John Curl's Blowtorch preamplifier part II - Page 1934 - diyAudio
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Old 16th December 2011, 05:11 PM   #19331
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Quote:
Originally Posted by scott wurcer View Post
You can also put the RIAA in the feedback, but Walt thought that was going too far for an ADI app note.

Anyway Ed, Thorsten was talking about two speakers in essentially an acoustic bridge to null the difference. You mentioned using one speaker as a drive and another as a microphone to measure the absolute frequency response without a microphone. I sent that B&K link because it is a no holds barred math and apparatus description of the process. Spare the maths spoil the project.
Scott,

It is pretty simple arithmetic when you look at it. Some place there is the tale of how all the standards folks ship their microphones around for comparison and who has the most traveled and best calibrated one.

The actual first important use of the reciprocity principle was in making machine screws! One of the foundations of all modern equipment is the ability to position things accurately. Things such as a screw cutting lathe require a gear box and feed screw.

As you know even the ancient Greeks could file gears and build calculating machines. What is one of the modern wonders is the precision screw. To make the first screws required placing uniform guide marks on a rod and then using a triangle file to form the threads.

One fellow did this for a few pieces and then used a primitive version of the modern lathe to use one screw to trim up another, back and forth, front to back etc. He kept refining his screws. Virtually all modern screws were made from his standard. Now that is taking reciprocity to the extreme.

Around 1947 is when enough was known about interferometry to make more accurate screws! Of course that didn't really become practical until you had a laser light source in the 60's!
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Old 16th December 2011, 09:06 PM   #19332
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RE: JC-1 AC, Levinson product designed in 1975. A real dog and a mistake, open loop complementary cascode input design, too low of input Z for most phono cartridges. YES, loading makes it sound different.
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Old 16th December 2011, 09:54 PM   #19333
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Originally Posted by john curl View Post
RE: JC-1 AC, Levinson product designed in 1975. A real dog and a mistake, open loop complementary cascode input design, too low of input Z for most phono cartridges. YES, loading makes it sound different.
$ 170 at that time.
JC1 : Cartridge Preamplifier
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Old 16th December 2011, 10:27 PM   #19334
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The original JC-1 was actually better, subjectively, than the JC-1AC or JC-1DC which were 'improved' versions of the JC-1. I did not know what input loading did at the time. I did an A-B test with a JC-1AC to prove the point, subjectively. It was unfortunate, and it shows how difficult it is to predict subjective audio quality. It measured OK.
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Old 17th December 2011, 12:02 AM   #19335
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Originally Posted by simon7000 View Post
Scott,

The actual first important use of the reciprocity principle was in making machine screws! One of the foundations of all modern equipment is the ability to position things accurately. Things such as a screw cutting lathe require a gear box and feed screw.

!
We might have a slightly semantic difference in the definition of reciprocity, better to let it go and await the physical results.
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Old 17th December 2011, 02:54 AM   #19336
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John,

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Originally Posted by john curl View Post
Why you guys want to go at each other is beyond me. I respect you both, and I have told you both this, but I respect Ed Simon and many others here too.
What is going on is simple.Ther are some who will champion unorthoox ideas that have merit while others feel threatened by unorthodox ideas and feel the need to opose them strongly, to the point where they publicise falacious proofs of just how bad an idea it is.

Then they receive of course strong opposition as they basically posted balderdash, which they often take personal.

I have no beef with Pavel, but his reaction to current drive would be comical ifhewas not so serious that is the greatest evil in audio...

Ciao T
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Old 17th December 2011, 04:42 AM   #19337
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As far as i understand reciprocity needs 3 reversible transducers and devision of the last two transfer functions to extract the error component. A dynamic loudspeaker is not 100% reversible. It works for capacitive drivers-receivers though. An example of a non reversible speaker is a bending wave transducer. Over the coincident frequency sound that is send to the transducer is transferred into heat. It is really not that simple but i pass on that. The next 100 posts about nothing. A last question : who has hands on experience with reciprocity ?
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Old 17th December 2011, 03:10 PM   #19338
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Quote:
Originally Posted by Joachim Gerhard View Post
As far as i understand reciprocity needs 3 reversible transducers and devision of the last two transfer functions to extract the error component. A dynamic loudspeaker is not 100% reversible. It works for capacitive drivers-receivers though. An example of a non reversible speaker is a bending wave transducer. Over the coincident frequency sound that is send to the transducer is transferred into heat. It is really not that simple but i pass on that. The next 100 posts about nothing. A last question : who has hands on experience with reciprocity ?
That is correct, I question the reversibility of loudspeakers to the degree of getting any useful results, and I don't see any use for doing it with two.
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Old 17th December 2011, 03:13 PM   #19339
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Quote:
Originally Posted by Joachim Gerhard View Post
As far as i understand reciprocity needs 3 reversible transducers and devision of the last two transfer functions to extract the error component. A dynamic loudspeaker is not 100% reversible. It works for capacitive drivers-receivers though. An example of a non reversible speaker is a bending wave transducer. Over the coincident frequency sound that is send to the transducer is transferred into heat. It is really not that simple but i pass on that. The next 100 posts about nothing. A last question : who has hands on experience with reciprocity ?
What the hell are you talking about!
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Old 17th December 2011, 03:26 PM   #19340
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I second Joachim,,, much more can be gained by making the driver better, than trying to correct the errors they are born with, besides any driver that has mechanical damping cant be reversed, as its components are neither linear or amplitude consistent...
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