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Old 3rd March 2013, 01:23 AM   #1131
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Originally Posted by Kindhornman View Post
Power compression is something we talk about in pro-audio where you are running very high voltage and current through a device on a long term basis.
It's also worth noting that thermal issues obey diffusion equations and modling by R's and C's has limited utility. We were surprised at the self heating of transistors having some very fast (usec) local heating issues even though the long term die/package time constants are on the order of seconds.
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Old 3rd March 2013, 01:32 AM   #1132
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Scott,
I understand what you are saying on the micro sized die that a transistor must face. I have had to have this discussion in tooling design many times where someone would fall for the hype that you could use epoxy with aluminum filler to transfer heat and dissipate heat in tooling used to mold thermoset materials that had an extremely fast exponential heat rise. You could add all the aluminum you wanted to the epoxy but each and every grain of aluminum was surrounded by the epoxy which was an insulator so that the heat transfer would not and could not keep up with the heat output from reaction. People just couldn't follow this simple phenomena and it lead to many unsuccessful tooling applications by misinformed people.
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Old 3rd March 2013, 02:08 AM   #1133
ScottG is offline ScottG  United States
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Originally Posted by john k... View Post


If the VC is essentially "cooking" for a while at a higher spl - yet still reasonably linear because of continually low-level transients (from the average), but then accepts a short burst of power from a strong transient..

-would that cause an "instantaneous" problem?


Also, (..in the realm of "cooking" - and I say this just having grilled a few hamburgers ), might there be other sources heating-up and "draining" into the VC of a tiny tweeter? (..or is there no effect like that happening?)
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Old 3rd March 2013, 02:14 AM   #1134
ScottG is offline ScottG  United States
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Originally Posted by dewardh View Post
Lots of emphasis on the "may" there, I would hope.
Oh yeah.. caveats galore!

..I've also heard that about current amps as well, that with a reduction in either 2nd or 3rd order non-linear distortion (..don't remember which order though.)
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Old 3rd March 2013, 02:36 AM   #1135
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Scott,
I understand what you are saying on the micro sized die that a transistor must face.
Some SOI transistors face an initial transient heating of 1000-3000 C/W because the oxide pocket is to the first order a thermal as well as electrical insulator.
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Old 3rd March 2013, 02:58 AM   #1136
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Yes that is some heat rise Scott. I can understand how an instantaneous rise like that would happen when moving electrons around through such a small junction. I don't know what the actual temperature was that was reached in a fast urethane reaction but it is plenty and for a chemical reaction is fairly fast. Not as fast as pouring water into an acid, but fast enough. I always used aluminum tooling unless it had to be steel. All these tools were water temperature controlled, but that was of little consequence if the tool was epoxy. All the final material properties would be out the window if you got a decent looking part at all. I can completely understand what you have to go through on a much lesser scale by many factors different, but bad results in both situation.
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Old 3rd March 2013, 02:58 AM   #1137
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John K,
I would think that the impedance rise of the voicecoil would be very dependent on the input level you were using the device and also the gap dimensions and also the differences of short and long coils vs gap length. There are many variables that would affect the temperature rise and usually power compression is only at high levels of input power. Under normal listening levels it is probably only a minimal factor in the overall picture.
Yes, all that matters. The heat generation is the easy part and knowing the heat generation rate it is pretty easy to figure the maximum rate of temperature increase possible for any given power level. It's sort of a thermal slew rate. So even if you ignore cooling you can still look at how fast the temperature can rise and the result is that the temperature simply can not follow the transients in music. The temperature as a function of time is an integral of the heat generation rate minus the heat lost to the surrounding. The integration process, even in the absence of cooling, is a smoothing process and short duration, high generation rates don't contribute much to the temperature increase. Cooling effects limit the max temperature than can be reached and slow the rate of increase. Think of heating like interest rates. If I loan you $100 at an annual rate of 36.5% and you pay back the loan in one day you would owe only $0.10 interest. But if I charge you 3.65% and you take a year to pay it back $3.65. It's the longer term average power that yields the temperature increase and the resulting thermal compression. The sharp spikes in power have their contribution, but you don't see jumps up and down in temperature following those spikes.
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Old 3rd March 2013, 03:13 AM   #1138
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John,
Yes in a worse case situation you can look at this as only the temperature rise of a voicecoil in air. The transfer to air is much less than the transfer when you have the voicecoil and the steel structure there. Yes you can say that it will be an average temperature rise and that it smooths the average peaks, but there are still extremely fast rise times of heat only they are delayed from the signal. they are let's say as I don't know how to say it, out of phase with each other. The heating of the coil would lag the voltage rise I think. It is just that the, I will call it black body, of the steel absorbs the heat spikes by radiation. So no matter what the heat rise is whether it is less than or higher than either one of us thinks, the resistance value of the voicecoil is changing with the signal but, thermal rise is lagging behind, and this is a modulation of the signal that would happen in time, not at a given instance.
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Old 3rd March 2013, 04:08 AM   #1139
Pano is offline Pano  United States
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As an aside, my subjective impression from my short listen (AXPONA last year) was that the Orion is a bit "rounded off" dynamically.
I would say that's putting it politely.
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Old 3rd March 2013, 09:02 AM   #1140
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Originally Posted by Kindhornman View Post
As stated in that paper if you are only talking about narrow band low frequencies localization is out of the question, but music is not narrow band. This is the problem with so much of this information it is taken out of context to a true musical source.
Objectice data easily become subjective opinion if we insist on looking only to the part of data that supports our preconceptions. In this regard Earls look at objective data is a bit positivistic.

So please look at the green part of the diagram too and just keep in mind, that the lower frequencies are still part of the broadband signal:
theile Bild 21a.gif
Doesn't it appear to you how the 0.5 and 1 kHz signals follows the precedence "rule" for the first 0.5 ms quite exactly and then get all over the place? In contrast the 2 kHz signal gets nearer to the broadband signal with rising delta t.
What I am getting from this: For larger time intervals between first and second signals (like in room reflections - and that is what we are talking about here) lower frequencies contribute less and less to the forming of an (annoying) image shift or source broadening. It is the frequencies from 1 kHz up which "fix" the perceived direction of the precedence effect at larger ITDs.

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