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Old 10th June 2009, 12:15 AM   #21
KSTR is offline KSTR  Germany
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Hi,
My first and unsorted thoughts on this....
Quote:
Originally posted by 1audio
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?
With a piezo-stack as the source things are rather uncontrolled I'd guess. But thats the first option for DIYers, thogh we could check out what the tesla coilers and coin shrinkers have at hand...

One might get the pulse duration by measuring the current with a shunt in the loop and a pretty fast DSO. Pulse duration (again referring to the time the spark is "up") will only alter absolute level (think of dipole speaker below the dipole freq as an analogy) but not the relative response captured by the mic. One also might need a series of measurements, apply the integration to them, normalize the results and do a best-curve-fit to get more reliable data. And have the S/N issues addressed etc...

A problem I see, Scott mentioned it, is knowledge or estimation of the wavefront hitting the mic... If you look at the piezo spark (cigarette smokers, anyone?) one can see the spark is not well controlled in shape, which would blur the two doublet pulses... but I guess both pulses should have the same shape exept for polarity (unless the spark changes its shape during its lifetime -- or if build-up and extinction are different). If both shape and diameter of the air column that gets ionized is well controlled all would be fine. And we'd need knowledge about the time constants of the ionization, a tiny spark might have higher acoustical rise and fall times than a bigger one (more mass).

Indeed complicated matters, lot's of major and minor points to consider (ESD impact on the mic's eletronics)... time for both a lot of armchair reasoning (the Sherlock Holmes approach) and "just-go-for-it" measurements, like Scott has already exercised for us.

Any empircial physicist reading this and willing to comment?

- Klaus
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Old 10th June 2009, 12:51 AM   #22
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Quote:
Originally posted by 1audio
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.
Mr. Langen refers directly to the current Manger product page as the source for his sample. I can only imagine that they have improved the manufacture of it in 22yr. current CNC tooling is quite a bit better.
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Old 10th June 2009, 12:58 AM   #23
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Quote:
Originally posted by KSTR


Any empircial physicist reading this and willing to comment?

- Klaus
Neumann has a few papers in German and a short summary in English by Peus. They use the spark response in a very qualitative "seat of the pants" way to show impulsive and time smearing mic behavior. Several mics show very clear doublet behavior proving a good spark can be made. Reading between the lines I think they get a 60kHz limit. Earthworks claims 100kHz but keep the good stuff secret.
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Old 10th June 2009, 03:06 AM   #24
1audio is offline 1audio  United States
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After much prodding Earthworks revealed that the best mike was the Gefell MK301 1/4" mike. They use that as a baseline. They did claim 100 KHz is possible and that they had to work some tricks to do it.

I'll ask around to see if I can access a Manger driver to try. Perhaps its optimized to give a really good transient response with a very fast rise time.
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Old 10th June 2009, 04:13 PM   #25
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I have a demo CD from Earthwork with samples of a drum kit recorded using 20KHz and 50 KHz microphones. Indeed, differences exist even though it is recorded on an ordinary CD, and what I hear, different low frequency components of sounds of snares.
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Old 10th June 2009, 04:36 PM   #26
KSTR is offline KSTR  Germany
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Maybe they didn't use the closest possible spacing between the 50k and 20k mics?
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Old 10th June 2009, 04:40 PM   #27
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Quote:
Originally posted by KSTR
Maybe they didn't use the closest possible spacing between the 50k and 20k mics?
Do you mean they are cheating for marketing purposes?

I believe that transients are different.
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Old 10th June 2009, 06:36 PM   #28
KSTR is offline KSTR  Germany
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Quote:
Originally posted by Wavebourn
Do you mean they are cheating for marketing purposes?
No Anatoliy, Earthworks sure *are* serious guys from what all I know.

Quote:
I believe that transients are different.
To get at it we'd need to look at said snare hits (assuming it was a simultaneous recording) in close detail, that is analyse those signals differences in depth. Assuming all else equal, from differences in phase (from their different roll-offs) we should expect to see different waveshapes, even below the 22k CD brickwall. If you could provide the same identical snare hit in both 20k and 50k versions I could try to analize it (WAV or FLAC, not MP3).

But again we're polluting someone's thread...
EDIT: you are fully entitled to pollute your "own" thread, of course

On topic, I'm currently modifying one of my piezo spark gaps and will try to do the experiment myself (with WM61A and another capsule salvaged from an very LoFi old cassette recorder).

- Klaus
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Old 10th June 2009, 08:14 PM   #29
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KSTR - You're in the correct subject and thread here... non-polluting and about calibration of mics. Although, again I think this is an acoustics, not a Solid State matter... but whatever...

DM, I was not impressed with the Manger I auditioned here - it requires an IEC or larger baffle to get the response flat (I did not use such...) as far as I can tell... it was very beamy in the highs... sounded downright wierd, not bad, wierd. A stereo pair would have told me more, but I only had one available. I suspect that the soundstage would have been "unusual"... but I can't be sure of that. I'll be curious to know your results, subjective and measured... and there is a Manger thread or two over in Loudspeakers, fwiw...

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Old 10th June 2009, 08:33 PM   #30
KSTR is offline KSTR  Germany
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WORD OF CAUTION:

SPARKS FROM PIEZO LIGHTERS ETC CAN ZAP YOU SEVERLY! TAKE ALL PRECAUTIONS WHEN EXPERIMENTING! KEEP YOUR STUFF AWAY FROM CHILDREN ETC

- Klaus (got reminded of this IMPORTANT THING just a minute ago)
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