40 Watts amplifier for the Trumpet speaker, includes 15VDC UL listed power supply, 93dB sensitivity. Note: Effectively drive up to 4 each model TRP470 (4 Ohms trumpet speakers). The AMPBACKPLATE is the amplifier module that makes the regular Trumpet Speaker into a self-amplified speaker. This module is being attached at the back to replace the plastic cover of the TRP470.