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In Reply to: Re: Temporal distortion - measurable? posted by john curl on November 21, 2002 at 09:41:30:
Dear John,thanks for the info you wrote. Some are very interesting.
About: "delay problem is very small..."
I have verified the following:
1 - got a very good F.B. S.S. amp
2 - connect a no crossover speaker 2 ways with only a 24 db filter on TW at 9 KHz acustic cross roughly.
3 - heard the big sound compession on medium frequencies the amp produces compared to a no F.B. TUBE ampthen
4 - connected a 3.3 ohm from amp output to the speaker (speaker is 3.3 ohm coil)..in series to the WF that reproduce most of the spectrum
Now this is what happens:
5 - the acoustic reduction is not that much, still the sound is comparable (as ear sensation) to when the resistor was not there (very small reduction even on base sounding).
6 - the speaker now sounds really (nearby) like to be connected to a NO.F.B. amp.I know damping has been reduced, due to the higher impedance, but also Backward ElectroMotive Energy has been reduced.
Sound compression normally happens when things are out of phase. So the out of phase seems to be very high. The delay in this case is not due to the length of the cable but to the inertia of the WF, that takes time to move and then to produce energy..Now the problem could be which one is the cause that makes the speaker sounding so much better: more detail, a Coda piano is really nearly enough at it should, and so on.
Truth is always in the middle..
both of the above are the causes of better sound, less damping and less BEMF to the F.B. loop.I know it is difficult to divide things.
Another topic on which I am actually working on is: "return loss on connections... between pre & amps or CDP & amps.."
I have in my mind something that tells me that this is another point where we get distortion even if there is a meter of cable.
Having a 100 ohm CDP output & 10 Kohms (or more) PREAMP input, is not as to have as an example output & input impedance the same even if in this second case we lose 6 dBs. The perfect coupling of impedances seems to create good sound. This was also tenth of years ago when transformers were used to couple devices.
Now this also is coherent with the above experiment on the 3.3 ohm in series to the speaker. In this case some hi-range more was present due to the higher Tweeter response, but it was just for test purposes.
if it comes out onto yr mind something else.. please return on the topic..
it is very interesting to go thru..thanks
Roberto
Follow Ups:
Without specifically commenting on you work, I would like to refer you and others to two papers presented at the AES approximately 20 years ago. The first is: 'Intermodulation Distortion in the the Amplifier Loudspeaker Interface' presented at the AES Hamburg convention preprint # 1336. 1978
The second is: 'Power Amplifier Design Parameters and Intermodulation in the Amplifier Loudspeaker Interface' London convention preprint #1608. 1980
Both papers are written by J Lammasniemi and Matti Otala.
I will stand by their work. I can E-mail you copies of these papers if you wish.
I would be very interested in those papers, john thanks.
My e-mail is: robertoamato@mclink.it
Hi, John:Thanks very much for the offer, please email the articles to me at:
randyb@ossaudio.com
For future reference, is there a way to locate and obtain articles from AES by the general public, or would one have to apply and be accepted for membership in the AES to do this?
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