Design Investigation of Passive Radiators in Loudspeakers

Abstract: Passive radiators are components that can be integrated into loudspeakers to amplify the bass frequencies. To ensure good sound quality, the passive radiator, the speaker driver, and the loudspeaker enclosure must all be well-dimensioned and fine-tuned in relation to each other. This master’s thesis, written at the Department of Design Sciences at Lund University, aims to deliver a set of general design guidelines to consider when designing loudspeakers incorporating passive radiators. The report consists of theory and background to give a deeper explanation of how loudspeakers function. It further explores different parameters concerning passive radiators, drivers, and enclosures. Moreover, it investigates several utilities and test methods that allow measurements and determination of relevant parameters needed for designing optimised loudspeakers. Prototypes of loudspeakers as well as in-house made passive radiators were developed to perform sound measurements, the results of which were analysed and compared to simulations. The project findings brought about a selection of important parameters to be considered when developing products with passive radiators. The project also resulted in defined test methods for measuring these parameters and detailed procedures for analysing the collected data information. Furthermore, the comparison between measured values and simulations led to reflections regarding tuning adjustments and the trustworthiness of above-mentioned test methods. Conclusively this thesis acts as a helpful tool to potentially facilitate and streamline the design process when creating good sounding loudspeakers incorporating passive radiators.