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Measurement Microphone Suggestions

Discussion in 'Microphones' started by aether, Jan 25, 2012.

  1. aether

    aether Active Member

    Hello, I'm a student looking to build an impedance tube setup and need some expert knowledge on the microphones. For those unfamiliar with impedance tube they basically setup a standing wave along the length of the tube and the pressure is measured at various locations which in turn allows you to calculate the acoustic impedance at the sample end.

    I am currently using very cheap microphones (<$10) as a quick mock up and they are proving quite unreliable. My budget would preferably be in the few hundred dollar range, the less the better ;)

    For this application:

    -the smaller the width the better (ie 1/2" or 1/4")

    -unidirectional, the only pressure I'm interested in is from the plane waves at the surface of the tube.
    -I am using measurement equipment that has a maximum input voltage of +-7 V @ 50 ohms, so I'm not sure which power system to use. Currently with the cheap electret mics, I am just using a simple op amp pre-amplifier. Can I get away with not having a high voltage phantom power setup?
    -Flat frequency response is not so important as I will be measuring relative changes at specific frequencies. My biggest need is for them to be highly repeatable so to have very small changes with temperature and a linear response with amplitude.

    Could you suggest any microphones that you have used or know of that could perform this task well? Thanks for your time!
  2. dvdhawk

    dvdhawk Well-Known Member

    You might consider a mic one would use with a audio analyzer. The dbx RTA-M for example is about $100 and meets almost all of your criteria, except that it is omni-directional as all RTA mics would be. It would require phantom power.

    There are similar mics that are cheaper and others much more expensive, for me this was the least expensive mic of its type I felt I could trust.
  3. RemyRAD

    RemyRAD Well-Known Member

    $.98 Omni-directional capsules, that don't require phantom power, generally have relatively flat responses from 20-20,000, would work fine for your application. You really don't want Uni-directional as their response varies with proximity to signal sources from their " proximity effect ". Simple electret Capsules have a ground, an output & a wire for 1.5 V of DC and don't require phantom at 48 V. Those too are utilized for RTA lower-cost analyzers and are 100% adequate for your purposes. You're doing this for controlled experiments not of a high fidelity nature. So you don't need the precision that higher-priced microphone capsules offer. So you need a flat omnidirectional microphone for measurement purposes.

    I'm only testing... your intelligence.
    Mx. Remy Ann David
  4. aether

    aether Active Member

    I am currently using the cheap electret microphones but their gain drifts over extended use.

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