testing listeners & listening.

Last edited by kgrlee; 6th November 2012 at 12:12 AM.
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