Active Eighth-Order Band-Pass Loudspeaker Systems

Band-pass loudspeaker systems are widely used as subwoofers to reproduce sound in the bass range. This paper presents design procedures and theoretical analysis of the active eighth order band-pass loudspeaker system that consists of an active low-pass filter and a first or second-type sixth-order band-pass loudspeaker system. Based on the reactance transformation method, the overall system response can be shaped to a symmetric filter function with a Butterworth or Chebyshev alignment. Four classes of alignments are derived for aligning the two types of systems, which yields a total of eight groups of system implementations. Although the derivation of eighth-order alignments is relatively complex, analytical expressions for required loudspeaker system parameters are successfully obtained, facilitating an easily executed design. Based on the alignment parameters, a thorough analysis of system small to large-signal performance, including sensitivity, efficiency, displacement, transient behavior, and acoustic power rating, is presented, enabling comparisons of the different system implementations. Therefore, designers can choose an optimal alignment class and system type to satisfy various design requirements.