Oscope & Condesner Mic

Discussion in 'General Electronics Chat' started by DC_Kid, Dec 30, 2015.

  1. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    i have a digital storage oscope (school type, owon, etc). i want to use it to capture some sound wave info, specifically to use the data to look at SPL levels of certain types of sounds. the mic i have in mind is a GRAS 40DP.

    what would be the best way to do this? i am new to mic's, the spec sheet on the mic says 1mV/Pa. the range i am looking at will be like 0.1Pa(~75db SPL) to 2000Pa(~160 db SPL).

    i suspect i need a small opamp to boost the output some so i can get better range on the scope.

    your thoughts?
     
  2. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    You probably want to get the output up to a volt or so. You're looking at a gain of fourty db, so a cascade of at two op-amps might be better.
     
  3. #12

    Expert

    Nov 30, 2010
    16,340
    6,824
    Buy a sound level meter with an output jack. I got mine at Radio Shack for under $30
    60 db to 126 db in 6 ranges. "A" weighted or "C" weighted.
     
  4. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    not gonna work, i need a tool with very fast rise time and can work out to 175db SPL (~11kPa). are there any handhelds that are in this range for not so much $$?

    the pre-amp that attaches to the 40DP needs 28vdc(or more) + 200V to polarize mic. i can build both of those fairly cheap.
     
    Last edited: Dec 30, 2015
  5. #12

    Expert

    Nov 30, 2010
    16,340
    6,824
    Not likely when you consider that a Saturn rocket comes in at 160 db.
     
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    That's a pretty big range. 0.1mv to 2 volts. So with a gain of 10 you could maybe get 1 mv to 20 volts. So your gonna need some range changes somewhere.
    What are you measuring? Gunshots?:D
     
  7. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    exactly, rifle blasts. 12ga is in that 165+ area. the mic range needs to extend past that, etc, which the 40DP does.
    i can perhaps use a fixed gain on the signal and then adjust oscope voltage scale.

    i also have a DataQ datalogger that has a decent sampling rate (10kHz) and the software allows me to add scaling factors, etc. i dint know what my own scope sampling rate is. i guess i will want to use the one that has highest sampling rate.

    from some other online test data the rise times are very fast, within 0.15ms, 10kHz is not fast enough to capture all the details between.

    yeah, my scope is 100MHz(acquisition mode) sampling rate, so the scope would be better to capture with.

    the max SPL i would ever see is likely 168dbSPL (5023Pa). so my detection range is .1mv to 5v. i guess i can have some fixed gains for the opamp, maybe 10x 5x 2x 1x, i can adjust scale on scope to see more, etc.
     
    Last edited: Dec 31, 2015
  8. Veracohr

    Well-Known Member

    Jan 3, 2011
    552
    76
    Seems to me like the datalogger would be a better tool for your situation.

    If you put any amplification between the mic & datalogger you'll need to measure the amplification factor accurately.
     
  9. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    my datalogger is only 10kHz though, scope is 100MHz. in essence, the acquisition function of the scope makes it a datalogger?

    i believe i can download the acquisition to computer and use owon software to look at it.

    cant i measure actual gain of opamp using a reference voltage IC ?
     
  10. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    so, the gras 40DP need 200v, the PCB 1/4" 378C10 is pre-charged, which makes things easier. almost impossible to get pricing on these items. ah, ok, the PCB is $1400 w/ the preamp, $900 for just the mic cartridge. i guess i could save $500 if i built my own preamp.
     
  11. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    So if you are recording gun shots, why worry about the low amplitudes? What are you doing with the data?
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    Since you have to amplify it, calibration becomes a factor that wasn't present with the original instrument.

    You might just as well pick a top quality electret type and bias it in the emitter circuit of a grounded base stage.

    Typical bias voltage will be around 2V, you simply set that with the ratio of the decoupled base bias divider (not overlooking Vbe of course).

    The collector current will be just a tiny bit less than the emitter puts through the MIC, and that current is probably only a few tens of micro amps. The collector resistor will be quite high and you may have to select on test, but you get a large voltage gain. The grounded base configuration is the fastest of the 3 permutations and you can put an emitter follower on the collector without slowing it down *ALL THAT* much.
     
  13. BR-549

    Well-Known Member

    Sep 22, 2013
    2,004
    394
    Why not vary the distance of mic? You might find a sweet spot where the muzzle, mic and scope cooperate. All it cost is a little time.

    This is outdoors, right? i.e. minimum echo.

    Along with distance, you might consider angle also. From the side to the front of muzzle.

    Not sure what your looking for, but sometimes it helps to use more than one reference.

    You might want to record beginning of event from the front and the latter part from the side.
     
  14. #12

    Expert

    Nov 30, 2010
    16,340
    6,824
    That's what I was thinking. Sound decrease across distance can be calculated.
    In other words, nobody put a microphone under the Saturn rocket to measure its loudness.
     
  15. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    @ronv - my data being collected is for personal use in the design of muzzle devices. if any one design proves worthy in the context of $ value, i might pursue a patent and then either sell the patent or try and license it. getting into manufacturing is not in my playbook.

    the methods for sound testing muzzle blasts are well documented. i am using similar method(s). however, the methods do not have a standard, meaning positions and environments (shooter ear, downrange, off to side, ground plane only, hill wedge, indoor range, etc). having a std for the latter would help define "best bang for the $" when applying the testing to muzzle brakes, compensators, and silencers. of the published docs i have found thus far none of them have a collection of tests using various firearms and every one of them are open ground plane tests, etc.

    the PCB mic with pre-amp can deliver ±8v near its peak SPL. all i need to do is power it. i might not need any amp stage at all because i can adjust vertical scaling on my scope, etc.

    does this (mic w/ scope) sound about right? the OEM preamp for the PCB mic is 2V/μs. i would need a way to determine calibration of the setup since a 0.5v err on the scope means huge err in SPL, etc. it perhaps would need to go to someone like Dayton T Brown to be subjected to a reference SPL in a anechoic chamber. or, perhaps i can feed the preamp with a reference signal from my signal generator and then verify that the output matches the input? the OEM preamps seem to be impedance buffer and does not provide gain.
     
    Last edited: Jan 3, 2016
  16. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    I'm just going to think out loud and you can see if it make any sense.
    If the mic is okay for your loudest gun it seems like the mic calibration is all you need.
    I think rather than a scope where the width of the line is significant I would try to peak detect the signal and read it with a good voltmeter - say 2.047 volts, rather than 4 divisions on a scope.
    Whatca think?
     
  17. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    i believe my scope will give me peak of a selected section of waveform (i can do offline analysis too). using a peak & hold volt meter is also ok as long as the meter itself can sample fast enough. the published docs suggest that rise times should be no more than 20μs. my scope says it can sample at 10ns (100MHz). i have a fluke-25, not sure if that will work, need to check.
     
  18. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    If the scope accuracy is good enough that might be the way to go.
     
Loading...