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Old 26th August 2014, 09:26 AM   #56071
PMA is offline PMA  Europe
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Asymmetric wave, phase shift 45. Please note that amplitude spectra of symmetric and asymmetric waves are identical (input signal spectra). We can see some differences in spectra at amplifier output, due to different amplitude stress and amplifier nonlinearity.
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Old 26th August 2014, 10:36 AM   #56072
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Quote:
Originally Posted by a.wayne View Post
Frenchie ,

JBL :
600 W AES continuous pink noise
Sensitivity: 97 dB SPL, 1 W, 1 m (3.3 ft)
Frequency Range
: 30 Hz - 2.5 kHz

Power Compression:

at –10 dB power (60 W): 0.7 dB***
at –3 dB power (300 W): 2.5 dB
at rated power (600 W): 4.0 dB

@ 60 watt power compression on their bass unit is .7db, consistent with what we found 20 yrs ago, when testing RMS below 32 watts and consistent also when used in typical domestic hi-fi, VCID would not be an issue.

60 watts RMS would translate to over 720 watts peak power when used in domestic hi-fi situation. even you head banging nutters couldn't go there ..
Thank you for proving my point.

If all this compression were due to thermal resistance increase, this would correspond to VC temperatures of 43, 197 and 387 degrees K above ambient. Obviously, their are mechanical non-linearities in the suspension which also produce compression, but it gives you a sense of the numbers.

Now, with this example, you used a professional JBL driver that can handle 600 Watts continous noise power. Typical drivers in living room speakers will handle less than 60 Watts noise power. 30 Watts is even optimistic for most.

About your 'test' I vented some doubts earlier (posted at #56027). How can you go from 1 to 16 Watts without an increase in distortion or impedance? All drivers have increasing distortion with increasing power. You should have seen impedance increase as well. It looks like you pulled these results out of your brown star.

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Old 26th August 2014, 11:14 AM   #56073
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Pavel

Have you tried the same ratios at a lower frequency to identify the thermal component?
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Old 26th August 2014, 11:46 AM   #56074
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No, I may try it.
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Old 26th August 2014, 02:03 PM   #56075
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Quote:
Originally Posted by simon7000 View Post
Pavel

Have you tried the same ratios at a lower frequency to identify the thermal component?
Just tried. No thermal components, with signals down to 10Hz. With signals down to 1Hz FFT resolution is insufficient.
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Old 26th August 2014, 04:04 PM   #56076
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Quote:
Originally Posted by dvv View Post
Does it exist in electronic form?
If so, a link would be much appreciated.
http://waltjung.org/PDFs/Picking_Capacitors_1.pdf
http://waltjung.org/PDFs/Picking_Capacitors_2.pdf

George
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Old 26th August 2014, 08:24 PM   #56077
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Quote:
Originally Posted by PMA View Post
Asymmetric wave, phase shift 45. Please note that amplitude spectra of symmetric and asymmetric waves are identical (input signal spectra). We can see some differences in spectra at amplifier output, due to different amplitude stress and amplifier nonlinearity.
Pavel, I spent some time years ago with this asymmetric signal stuff and could not get through to anyone involved. The question is topology signature or just bad design signature, IMHO positive results were obtained when full power bandwidth was reached/exceeded (old news). This should rest with testing the uA741 for audio.
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Last edited by scott wurcer; 26th August 2014 at 08:27 PM.
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Old 26th August 2014, 08:30 PM   #56078
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Scott, thanks for the info.
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Old 26th August 2014, 08:31 PM   #56079
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A.wayne,
Could you tell us how you did those thermal temperature measurements with an infra-red device. Was the dust cap removed to see the gap temps? What about a time factor in those measurements? I would love to believe that I could just forget about the temperature rise it would mean I could just use the lowest curie point magnets and forget about demagnetization. Motor mass will definitely affect the results over time and the maximum temp reached but in a small consumer motor you will also have much less mass to absorb any heat to dissipate. One factor we have to look at is the diaphragm area and excursion needed to produce a certain sound pressure level, it won't take much with a 15" cone in a house to get really loud but a smaller 6" or 8" speaker is going to have to work much harder to reach those same sound levels and much more input power to the voicecoil. We also have to consider voicecoil diameter in all this.

I don't want to get into an argument about this, I really want to understand under what conditions your measurement were made.
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Old 26th August 2014, 08:58 PM   #56080
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Many thanks, George, that's EXACTLY what I was looking for.
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