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Recording peak amplitude of muzzle blast

R

Rich Grise

Jan 1, 1970
0
I would like to setup 5 microphones to record the peak
amplitude of a muzzle blast, N,S,E,W, and above.
All I need are relative measurements to compare against each other.
I want to do this a very low cash outlay. I will build a peak
detector/sample hold for each mic.
I'm thinking of using the WM-61A mic.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=P9925-ND
The mics will be placed within 4ft of the muzzle,
Do I need to place some type of mechanical attenuator around the mics?
How would you suggest doing that?
Regarding the peak detector, sample and hold, display.
Easy part first, Display- use existing DVM, maybe with a 5 position switch
to
select held data from mics.
Looking for peak detector and sample/hold ideas, or if there is another
method?
Have good stock of transistors and some basic ICs.
Cost is important.
http://www.google.com/search?hl=en&q=gunshot+sound+level

Hope This Helps!
Rich
 
J

Joerg

Jan 1, 1970
0
GregS said:
Well, I think they are better than electrets. I also thought about bimorphs and pressure
sensors. I don't think piezos are that linear and sensors are typically slow.


The PZT-5H material we use is quite linear. I don't know much about
audio ceramics but I don't think Mike needs this to be particularly
linear, he just wants to find the peak timings.

I'm getting search results of gifles and gunshot sounds from 140 dB to over 170.
Here is a piece by Shure....

http://shure.custhelp.com/cgi-bin/shure.cfg/php/enduser/std_adp.php?p_faqid=75

Quote: "In the 10 kHz range, 180 dB SPL is the MAX SPL of the SM58.
However, this is a calculated measurement as Shure Engineering had no
means to create such enormous and dangerous SPL."

Maybe they should hire an engineer who is a NRA member :)

[...]
 
A

amdx

Jan 1, 1970
0
Joerg said:
The PZT-5H material we use is quite linear. I don't know much about audio
ceramics but I don't think Mike needs this to be particularly linear, he
just wants to find the peak timings.
Just a clarification:
I want to compare relative amplitude of different impulses.
Mike
 
Q

qrk

Jan 1, 1970
0
GregS said:
Well, I think they are better than electrets. I also thought about bimorphs and pressure
sensors. I don't think piezos are that linear and sensors are typically slow.


The PZT-5H material we use is quite linear. I don't know much about
audio ceramics but I don't think Mike needs this to be particularly
linear, he just wants to find the peak timings.

I'm getting search results of gifles and gunshot sounds from 140 dB to over 170.
Here is a piece by Shure....

http://shure.custhelp.com/cgi-bin/shure.cfg/php/enduser/std_adp.php?p_faqid=75

Quote: "In the 10 kHz range, 180 dB SPL is the MAX SPL of the SM58.
However, this is a calculated measurement as Shure Engineering had no
means to create such enormous and dangerous SPL."

Maybe they should hire an engineer who is a NRA member :)

[...]

As Joerg states, PZT ceramics are linear up to very high levels. In
air, you'll have a natural attenuator due to the impedance mismatch.
You also have good impulse response with ceramics. As for sampling,
use a 4-channel digital oscilloscope. You can save all your results
for post processing (best to save table of numbers than visuals).
 
J

Joerg

Jan 1, 1970
0
amdx said:
Just a clarification:
I want to compare relative amplitude of different impulses.
Mike

Oh. Then it has to be linear and sound muffling will probably be out as
well because moisture and whatnot will change its muffling performance.

You'll probably have to look into piezos and ceramic capacitors as mikes
if it has to be cheap. Professional stuff like this will be pricey:
http://www.gras.dk/00012/00013/00029/00116/
 
J

Joerg

Jan 1, 1970
0
qrk said:
GregS said:
GregS wrote:
Hi All,
I would like to setup 5 microphones to record the peak
amplitude of a muzzle blast, N,S,E,W, and above.
All I need are relative measurements to compare against each other.
I want to do this a very low cash outlay. I will build a peak
detector/sample hold for each mic.
I'm thinking of using the WM-61A mic.
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=P9925-ND
The mics will be placed within 4ft of the muzzle,
Do I need to place some type of mechanical attenuator around the mics?
How would you suggest doing that?
Regarding the peak detector, sample and hold, display.
Easy part first, Display- use existing DVM, maybe with a 5 position switch
to
select held data from mics.
Looking for peak detector and sample/hold ideas, or if there is another
method?
Have good stock of transistors and some basic ICs.
Cost is important.
Thanks, Mike
After thinking dynamic microphone so far I dug up this. I don't think you
will
need any other amplifier.

http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMsYQxPYEnGVuLJZuW8
W
b6%252bkxlI5RpqXChs%3d
Dynamic mikes can saturate quickly, big time. BTDT.
Well, I think they are better than electrets. I also thought about bimorphs and pressure
sensors. I don't think piezos are that linear and sensors are typically slow.

