Hi Ilse,
Perhaps more one for the phonography list on
http://launch.groups.yahoo.com/group/phonography
The item used in the project you are referring to was a contact mic -
a wood picker, not
woodpecker
http://www.simbaproducts.com/cgi-bin/musicstore.cgi?
store=3D&search=3Dyes&detail=3Dyes&product=3D1&category=3DWoodPicker&keywor=
ds=3D&h
its_seen=3D&page=3Dsearch.html&and=3D&affiliate_id=3D&exact_match=3Dyes
these usually want to see a very high impedance input of 1Megohm or
more if you want to keep low frequencies - most are piezoelectric
elements which are cheap enough. You can DIY this
http://home.earthlink.net/~erinys/contactmic.html
Getting a high-impedance input and a recorder with a low enough LF
cut-off will be the challenge. With a contact mic unless you are
using the bending of an instrument soundbox you will also need a
large mass to act as the counterpoise.
For picking up infrasound propagated through the air you need to use
an omnidirectional mic. Directional mics tend to have a poorer LF
response by their nature. City low frequency noise is so loud you'd
probably get away with an omni electret capsule.
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