Rolloff

A request for this one resulted from last week’s TTOTD and WFTD on Crossovers (see inSync 10/29/99). Roll Off (or Rolloff) – Specifically rolloff refers to the action of a specific type of filter; one designed to roll off frequencies above or below a certain point. It is called roll off because the process is gradual. Hi pass and low pass filters both roll off frequencies outside of their range, but they don’t immediately eliminate all frequencies outside their range. The sound is gently (or not so gently) “rolled off” with frequencies further above or below the cutoff frequency becoming more and more attenuated. Rolloff steepness is generally stated in dB per Octave, with higher numbers indicating a steeper filter. 24 dB/Octave is steeper than 12 dB/Octave.