Using the Panasonic WM61A as a Measurement Microphone

  
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Measurement microphones differ from recording microphones and sound meters-they have a flat response, (usually to well below 20 Hz. , and above 20 kHz. , ) and do not have `weighted, ` or equalized frequency response. They are also optimized for measuringhigh SPL sound intensity, (for example, measurements taken at fraction of an inch from a speaker driver-to
Using the Panasonic WM61A as a Measurement Microphone - schematic

measure speaker response. ) Measurement microphones retail for US $100 to over US $500, but very adequate measurement microphones can be made using the Panasonic WM61A back electret microphone cartridge, which can be purchased through Digi-Key, part number P9925-ND, for under US $2. 00, each. Figure I, (which is available in larger size jpeg, or xfig, format, ) is a partial schematic for interfacing the Panasonic WM61A Electret Microphone cartridge to the SoundBlaster CT4810 PC Sound Card, including approximate signal voltage levels. Figure II, (which is available in larger size jpeg, or xfig, format, ) shows the construction of a Measurement Microphone using the Panasonic WM61A Electret cartridge. The electret cartridge should be covered with silicon sealant, (I use GE`s Silicon II, Household Glue-which is available in the paint department of home improvement centers, ) taking special care that none of the sealant gets on the black cloth cover of the cartridge-the cartridge-to-case should be an air tight seal. The wires should be soldered to the cartridge first, cut to length, and soldered to the plug-and the length checked by screwing the plug/cartridge into the casing, then the sealant applied, and the microphone assembled, (there are pictures, below, that show how to drill the hole for the cartridge, etc. ) The measurement microphone is specified at -35 dB +/- 4 dB, (0 dB = 1 V / Pa, ) with an load resistance of 2. 2K,...



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