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TECHNICAL FIELD The present invention relates to a sound field correction device, and more
particularly to a device that corrects a sound field at a predetermined listening point in a sound
field produced by a direct radiation sound from a speaker and its reflection sound.
BACKGROUND ART As an example of an acoustic device, there is one as shown in FIG. In the
figure, a reproduction signal from the magnetic tape reproduction head 1 is amplified by a
reproduction amplifier 2 and supplied to a frequency characteristic adjustment amplifier 3. The
output of the amplifier 3 amplifies the power by the speaker drive amplifier 4 and drives the
speaker 5. In the above configuration, the signal obtained by the reproducing head 1 is converted
to a signal having a normal frequency characteristic by the reproducing amplifier 2 and
amplified, and the frequency characteristic variable such as the graphic equalizer in the next
stage or the bus treble control is variable. The amplifier 3 is adjusted to a desired reproduction
frequency characteristic to operate as a speaker drive signal. In the case of the sound system, the
path of the sound emitted from the speaker 5 reaching the predetermined listening point 6 in the
sound field shown in FIG. 2 is, for example, a direct sound as indicated by the solid line 7 and a
dotted line 8 There is a reflected sound from a wall or the like as shown. In this case, at the
listening point 6, a peak or dip occurs at a frequency due to mutual interference of sounds by the
both, and disturbance occurs in the frequency characteristic at the listening point 6. Therefore,
the disturbance of the frequency is corrected by the graphic equalizer 3 or the like. Here, the
principle of occurrence of peaks and dips in frequency characteristics will be briefly described
below. In FIG. 2, assuming that the distance to the listening point 6 of the direct sound path 7 is
ll, that of the reflected sound path 8 is t2, and the speed of sound is C, the direct sound ss and
the reflected sound S before the listening point It is expressed by the sum of 匙 and becomes the
following formula. SM = 88 + SR = (A / 11) · ′ ′ ′ ′ (t−1 · / C) − (+ (KA / 12) g ′ ′ ′ ′
′ ′ ′ ′ ′ ′ ′ ′ ′ (1) where K is the reflectance of a wall or the like, a person Is the signal
strength at the vibrating surface of the speaker. The reflected sound SR is considered to be fixedend reflection in most cases, so the acoustic impedance is large and it may be considered that
reflection occurs in the same phase (but in the case of free-end reflection, the acoustic impedance
is low). , 0), the following equation is obtained by modifying the equation (1). sM: (A / Z,) (,) '(1)
(t-11 / C) + B-(t-1 y' c)) (2) where B = Kl □ / 12 I assume. Now, assuming that B = 1 for
simplification, the frequency at which the peak occurs is f = nc / (Z2 h) '(3), and the frequency at
which the dip occurs is / = (n + 1 / 2) '/ (Z2Zl)--(4).
Le is an integer. The results of equations (3) and (4) are shown in FIG. 3, but since B% 1 is in fact,
the sound pressure at the dip frequency can not be zero, and also at the peak frequency. SM can
not be 2 A / Zt. The dotted lines in the figure indicate the case of free end reflection for
reference. Expressing the above as a general expression, it is as follows. Let the transfer function
of the direct sound 7 path be G1 (') 1 and that of the reflected sound 8 be G (.tau.). G (s.G2 (-).
Here, G 1 (′ ′) and G 2 (′) are transfer functions determined by the distance of the
transmission path, G (τ) is a coefficient indicating the phase and time delay due to the distance
difference, and G (K) is the reflection state such as reflectance It is a coefficient to represent. The
transfer function GA (S) from the speaker 5 to the listening point 6 is GA (") = G1 (s) + G (T) .G (K)
.G2 (S = Gl (8) (one G (T) ) G (K) Gz (") / Gx (8) 1 (5) That is, the disturbance of the frequency
characteristic as shown in FIG. 3 occurs due to G (τ) which is a function of the arrival distance
difference of the rain sound. Therefore, when the installation state of the device or the listening
position changes, the frequency of the peak or dip changes. Therefore, for example, in the case of
correcting the system by the graphic equalizer 3, a large number of circuits are required and the
adjustment thereof Will be very difficult. Furthermore, it is impossible to make corrections for
peaks and dips in an apparatus having only a treble control function. SUMMARY OF THE
INVENTION The present invention has been made to eliminate the above-mentioned drawbacks
of the prior art, and the object of the present invention is to provide a correction circuit which
has an inverse characteristic to the acoustic transfer characteristic from the speaker to the
listening point. A sound field correction apparatus according to the present invention is to
provide a sound field correction apparatus inserted between a signal source and a speaker to
achieve equalization of frequency characteristics in the sound field. A sound field correction
device for correcting a sound field produced by a sound and its reflected sound, comprising a
feedback loop in an amplification path from a signal source to a speaker, and a transfer function
concerning frequency vs. level and phase of this feedback loop Is set to a predetermined value to
eliminate the influence of the reflected sound at a predetermined listening point in the sound
field. Another sound field correction device according to the present invention is a sound field
correction device that corrects the sound field produced by direct radiation sound and its
reflection sound by left and right channel speakers for stereo reproduction, and corresponds
from the left and right channel signal sources. The subtraction means respectively provided at
each input stage of the amplification means to the left and right channel speakers, and the
transmission means for applying one part of each of the application signals to the left and right
channel speakers as one hand of the subtraction means of another channel system The present
invention is characterized in that transfer functions related to frequency level and phase of the
transmission means are respectively set to predetermined values so as to eliminate the influence
of the reflected sound at predetermined listening points in the sound field.
