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Spark calibration of microphones
Spark calibration of microphones
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Old 29th May 2020, 03:35 AM   #141
ARailsback is offline ARailsback
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is a pistol gun shot (blanks) more consistent source than sparks?

Just curious.
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Old 29th May 2020, 03:58 AM   #142
keantoken is offline keantoken  United States
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It depends solely on the spark generator. My generator is inconsistent because it relies on air breakdown voltage which is highly variable. 1audio's generator should be very consistent.

I don't think you could load gunpowder, or ignite it to the precision of a good spark generator.
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Old 29th May 2020, 04:05 AM   #143
1audio is offline 1audio  United States
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Spark calibration of microphones
Maybe but not for me. Also the SPL is much too high to be useful.

Parts of this do not make sense. I'm pretty confident of the current transformers (Pearson and Stangenes) but the EMI is getting into everything. The Tek THS720 which I have used for years measuring discharges is getting pickup from the arc. Same for the newer scope. I need to figure out a much better isolation for the generator since I seem to get significant noise currents on its power cord. Once those confusors are under control then the controlled times spark would be pretty ideal. its actually an interesting problem but its testing all my measurement reserves.
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Old 29th May 2020, 06:02 AM   #144
keantoken is offline keantoken  United States
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The BW limit is getting lower and lower as I figure out the best way to cull and average recordings. It helps to have a fresh battery and play with electrode approach angle to minimize interference. Group delay shows the impulse response extending to below 1KHz.

I wonder how much the >1KHz stuff is influenced by boundary reinforcement.
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File Type: png averaged-groupdelay.png (25.7 KB, 27 views)
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Old 29th May 2020, 06:24 AM   #145
1audio is offline 1audio  United States
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Spark calibration of microphones
I think I have figured out where the current is coming from. its a very short peak. The coil is around 7K Ohms of resistance which would limit the current but there is a fair amount of energy stored in the stray capacitance in the HV circuit and very little inductance when it discharges which would explain the high peak current I think. More to explore tomorrow.

I'll try recording a number of discharges in various ways and see what I learn.
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Old 29th May 2020, 06:41 AM   #146
keantoken is offline keantoken  United States
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One thing I did which helped some is add a ferrite bead right at the spark gap. The one I used was sort of like a 34ohm resistor in parallel with a 1.59uH inductor. With the coilpack, too large a bead would prevent it from sparking altogether. I haven't tried that with the taser. It would be neat if I could get a spark to go across the outside of a bead.

The stray capacitance does seem to play a role especially with a high coil resistance. My taser has much less output resistance than your automotive coil. But I would assume that the coil leakage inductance would dominate in either case. The spark resistance itself increases with spark length, so short gaps would have higher initial discharge current. This agrees with my finding that too small a gap actually increases interference even though it reduces SPL.

Is it possible that the interference is coming from >100MHz noise not caught by your current probe? I remember that with ESD, sparks can generate noise into the GHz powerful enough to destroy small diode junctions.
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Old Yesterday, 01:15 AM   #147
1audio is offline 1audio  United States
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Spark calibration of microphones
I found that the spark generator was "not well" grounded inside and did a lot with scraping pant and re arranging connections which brought the interference down a lot. Some of the ground return current was getting coupled into the AC ground return. Lots of bad consequences to that. Its much better now. There still is considerable jitter, around 2 uS peak to peak.

You can see from the screencap that the HV starts at the same place and climbs at the same rate (15 KV in around 15 uS) with the overlapping curve. But the breakdown has about 2 uS jitter. For audio measurements 2 uS jitter will not be an issue. I have read that using a laser to trigger the spark would get the lowest jitter and that makes sense.

The spark appears to have 48A peak to peak. If I can find a small cap good for 30 KV (10 pF or so) I can test the current vs cap hypothesis.

The scope still periodically locks up from the EMI but at least it recovers.
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