A Pioneer B13EU14-53F woofer has been selected because it worked out well in a very small box. The woofer is 5.25-inch in diameter with a resonant frequency of 70Hz. With only a 4l box I was able to get the low rolloff point at 73Hz or so with a 73Hz box tuning.
http://www.andrewkilpatrick.org/mind/little_speakers/
A homemade speaker using a plastic cup, business card, wire, magnet and some Lego blocks. I built this speaker from scratch; I was surprised of the quality of the sound.
http://www.josepino.com/other_projects/index?howto-speaker.jpc
Unity gain frequencies are about 4Hz and 63Hz with the pot 20k centred.
http://sound.westhost.com/project48.htm