Design of high efficiency loudspeakers for use in fire alarms
University of Southampton, School of Engineering Sciences,
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Much work has been carried out into the operation of loudspeakers for use in audio applications. This thesis examines loudspeaker operation from an alternative point of view. For use in fire alarms, the loudspeaker is required to produce as much sound power as possible at a particular frequency whilst being as efficient as possible.
The moving coil loudspeaker is used as a starting point due to its widespread use. Many papers describing its operation are available and as such is a good loudspeaker with which to examine modelling techniques. An impedance model of the moving coil loudspeaker is developed and shown to be a good simulation of its operation.
The loudspeaker currently used in fire alarm units is the balanced armature loudspeaker. A lumped parameter model of this loudspeaker is developed using SIMULINK. Results from this simulation are compared with experimental measurements to verify the accuracy of the model.
A new design of loudspeaker is then described. The modelling technique developed for the balanced armature loudspeaker is then applied to this design. The results again compare well to experimental measurements. The effect of varying the acoustic loading on each loudspeaker is considered along with an overview of the piezoelectric sounder. The thesis concludes with a discussion of the use of each loudspeaker in fire alarm units along with suggestions for possible design improvements implied by the models.
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