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Old 6th November 2012, 10:50 PM   #29021
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Frank; you probably forgot about the difference between output of active monitors and sensitivity of passive speakers.
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Old 6th November 2012, 10:59 PM   #29022
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Then try arrays. No sweet spot at all. Dispersed sound, like it goes from beyond the speakers. The next year I will bring on BAF 3-row arrays, open baffles: open baffles and dipoles are getting popular.

My arrays at home are currently in walls.
Which brings me back to point sources, , they work for me! But, only because the electronics are sorted out well enough ... if they're off colour, even slightly, then the whole "mirage" collapses. The key is eliminating audible distortion, if this is too high then the ear/brain refuses to accept the "message" the system is trying to present, and you're back to YAH, yet another hifi ...

As Tom Danley points out, what the ears pick up is pretty close to being a complete mess, it's only the brain decoding it competently that gives us a good mental representation of what's actually happening, even with live sound. Overload our poor old heads with yet another layer of mess added by the reproduction system misbehaving, and our brains give up, we get a headache, listening fatigue ...

Frank
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Old 6th November 2012, 11:04 PM   #29023
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Best,
Tom Danley
Danley Sound Labs
Mr. Danley

What can not be modelled I guess (and thus corrected by pre distortion) in a horn is the mess that happens in the compression chamber (the volume between the driver diaphragm and the throat aperture of the horn), especially when there is no phase plug. “Near field” amplitude/phase variations, internal cross reflections, diffraction effects, volume resonances., high pressure chaos.

Jneutron, the process is adiabatic. Front of the wave, hot. Back of the wave, cool. As you say, heat travels with the wave. See left attachment for wave distortion that Mr. Danley is speaking of. On the right, Pick your curve and draw the distorted wave.

https://ccrma.stanford.edu/~dpberner/Thesis/thesis.pdf

http://www.diy-audio.narod.ru/litr/M...Enclosures.pdf

http://www.volvotreter.de/downloads/...le_Horns_1.pdf

http://www.volvotreter.de/downloads/...le_Horns_2.pdf

George


>Edit. Steven has already posted this and Jneutron responded.
I missed it. Sorry
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I'm not quite sure what all the
Attached Images
File Type: jpg adiabatic.jpg (45.8 KB, 127 views)
File Type: jpg adiab curves.jpg (105.7 KB, 124 views)
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Old 6th November 2012, 11:08 PM   #29024
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Frank; you probably forgot about the difference between output of active monitors and sensitivity of passive speakers.
Huhh?? Speakers are speakers, amplifiers are amplifiers; actives are only so because the length of speaker cable is very short, and the output stage doesn't have to pump unused amps into the crossover. As I said in another post, electrically every system should be considered as a totally integrated mechanism; actives win over passives because the engineering between the amps and the speaker drivers is better sorted out ...

Frank
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Old 6th November 2012, 11:22 PM   #29025
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Jneutron, the process is adiabatic. Front of the wave, hot. Back of the wave, cool. As you say, heat travels with the wave.
Ah, wait...the assumption is ideal gas law. With high spl and energy density, that isn't accurate. I pointed out that concern a coupla posts ago. The equation P1V1/T1 = P2V2/T2 no longer holds. All you can do is drop back to the relation P1/T1 = P2/T2 (Gay-Lussac's). Volume is not constant through the pressure wave, nor is temp. (The pv/t=pv/t equation is not deterministic by virtue of the model..as the wave passes, we are not talking about the same quantity of gas, the equation only holds for a specific quantity of molecules. Gay-Lussac's avoids that constraint.

As with all physical processes the temperature of the gas will lag the instantaneous pressure..heat capacity. That difference merely modifies the wave profile a bit over a zero heat capacity model, but the same basic effect as Tom mentions.

Very nice links. Grazed through the first one, very interesting. He was thanking the fusion guys at LBNL..

