JPH07226995

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DESCRIPTION JPH07226995
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
alarm sound generator used in emergency vehicles and the like, and more particularly to
improvement of directivity.
[0002]
2. Description of the Related Art In a conventional vehicle 2 such as an emergency car, two
directional speakers S1 and S2 are usually arranged side by side as shown in FIG. 7A and
simultaneously driven from one signal generator. An alarm sound is generated. As a result, the
sound wave is generated with directivity as if the characteristics of B and C in FIG. 7 were
multiplied far enough. Fig. B shows directivity by driving two speakers with the same signal, and
Fig. C shows directivity unique to the speakers. However, its directivity is not sufficient.
[0003]
An object of the present invention is to provide an alarm sound generator having directivity as
sharp as possible.
[0004]
According to a first aspect of the present invention, there is provided an alarm sound generating
device comprising: a speed measuring unit for measuring a traveling speed of the vehicle; and a
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forward and backward shift of the vehicle in the vehicle. And a plurality of speakers, and a signal
generation unit for distributing and supplying an alarm signal to the speakers in the front row (or
the last row) of the speakers and a predetermined portion in the apparatus, and an alarm signal
distributed and supplied from the signal generation unit Create a signal that is biased according
to the traveling speed for each speaker except the speakers in the front row (or the last row) so
that the time average power of sound waves in front of the vehicle is maximized. And a phase
shift unit to be input to each speaker.
[0005]
(2) According to the invention of claim 2, in the alarm sound generating device according to the
item (1), the phase shift portion is a speaker excluding the speakers in the front row (or the last
row) of the plurality of speakers. The phase difference between the input signal of each speaker
except for the voltage controlled oscillator unit for inputting the alarm signal and the speaker for
the front row (or the last row) with respect to the input signal of the speaker for the front row (or
last row) Phase difference setting unit configured according to the traveling speed so as to
maximize the time average power of the sound wave, and the phase between the input signal of
each speaker and the input signal of the front row (or last row) speaker And a phase comparison
unit that controls the voltage control oscillator unit such that the phase difference of the former
with respect to the latter matches the value set by the phase difference setting unit.
[0006]
(3) In the alarm sound generating device according to the item (1), in the invention of claim 3,
the speaker is a first speaker to a front row (or last row) to a first speaker to a last row (or front
row) n ≧ 3), and the signal generation unit generates an alarm signal of a first frequency f1, a
second frequency f2, ..., an (n-1) frequency fn-1 (where f1> f2 ...> fn-1). Each of the second to n-th
speakers corresponds to the phase of the alarm signal of the first to (n-1) frequency distributed
and supplied from the signal generator. A signal that is biased at each time is created and input
to each speaker.
[0007]
(4) The alarm sound generator according to the item (3), wherein the phase-shifting part inputs
an alarm signal to the second to n-th speakers, and the voltage-controlled oscillator part
according to the item (3). A phase difference setting unit for setting a phase difference between
each of the input signals of the second to n-th speakers with respect to the alarm signal of the
first to (n-1) frequencies; and each input signal of the second to n-th speakers The voltage control
oscillator compares the phase with the alarm signal of the first to (n-1) frequencies, and the
phase difference of the former with respect to the latter matches the value set by the phase
difference setting unit. And a phase comparison unit that controls the unit.
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[0008]
(5) According to the invention of claim 5, in the alarm sound generator according to any one of
the items (1) to (4), the frequency of the alarm signal and the respective speakers and the front
row (or the last row) The anteroposterior spacing of the loudspeakers is set in such a way that
the time-averaged power of the sound waves behind the vehicle is substantially minimal.
(6) According to the invention of claim 6, in the alarm sound generating device according to any
one of the items (1) to (5), the speed measuring unit generates a signal for measurement and an
output of the generator. A sound generator for emitting sound toward the front of the vehicle,
first and second microphones disposed close to the front and the rear of the sound generator, a
sound wave emitted from the sound generator, and A time difference measurement unit that
measures time differences between sound waves received by the first and second microphones,
and a traveling speed measurement unit that measures the traveling speed of the vehicle from
the measurement values of the time difference measurement unit. .
[0009]
(7) According to the invention of claim 7, in the alarm sound generating device according to any
one of the items (1) to (6), the speed measuring unit measures the speed of sound as well as the
traveling speed of the vehicle. The phase shift unit controls the phase of each of the speaker
input signals according to the traveling speed and the speed of sound.
[0010]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is
characterized in that a plurality of speakers are arranged in the front-rear direction of a vehicle,
and sharp directivity is provided by controlling the phases of the generated sound waves.
At the same time, the Doppler effect depending on the traveling speed of a car or the like is also
taken into consideration.
FIG. 5 shows an example of the arrangement of speakers in the present invention.
