Bass amplifier

The complete name would be electric bass guitar amplifier. Like guitar amplifiers, there are bass amplifiers with speakers as combos, or bass amplifier heads or bass heads to be used with a speaker cabinet. Since they reproduce lower frequencies than guitars, the speakers have to be larger. Even further larger in order to compensate for the fact that human hearing is less sensitive to the lower frequencies in an unlinear manner.

As with guitar amplifiers, the first bass amplifiers all used tubes. As described for the guitar amplifiers above, bass transistor amplifiers became more popular in the late 60s and in the following years.

Electric bass guitar sound has later become more put directly into PA systems since the sound is darker and less sharp and therefore easier to handle. It does not have the same amount of certain nuances and harmonic overtones like electric guitars have. However some serious bass players who favor the subtle nuances in his/her sound strive to have own tuned in amplification equipment, just like electric guitar players.

Some guitar players may prefer bass amps because they provide more of the low end.

Link:
Some useful info about bass amps - sound.westhost.com