Resonator Design for Multiway Thermo-Acoustic Loudspeaker

Abstract

Thermo-acoustic (TA) loudspeakers based on carbon nanotubes are emerging as the alternative of conventional loudspeakers due to its low heat capacity. Since TA loudspeakers produce sound using an ultra-thin conductor, they have many practical advantages, such as a simple fabrication process, installation on a curved surface and omnidirectional radiation characteristic. Nevertheless, sound pressure levels of TA loudspeakers show high-pass characteristics, which lead to poor performance in a low-frequency region. To amplify a low-frequency range, we attempt to design multiple resonators and implement a multiway loudspeaker by combining the resonators with an open-type TA loudspeaker. For accurate tuning of TA resonators, we derive a mechanical model of a TA resonator and investigate key design parameters involved with a resonance frequency. Three TA resonators are designed and fabricated for boosting SPLs over 0.5 kHz ~ 1.5 kHz and fine-tuned through the use of different plate materials and additional mass loading layers. Because TA resonators produce high-Q resonances, anti-resonances, as well as phase inversion across the resonance frequencies, we implement a crossover network equalizing the irregular frequency response of the multiway speaker. The frequency response of the fabricated multiway speaker shows amplified sound pressure level than that of an open-type TA loudspeaker.