Calibrating microphones and speakers

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If to use less than 17 KV per CM and ignite it using HF pulse? Will it be better controllable?

cbdb said:
I think it was a custom built optoisolater I made myself, unless they have improved the chip ones had a voltage limit of 7500v. This is starting to get compicated for DIY.

Here we are not limited by ground return path, unlike in car engines, so isolation is not necessary.
 
The 17kv/cm is the breakdown voltage of air (at STP and a certain humidity).

Here we are not limited by ground return path, unlike in car engines, so isolation is not necessary.

The problem is meausruing the spark current.
May be possible if you ground lift the scope and dont exceed any scope internal breakdown voltages. Not that simple and this might get dangerous, or at least painful, nothing like a shock to get the adrenaline flowing. (happened more than once in the good old days))
 
bear said:

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...

_-_-bear

How long ago did you listen to it? Maybe it was an older model?

I do not see why it would require an huge baffle to have a flat curve in the mid-highs.
 
With a piezo or battery powered spark source I don't see any issues in measuring the current pulse with a suitable shunt, one end of the shunt defines the "GND" of the spark circuit (the scope's GND). More problems I see in having low inductivity (loop area) of the assembly and such...
 
cbdb said:
The 17kv/cm is the breakdown voltage of air (at STP and a certain humidity).


I believe you. But if to ionize it by HF pulse less voltage will be needed than a brekdown one, so breakdown would depend on when we ionize it, instead of when it decides to ionize. Prepare the voltage (stable, regulated!), then apply HF pulse. That's it.


The problem is meausruing the spark current.
May be possible if you ground lift the scope and dont exceed any scope internal breakdown voltages. Not that simple and this might get dangerous, or at least painful, nothing like a shock to get the adrenaline flowing. (happened more than once in the good old days))

I don't see any problem here. Suppose, we use a flyback transformer/rectifier from a computer monitor, and it's ground side connect to the ground through a resistor. When discharge happens, measure a negative pulse on the resistor that depends on current and it's value. It is exactly what I implemented when designed an electric fence in South Africa: a negative pulse of the corresponding part of the fence charging device activated a photo camera and triggered alarm signal. I was limited by negative pulses because intruders would ground the wire, but if we use a symmetrical charging/discharging device we are free to measure either current flowing from the negative wire to ground, or from the negative output of the rectifier/capacitor to the ground. In first case the pulse will be negative, in second case it will be positive, but it will be measured in respect to the ground in both cases.
 
cbdb said:


What is the voltage across the shunt before we reach the breakdown voltage of lets say 17kv and no current flows? Not a little less than 17kv?

0 (Zero). When we ignite the spark, it will be I*R. You have to go down from the positive contact of the spark gap, through the wire, to the positive contact of the HV supply, go through it to it's negative contact, and come to the resistor's upper end. Go down through this resistor on the ground. Now, take a scope, and connect it's probe to the upper leg of the resistor, and the scope's ground wire to the ground.

Do you feel it now?
 
Duh! Of course the other side! Sorry. Back in the day we also made igniters using 120 AC neon light transformers so the current sense had to take the high voltage. One more consideration (not major), when the current flows the resistance (and voltage ) of the gap is quite small (ionized cloud), cant remeber any numbers.
 
cbdb said:
Duh! Of course the other side! Sorry. Back in the day we also made igniters using 120 AC neon light transformers so the current sense had to take the high voltage. One more consideration (not major), when the current flows the resistance (and voltage ) of the gap is quite small (ionized cloud), cant remeber any numbers.

Don't worry, it's my fault: I spoke wrong language when used visual and audial predicates. Now I know how to explain you my feelings about amplifier distortions: where they are coming from, how do they go, and how to approach the solution of the problem. ;)
 
Don't worry, it's my fault: I spoke wrong language when used visual and audial predicates. Now I know how to explain you my feelings about amplifier distortions: where they are coming from, how do they go, and how to approach the solution of the problem.

Not your fault, Iwasnt thinking. Look forward to more "great amp" thread, see you over there later. now I have to pick up kid and finish this bad movie!
 
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To measure the current make a current transformer with a ferrite donut and a few turns on the secondary loaded with a resistor. Calibrate it with an audio generator. Should be good from 1 KHz to something very high and well insulated. Use it on the low side for safety.

The ionized air is the Ionovac / Hill Plasmatronics approach. Dr. Hill explained that its a thermal-acoustic transducer actually. He described plans to me make one working down to 100 Hz that would be enormous. Never happened.

The length of the spark may create a phase difference between the ends but the discharge will be well faster than the speed of sound across the gap. I would expect that it would have a cylindrical radiation pattern and should be pretty planar when parallel to the gap.

The magnetic field might register in the output if the shielding isn't effective. Could be tested by discharging into a shorted gap.
 
Ouroboros said:
Does it have to be a spark?

Can a similar short impulse be generated by exploding a short length of fuse wire by discharging a large capacitor through the wire?

Yes, and pistol shots have been used too. It's just that it's nice to not have to reload.

I picked an old electronic starter for a residential stove off of a discarded one the other day. This looks like it could be rigged to trigger automatically.
 
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We have been talking about a spark in free space. What about a surface gap spark plug flush mounted on a flat plane? The spark on the surface won't have a reflection, nothing can vibrate with the energy, etc.

The frequency range of interest is above 1 KHz so a 1M diameter disk or minimum rectangle should be enough to get good info.
 
Demian,

Excellent idea, it seems... like on a piece of clean(!) sheet of glass or other suitable material? This would also lessen the impact from the mechanical noise from actuating a piezo stack when we feed the gap from "behind" that pane.

- Klaus
 
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FWIW, I experimented with spark recordings about 3 years ago.
The device on the left was made with a surplus 7.5 kV "air ionizer"
It was a form of spark gap relaxation oscillator.
The voltage would build up on the caps until a spark occurred and the process would repeat about once a second.
Very loud but -- the recordings were useless for getting a response curve.

The device on the right was a line powered dual gas stove igniter.
I wired the output coils in series.
This works by charging a cap and then discharging it through a primary coil. Repeats at about once a second.
I got very consistant sparks and was able to get useful response curves from the spark recordings.

Cheers.

ZAP
 
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