When Kate and Mac are in the storage closet,
Mac grabbed an audio generator and a speaker to make a ear-piercing din to mount an unsuccessful bid to escape.
Mac plugs the generator into the cab and goes to it.
The problem with this (At least with that Acoustic or maybe Peavey cabinet he was using)
is that speaker cabinets require an amplifier to run.
He clearly plugs the gen into the speaker inputs.