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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
car audio system in which a graphic 7 equalizer, a surround circuit and a position selector are
combined. [Conventional technology] A conventional on-vehicle equalizer amplifier is mainly
composed of a graphic equalizer, so it has a position selector that selects the sound field balance
by making a level difference between left and right stereo signals L and H, and a signal. It is
necessary to separately provide a surround circuit for mixing R to produce an acoustic effect.
[Problems to be Solved by the Invention] However, forming the three types of circuits described
above in separate housings not only increases the installation space but also requires external
wiring between each other. Further, the conventional position selector has no delay function, and
there is also a problem that the bass portion is insufficient in the surround circuit. The present
invention solves these problems and is intended to construct a stereo audio device suitable for
use in vehicles. [Means for Solving the Problems] The present invention relates to a stereo system
car audio apparatus for producing left and right front side outputs FL, FR and left and right rear
side outputs RL, RR. , Graphic equalizer for switching the frequency characteristic of FR1, and
one of left and right stereo signals L and R output from the equalizer by subtracting the other
from the other at a predetermined ratio to obtain two surround signals L-kR and R-kL A surround
circuit to output, a function to create left or right signal L + mR or R + mL obtained by adding the
other to one of the stereo signals L and R at an arbitrary ratio m and then delaying it, adding the
stereo signals L and R To select one of the signals L + mR or R + mL to select the left / right front
side output FL or A position selector having a function of setting R and a function of selecting
one pair of the signal L + R and the surround signal L-kR, R-kL and setting it as a rear side output
RL, RR. It is said that. FIG. 1 is a basic block diagram of the present invention, wherein l is a
graphic equalizer, 2 is a surround circuit, and 3 is a position selector. [Operation] The graphic
equalizer 1 is not of the type by frequency division but of the type of boosting only a specific
frequency, and sets a plurality of kinds of frequency characteristic patterns by the combination
thereof. The surround circuit 2 has two subtraction circuits OPI and OP2, and creates surround
signals L-kR and R-kL from the outputs L and R of the equalizer 1.
k is an attenuation amount for the subtraction side signal, and k <l. The position selector 3 can
select the sound field balance in accordance with the seating position. This is mainly for the
driver's or passenger's seat, but not only for these front seats but also for the rear seats.
However, in the case of the front seat (front position), the rear speakers RL and RR can be used
for surround, but in the case of the rear seat (rear position), low frequency components because
the rear speakers RL and RR are used as woofer Only output. At this time, the surround circuit is
returned to the normal position for passing L and R. FIG. 2 is a circuit diagram showing an
embodiment of the present invention, showing details of the position selector and the surround
circuit. The position selector has eight switches SW1 to SW8, which are switched to the make M
(white circle) or break B (black circle) position according to the control signal. The pattern to be
switched is determined by the target seat of the sound field balance. An example is shown in the
table below. Table 1 (--M or B is acceptable) Figure 2 (al is a circuit state where the sound field
balance is adapted to the driver's seat, the left signal FL2 on the front side is signaled The L
signal on the front side and the right signal FR2 on the front side are delayed signals R to 10 m L.
This delayed signal is obtained by multiplying the signal number by m in the buffer BUF and the
attenuator ATT2, adding it to the signal R, delaying it in the delay circuit DLY, and further
attenuating appropriately by the attenuator A T T +. is there. In this way, the sound image on the
front side shifts to the right (driver's seat side). At this time, the rear side signal RL2. Since RR2
becomes the signals L-kR and R-kL from the surround circuit, a feeling of expansion of the sound
field like a concert hall comes out. Incidentally, when the surround circuit is configured as shown
in FIG. 2 (b), a sense of shortage of the bass region does not occur. In the figure, in the figure, R1
and R3 are input resistances of the subtraction circuit OP +, R2 is a feedback resistance, R4 is a
bias resistance, and CI. C2 is a coupling capacitor, and 8 is a bias voltage. The amount of
subtraction is determined by the values of R1-R4. In this figure, a transfer function G (31 is
viewed from the R input side which gives a signal to be subtracted) is expressed by the following
equation. Also, the cutoff frequency [C is. Although fc is generally taken at a low frequency of
about 10 Hz, here, a bypass filter HPF is configured by CI and R + by setting about 200 Hz. If this
circuit is used, subtraction is not performed in the low frequency range below 200 Hz.
Therefore, even if the rear side speakers RL and RR excellent in bass reproduction ability are
used for the number round, there is no shortage of bass. The position selector shown in FIG. 2 (a)
produces an L + R signal by the mixer MIX, and extracts a component of 80 Hz or less by the low
pass filter LPF. Therefore, the switch SW7. The switch SW8 is switched to the rear side signal
RL2. If it is commonly used for RR2, the low range can be emphasized. In order to shift the sound
image balance to the passenger side, the switches 5W1-3W4 may be set to the break B side.
Switch SW7 to transfer to the rear seat. The SW 8 should be on the break B side. Further, if all
switches 5WII to 5W14 are switched as shown in FIG. 1, the final outputs FL, FR, RL, and RR to
the speaker are output from the position selector 3 as FL2. FR2,RL2. RR2 or the signal
FL LFL2. It is possible to select RLI and RRI, and also in the surround circuit 2, the through
outputs L and R can be generated by the switch 5W21 ° SW22. As described above, according
to the present invention, the functions of the graphic equalizer, the surround circuit, and the
position selector can be combined into one circuit (for example, an equalizer amplifier).
Functionalization, miniaturization, simplification of the configuration, and the like can be
Brief description of the drawings
FIG. 1 is a basic block diagram of the present invention, and FIG. 2 is a circuit diagram of each
part showing an embodiment of the present invention.
In the figure, 1 is a graphic equalizer, 2 is a surround circuit, 3 is a position selector, DLY is a
delay circuit, BUF is a buffer, MIX is a mixer, LPF is a low pass filter, ATT1 and ATT2 are
attenuators, SWI to SW8 are switches and OP1. OF2 is a subtraction circuit, and HPF is a bypass
filter. Applicants Fujitsu Ten Ltd. Attorney Attorney Mr. Ao Yanagi Emissary of non-compliance
with the law of the court
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