> James Shatto <> wrote:
> I got the MM-1's to IMPROVE the low end
And I have no doubt that it did that. My counter-recommendation is based o=
n
incomplete data. Let me explain.
I know that the MM-1 is spec'd as having flat response +0.1 / -0.5 dB from =
20 Hz
to 20 kHz, and elsewhere it's stated to have 10 Hz to 20 kHz bandwidth. It=
's
also stated that the input and output are transformer coupled. The unit tha=
t I
had experience with was being used for theatre calibration and that system =
was
returning results that were inconsistent with other measurements. This was=
in
conjunction with an array of Countryman B3 lavalier microphones. I measure=
d the
system of preamp and microphones and it was considerably attenuated at 20 H=
z
relative to the midband. I measured the microphones and they were flat to =
20
Hz. My conclusion is that it was the preamp that was at fault. But that c=
ould
be due to a system level problem and not necessarily to either the preamp o=
r the
microphones individually. Microphones that are capacitively coupled on the=
output have an impedance that rises towards low frequencies. Preamps that =
are
transformer coupled have an impedance that falls at low frequencies. The
combination of the two could result in a rapid roll-off of low frequencies,=
depending on exactly what components are being used.
So my recommendation is basically that, if your intention is to record
infrasound then a transformer coupled preamp is not the way to go. If you=
really want to know how the recording system performs at low frequencies th=
en
it's probably necessary to test the system as a whole.
Eric
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