Setting aside the downstream components, there is considerable earlier disc=
ussion in this group of infrasound capability of the MKH-110 and 110-1, 'ob=
solete' microphones that appear on Ebay at times. These are mentioned in fi=
eld work reports on elephant vocalizations. There is more discussion of the=
se and other infrasound microphones at:
http://www.tomshardware.com/forum/42405-6-very-frequency-recording
Bill r.
>
> Hi!
>
> I agree with James. The preamp and amplifier/digitizer=C3=82=C2=A0circuit=
ry of whatever you
> you are using to record the infrasound is the first factor to consider wh=
en
> attempting to record these sounds. If the recording device doesn't go low=
enough
> in frequency without=C3=82=C2=A0rolloff to get what you want, then you ar=
e wasting your
> time trying to find the proper transducer or microphone.
>
>
> The transducer should then be a pressure transducer. An omnidirectional m=
ic is a
> pressure transducer, but depending on how low you wish to go below 20 Hz.=
actual
> industrial pressure transducers or microflown transducers=C3=82=C2=A0may =
be what you want
> to use. But you haven't quantified what actual range of frequencies you w=
ant to
> record, nor have you told us the purpose of your work. It is difficult to=
record
> sounds outside of the "normal" 20Hz - 20 KHz range that most mics and rec=
orders
> can handle; anything outside of that range often requires special equipme=
nt,
> gear that can only be specified when the exact requirements are known.
>
> Many of the folks that are intimately familiar with infrasound recording =
are
> either studying volcanoes, seismic events (including remote nuclear explo=
sion
> detection) and elephants. There is plenty to learn from them: just Google=
> "infrasound microphone" and you'll get a lot of useful info!
>
> One more thing about this field. The NOAA ESRL site has a paper about inf=
rasound
> and near-infrasound which is very interesting and would be a good introdu=
ctory
> paper on infrasound:
> http://www.esrl.noaa.gov/psd/programs/infrasound/infrasonic.html
> It clarifies the definitions for what we are talking about: "...periods b=
etween
> .05 to 1 second (20 to 1 Hz) are logically called near-infrasound (an ana=
log to
> near-infrared). Periods between 1 and about 100 seconds (1 to .01 Hz) def=
ine the
> range of infrasound (well below the human hearing), and signals with peri=
ods
> greater than 100 seconds can be designated acoustic/gravity waves..".
>
>
> So infrasound=C3=82=C2=A0is really the world below 1 Hz to ~0.01 Hz. Is t=
his the area of
> your interest?=C3=82=C2=A0This prompts one to look for special equipment =
such as a B&K 4147
> mic and a PC acquisition (instrument recording) system that has good, fla=
t
> response down to DC. But that is only one possibility of many.
>
> Good luck and good hunting!
>
>
> -Greg
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