Abstract

In the past few years, development by the likes of M. Morgan J., D. Morgan and J. Vansickl for a new type of low frequency loudspeaker with high efficiency called “Paraflex” has brought up an alternative to the well established horn loaded or bass reflex loudspeaker designs for “Public Address” systems. This new design is based on so called quarter wave resonators, which are highly related to acoustic transmission lines as used for “Transmission Line” loudspeaker systems. A lot of research has been made concerning this type of loudspeaker cabinet, dealing with wave propagation in acoustic tubes filled with absorbing materials and describing computational methods to deal with this kind of setup. However, the special configuration of a “Paraflex” loudspeaker with two transmission lines sitting at the front and back of the loudspeaker driver, merging close to the open end of the system, has not yet been reviewed. This work therefore focuses on deriving a computational model for this kind of setup which yields the possibility of simulating most important system characteristics such as sound pressure output, phase response or electric impedance for a “Paraflex” loudspeaker cabinet. This is done by first making use of acoustic transmission line theory to obtain acoustic input impedance of the respective resonators. Subsequently, the electric analogous circuit of the system containing lumped elements only is analysed, which crucially makes it possible to compute membrane velocity as well as input sound pressure to the lines. Finally, output sound pressure can be obtained by again making use of acoustic transmission line theory. Simulation results of two specific setups will be discussed at the end of this work.

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