Will peruse the rest when I get a chance..

jn

ps. the second link appears to be cyrrilic.

ah, 3rd and 4th link, mention adiabatic. That is only true for an ideal gas with spl's not excessive.

As I recall, Abraham B Cohen (sp) discussed the adiabatic distortion of the throat, and I think he used the back compression chamber to balance that out. He never really formed many equations, but did seem to know what he was doing..Wasn't he a violin player?

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Old 6th November 2012, 11:38 PM   #29026
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test
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File Type: pdf tn_v1n21.pdf (446.0 KB, 62 views)
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Old 6th November 2012, 11:42 PM   #29027
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Originally Posted by john curl View Post
test
It worked..thanks.

Now, we need tech note volume one, number 8...

Quote:
As discussed in JBL Technical Note Volume One,
Number Eight, second harmonic distortion in
horn/driver combinations is due to thermodynamic air
overload
jn

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Old 6th November 2012, 11:54 PM   #29028
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But the signals are correlated, if the piano is centre then a note struck is very close to being purely additive, from the 2 channels.
You are right for large waves lengths, I believe not shorter ones (depend of the distance between the speakers and listener position) where it add only average 3dB.
That is to be taken in consideration too when we design filters, depending of the diameter and distance from the speakers (Pink noise measurements helps for that).
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Old 7th November 2012, 12:00 AM   #29029
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Huh?!! Forgetting about stereo setups, doubling the power gives you an extra 3dB from the speaker: so 1W, 94db; 2W; 97; 4W, 100; 8W; 103; 16W, 106; 32W, 109; 64W, 112; 128W, 115; 256W; 118. We're now at a level just below the maximum that can be experienced by a player in an orchestra, seated immediately in front of the brass section. A solo piano is not as loud as that, the amp's power is not a problem!

We do have a upright piano at home, in the listening area; using that as a reference, four clicks below maximum volume on a typical classical recording, say Brendel sonatas, gives me equivalent SPLs, with considerably better tone from the recording, as it should with a top notch Steinway, etc, at his service ...
Frank, you can easily check this by recording your own upright with a good pianist at home and playing it back later. Something like a Behringer ECM8000 is sufficient. Beg or borrow a soundcard with P48V mike preamp. We are only checking for clipping which you can extrapolate to a 1000W amp.

It's not the average levels but the peak levels which are a problem. I used to sing with a choir that often sat in front of the brass section so I know how loud this gets.

Recording good small choirs is more difficult. There are various levels of 'in-tune'. If good enough, a choir of 12-20 can sometime show amazing peaks at very modest levels. What happens is that they sing so 'in tune', they add 6dB rather than 3dB for 2 voices for very short periods. When this happens, the short peaks are so high you can hear the intermod in your ears and your peak meters go through the roof. Only happens with the very best choirs.

I recommend anyone involved in audio to go out and make some recordings yourself. You don't need the very best mikes & supa equipment though it is far easier to get really good stuff this millenium. But your outlook on reproduced sound will change.

Last edited by kgrlee; 7th November 2012 at 12:26 AM.
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Old 7th November 2012, 12:18 AM   #29030
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If you want to hear how accurate a loudspeaker is, make a generation loss recording with a measurement mic in a semi anechoic condition (outdoors on a quiet day). Like any part of the chain, the more passes it will tolerate before transmogrifying the signal, the more accurate it is.
At work, we used this at work developing our loudspeakers (large scale sound) and it was eye opening many times.. It is surprising how few passes even some good loudspeakers will last, each generation an increasing caricature of what is wrong.
This is exactly what's done with a few extra bells & whistles in
AES E-Library Loudspeakers: An Approach to Objective Listening

We later highlighted the limitations of considering the speaker as a 1D transmission channel in AES E-Library Absolute Listening Tests-Further Progress

I coined the term Room Interface Profile as the most important characteristic of a domestic speaker. Pseudo prophet Floyd pretends to pontificate on all this.
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