Car-loudspeaker

Abstract: A loudspeaker has a magnetic circuit (1) and a speaker frame (2) attached to the magnetic circuit (1), which is mounted on a rear tray (6) of an automobile. A grille (3a) is attached to the speaker frame (2) so as to reflect sound generated by the magnetic circuit (1). The grille (3a) has a slit (3e) so as to radiate the sound in a forward direction of the automobile.

Description: BACKGROUND OF THE INVENTION The present invention relates to a loudspeaker installed in an automobile. Mounting restrictions due to the interior of automobiles impose various limits on the installation of a car loudspeaker. In other words, problems peculiar to the car speakers but not to home speakers arise. One of these problems is that a dip caused by reflected sound appears in the frequency response of the speaker. Referring to Fig. 10, a conventional loudspeaker has a magnetic circuit 1 and a speaker frame 2, an opening of which is covered with a net 4 through a grille 3. The speaker is mounted on a rear tray 6 behind a rear seat 5 so that the axis of the speaker is set in a vertical direction. As a result, the opening of the speaker frame 2 faces a rear window 7. Sound from the speaker propagates through the interior space of the automobile to a listener 8. In the conventional speaker, the sound which is transmitted to the listener 8 comprises directly propagating sound γ and reflected sound (β+α). So, there is a difference of time (α+β-γ)/c (c is the speed of sound)between the direct sound γ and the reflected sound (β+α). Therefore, a dip appears near 500 Hz the frequency response shown in Fig. 11. The dip prevents a clear sound reproduction. In order to obtain a flat characteristic in the vicinity of 500-1000 Hz JP-A-61 277 297 proposed to mount the speaker unit reversely on the rear tray, so that the low pitch sound is radiated in a diffused way. SUMMARY OF THE INVENTION The object of the present invention is to provide a loudspeaker for an automobile which reproduces clear sound. According to the present invention there is provided a loudspeaker according to claim 1. According to further aspects of the invention, a sound absorbent is provided in the grille so as to absorb sound propagating in a rearward direction, and a horizontal panel is provided in the grille to define an upper chamber in the grille. Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 is a sectional view of a loudspeaker according to the present invention; Fig. 2 is a plan view of the loudspeaker of Fig. 1; Fig. 3 is a graph showing the frequency response of the speaker of Fig. 1; Fig. 4 is a sectional view of the loudspeaker of a second embodiment of the present invention; Fig. 5 is graph showing the frequency response of the speaker of Fig. 4; Fig. 6 is a sectional view of a speaker of a third embodiment of the present invention; Fig. 7 is a graph showing the frequency response of the speaker of Fig. 6; Fig. 8 is a sectional view of a speaker of a fourth embodiment of the present invention; Fig. 9 shows an equivalent circuit of a rectifying chamber provided in the speaker shown in Fig. 8; Fig. 10 shows a conventional speaker installed in an automobile; and Fig. 11 is a graph showing the frequency response of the conventional speaker. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. 1 and 2, in a loudspeaker of the present invention, the magnetic circuit 1 and the speaker frame 2 are the same as in the conventional speaker shown in Fig. 10. The speaker frame 2 has a rectangular opening, around the periphery of which is mounted a grille 3a. A horizontal slit 3e is formed in the grille 3a on three sides thereof except the rear side thereof which is adjacent to the rear window of an automobile as shown in Fig. 2. The loudspeaker is mounted on the rear tray 6, setting the axis thereof vertically. Hence the sound is horizontally radiated in the three directions passing through the slit 3e. The frequency response of the speaker is shown by a line Y in the graph of Fig. 3. Compared with the frequency response of a conventional speaker shown by a dotted line X, a dip is significantly reduced, particularly in the frequencies adjacent 500 Hz. The reason of this improvement is that the sound reflected by the glass of the rear window is reduced in the present invention. Thus the sound can clearly be reproduced. Fig. 4 shows the second embodiment of the present invention having a grille 3b formed with the slit 3e only at the front side of the speaker. In this embodiment, a sound absorbent 3b1 such as a piece of sponge, is disposed in the grille 3b at a side adjacent to the rear window. The absorbent 3b1 is preferably made of a material which absorbs sound in the middle frequency range. Therefore, reflected sound C inside the grille 3b is absorbed by the absorbent 3b1 so as to reduce interference thereof with direct sound A . It is evident from the frequency response of the speaker of the second embodiment shown in Fig. 5 that a peak in the middle frequency range is reduced. Referring to Fig. 6, the speaker of the third embodiment of the present invention has a grille 3C similar to the grille 3b in the first embodiment for covering the opening of the speaker frame 2. The inner space in the grille 3C is divided into two by a horizontal panel 3Cl and a sponge sound absorbent 3C2 provided to close an opening 3f formed in the panel 3C1. A sound absorbent 3C4, for example glass wool, is disposed in an upper chamber 3C3 formed by the panel 3C1, so that the upper chamber acts as a Helmholtz resonator. In operation, the reflected sound C inside the grille 3C is attenuated by the resonating function of the upper chamber 3C3. Hence the interference of the reflected sound C with the direct sound A is suppressed. As a result, as shown in Fig. 7, the peak in the frequency response is reduced more efficiently than in the previous embodiment. A speaker of the fourth embodiment shown in Fig. 8 has an inverted construction. Namely, a speaker frame 2a is mounted on the rear tray 6 of the automobile and the magnetic circuit 1 is positioned on the top of the speaker frame. A grille 3d having the slit 3e is mounted on the rear tray 6, thereby covering the speaker frame 2a and the magnetic circuit 1. In the periphery of the speaker frame 2a are formed a plurality of openings 2b through which the direct sound A propagates. A horizontal panel 3d1 and the absorbent 3C2 are provided in the grille 3d, thus defining an upper chamber 3d2 wherein the magnetic circuit 1 is positioned. The sound absorbent 3C4 is disposed in the chamber 3d2 in the same manner as in the third embodiment. Hence the chamber 3d2 serves as a sound matching chamber having the function of the Helmholtz resonator. The direct sound A is propagating and passing through the openings 2b of the speaker frame 2a, so that the reflected sound generated inside the grille 3d is more reduced than in the speaker shown in Fig. 6. In addition, the chamber 3d2 serves to attenuate the reflected sound thereby significantly reducing any interference of the sound waves with the direct sound A . Fig. 9 shows an equivalent circuit which approximately equals the sound matching chamber. An inductance L1, resistance R1 and capacitance C1 represent various parameters determining the matching characteristics of the chamber 3d2. Thus by adjusting the parameters, the quality of sound can be easily improved. In accordance with the present invention, the sound is restrained from propagating towards the rear window. Hence sound reflected by the glass of the rear window is decreased, thereby reducing disturbance of the frequencies in the order of 500 Hz which otherwise is caused by a dip. Consequently, a clear sound reproduction is obtained by the invention. While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as defined in the claims.

