My suggestion is a pair of
Eminence B102 speakers in a 3 cubic foot box tuned to 48 Hz (4" diameter port, 2" long). You'll get honest extension to the upper 50's (-3 dB) so you can hear the first overtone of a low B, trading off some excursion-limited power handling along the way... which you probably won't need for practice at home. Also, with this tuning you'd get zero upper bass bumpage, so you can crank in a bit of EQ without over-boosting some notes. The B102 has a wizzer cone so you get decent top end extension to 5 kHz or so, which means you don't have to go to the trouble of adding a tweeter... or if you do add one, you won't have a hole in the upper mid/lower treble region caused by the woofer not reaching up high enough to meet the tweeter.
And, the B102 is reasonably priced at $75 each.
Any decent plywood 1/2" or thicker should work well. Thinner wood with bracing is better than thicker wood with no bracing. Line most of the inside with open-cell foam, but keep the area around the port free from foam.