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A speaker is provided by shifting the vehicle 2 in the front-rear direction.
The interval is approximately 1⁄4 of the wavelength of the generated sound.
As the number of speakers is increased, the directivity can be made stronger.
[0011]
FIG. 1A shows the configuration of the embodiment of claim 1 of the present invention. Here, a
sine wave is used as an alarm signal, and the number of speakers is four. The output of the signal
generator 4 is supplied directly to the speaker S1 in the front row and to the speakers S2 to S4
through the phase shift unit 5. The phase shift unit 5 controls the phase of the alarm signal for
each speaker based on the phase of the input of the speaker S1. This can be realized by a PLL
control using a VCO and a phase comparator or a method of controlling by a controller a delay
unit. Although the phase adjustment method will be described later, it is determined to obtain a
desired directivity depending on the speaker spacing, the frequency of the alarm signal, and the
traveling speed of the vehicle.
[0012]
FIG. 2 is a diagram showing the configuration of a second embodiment of the present invention.
In this example, the phase shift unit 5 includes a VCO unit 8, a phase comparison unit 9, and a
phase difference (offset) setting unit 10. Further, the signal generating unit 4 is composed of the
VCO 4a and the control voltage generator 4b. In this case, a voltage controlled oscillator (VCO) is
prepared for each of the speakers S2, S3 and S4, and the phase of each output is a reference
signal. PLL control is used to control the phase so as to be maintained at the desired phase
difference (offset) with the output of the generator 4. The phase difference is again set by the
spacing between the loudspeakers and the oscillation frequency and travel speed. In the
configuration of FIG. 2, since control is performed in a closed loop using the output of each
oscillator, it is possible to flexibly follow changes in the frequency of the alarm signal and
changes in the traveling speed.
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[0013]
FIG. 4 shows a method of measuring the traveling speed v together with the speed of sound V. A
speaker 21 is prepared separately from the speaker for alarm sound generation, and driven with
a pulse train or M-sequence noise. The output of the speaker 21 is received by the microphones
22 and 23, and the traveling speed v of the vehicle is calculated from the time differences
.DELTA.t1 and .DELTA.t2 of the outputs M1 (t) and M2 (t) of the respective microphones from
the speaker drive signal S (t). calculate. Although the difference V-v = L1 / [Delta] t1 between the
sound velocity V and the traveling speed v can be measured with the front microphone 21 alone,
the speed at which each of them is separated is not known. When the time difference .DELTA.t2
is measured with another microphone 23 at the rear, the sum V + v = L2 / .DELTA.t2 of the
sound velocity V and the traveling speed v can be measured. Here, L 1 and L 2 are the intervals
between the microphones 22 and 23 and the speaker 21. From the difference and sum of each
velocity, V and v can be measured. This result may be used to control the phase difference for
each speaker. It is also possible to share the speaker 21 for speed measurement with the speaker
for alarm sound generation and superimpose an M-sequence signal for speed measurement on
the alarm sound. When the alarm sound is a sine wave, the time difference can be measured by
filtering out the component.
[0014]
The method of setting the phase difference will be described for the case of FIG. 5 in which the
two speakers S1 and S2 are arranged offset to the front and rear of the vehicle for simplification.
The speaker interval is L, the frequency of the alarm signal is f, the phase difference with respect
to the input of the speaker S1 before the input of the speaker S2 later with respect to the
traveling direction is θ, the speed of sound and the traveling speed are V and v, and the front
and rear speakers Assuming that the amplitudes of the sound waves from x are a and b,
respectively, the instantaneous power P (t) of the sound waves at a sufficiently far front can be
calculated as follows.
[0015]
P (t) = ¦ asin {2πVft / (V−v)} + b sin [{2πVf (t−L / V) / (V−v)} + θ] ¦ 2 (1) Therefore, the time
average power Pa is Pa = A 2 + b 2 + 2 ab cos [2 π f {L / (V-v)} + θ] (2) Similarly, at a sufficiently
far distance, the average power Pa (φ) in the direction of angle φ from the front is {L cos .phi ./
(V-v cos .phi.)} +. Theta.] (3) It should be noted that when .phi. = 0, the forward direction is
forward, that is, when the vehicle goes straight ahead of the vehicle, when .phi. =. Pi./2 is just
lateral, The case of = π corresponds directly behind.
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[0016]
(2) In order to maximize the average power Pa in front of the vehicle of the equation (2),
according to the traveling speed v such that 2πf {L / (V−v)} + θ = 0 ± 2 mπ (4) is satisfied.
The phase difference θ may be controlled.
Θ θ = ± 2mπ−2πfL / (V−v) (4 ′) Further, in order to minimize the average power Pa
behind the vehicle with φ = π in the equation (3), −2πf {L / (V + v) ) + Θ = ± π ± 2 mπ (5).
