11-11-2023, 12:56 AM
Quote:international standards have established 1 Pascal (Pa) for specifying the sensitivity of microphones. This is equivalent to a sound pressure level 94 dB SPL. (Interestingly, a 1939 RCA product catalog specified their microphones at 10 dynes/cm2, which is 1 Pa!) A microphone with a specified sensitivity of –42 dB referenced to 1 V/Pa, for example, would produce a voltage of 7.9 mV/Pa:From https://www.radioworld.com/news-and-busi...icrophones
According to DIN standard 45500, the overload limit of the amplifier must, for semi-professional use, be high enough so that an SPL 10 Pa can be handled at less than 1% distortion. This is 10-fold increase in SPL would produce 79 mV of signal voltage.
Quote:ECM manufacturers try to optimize the electret transducer and the JFET characteristics to minimize distortion. Literature on mic testing shows that, as expected, many ECMs begin overloading above 110 dB SPL, probably due to JFET distortion. The diaphragm itself may be capable of handling SPLs near 130 dB before their motion, and their output signal, become distorted.
Table from the site.
Using 2x 1.5V Alkaline cells ensures an end point of about 1.8V rather than 0.9V of a single cell.
The Id values I measured of 0.23 mA and 0.35 mA seem more typical for the data of jFET used in ECMs and similar to that table.
Cutting the PCB at the source pin and adding a series resistor may improve large signal distortion but is terrible for gain and noise level.
Many phones and all Apple's models now use mem chip microphones which have poor LF response and other issues including poorer dynamic range, but they are skinny.
It's still hard to beat a robust dynamic mic for S/N (assuming the preamp is good) and dynamic range, but frequency response at treble is worse. I think safer for audio narration and vocals than an electret, and that doesn't need the extended treble response. Obviously the electret is good for element in a shotgun mice or for a crossed cardioid pair for simple stereo, or a pair either side of a disc as a "dummy head" for binaural recording.
