Subject: Re: diaphragm output & phase: HC selectivity ... and the lateral organ of the fish From: Steve Beet <steve.beet@xxxxxxxx> Date: Sat, 6 Oct 2007 20:13:05 +0100 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>Hi Kevin, I'll keep this short because it's getting a bit off-topic, but if you look at B&K's web site (http://www.bksv.com/3095.asp) and search for very low frequency microphones, you'll find the only ones which go down to DC are "piezoresistive" designs. The lowest frequency they quote for a condenser is 0.07 Hz. Pretty low, but not DC. I believe RF condenser microphones can extend down to DC too, but the most common condenser mikes rely on a high impedance DC bias voltage, with that (resistive) impedance combining with the capacitance of the microphone itself to make a low-frequency time constant which prevents a true DC response. Steve