From the equations (4 ') and (5), f = (1 + 2 m) (V2-v2) / 4 VL (6) (4) If f and θ are set to satisfy
the equation (5) Can transmit sound waves weakly backwards. However, the equation (5)
required to minimize the average power Pa behind the vehicle is approximately as important as
the equation (4) needed to maximize the average power Pa ahead of the vehicle. do it. Then, since
V >> v, v is omitted, and a frequency f satisfying f ≒ (1 + 2 m) V / 4 L (6 ′) is set.
[0017]
When the frequency f is a specified constant value, the speaker spacing L may be set to L = (1 +
2m) (V2-v2) / (4f × V) (7) from the equation (6). By the way, since it is generally impossible to
change the speaker interval L according to the traveling speed v in the equation (7), if v is
omitted for V, L れ ば (1 + 2 m) V / 4 f (7 ') Equation (5) is approximately satisfied. Thus, when f
is constant, the intervals L and θ may be determined. In any case, f and L are set so that the rear
power is almost maximum (claim 5).
[0018]
It should be noted that both the equations (4) and (5) have 2 mπ (m is a natural number) on the
right side, and a convenient combination can be selected. However, in this case, the directionality
can be strong also in the lateral direction by only m in addition to the front (see FIG. 5). So far,
the case of two speakers has been described, but in the case of two or more speakers, similarly,
the interval Li between the phase difference θi of each speaker Si input to the speaker S1 input
and S1 is expressed by equation (4) (5) It may be set by the equation.
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[0019]
In the case of two types of frequencies f1 and f2 (f1> f2) as in an ambulance, as shown in FIGS. 2
and 4B, at least three speakers are arranged in the front-rear direction of the vehicle to increase
the frequency (f = f1) In some cases, if the small loudspeakers S1 and S2 of the interval L1 are
used and the loudspeakers S1 and S3 of the large interval L2 are used at low frequencies (f = f2),
desired directivity can be obtained for both frequencies. When the frequency is (n-1) types, n
speakers may be used.
[0020]
FIG. 2B is a case where PLL control is performed by configuring the VCO unit 8 with the phase
comparison unit 9 and the phase difference setting unit 10 as in the case of FIG. 1B. In the
arrangement shown in FIG. 4D, the horizontally arranged central speakers S2 and S2 'are on the
central axis in the traveling direction, and the intervals L1 and L2 are similarly set as in the case
of FIG. 4B. Can control the backward directionality. In the arrangement of FIG. 4D, it is possible
to further provide lateral directivity (different directivity in right and left directions).
[0021]
Specific numerical examples are shown below for the case of FIG. 4C. (4) If θ is set so as to
satisfy the equation, the forward power is Pa (0) = a2 + b2 + 2ab (8), but the backward power is
Pa (π) = a2 + b2 + 2ab cos {4πfVL / (V2 −v2)} (9)
[0022]
If f = 500 (Hz), V = 340 (m / s), v = 0 (m / s), L is L = (1 + 2 m) according to the equation (6 ') or
(7') Assuming that V / 4f = V / 4f = 0.17 (m) (m = 0), θ is given by θ = −2πfL / V = −π / 2
from the equation (4) or (4 ′). If the vehicle speed v increases, changing θ accordingly to
satisfy the equation (4), the equation (5) does not hold, but the power to the rear increases
slightly from the minimum value because V >> v Just do it. Alternatively, L may be set to m = 1
and L = 3 V / 4 f = 0.51 (m) or m may be set to L = 5 V / 4 f = 0.85 (m). The directional
characteristics in these cases are shown in FIG.
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[0023]
In the description above, the speaker (also referred to as a reference speaker) S1 corresponding
to the input signal giving the phase reference is in the front row, but even if the reference
speaker S1 is in the last row, It is apparent that the directivity can be improved by controlling the
phase of each speaker input as in the past. In the description above, the phase shift unit 5
controls the phase of each speaker input according to the traveling speed v of the vehicle
measured by the speed measurement unit 7, but to improve the accuracy, the speed
measurement is performed. The speed of sound V (which changes with the wind direction, the
wind speed, the air pressure, etc.) is measured together with the traveling speed v in the unit, and
phase control may be performed to satisfy the equation (4) according to the change in both. Item
7).
[0024]
According to the present invention, a plurality of speakers are disposed in the front-rear direction
of the vehicle, and the phase of each speaker input is adjusted according to the traveling speed
so that the time average power of sound waves in front of the vehicle becomes maximum. Since
the control is performed, it is possible to make the directivity of the sound wave in front of the
vehicle sharper than before.
[0025]
Also, by selecting the frequency of the alarm signal and the speaker spacing, the average power
behind the vehicle can be substantially minimized.
The present invention can also be applied to the case where an alarm sound of different
frequency is switched and emitted like an ambulance.
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