Claims: A loudspeaker having a magnetic circuit (1) and a speaker frame (2, 2a) attached to the magnetic circuit (1), wherein the loudspeaker is mounted on a substantially horizontal rear tray (6) provided in an automobile and wherein the axis of the loudspeaker is arranged vertically with respect to the horizontal rear tray (6), characterized in that a grille (3, 3a, 3b, 3C, 3d) is attached to the speaker frame (2, 2a) so as to reflect sound generated by the magnetic circuit (1), in that the grille (3, 3a, 3b, 3C, 3d) extends above the loudspeaker and has an upstanding side plate provided at least at the rear side and extending from the rear tray (6), and a horizontal top plate continuing the side plate from the rear side towards the front, where by a slit (3e) is formed in the grille (3, 3a, 3b, 3C, 3d) so as to prevent sound from emanating to the rear of the automobile and radiate sound through the slit mainly in the forward direction of the automobile to a listener. The loudspeaker according to claim 1, characterized in that the slit (3e) is formed at three sides, except the rear side in the grille (3, 3a, 3b, 3C, 3d). The loudspeaker according to claim 1 or 2, characterized in that it comprises a sound absorbent (3b1, 3C2) provided in the grille (3, 3a, 3b, 3C, 3d) so as to absorb sound propagating in the rearward direction of the automobile. The loudspeaker according to any of claims 1 to 3, characterized in that it comprises a horizontal panel (3C1, 3d1) provided in the grille (3C, 3d) to define an upper chamber (3C3, 3d2) in the grille (3C, 3d), and a sound absorbent (3C4) provided in the upper chamber (3C3, 3d2).

Inventors: ANDO TOMIAKI, KOBAYASHI HIROYUKI, TOKUSYO TAKESHI, ANDO, TOMIAKI,, KOBAYASHI, HIROYUKI, TOKUSYO, TAKESHI,, Ando, Tomiaki, c/o Tohoku Pioneer Elec. Corp, Kobayashi, Hiroyuki, c/o Tohoku Pioneer Elec. Corp, Tokusyo, Takeshi, c/o Tohoku Pioneer Elec. Corp
Applicants: PIONEER ELECTRONIC CORP, PIONEER ELECTRONIC CORPORATION
Application year: 1991
Main classification: H04R1
IPC codes: H04R1, B60R11