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Old 9th June 2009, 07:35 PM   #11
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Default Re: Re: Calibrating microphones and speakers

Quote:
Originally posted by cuibono



Used as an impulse source nearfield?
Yes, but there is a nice AES paper from Schoeps with a derivation of the wavefront as a doublet (+20dB/decade) which is what I had found empirically and was baffled over. Sorry I never got around to coming by, I built a piston chamber that contains the SPL. I can hard clip most mics and no one else can hear it (but only at 350Hz).
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Old 9th June 2009, 07:49 PM   #12
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Quote:
Originally posted by scott wurcer


File is too big and I'm not allowed to host anything here. Anyone that gets it is welcome to host it, it's not that big a deal anyway. My homemade piston chamber is more fun, I will add that when I am done.
(Crossing fingers: I have limited bandwidth )

http://wavebourn.com/images/audio/Proins/spark.pdf
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Old 9th June 2009, 08:01 PM   #13
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Thanks Scott, thanks Wavebourn! So simple, nice work!

Scott, what distance do you keep between the mic and spark? I would imagine as close as possible (<10cm), but that may be an issue for cardioid mics (proximity effect).
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Old 9th June 2009, 09:07 PM   #14
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Default Re: I was searching for something alike, and found

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Originally posted by destroyer X



What do you think Wavebourne?


I think I want some very tiny device with no diaphragm at all that will sense movement of air molecules transforming it to an electricity to answer your question.

Spark gap is a good device to produce sound pulse, it is what Scott demonstrated in his work. Corona discharge speakers are used as fine tweaters. But what to use for microphones?
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Old 9th June 2009, 09:47 PM   #15
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I am very interesting in the topic, but I think it is in the wrong section... send me whatcha got Scott! :_)

I'll PM if you wish... EDIT: oh nvm,that's the link... hmmm...

Ok, how to eliminate the EQ fudge?? The hf is the hardest to get right...

EDIT2: is the HF issue a function of an A/D limitation in the soundcard?? (slope and all that...) just thinking out loud...



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Old 9th June 2009, 10:15 PM   #16
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Good start. I'll try Scott's trick and see if I can get some correlation on the charts I have for my mikes. I may use a different source for the spark, one that I can sync with my Praxis system.

HF correction is only part of the calibration task. Overall sensitivity is another part.

John Curl sent me the Manger paper and Manger discusses these issues as well. He describes an M-Transducer but doesn't explain what it is. I would like to figure it out. It generates a step with a very fast risetime, not a doublet. The doublet of the spark discharge must be related to the risetime and duration of the spark I guess. Is there a way to shorten or lengthen it?
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Old 9th June 2009, 10:38 PM   #17
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Quote:
Originally posted by 1audio

John Curl sent me the Manger paper and Manger discusses these issues as well. He describes an M-Transducer but doesn't explain what it is. I would like to figure it out. It generates a step with a very fast risetime, not a doublet. The doublet of the spark discharge must be related to the risetime and duration of the spark I guess. Is there a way to shorten or lengthen it?
The Manger web site has a description of it.

If you have AES access the paper in the pic derives the spark response and talks about using the Manger driver.
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File Type: jpg paper.jpg (33.2 KB, 360 views)
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Old 9th June 2009, 11:40 PM   #18
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Quote:
Originally posted by 1audio
Is there a way to shorten or lengthen it?

Arc welder.
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Old 9th June 2009, 11:46 PM   #19
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Quote:
Originally posted by 1audio
Good start. I'll try Scott's trick and see if I can get some correlation on the charts I have for my mikes. I may use a different source for the spark, one that I can sync with my Praxis system.

HF correction is only part of the calibration task. Overall sensitivity is another part.

John Curl sent me the Manger paper and Manger discusses these issues as well. He describes an M-Transducer but doesn't explain what it is. I would like to figure it out. It generates a step with a very fast risetime, not a doublet. The doublet of the spark discharge must be related to the risetime and duration of the spark I guess. Is there a way to shorten or lengthen it?
Maybe the M-Transducer is a Manger driver?

Anyhow the duration of the spark is probably related to the energy available to discharge, the tuning of the discharge system, and the length of the gap.

If you were discharging a capacitively charged system, the duration would have a relationship to the capacitance, the current drawn in the spark and the breakdown voltage in the gap, as well as the charge voltage in the cap... then there is the voltage and current required to maintain the spark/plasma. So there are the start end and end parameters. How to manage them theoretically is probably well known to sparkplug designers?

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Old 9th June 2009, 11:47 PM   #20
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Is the M-Transducer in the AES paper the same? The performance is quite different. I have measured and heard Manger drivers before. I didn't see any real magic and some bizarre off axis response. And the measurements on the site don't match the measurements in his paper from 20 years ago.
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