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Sep 18, 2005

ProSoundNews has a nice writeup on Crowley And Tripp Microphones (full disclosure: Soundwave Research Labs is a client of mine):

“Didi said that in 25 years, she’s never heard a microphone so dynamic and open,” explained Resta about their use of the Studio Vocalist. “She was astounded, and that’s more impressive than my bragging about it—she’s an amazing singer.”

I’ve previously written about my experience with the Proscenium microphone.

I performed the independent testing on the Crowley And Tripp Microphones (you can download the results here). I was asked to describe my testing process, so I’ll comment a bit below.

I have a variety of testing apparatus that I use to measure the performance of standard 1-inch, ½-inch, or ¼-inch microphones. There are lots of methods that can be used to measure the performance of microphones such as the the reciprocity method (described in ANSI S1.10-1966), acoustical calibrators, or electrostatic actuators. However, the shape and figure-of-eight directivity of the Crowley and Tripp microphones make these methods impractical.

As a result, I settled on the “substitution” method to test the Crowley and Tripp mics (in fact I generally use the substitution method to measure mics that don’t have the standard 1-, ½-, or ¼-inch diameters - that is to say, pretty much any non-measurement microphone).

I use a reference microphone to measure the output (a maximum length sequence, MLS) of a full-range driver mounted in a large baffle. The reference microphone (usually my TerraSonde or ACO Pacific ½-inch mic) has been calibrated by a NIST-traceable calibration lab. I then substitute the device-under-test (DUT) in the same position, and measure the same test signal. By subtracting the DUT curve from the (known) reference curve, I can compute the frequency response for the DUT.

The low-frequency response of ribbon microphones will change based on the distance between the microphone and the noise source. Specifically, the low-frequency response of ribbon mics will increase as the mic moves closer to the sound source (the “proximity effect”). I performed the mic measurement at a distance of 25-inches to obtain the “flat” curve for the tested microphones.

Given that these mics are used for audio recordings, as opposed to audio measurements, the mics themselves are basically musical instruments and will be positioned according to the tastes of the musicians and engineers. The point of using a 25-inch reference distance is to demonstrate that the mics can have a flat frequency response, if desired. In practice, you will see (and hear) a more pronounced bass boost if you use close-miked techniques. If I have a chance, perhaps I’ll do some close-in frequency response measurements to better demonstrate the proximity effect of Crowley and Tripp Microphones.

That’s the measurement procedure in a nutshell. Comments, questions, and suggestions are welcome.

Bob, Chris and Hugh from Soundwave Research Labs will be showing off their mics at AES; I’ll be there as well. Hope to see you there!

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