Weber Speakers Amp Attenuator Mass III This MASS is unique in that it has an actual tone stack for the speaker signal -- BASS - MIDS - TREBLE. 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. 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.