James Gordon McLean

The use of numerical optimization techniques in the design of acoustic horn loudspeakers

The use of numerical optimization techniques in the design of acoustic horn loudspeaker systems is considered. Conventional synthesis techniques (i.e., stepped impedance transformer or nonuniform line) are inadequate for horn loudspeaker design due to the frequency‐dependent nature of the radiative load at the mouth and the complex behavior of the driver. In this paper, the horn is modeled as an n‐section commensurate stepped impedance transformer terminated in a one‐port network that represents the complex frequency‐dependent radiation impedance. The driver is modeled as a linear two‐port transducer using measured data as described in an earlier presentation [J. S. McLean and E. L. Hixson, J. Acoust. Soc. Am. Suppl. 1 79, S90 (1986)]. The entire horn/driver system is optimized to exhibit equiripple frequency response using the characteristic impedances of the individual transformer sections as the optimization variables. The system is optimized as a singly terminated filter in order that it may be driven...

Impedence matching in the design of constant directivity horns

A model capable of predicting impedance and power transfer characteristics of so‐called “constant directivity” (CD) horns was developed and presented at the spring 1986 meeting of the Society [J. Acoust. Soc. Am. Suppl. 1 79, S90 (1986)]. It is well known that a CD horn does not exhibit flat frequency response because reflections occurring at the diffraction slot cause resonances in the matching section. This model has been used to apply distributed circuit design techniques to CD horns in order to reduce the resonant peaks in the driving point impedance of a particular CD horn, the JBL 2360. Modifying the matching section of the CD horn yields a more nearly constant and resistive driving point impedance without adversely affecting its constant directivity characteristics. Several alternative designs for the 2360 will be presented and the relative merits of each will be discussed.

The modeling of rigid‐walled acoustic horns with sharp flare discontinuities

A composite model capable of predicting the throat impedance of so‐called “constant directivity” horns is presented. These horns cannot be modeled using methods based solely on Websters equation because they possess a sharp discontinuity which is necessary to achieve the desired radiative characteristics. The composite model combines one‐ and two‐dimensional analyses. A two‐dimensional mode‐matching technique is used to modal the portion of the horn in which the flare is discontinuous. The parts of the horn which flare smoothly are modeled using a generalized transmission line approach which can account for viscous losses and is shown to be equivalent to Websters equation when losses are absent. It is necessary to use this generalized transmission line approach for the smoothly flared portions of the horn because the complex geometry of the horn prohibits analytical solution of Websters equation. The composite model is used to predict the performance of a horn typical of the “constant directivity” horn...