The cutoff frequency or frequencies for the built-in low pass crossover. Crossovers are characterized by their frequency (Hz or kHz), and by the steepness of their roll-off slopes (the rate of attenuation outside their pass bands) as measured in decibels per interval (dB/octave). A low-pass crossover is generally used for subwoofers - it allows frequencies below the crossover point to pass, while frequencies above the crossover point are gently or harshly rolled-off, depending on the slope.