This MASS is unique in that it has an actual tone stack for the speaker signal -- BASS - MIDS - TREBLE. It also has the internal speaker motor for the load, and has a variable line out signal with volume and tone. The unit has two speaker output jacks to support multiple cabinets. The three tone controls can take the signal from whisper quiet to full on with slight humps in the bass, mids, and treble. Additionally, the MASS III has an active bypass circuit with a footswitch so you can run attenuated or bypassed. The footswitch has a 12' cable, and the power pack for the switching relays is a 6VDC wall wart. With no power applied, the attenuator is engaged. Like all Weber attenuators, you can turn all attenuator controls to zero, pull the speaker, and just use the line out, making the MASS III an (expensive) dummy load.