Abstract: A speaker unit is realized which directly drives a vibration plate having a low density, light weight, yet sufficient rigidity with a digital audio signal, and can thereby transmit vibration of a voice coil thereof to a carbonaceous acoustic vibration plate without loss. The present invention provides a digital speaker unit including a speaker body (14) comprising a carbonaceous acoustic vibration plate (25), a delta-sigma modulator (11) and a thermometer code conversion section (12) that convert a multi-value bit digital audio signal supplied from a digital sound source (10) to a digital signal with required bits, a plurality of voice coils (24) that cause to vibrate a plurality of the carbonaceous acoustic vibration plates (25) provided in accordance with the number of digital signal bits and a driver circuit (13) that individually drives each voice coil (24) based on the digital signal.

Abstract: A carbonaceous acoustic diaphragm whose density is reduced while retaining the required stiffness is provided. Carbon nanofibers and spherical particles of PMMA are mixed into a carbon-containing resin such as a polyvinyl chloride resin, and the mixture is carbonized to vaporize the spherical particles of PMMA, thereby forming a porous structure having pores with the carbon nanofibers in a powdered form uniformly dispersed through amorphous carbon. By forming a multilayer structure by combining the porous layer with a layer that does not use PMMA, the density can be further reduced while retaining the stiffness.