ACT - ACtive Transducer

Purpose: With today's technology high efficiency switch mode, class D, audio power amplifiers based on pulse width modulation is realizable. With the class D technique consumer audio systems can make use of the much improved energy efficiency and compactness of the class D technique because they don't need the heavy and bulky heat sinks leading to a much power price. The subject of this project is a total integration of a switch mode audio power amplifier and an electro dynamic loudspeaker into a single unit using the voice coil of the loudspeaker as an output filter for the amplifier. The perspectives are power energy losses in the total system, power system volume, and lower system price. Execution: Standard switch mode audio power amplifiers and loudspeakers are designed for use in traditional audio systems and they can only with considerable modifications be used in an integrated system without compromising the energy efficiency. For this reason techniques for dedication of the amplifier and the loudspeaker to this purpose have had high priority in this project. The project have given a fundamental study of the loss mechanism in loudspeakers and amplifiers together with suggestions for optimization to reduce the total system losses and price without compromising the audio performance. The theoretical results are verified by measurements and listening tests on a woofer with different prototype amplifiers. Results: The goals were: 1) 4 times higher efficiency for the combination of amplifier and loudspeaker. 2) substantial savings on materials and components, among other things elimination of the heat sink. 3) halving the idle losses compared to the ICEpower technology. Some of the results achieved are redesign and optimization of the parts in the loudspeaker for use as output filter in the amplifier without substantial power losses in addition to guidelines for integration of loudspeaker and amplifier with remarkable power system losses. Furthermore the work in this project has resulted in new topologies for switch mode audio power amplifiers with remarkable high audio performance at an extremely low price. The achieved goals are: 1) halving the power loss at full output power for the combination of amplifier and loudspeaker. 2) substantial savings on materials and components, elimination of the heat sink and output filter. 3) reduction by at least a factor 2 of the total idle losses. Conclusion: The participants have by the large achieved the expected from this project. The knowledge and the practical experiments have meant that the companies in the future are able to realize active transducers in the woofer range. On the midrange and tweeter range further work are needed. This is knowledge, which will be used in future products. Generally the project has fulfilled the expectations. The participants have gained a general overview of known technologies, their advantages and disadvantages, in addition to a complete new range of circuits with excellent new possibilities when used for active transducers