Date of Award

Spring 1997

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering - (M.S.)

Department

Mechanical Engineering

First Advisor

Ira Cochin

Second Advisor

Rong-Yaw Chen

Third Advisor

Zhiming Ji

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.

Share

COinS