John Curl's Blowtorch preamplifier part II - Page 1937 - diyAudio
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Old 17th December 2011, 10:44 PM   #19361
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Right you are.
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Old 17th December 2011, 10:48 PM   #19362
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Sometimes, medium Z drive, like 4 ohms actually sounds better. There are several reasons for this, one is the BL product of the loudspeaker. IF it is over-damped, then a higher drive impedance MIGHT improve the overall bass and even the overall sound. I found this out in 1964, (when most of you were young) with an Acoustic Research AR-1 loudspeaker, driven by a Dyna MK 3, 60W amp. (more later)
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Old 17th December 2011, 11:15 PM   #19363
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A good nastinessometer can be made of a source of powerful sinewave and resistor.Say, to test 100W amp on 8 Ohm load we need 100W of a sine wave and 100W resistor. Feed this signal to the output of the amp in question and see FFT plot there. It is revealing. Actually, how big the output resistance of the amp is, does not matter: it is not a dirt. What is a real dirt, is what the amp adds trying to compensate this sinewave. Some amps that in conventional measurements show perfect results add very nasty dirt due to their non linear and complex output resistances, even though they are very low. Adding say 0.5 Ohm resistor to output of such an amp makes it's output resistance higher, but more linear.
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Old 17th December 2011, 11:46 PM   #19364
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Actually, no. They are accurate across the range they work across, usually not much above 350 Hz, or you get the equivalent of valve float. Since a pistonphone is a very constant known displacement transducer the pressure is constant (or so the manual says, with instructions for doing just this).

.
I thought that was what I said the little piston moves at a fixed frequency, they are intended for an absolute sensitivity at some low frequency. Most microphones behave in an ideal sense at low to 500Hz or so.
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Old 17th December 2011, 11:54 PM   #19365
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I have a large collection of measurement microphones as well but the Girardin (Panasonic) mikes that come with Praxis make everything too easy so they don't see much use.

I have been using ground plane measurements time windowed in a basketball court in the warehouse very effectively. No reflections for more than 50 mS gives very good low frequency extension to the measurements. It even works when the crusher is running at the other end of the warehouse.
As I said $$$ software and hardware are not for the little guy, nothing would give me more pleasure than to give the average DIY'er the same capabilities for free.
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Old 18th December 2011, 12:01 AM   #19366
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I just spoke to Jack Bybee today. He was complaining that one of the front tires on his Mercedes started to disintegrate while he was driving, after only 10,000 mi. .
I thought he drove a Bentley, I got rid of my Mercedes the tires were the least of the problems. We are an all BMW family now.
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Old 18th December 2011, 12:05 AM   #19367
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Sometimes, medium Z drive, like 4 ohms actually sounds better. There are several reasons for this, one is the BL product of the loudspeaker. IF it is over-damped, then a higher drive impedance MIGHT improve the overall bass and even the overall sound. I found this out in 1964, (when most of you were young) with an Acoustic Research AR-1 loudspeaker, driven by a Dyna MK 3, 60W amp. (more later)
You are definately right, we did lots of experiments with the "wrong" impedance taps on the output. Rarely did the "right" one give the best overall sound.
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Old 18th December 2011, 01:15 AM   #19368
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Jack drives both.
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Old 18th December 2011, 02:37 AM   #19369
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Jack drives both.
To the bank I hope.
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Old 18th December 2011, 02:38 AM   #19370
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Hi,

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Thorsten, this is just one one the things i recently did on one of my drivers
I don't think this much to help with nonlinearities I listed, which depend on voicecoil current.

Ciao T
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