Loudspeaker characterization and compensation

From SoftwarePractice.org

This article describes a project to implement a measurement and characterization program for loudspeaker drivers. The program will also have options for compensating driver frequency response and tailoring a passband response for cross-over to other drivers.

The project is suitable for a team implementation and design project in a second class in signals and systems.

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Overview

Loudspeaker drivers are a complex electromechanical system, with corresponding complex behavior in both the time and frequency domains. Measurements of the performance of drivers have typically focussed on the on-axis frequency response, with less attention paid to off-axis frequency response and distortion.

For the sake of evaluating different drivers for inclusion into a loudspeaker design, it would be useful to have more comprehensive measurement and evaluation tools. For example, while plots of THD versus frequency are often seen, these are generally at only one signal level (typically with one watt electrical power input). The performance of the driver at higher signal levels is left unexamined.

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Project description

You will implement a loudspeaker driver characterization and compensation program in Matlab. The program should automatically run and produce a series of measurements of a connected loudspeaker driver. Apart from the frequency response, a series of distortion measurements at different frequencies and power levels should be used to provide the loudspeaker designer with an overall picture of the driver's performance. Time-domain and time-frequency domain characterizations, such as step response and waterfall plots, should also be generated.

The input to the program will be a set of parameters (that you define). These parameters control the overall operation of the program, such as the frequency range of interest, range of power to test with, selection of different tests, and so on.

In addition, a second part of your program will correct for frequency response anomalies in the driver, and "roll off" the driver at one or both frequency extremes, in order that the driver can be used in conjunction with other drivers that cover the higher or lower frequency ranges. In other words, this section of the program aims to convert an imperfect driver into a "perfect" driver with a well-defined passband.

Your project documentation should address at least the following:

The theory behind your signal generation, measurement, and analysis
A description of your implementation, including issues encountered and proposed enhancements
Sample Matlab code to illustrate key points
Plots and spectra to show how your program behaves with a real loudspeaker driver
A discussion of the benefits and limitations of your chosen characterization and compensation methods
Notes on how these techniques can be implemented in a realtime system

Your aim in your project documentation is to also demonstrate that you have followed an engineering approach to the problem. You are expected to do your own research to locate existing approaches, to analyze them, and to discuss the various choices that you have made in your own implementation. You are expected to paint a systems view of the overall problem and to discuss how your particular solutions fits into that systems view.

Extra credit will be awarded to teams who not only do an excellent job of implementing and documenting the program as described above, but also implement a useful and usable GUI to the program.

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