The acoustic characteristics of the sound field inside a vehicle cabin were analyzed. On the basis of the analysis results, a three-way horn speaker system for vehicles was developed, comprising a woofer, a mid-range, and a tweeter.For a woofer, we developed a speaker system utilizing resonation of acoustic tubes, in which the acoustic tubes provide acoustic impedance well matched to the acoustic impedance of a vehicle cabin space. In this paper, to identify the influence of standing waves inside a vehicle cabin, we evaluate the sound field reactivity in terms between sound field reactivity and sound image localization or the frequency characteristics.For a mid-range, we developed a speaker system with its directivity controlled by a sound source with a rectangular shape, thereby realizing a well-diffused sound field even in a restricted narrow cavity providing us with the tendency of an expanding sound image. For comparison with the conventional speaker system, data including the accumulative power characteristics and binaural correlation characteristics of this speaker system are presented in this paper.For a tweeter, we developed a system which combines a directivity controlled multi-horn speaker and a digital filter, thus realizing an improved asymmetric sound field and definite sound image localization. For this development, we analyzed the sound field inside a vehicle cabin using the acoustic ray tracing method, and the wave front in the horns by the finite element method.With the above systems, a car audio system has been realized which permits definite sound image localization just in front of a listener, and stereophonic balanced sound reproduction for both the driver's and passenger's seats, for all frequency ranges.