The PZT-5H material we use is quite linear. I don't know much about
audio ceramics but I don't think Mike needs this to be particularly
linear, he just wants to find the peak timings.

I'm getting search results of gifles and gunshot sounds from 140 dB to over 170.
Here is a piece by Shure....

http://shure.custhelp.com/cgi-bin/shure.cfg/php/enduser/std_adp.php?p_faqid=75
Quote: "In the 10 kHz range, 180 dB SPL is the MAX SPL of the SM58.
However, this is a calculated measurement as Shure Engineering had no
means to create such enormous and dangerous SPL."

Maybe they should hire an engineer who is a NRA member :)

[...]

As Joerg states, PZT ceramics are linear up to very high levels. In
air, you'll have a natural attenuator due to the impedance mismatch.
You also have good impulse response with ceramics. As for sampling,
use a 4-channel digital oscilloscope. You can save all your results
for post processing (best to save table of numbers than visuals).

DSOs offer poor dynamic range. 6 ENOBs if you are lucky, maybe around
35dB. My Instek here is a bit better but still nothing to write home
about in terms of dynamic range. I'd go the sound card route where you
can easily obtain >16 ENOBs on the cheap. If you can find one with five
or more inputs, that is.
 
P

Phil Allison

Jan 1, 1970
0
"GregS"
Joerg


** Absolute bullshit.

Any dynamic mic worth the name will handle huge SPL levels.

Well, I think they are better than electrets.


** Very much better than low cost electret capsules.



....... Phil
 
G

Glen Walpert

Jan 1, 1970
0
Oh. Then it has to be linear and sound muffling will probably be out as
well because moisture and whatnot will change its muffling performance.

You'll probably have to look into piezos and ceramic capacitors as mikes
if it has to be cheap. Professional stuff like this will be pricey:
http://www.gras.dk/00012/00013/00029/00116/

Bruel & Kjaer is another manufacturer (the original) often found used
on ebay, and BSWA Tech is a Chinese manufacturer of equivalent
microphones at lower cost but still expensive and not much available
used. For a reasonably accurate peak pressure measurement one of
these solid metal diaphragm measurement microphones is the only real
alternative, so it is a good thing that is not what the OP wants :).

Even the best available measurement microphones cannot resolve the
rise time of the shock wave from the muzzle blast of a supersonic
round, thus missing the exact peak by a bit. Even custom microphones
with 200 ns risetime to a shock wave can't do that, and getting even
that slow (compared to actual shock) risetime requires having the bare
microphone diaphragm mounted perpindicular to the direction of shock
wave propogation quite accurately.

I like the piezo idea, calibrated for the same respone when placed in
a small group equidistant from the muzzle, and checked at various
distances for linearity assuming inverse square attenuation
(neglecting losses) with no reflections involved - complete your
measurement before the first reflection can reach the microphone.
 
J

Joerg

Jan 1, 1970
0
Glen said:
amdx wrote:
[...]
Oh. Then it has to be linear and sound muffling will probably be out as
well because moisture and whatnot will change its muffling performance.

You'll probably have to look into piezos and ceramic capacitors as mikes
if it has to be cheap. Professional stuff like this will be pricey:
http://www.gras.dk/00012/00013/00029/00116/

Bruel & Kjaer is another manufacturer (the original) often found used
on ebay, and BSWA Tech is a Chinese manufacturer of equivalent
microphones at lower cost but still expensive and not much available
used. For a reasonably accurate peak pressure measurement one of
these solid metal diaphragm measurement microphones is the only real
alternative, so it is a good thing that is not what the OP wants :).

Even the best available measurement microphones cannot resolve the
rise time of the shock wave from the muzzle blast of a supersonic
round, thus missing the exact peak by a bit. Even custom microphones
with 200 ns risetime to a shock wave can't do that, and getting even
that slow (compared to actual shock) risetime requires having the bare
microphone diaphragm mounted perpindicular to the direction of shock
wave propogation quite accurately.

