The New Jersey Institute of Technology's
Electronic Theses & Dissertations Project

Title:	Equivalent circuit analysis of a seventh order bandpass loudspeaker system
Author:	Johnson, Michael Gunnar
View Online:	njit-etd1997-059 (xii, 76 pages ~ 2.9 MB pdf)
Department:	Department of Mechanical Engineering
Degree:	Master of Science
Program:	Mechanical Engineering
Document Type:	Thesis
Advisory Committee:	Cochin, Ira (Committee chair) Chen, Rong-Yaw (Committee member) Ji, Zhiming (Committee member)
Date:	1997-05
Keywords:	Loudspeakers. Electric circuit analysis.
Availability:	Unrestricted
Abstract:	A seventh order bandpass loudspeaker system was designed using an equivalent circuit analysis. The electrical, mechanical and acoustic systems were each modeled as separate subcircuits derived by using a Voltage-Force-Pressure or impedance analogy; the interactions between the subcircuits were modeled using coupled controlled-sources. The equivalent circuit was analyzed using SPICE (Simulation Program with Integrated Circuit Emphasis). A technique for modeling port and cavity resonances inside the enclosure using distributed element approximations for the resonant components was developed and verified by measurement. A complete microcomputer based experimental loudspeaker testing system was designed incorporating a sweep frequency oscillator, a gain-controlled audio power amplifier, a true rms microphone interface, and a 12-bit, multiplexed, 100 ksamples/second AID data acquisition system connected to an IBM compatible personal computer. The frequency response of the system, as measured by a microphone in dB SPL (decibels, Sound Pressure Level), agreed with the predicted response to within 2 dB in the passband. Above the bandpass cutoff frequency, peaks in the response are shown to be caused by port and enclosure cavity resonances; dips in the response are shown by finite element modal analysis to be caused by enclosure wall resonances. The technique of modeling the electro-mechanical-acoustic system using an equivalent circuit analysis with distributed element resonant components has been shown to be a valid design tool for high-order loudspeaker systems.