EXAMPLES The present invention will be described in detail below with reference to the
drawings. FIG. 4 is a Bukonok diagram of one embodiment of the present invention, an input
signal IN j from a single word North (not shown), an increase with a transfer function G3 (s) via jsubtraction 5to.・ Input to the cylinder 11. This amplified output can be used as a speaker drive
signal via the amplifier amplifier 13 and also as an input of a feedback loop. This feedback loop
has a device 14 having a phase and time delay function, which is composed of a delay device
such as a CCD (charge coupled device) and a phase shifter, and the transmission ratio 註 is G (τ).
Is represented. The output of the delay unit 14 has a level adjustment function corresponding to
the level of the reflected wave in the level adjustment unit 15, and its transfer characteristic is G
(K). The output of the level adjuster 15 is the other input of the subtractor 1o via the transfer
characteristic G4 (the amplifier 16 having a resistance of 0). If the gain by the power amplifier
13 is 1 for simplification, (Gly (Gly G3 (s) / (1 + G3 (s) · G, (s) · G (K) · G (τ))) (6) ). On the other
hand, since the transfer characteristic from the speaker to the listening point is GA as described
above, the overall characteristic G (-) is G (') "Gc' GA = 03 (S / (1, 103 (s) G, (8) c (x)-c (r) X GI (8)
(1 + c (r)-G (K)-c, (s) / G x (s) = (1 + (G 2 (s / G l (s) August · G (f)-G (s) 7 (l 1003 (s)-G 4 (1 ')-G (K)'
G (τ) 1 x c 1 (s · G 3 (s)-· · · (( 7) In this formula, if G2 (') / Gl (") = G3 ('). G4 (s)-(8), then G (S) = Gl
(S) .Ga ('). As (9), it becomes possible to eliminate the disturbance of the frequency characteristic
caused by the phase 1 time delay reflected by the wall or the like. That is, the term of G (τ) can
be eliminated. Note that G (τ) and G (K) in the equation (5) are the time delay part of the
reflected wave and the part due to reflection, and the G (τ) and G (K) of (6) G (τ) can be set by
using a delay element such as COD to set a delay time determined by reflection of a wall or the
like. It is better to use an attenuator because it is. In a relatively narrow listening space or a
sound field such as a car interior, the reflection state is complicated, so a low pass filter, an A
band pass filter, etc. may be inserted in the feedback line t under certain conditions. If the
transfer characteristics are changed variously, more complicated space transfer characteristics
can be corrected.
In the present example, only one reflected sound was considered, but in reality there are a
plurality of reflected sounds, so as shown in FIG. The transfer characteristics G (.tau.) And the
transfer characteristics G.sub. (K) of the level adjusters 15.sub.1-15.sub.L can be set to
compensate for each of a plurality of reflected sounds. FIG. 6 shows an example in the case of
stereo sound field, and the direct radiation sounds by the left and right channel speakers 5L, 5R
are 7L, 7R, and these reach the left and right ears of the listener (dummy head) 9, Reflected
sound 8L of the sound emitted by the channel speakers 5L and 5R. When 8R reaches 0 to the
right and left ears of the dummy head 9, respectively, a block as shown in FIG. 7 is used. That is,
the signals of the other channels are applied to the respective subtraction inputs of the
subtractor 10L and IOH. Output of left channel amplifier 12L, delay unit 14L, level adjuster 15L.
The amplifier 16L passes the subtraction input of the subtracter 10H, and the output of the right
channel amplifier 12R passes the delay unit 14R, the level adjuster 15R, and the amplifier 16R
and the subtraction input of the subtractor 10L. In addition to the sound field as shown in FIG. 6,
when a reflecting wall is also present in front of the listening point 9 as shown in FIG. 8, each
reflected wave 19L, 19R by this reflecting wall is of the dummy head 9 respectively. Incident to
left and right ears. In order to cancel this, the embodiment as shown in FIG. 9 is used. In the
figure, parts equivalent to those in FIG. 7 are indicated by the same reference numerals. In this
example, in addition to the octopus shown in FIG. 7, delay units 14L-1, 14R.1. A circuit system
consisting of level controller 15L · 1 ° 15R · 1 and amplifier 16L · 1, 16R · 1 is added, and the
output of this left channel circuit system is input to left channel subtractor 10L, and the right
channel circuit system is also added. The output of is input to the subtracter 10 · R for the right
channel. In the example of FIGS. 7 and 9, the characteristic of the corresponding delay is set to be
a function of the difference between the path of each reflected wave and the path of the direct
wave, and the characteristic of the corresponding level adjuster is also the same. It is set by a
function of the direct wave and the reflected wave. Effect According to the present invention, a
feedback loop that is reverse to the acoustic transfer characteristic from the speaker to the
listening point is inserted between the signal source and the speaker, and the phase and level
characteristics of the loop are set as desired. (2) Since interference due to reflected waves is
eliminated, it becomes possible to obtain flat frequency characteristics at the listening point 0
Brief description of the drawings
1 is a block diagram of one side of the audio reproduction system, FIG. 2 is a diagram showing an
example of a sound field, and FIG. 3 is a diagram showing an example of frequency
characteristics of the sound field of FIG. 5 is a block diagram of an embodiment of the present
invention, FIG. 6 is a diagram showing an example of a stereo sound field, and FIG. 7 is a block
diagram of the embodiment of the present invention suitable for sound field correction of FIG.
FIG. 8 is a view showing another example of the stereo sound field, and FIG. 9 is a block diagram
of another embodiment of the present invention suitable for the sound field correction of FIG.
Explanation of symbols of main parts 5: Speaker 6: listening point 7: direct sound 8: reflected
sound 10: subtractor 14: delay device 15: level adjuster applicant Pioneer Corporation Attorney
Attorney Fujimura Motohiko
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