Sound reproducing apparatus for use in vehicle

DETAILED DESCRIPTION In consideration of the above-described problems, the present invention provides a sound reproducing apparatus for use in a vehicle which is capable of making the sound pressure frequency response curve relatively flat without increasing the level of distortion in the low-frequency range even when applied to a type of vehicle having no closed space and which can be designed most suitably in accordance with the type of vehicle and its mounted position.
To this end, the present invention provides a sound reproducing apparatus for use in a vehicle which is arranged such that there is a lowest frequency Fs in a frequency range within which the imaginary part of the acoustic impedance at the sound radiating surface of a speaker system in the direction of the space within the passenger compartment is zero, and the first low-range resonance frequency of the speaker system itself in the free space is F0, where F0 and Fs are substantially equal to each other.
The frequency Fs is obtained by simultation or observation effected at the position at which the speaker system is mounted in the closed space or the passenger compartment.
It has been found that when a speaker unit operates in a stiffness-control region at frequencies lower than Fs, as in the case of a so-called headphone, the sound pressure will increase under the driving condition of a constant acceleration.
It is possible to design the speaker system by estimating a sound pressure frequency characteristic in the low-frequency range in the passenger compartment as mentioned above.
If the speaker system is constructed so as to have an acoustic duct, the level of vibration of the speaker unit and, hence, distortion caused by the vibration are greatly reduced in a low frequency range in the vicinity of Fs because of the phenomenon of resonance of the acoustic duct.