BSS Audio FDS 355 Specifications download pdf (Page 40)

The FDS-334/336 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.

Filter Edge Identification

Phase Compensation

Phase Compensation to active crossovers was introduced in the classic FDS-355 Omnidrive

Compact Loudspeaker Management System. Minidrive includes this feature, freeing the user of

worry about phase alignment between bands.

A properly designed 2 way crossover always exhibits the inter-band phase relationships that is

characteristic of the chosen crossover shape. For example, the Linkwitz-Riley filter shape, with

its low-pass filter for the low band, and high-pass filter for the high band, will maintain zero

phase difference between these bands at all frequencies, which means that the acoustic outputs

from the drivers will sum to a flat response, free of any shifting in polar response.

In 3 way (or more) systems, things can start to go wrong. The mid band in a 3 way system for

example, has not one filter, but two (high-pass, and low-pass). The low-pass filter, set at the

mid-high crossover frequency will produce some phase disturbance at the low-mid crossover

frequency, causing the low-mid crossover filter pair to be misaligned. The same is true of the

high-pass filter, which will cause the Mid-High crossover filter pair to be misaligned. This

misalignment causes incorrect acoustic summing, which results in a non-flat response, and a

polar response which shifts with frequency, causing further response problems in some listening

positions. Although these effects may be subtle when the crossover frequencies are well

separated, 4 and 5 way systems particularly can produce significant errors.

The phase compensation scheme employed in Minidrive analyses these phase anomalies

whenever adjustments are made, and automatically introduces phase adjustment into certain

bands such that the phase difference between adjacent bands is always close to zero degrees.

Intentional phase differences can be introduced using the delay parameter. Minidrive will not

attempt to apply phase compensation if the high and low frequencies or shapes of the adjacent

bands do not match, on the assumption that the user does not expect to produce a standard

crossover alignment.

Outputs Crossover Shapes and Frequencies

1 2 ... 35 36 37 38 39 40 41 42 43 44 45 ... 53 54

No comments

BSS Audio FDS 355 Specifications Page 40