In recent years, the production of small and thin electronic devices has been advanced with development of electronic technology and a growing consumers' demand for thinner and smaller home electronic apparatuses. Indeed, various kinds of television receivers are now available, which are constituted by using thin CRTs, LCD panels and plasma-display panels. The television receivers have video reproducing function and sound reproducing function. The latter function is realized generally by means of loudspeakers.
FIGS. 1 and 2 illustrate a typical exemplary structure of a loudspeaker portion of a conventional television receiver (e.g., see the following Patent Document 1). FIG. 1(A) is a perspective view of an essential portion of a television receiver in which a loudspeaker box is mounted on an installing place. FIG. 1(B) is a perspective view of a portion of a television receiver cabinet to which a single loudspeaker unit is directly attached.
In FIG. 1(A), the television receiver 101 is composed mainly of a front cabinet 102, a display (e.g., CRT) 103, and a rear cover 104. A loudspeaker box 107 with a loudspeaker 106 mounted therein is fitted to the front cabinet 102 via a vibration-proof material 108 with a machine screw 109. Sound generated from the loudspeaker 106 is output through a vent hole (not shown) mounted on the front cabinet 102 and spread forward at the front face of the television receiver 101.
In FIG. 1(B), a loudspeaker 106 is fixed to a front cabinet 102 of a television receiver 101 via a vibration-proof material 108 with a machine screw 109. Similarly, as described in the case of FIG. 1(A), sound generated from the loudspeaker 106 is output through a vent hole (not shown) mounted on the front cabinet 102 and spread forward at the front face of the television receiver 101.
FIG. 2 is a perspective view of another example of a conventional television receiver. In the shown example, an L-shaped bent part of a loudspeaker box 107 is placed between a display 103 and a rear cover 104. Thus, the loudspeaker box can reproduce high quality sound while realizing a thin profile of the television receiver.
FIG. 3 is a plan view of another example of a conventional television receiver wherein a pair of right and left loudspeakers 111 for reproducing sounds of relatively high frequency (in a range of middle and high sound frequencies) are provided at a front face of the television receiver 110 and a loudspeaker 112 for reproducing sounds of relatively low frequency is provided at a rear face of the television receiver 110, expanding a sound field (e.g., see the following Patent Document 2). In this case, as indicated in FIG. 3, the left and right sound signals of relatively high frequency from the left and right loudspeakers travel along corresponding paths D and directly reach a listener 120. Sound of low frequency from the low frequency loudspeaker 112 reflects from the rear wall 113 and the left and right walls 114, 115, travels along the corresponding paths R and reaches the listener 120. The remaining portion of sound from the same loudspeaker 112 diffracts, travels along the left and right side walls 110a, 110b of the television receiver 110 and reaches the listener 120. Thus, the sound field is expanded sufficiently without increasing the lateral width of the television receiver 110.
FIG. 4 illustrates another exemplary construction of a conventional television receiver having a loudspeaker device composed of a loudspeaker 138 with a sound introducing pipe 137 arranged on the front face thereof and a woofer box 131 arranged on the rear face thereof. The woofer box 131 has a downwardly directed port 140. The television receiver has a cabinet 132 housing a CRT 134, a control circuit board 135 and a loudspeaker device and a back cover 133. The cabinet 132 has a sound emitting port 139 corresponding to the sound guiding pipe 137 in the front side and an opening 136 corresponding to the port 140 in the underside so as to enhance the effect of sound of low frequency (e.g., see the following Patent Document 3).
Any television receiver is required to use a large loudspeaker designed to reproduce sounds of relatively low frequency in conjunction with two loudspeakers designed to reproduce sounds of middle and high frequencies. On the other hand, recent television receivers have a very restricted space allocated for loudspeakers so as to achieve sophisticated design and appearance. For this reason, a small-sized loudspeaker is necessarily applied as a woofer. In other words, the appearance of the article has been improved at the sacrifice of the quality of reproducible sound of low frequency.
The conventional television receiver having a reduced lateral width as shown in FIG. 1(A) has the following drawbacks. It has no space for locating a loudspeaker box having a normal size and requires a reduced profile of the loudspeaker box at the sacrifice of the quality of reproducible sound. The conventional television receiver as shown in FIG. 1(B) has the following drawbacks. Because of the absence of a loudspeaker box, the television receiver has a small dynamic range of its sound system and therefore cannot deliver high quality sound reproduction. The conventional television receiver as shown in FIG. 4 is a CRT type receiver whose design cannot be applicable as a solution of improving the sound reproduction system of wall-mounted television receivers using LCD panels.
In view of the above-described circumstances, the present invention was made to provide an image display device which has a high-fidelity sound-reproduction system composed of a loudspeaker (woofer) for reproducing sounds of low frequency and two loudspeakers (tweeters) for reproducing middle and high frequencies, which is featured by the effect of expanded sound field with improved external/internal design and is applicable in particular to personal computers or television receivers equipped with a thin display unit such as a LCD and PD panel.
Patent Document 1: Japanese Laid-Open Patent Publication No. 09-284674
Patent Document 2: Japanese Laid-Open Patent Publication No. 59-201600
Patent Document 3: Japanese Laid-Open Patent Publication No. 2001-145186