alternative amplifier for vibration exciter (shaker)
These amplifiers have a good low frequency response, usually down to DC, which allows testing like the MIL-STD-810 tests that run down to 5Hz, and also shock testing, where a one-sided pulse is applied, and a low ramp in the opposite direction is often used to position the head before the pulse to allow the full travel of the head to be used.
  If you're only using sine excitation within audio frequencies, a regular audio amplifier would work, though you need to look at the gain variation with frequency - less of an issue if you have a controller that is actively monitoring the EUT amplitude with an accelerometer, but it's not in any case a small amplifier. A pair of car amplifiers in bridge mode might be the cheapest option, because of the limited supply voltage they are generally well suited to driving low impedance loads.