BSS 366T OmniDrive [19/112] Crossover shapes and frequencies

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FDS-366T

It is not possible to provide one loudspeaker driver to cover all audible

frequencies. Even if the frequency response could be achieved, the large size

of the driver required to shift enough air at low frequencies would offer an

impossibly directional beam at high frequencies because at small wavelengths,

the differing path lengths from the extremities of the diaphragm to the listener

would cause cancellations off-axis. Therefore, it is necessary to use more than

one driver and to split the bands with an electrical filter or crossover. This

filtering can be done by passive, active or digital means, external to or within

the loudspeaker cabinet.

Ideally, the filtering is done so that when acoustically combined, the drivers

produce a constant output across the required range of frequencies.

Additionally, the signal phase behavior with frequency should offer smooth

transitions across all the drivers to achieve a constant group delay. Another

important consideration is that the crossover should control the beaming

properties, also known as the polar response, so that listeners off-axis do not

hear anomalies in the sound range. Many crossover filter designs do not

achieve these goals.

Finally, the signal should be quickly attenuated outside the optimum band of

operation for each driver to avoid driver anomalies such as resonance and

over-excursion distortion at low frequencies. In these instances some crossover

shapes have limitations.

The FDS-366T allows full control over each high and low pass filter of a

crossover segment in shape, slope and frequency. Graphically these

parameters are labelled as below.

7.0 Crossover Shapes and Frequencies

Filter Edge Identification