9/16 ver. 2017/06/19User Manual - SB1104.2. Excursion limitationHigh-amplitude signals with very low frequenciescause large membrane excursion. Excessive excur-sion causes harmonic distortion, which degrades thesound quality and causes a risk of damage to theloudspeaker.It is desirable to limit the amplitude of the deflections either by reducing theamplitude of the applied signal or by placing a high-pass filter upstream of theamplifier, for example, a second order Butterworth filter at 80Hz.