I like the piezo idea, calibrated for the same respone when placed in
a small group equidistant from the muzzle, and checked at various
distances for linearity assuming inverse square attenuation
(neglecting losses) with no reflections involved - complete your
measurement before the first reflection can reach the microphone.


Piezo material can take a huge punch. Some of the gear we designed had
to ultrasound-image during lithotriptor shots (to pulverize kidney
stones and such). That is like listening to a Mozart concerto next to an
ordnance disposal pit. The main challenges are in the recipe and
processing of the backing material.

Another option might be PVDF but I do not have experience how that fares
in the audible range.
 
J

Jasen Betts

Jan 1, 1970
0
I'm finding the initial peak is from 100usec to 800usec long, from 0 to peak
to 0.
I don't think I could ever be sure I caught the peak.

What do you think?

I think at 44200khz sample rate sound cards sample every 23us.
 
J

JosephKK

Jan 1, 1970
0
I'm finding the initial peak is from 100usec to 800usec long, from 0 to peak
to 0.
I don't think I could ever be sure I caught the peak.
What do you think?
Mike
That will get you 30 to 40 samples with a mediocre sampler and 60 to
80 with a better one. Plot them and look at the plots. Your eye will
tell you.
 
C

Carlos Murillo

Jan 1, 1970
0
Glen said:
Bruel & Kjaer is another manufacturer (the original) often found used
on ebay, and BSWA Tech is a Chinese manufacturer of equivalent
microphones at lower cost but still expensive and not much available
used. For a reasonably accurate peak pressure measurement one of
these solid metal diaphragm measurement microphones is the only real
alternative, so it is a good thing that is not what the OP wants :).

Even the best available measurement microphones cannot resolve the
rise time of the shock wave from the muzzle blast of a supersonic
round, thus missing the exact peak by a bit. Even custom microphones
with 200 ns risetime to a shock wave can't do that, and getting even
that slow (compared to actual shock) risetime requires having the bare
microphone diaphragm mounted perpindicular to the direction of shock
wave propogation quite accurately.

I like the piezo idea, calibrated for the same respone when placed in
a small group equidistant from the muzzle, and checked at various
distances for linearity assuming inverse square attenuation
(neglecting losses) with no reflections involved - complete your
measurement before the first reflection can reach the microphone.

A rather divergent idea: how about using a dynamic mike fed into
a current amplifier? The resulting high damping because of the low
input impedance might help keep the excursion within reasonable
mechanical limits, as well as diminish the sensitivity of the mike
enough that it might be able to handle the wave front (which I suppose
resembles more of a soliton).
Too crazy an idea?

carlos.
 
V

Vladimir Vassilevsky

Jan 1, 1970
0
Carlos said:
A rather divergent idea: how about using a dynamic mike fed into
a current amplifier? The resulting high damping because of the low
input impedance

How about recording the muzzle flash instead of the muzzle blast?


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
 
A

Angelo Campanella

Jan 1, 1970
0
The good measureemnt microphones have specs on the maximum SPL that
they can purvey linearly. Half inch random incidence mics are up to
anout 160 dB. Quarter inch mics go even higher.

My one excursion theerin was using a half inch mich recording a .22
caliber pistol discharged in the adjacent room in a residence. I think I
measured about 140 dB. But I did not see it on the meter directly.
Rather, I recorded the SLM (B&K 2203) AC output onto tape. Then I viewed
the palyback audio on an oscilliscope (his was a LONG time ago). I used
a pistonphone (124 dB RMS) signal recorded on the same tape and gain
settings as a calibration.

The devil is in the details. The question becomes whether the pulse
peak has been clipped somewhere in the elctronics chain, and also
whether the microphone is operating within its linear transducer range.
Condenser mic diaphragms can deflect too close to the backing plate, or
too far away, Dynamic mic coils can deflect too far awry in the magnetic
field just like loudspeakers. The only way to be sure that things are
linear is th reduce the pressure pulse by a factor of two (-6.0 dB) or
ten (-20.0 dB) and reckon whether the purveyed signal had the same
differential.

Angelo Campanella
 
B

BobG

Jan 1, 1970
0
Try to find a copy of Recording Engineer and Producer from the 70s or
80s with the Sennheiser ad showing the plot of an MD421 output
recording a starter pistol at 140dB.
 
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