Boston Audio Society Microphone Test Clinic Uses SoundCheck

On Sat Nov 21, Listen sales engineer Neil Rubado demonstrated SoundCheck’s capability for microphone testing at the Boston Audio Society Microphone test clinic. The test clinic, held at Joe Demarinis’ Winchester Lab, used a set of traditional and non-traditional tests to assist in characterizing a microphone’s performance, especially those parameters that correlate with subjective impressions.

Over 20 attendees brought microphones from their studios. They varied from new to old and included Royer ribbon SF-12 and a vintage AKG C24.

There were seven different tests carried out on each microphone: Frequency Response, Polar Response, Distortion, Impulse Response, SPL overload, Sensitivity and the Pink Noise Field Test. SoundCheck was used for the Frequency Response and Polar response. Although SoundCheck can also be used for other tests, for this event a variety of different test methods and equipment were selected for demonstration.

Frequency Response was measured using SoundCheck, a calibrated Listen SCM2 microphone and an Aura NS3-193-8A loudspeaker as the sound source. First the speaker was measured with the measurement microphone and then measured with the pro audio microphone under test. The response from the measurement microphone is subtracted from the response measured by the pro audio microphone. This effectively removes the influence of the source speaker’s response from the measurement, resulting in the frequency response curve including phase of the pro audio microphone only. Since the measurements were not made in an anechoic chamber, reflections above 200 Hz (due to room size limitations) were windowed out. After removing reflections, results from 200Hz to 20kHz were presented.

The Polar response was plotted using a standard SoundCheck directional response sequence (available free from Listen’s website). The microphone was rotated on a turntable and measurements made every 10 degrees. A log sweep stimulus was played from 100 Hz to 10 kHz at each angular increment, and the response acquired and analyzed using a Time Selective Response algorithm. This method allowed the test to be performed in a non-anechoic environment by placing a window around the direct signal, eliminating the influence of reflections.  The response at each angular increment was compared against the on-axis response to create a normalized curve.  This removed the influence of the device’s frequency response and sensitivity, such that the polar plot showed only the directional response. Microphones with switchable patterns were especially interesting to see how their Omni, Cardioid and Figure 8 responses plotted.

SoundCheck is a professional tool for R&D and Production line measurement of transducers, and is used by many microphone manufacturers around the world to ensure the quality of their microphones. Although testing microphones for end-users such as recording studios and music enthusiasts is not a typical application for SoundCheck, the tests that were demonstrated here are very similar to those that may be carried out in the R&D lab by the worlds leading microphone manufacturers.