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Old 27th October 2008, 06:21 PM   #4621
gedlee is offline gedlee  United States
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Sorry - that was a bit "out there", but I thought people might find it interesting.

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Old 27th October 2008, 06:25 PM   #4622
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Quote:
Originally posted by mige0



John, the software used here is LT-SPICE / swCAD-III.



Michael
As it turns out I do have that software. The modulated source is 2k hz/100 Hz and a midulation index of 1.0. For Doppler generated IM the modulation index can be expressed in terms of the necessary (low frequency) excursion as

MI = Pi * Fh * X / c ,

where Fh is the higher frequency.

The excursion (at 100 Hz) would thus need to be

X = MI * c / ( Pi * Fh) = 2.15"

for MI = 1.

First, I don't think you will see many tweeter reproducing 100 Hz. Second, looking at a typical tweeter (dome) Xmax is usually around 0.25mm which would yield a maximum MI of about 0.0045 at 2k Hz. At 20K hz this goes to 0.045. Since MI is much less that 1.0, this tells us that the maximum Doppler generated IM distortion in a tweeter is about 27dB down at 20K and about 47dB down at 20K.
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Old 27th October 2008, 06:57 PM   #4623
mige0 is offline mige0  Austria
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Default Re: Speaking of OT

Quote:
Originally posted by john k...


As it turns out I do have that software. The modulated source is 2k hz/100 Hz and a midulation index of 1.0. For Doppler generated IM the modulation index can be expressed in terms of the necessary (low frequency) excursion as

MI = Pi * Fh * X / c ,

where Fh is the higher frequency.

The excursion (at 100 Hz) would thus need to be

X = MI * c / ( Pi * Fh) = 2.15"

for MI = 1.

First, I don't think you will see many tweeter reproducing 100 Hz. Second, looking at a typical tweeter (dome) Xmax is usually around 0.25mm which would yield a maximum MI of about 0.0045 at 2k Hz. At 20K hz this goes to 0.045. Since MI is much less that 1.0, this tells us that the maximum Doppler generated IM distortion in a tweeter is about 27dB down at 20K and about 47dB down at 20K.

John, thanks for your maths regarding the modulation index.
Yeah 2.5" for a tweeter is slightly out of its nominal excursion, I guess.

The simus I did were in order to show the effects to be visible in the plots I hope I have stated this clearly

Michael.
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Old 27th October 2008, 06:58 PM   #4624
mige0 is offline mige0  Austria
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Quote:
Originally posted by gedlee



There is actually a hypothesis that the clocks of each particle do have jitter or at least do not have the same time reference for zero. This would exaplain why we have to view all interactions between particles as random events, because the clocks are not synchronous. But a particle can react with itself in perfect synchronization and as such acts like a wave. In other words, the clock jitter would explain the particle/wave duality and the need for probabilities in Quantum Mechanics that has troubled so many physicists for so long.
Bad news I already asked my sales agent to kontakt and sell them my clock.

But also good news maybe I do a slight modification to increase jitter and have the outstanding opportunity to sell as many clocks as there are atoms in the universe




Quote:
Originally posted by auplater
maybe the mods should rename this thread "Way, Way, Way... beyond the Ariel... eh?"


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Old 27th October 2008, 11:20 PM   #4625
mige0 is offline mige0  Austria
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Quote:
Originally posted by john k...




First, I don't think you will see many tweeter reproducing 100 Hz. Second, looking at a typical tweeter (dome) Xmax is usually around 0.25mm which would yield a maximum MI of about 0.0045 at 2k Hz. At 20K hz this goes to 0.045. Since MI is much less that 1.0, this tells us that the maximum Doppler generated IM distortion in a tweeter is about 27dB down at 20K and about 47dB down at 20K.
John, as I see it, such a typical dome tweeter of 1" you mentioned would provide the 27dB (4.5%) / -47dB (0.4%) at 20kHz / 2kHz respectively with a maximum SPL of about 100dB and a HP-XO point set to 1.8kHz

One should make sure the acoustic XO slope is 12db / octave - *at least* - as to keep IM at the specified levels above.

As can be seen in the IM barrier graph (in my spreadsheet) the tweeter *will* be operated down to 100Hz - and below right at its IM-excursion-limit when playing the whole speaker at 100dB at that low frequencies in case of HP-XO second order slope - quite frightening though !

Michael.
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Old 27th October 2008, 11:21 PM   #4626
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Quote:
Originally posted by gedlee
I don't think that I'm the one being closed minded and obnoxious here!

The data is clear and it wasn't just one person, but about 30 who failed to detect any nonlinearity in a compression driver and some of those were audio engineers. Just because the data is not to your likeing is no reason to reject it and "kill the messanger".
Please understand,
the test only shows a result for those people tested under those specific circumstances, and not for the population in general.
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Old 27th October 2008, 11:58 PM   #4627
gedlee is offline gedlee  United States
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While this is always the case, several studies have shown that the population in general does not have preferences or perceptions that are different from trained listeners. Trained listeners tend to have a smaller spread in the data (fewer subjects required for statistical significance), although I have seen cases where this too was not the case.

If we have to test everyone to make any statements about psychoacoustics then the whole process is doomed to failure from the start and we would have to go back to the process of design by listening. I prefer to move forward instead of backwards.
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Old 28th October 2008, 12:18 AM   #4628
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Quote:
Originally posted by gedlee
While this is always the case, several studies have shown that the population in general does not have preferences or perceptions that are different from trained listeners. Trained listeners tend to have a smaller spread in the data (fewer subjects required for statistical significance), although I have seen cases where this too was not the case.

If we have to test everyone to make any statements about psychoacoustics then the whole process is doomed to failure from the start and we would have to go back to the process of design by listening. I prefer to move forward instead of backwards.

so long as we understand possible exceptions and don't assume this data must apply to everyone.
even if it does apply to most.
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Old 28th October 2008, 12:47 AM   #4629
gedlee is offline gedlee  United States
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No one can ever say what any one individual will think or feel about a loudspeaker, but we can be fairly certain what "most" people will perceive. For those on the edges of "normal" I can only have sympathy, for they will most likely never be happy with any loudspeaker. None of them will ever be designed for them.
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Old 28th October 2008, 12:51 AM   #4630
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Quote:
Originally posted by mige0


John, as I see it, such a typical dome tweeter of 1" you mentioned would provide the 27dB (4.5%) / -47dB (0.4%) at 20kHz / 2kHz respectively with a maximum SPL of about 100dB and a HP-XO point set to 1.8kHz

One should make sure the acoustic XO slope is 12db / octave - *at least* - as to keep IM at the specified levels above.

As can be seen in the IM barrier graph (in my spreadsheet) the tweeter *will* be operated down to 100Hz - and below right at its IM-excursion-limit when playing the whole speaker at 100dB at that low frequencies in case of HP-XO second order slope - quite frightening though !

Michael.
You have just made the argument as to why a 12dB/octave acoustic roll off for a tweeter is insufficient in a high quality speaker. But dare I say, IM will be the least of the problem. There would be much more serious problems from other motor nonlinearities entering the picture at that point.
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