A speaker for the automotive audio system utilizes at least a part of a vehicle panel which constitutes a vehicle body independently of the speaker and adapted for oscillation at an audio frequency. The vehicle panel serving as a sound-producing medium comprises an inner section to be directly driven by a driver unit of the speaker and an outer section connected to the first section via a relatively flexible intermediate section. The relatively flexible intermediate section is adapted to transmit the audio frequency oscillation. The relatively flexible intermediate section serves for amplifying the magnitude of the audio frequency vibration of the vehicle panel and/or for expanding the audio frequency range to be reproduced. Especially, the relatively flexible intermediate section is adapted to improve reproduction of relatively low frequency range of audio sound.