Part 4.2: Elementary acoustic loads of a loudspeaker

In order to limit an excursion of a loudspeaker membrane, it is common to use a high-pass filtering. Since the cut-off frequency of such a filter is low (20 to 30 Hz), it is preferable to use an active filter. Example of an excursion response is shown at the figure below for the sealed enclosure, unfiltered vented enclosure and vented enclosure provided with a Sallen & Key filter with 17 Hz cut-off frequency. This figure shows that by adding a filter (green curve) excursion is reduced between 10 and 20 Hz.

Figure below shows that the loudspeaker excursion for non filtered vented enclosure is very high below the resonance frequency of a Helmholtz resonator. If the loudspeaker is used for very low frequency signals, it may generate distortions and, on the other hand, may provide a mechanical damage which does not exist in a case of closed enclosure (excursion being lower). Application of a high-pass filter helps to limit the value of excursion at low frequencies and thus to limit the distortion effects and to protect the loudspeaker.