just a little information about, how to use headphones and other alternative sources as microphones, as this might be usefull in some cases.

simple solution video:
blog.mctedoprogramming.com/2007/02/use-headphones-as-microphone.html

some read, maybe intresting for recording low frequency sounds by use of speakers:
duc.digidesign.com/showflat.php

intresting one:
www.minidisc.org/jim_coon/
art.simon.tripod.com/stealth.html

how does a microphone work basic principle:
www.pa.msu.edu/sciencet/ask_st/030393.html
www.connected-earth.com/FunandGames/Gadgets/Howdoesacarbonmicrophonework/index.htm

from pingpong ball:
scitoys.com/board/messages/2/1049.html

how to make a microphone casing(blimp?)
www.makezine.com/blog/archive/2006/05/how_to_make_a_microphone_blimp.html

idea to record vocalizations of night migrating birds alternative:
www.oldbird.org/mike_home.htm

how to make a microphone from a speaker:
www.instructables.com/id/SPKR-MiK--How-to-make-a-microphone-from-a-speaker/

Simple microphone preamplifier
www.ee.washington.edu/circuit_archive/circuits/micamp.html
low noise microphone preamplifier:
sound.westhost.com/project66.htm

popscreen:
www.jakeludington.com/project_studio/20050321_build_your_own_microphone_pop_screen.html

For around $20US) anyone can build an extremely accurate, life-like condenser microphone:
www.prosoundweb.com/recording/tapeop/buildmic/buildmic_16_1.shtml

contact microphone:
home.earthlink.net/~erinys/contactmic.html

more profi, cool self build one:
www.mp3forkidz.com/mic/