Session 5
5.2 Application of LinearPhase Digital Crossover Filters to PairWise Symmetric MultiWay
Loudspeakers
Part 1: Control of OffAxis Frequency Response
ULRICH HORBACH(1) & D. B. (DON) KEELE, JR.(2)
(1) Harman Consumer Group, Northridge, California, USA. (2) Harman/Becker Automotive Systems, Martinsville, Indiana, USA.
Various methods exist for crossing over multiway loudspeaker systems. These methods include those loosely
classified as LinkwitzRiley filters, constantvoltage filters, and D’Appolito configurations. All these methods do not
provide broadband constantbeamwidth or constantdirectivity operation because their vertical radiation patterns
change shape as a function of frequency. This paper describes a simple, noniterative linearphase crossover filter
design technique that provides uniform frequency responses vertically offaxis for a given multiway loudspeaker.
Distances between the individual drivers, and desired offaxis attenuation are prescribed as input parameters for
the design process, the outcome of which is a set of crossover frequencies and unique filter frequency responses
in each band. In order to obtain wideband constantbeamwidth, a loudspeaker array configuration composed of a
single central tweeter surrounded symmetrically by pairs of loweroperatingfrequency transducers arranged in a
vertical line is required. Practical implementation issues are outlined in the paper by means of various design
examples. Two design methods are presented in twoparts: Part 1: a general method which emphasizes flatness of
arbitrary offaxis frequency responses and Part 2: a simplified method that emphasizes frequency uniformity of
beam shape and coverage angle (vertical beamwidth) of the polar patterns.
