Virtual Loudspeaker Effect of Graphene-Based Hybrid Material To Improve Low-Frequency Acoustic Performance.

Closed-box loudspeaker systems (CBLSSs) are compact and simple air-suspension loudspeaker systems, and their low-frequency responses are determined by two fundamental parameters: resonance frequency and total damping. Recently, electronic devices have come to require more compact designs, so the volumes of loudspeaker should be reduced. However, a small loudspeaker cannot retain sufficient acoustic space, resulting in poor low-frequency acoustic performance. Herein, we investigated acoustic characterization of the CBLSS with different filling materials such as thermally expanded graphene oxide (TEGO), activated carbon, graphene platelets, and melamine foam (MF). Upon the powder-based test, the resonance frequency of the loudspeaker decreased and resulted in a volume increasing effect inside of the loudspeaker. The TEGO shows almost double volume increase rate, compared to other particle-based filling materials. Employing hybrid filling material that consists of TEGO in an MF cage (TEGO@MF), the volume increase rate of the novel loudspeaker was over 24% at 300 cc. Because of the high adsorptive characteristics and thermal properties of TEGO, the acoustic performance in the low-frequency domain was clearly enhanced, despite the reduced mass loading. Furthermore, these properties were observed to be highly effective for enhancing the low-frequency acoustic performance of the larger loudspeaker, achieving a volume increase rate of 49.5% in a 700 cc enclosure.