Towards Active Transducers

Søren Poulsen

    Research output: Book/ReportPh.D. thesis

    1100 Downloads (Pure)


    One of the trends within consumer audio systems is the requirement for surround sound systems, based on 5-7 or even more audio channels, resulting in the same number of power amplifier channels and loudspeakers for each system. Most systems on the market today are based on linear amplifiers techniques developed in the middle of last century, which is surprising when the last few decades’ development within the audio source material, that is CD, DVD and SACD to mention the most popular, are taken into account. Audio performance of linear amplifiers has reached a level suitable for high quality audio reproduction many product generations ago, but the biggest disadvantages are still left untouched; power efficiency, size and cost. With today’s technology, high efficient switch mode, or class D audio amplifiers based on pulse width modulation, PWM, are realizable. With the class D technology, consumer audio systems can benefit significantly from the highly increased power efficiency of class D amplifiers as well as their reduced size without need for bulky heat sinks, and also very important, low cost. The topic of this project is a total integration of switch mode audio amplifiers and loudspeakers into one single unit using the voice coil of the loudspeaker as output filter for the amplifier, with a perspective of highly reduced system power losses, system size and cost. Standard switch mode audio amplifiers and loudspeakers on the market are designed for use in traditional audio systems, and cannot without severe modifications be used for the integrated system without sacrifice of power efficiency. For this reason techniques for dedication of amplifier and loudspeaker for the specific purpose of the integration has been of major importance in this project. This thesis is a fundamental study of the loss mechanisms in loudspeakers and amplifiers and suggestions for optimizations are made to reduce the system power losses and cost without compromising the audio performance. Some of the results obtained in the project are redesign of and optimization of the parts in a loudspeaker, so the function of output filter for the amplifier can be obtained without significant power losses. Guidelines for dedication of speaker and amplifier to the integration process with significantly lower system power losses are also given. Furthermore, the work done in the project has resulted in new switch mode amplifier topologies, with very high audio performance realizable at a very low cost.
    Original languageEnglish
    Place of PublicationKgs. Lyngby
    PublisherTechnical University of Denmark, Department of Electrical Engineering
    Number of pages284
    ISBN (Print)87-91184-39-8
    Publication statusPublished - Dec 2004


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