Subwoofer Speaker box Auto Standby Normal or Reverse Phase Control Continuously Variable Control for Crossover Frequency, Home audio speaker, subwoofer,woofer, ... Cable, Speaker Stand, Loudspeaker, Sound box. FUNCTION:Auto StandbyNormal or Reverse Phase ControlContinuously Variable Control for Crossover Frequency,and Bass Volume. ... listening levels. Click here for a technical explanation speaker box