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ETF Mic vs Radio Shack SPL Meter

Discussion in 'Archived Threads 2001-2004' started by Pete Mazz, Jan 18, 2002.

  1. Pete Mazz

    Pete Mazz Supporting Actor

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    As promised, I compared the calibrated ETF mic and pre-amp against the RS SPL meter. I had already done the LF mod to the RS meter, so unless you've done the same, disregard the LF. All samples were taken with both mics at about 1 meter and pointing directly at the speaker. The line out from the sound card was fed into my B&K307 set to analog bypass, with only one speaker connected.
    Here is the 20Hz-20kHz graph:
    [​IMG]
    Here is a 2kHz-20kHz graph to show the upper response:
    [​IMG]
    The RS meter starts to roll off around 8-10kHz.
    Pete
     
  2. ThomasW

    ThomasW Cinematographer

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    Pete

    This is the $250 calibrated mic and mic pre-amp from ETF?

    Also is this with the .cal files loaded for each mic?

    Are you able to use the ETF RS.cal file after doing the LF mod to the RS meter?
     
  3. Mark Krawiec

    Mark Krawiec Agent

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    this is interesting. i assume you've done the whole curve at one meter in room. if this is the calibrated mic from etf, we'll assume it's accurate within a couple of db compared with a reference mic. it fairly well shows the rs trailing off at 12 db/octave after 4k, but also a hump of ~4-6db around 2-6k. Not very impressive for mids and highs.

    hey, can you try a true nearfield measurement with the mic very close to the driver. (how close-- ~1/10 the effective radius of the driver.) i'm curious to get a better graph of the low end. it's hard to tell, but the rs may be off 4-6db or more down there.

    did you do this a couple of times and was it fairly repeatable?

    how high was your speaker off the ground, and how close to the nearest wall was the speaker?
     
  4. Pete Mazz

    Pete Mazz Supporting Actor

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    This was done with the calibrated mic and pre-amp from ETF. The mic cal file was loaded to take this. The mic was placed on a tripod at tweeter level(36" high), of a vented Kit 281 (MTM). The speaker is about 3' from back wall and is 10' from any other. The equipment rack and RPTV are behind the speaker about 1'. Here's what it looks like. The right speaker was measured in place.
    [​IMG]
    When I switched to the RS SPL meter, no cal file was used as I modded this unit for low end accuracy. The SPL was adjusted in ETF to align the graphs using the overlay function.
     
  5. ThomasW

    ThomasW Cinematographer

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    Pete

    What's the LF mod for the RS? Can you detail it or have a link to a website?
     
  6. Mark Krawiec

    Mark Krawiec Agent

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  7. FrankD

    FrankD Stunt Coordinator

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    Great job! Please post any refinements to your test.

    Now for the money question. Would you suggest buying the mic and preamp form EFT? vs the RS?

    Also can the preamp from EFT run only on batteries?

    Regards
     
  8. Pete Mazz

    Pete Mazz Supporting Actor

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    OK, here's what I came up with.
    First: All measurements were done with mics at face of AV8. The three measurements are the RS SPL meter with and without cal file loaded and the ETF mic.
    [​IMG]
    Second: All measurements were done with mics at 2'. The three measurements are the RS SPL meter with and without cal file loaded and the ETF mic.
    [​IMG]
    It doesn't look like the cal file has any adjustments for LF. The upper end of the cal file seems to overcompensate for the RS meter, although I doubt the meters match up to one another that well.
    Thomas, I found the mod on Eric Wallens site:
    http://www.gti.net/wallin/audio/audio.html
    Frank, the pre-amp takes a 9V battery. I bought rechargeables, as the manual states it eats them up fairly quickly. You can use an adapter, but it cautions about adding noise. I chose to get the mic because after I bought the software and started playing with it I soon realized that all this info does no good if it's not reliable. I was tempted to build my own pre-amp, as I already did a DIY mic which is supposed to be very accurate, but again...who knows, without something to reference it all against. BTW, I will test the DIY mic against the ETF. The parts for the mic are only a few bucks, and other than some tiny soldering spots (2), it was a piece of cake. Here is the site:
    http://www.speakerbuilder.net/web_fi...mic/diymic.htm
    Pete
     
  9. BruceD

    BruceD Screenwriter

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    I you want to build your own calibrated mic wand and mic-preamp (9v battery lasts > year) here is some info:
    mic/mic-preamp
    I got is as a kit from a JM Neal when he was on the net, but I don't know where he is now (total cost was $88). I also have the entire file of construction photographs, but don't have a website to put them on.
     

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