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TECHNICAL FIELD OF THE INVENTION The present invention relates to a multi-unit speaker
system with improved directional characteristics in the vertical direction. Prior Art and Problems
When a loudspeaker arranged at a constant height is to the side of the listener, it is generally
considered that the optimum listening point is on the central axis of the loudspeaker. However,
when listening while sitting down like a car-mounted audio system, the position of the listener's
ear differs depending on the height and the like, and it is sufficiently predicted that the listener
will not get on the central axis. FIG. 1 shows this illustration, in which 1 is a seat, 2 is a listener
seated there, 3 is an ear, 4 is a cabin side wall, and 5 is a multi-unit speaker system called a roof
side speaker. The speaker system 5 is movable in the direction orthogonal to the paper surface,
but here, the directivity in the vertical direction is a problem. 6 is the central axis in the radial
direction of the system, and θ is the angle between the listening point (here, the ear) 3.
Generally, even if there is such an angle θ, it can be heard with some characteristic degradation,
but dips in the audio frequency band will be a problem if multiple units are made as shown in
FIG. 2 to increase the sound pressure. . That is, in the speaker system 5 of FIG. 2, six high sound
range speaker units 7 are divided into two rows on the xz plane and arranged at an up and down
interval d in a small diameter (for example, a diameter of 3 cm). is there. A point O is a central
point of the speaker system 5 and Po is a point on a central axis (7 axis) 6 passing the line point
O. Now, in order to consider the vertical characteristics of this system, it is assumed that a
listening point Pθ on a line forming an angle θ with the central axis 6 in the yz plane. Assuming
that A · −F is each central point of each speaker unit 7, the distance Pa 8 from the listening point
Pθ to the point A and the distance Pθ B from the point B can be expressed by the following
equations. ... (1) ... (2) Therefore, the difference in distance from the listening point Pθ to the
points A and B is ... (3). Assuming that the frequency of the sound from the speaker unit 7 is f, the
wavelength is λ, and the sound velocity is V (340 m / s), the sounds from points A and B
interfere with each other and weaken from the relationship of v = fλ. The minimum value of the
frequency (dip frequency) rθ can be obtained by the following equation. Therefore, assuming
PθO = 1 m and d = 44 m11 as a specific example, the equation (4) is simplified as follows.
Substituting the numerical example of θ into the equation (4 ′) gives the dip frequency fθ
shown in the following table. Tables 1 to 7 show these measured values (frequency
characteristics). A dip (indicated by an arrow) was observed at a frequency substantially
corresponding to the calculated value-0 This dip is seen from the listening point Pθ It is caused
by the difference in the distance to each speaker united in the direction (here, the left and right
direction does not matter), and Pa, C, D and E.
The same calculation holds for F. Then, in the arrangement shown in FIG. 2, the differences
between the distances between Pa and A and B, between Pa and C5D, and between Pa and E and
F are one and the same. The amount of dip above is noticeable. The object of the present
invention is to prevent large dips in the in-band t as much as possible so that the inevitable dip
frequencies generated in the unit sealed cans do not overlap as a whole. The multi-unit speaker
system according to the present invention arranges a plurality of speakers of the same
characteristic, which reproduce the same signal, along an arc line, and forms an overall listening
point in a direction intersecting a plane including the arc line. It will be described in detail below
with reference to the illustrated embodiment. Embodiment of the Invention FIG. 8 is a block
diagram of a multi-unit speaker system 5 showing an embodiment of the present invention. In
this example, six speaker units 7 having the same characteristics are disposed at equal intervals d
on the arc 8 of the half fxr. When the arrangement surface of the speaker unit 7 is an x-z plane,
the y-axis is the central axis 6 of the system 5. Pa is one point on the central axis 6, and Pa is a
listening point on a line forming an angle θ with the central axis 6 in the yz plane. When Pθ =
Po at θ−0 °, the distance from the listening point Po to the central point of each speaker unit
7 is PoA = PoB = PoC = − = PoF = f ““ Closed 7... (5 Since the output of each unit 7 is in phase
at the listening point Po and there is no interference between the units, the optimum listening
position is obtained. FIG. 9 shows the frequency characteristic in this case. On the other hand, the
listening point P.theta. Is moved up and down to make -P.theta. Because of P0D-PeF, all dip
frequencies generated by unit pairs separated in the vertical direction are different. As a result,
dips do not overlap at the same frequency to cause a large level drop. 11 and 12 show the
frequency characteristics of θ = −15 ° and θ = −30 ° measured by shifting the listening
point Pθ downward. The same applies to the case where the listening point Pθ is moved
upward. FIG. 10 shows frequency characteristics measured as θ- + 15 °. In either case, the
conventional large dip is not observed. The principle of the multi-unit speaker system of the
present invention is, as described above, based on the unit arrangement in which the dip
frequencies generated by the difference in distance from any two units to the listening point do
not overlap.
Therefore, in this regard, the units may be randomly arranged in the same plane. However, in this
case, the ideal listening point Pa is difficult to set or does not exist. Therefore, an arrangement on
a circular arc has been proposed as a unit arrangement in which there is an ideal listening point
Pa on or near the central axis 6 and the dip frequency for each unit does not overlap. As an
example in FIG. 8, a plurality of units 7 are arranged at equal intervals on a circular arc, but
arranging at irregular intervals as in the embodiment of FIG. 13 is more effective for dip
suppression. That is, in the example of FIG. 8, since PO3 is present, the influence of dips due to
the left and right unit pairs at the same height and the left and right unit pairs at the same height
different from that remains as shown in FIG. The dip does not occur if the height position of the
unit is changed. However, in this case, the ideal listening point is at a position different from Po
in FIG. Therefore, when the ideal listening point is set on the central axis, the even spacing
method of FIG. 8 is used, or when it is desired to suppress the dip as much as possible even if the
ideal listening point deviates slightly from the central axis. An uneven interval system as shown
in FIG. 13 may be employed. FIG. 14 is a modification in which the case of the system 5 is formed
in the same shape along the unit arrangement. The left and right di-knobs are not a problem on
each side described above, because this system 5 can be optimized by moving it in the X-axis
direction of FIG. Of course, the vertical and horizontal directions are for convenience of
description. Effects of the Invention As described above, according to the present invention, a
large dip does not occur even if the listening point deviates in the vertical direction, so that even
if there is a difference in the height of the listener, etc. There is an advantage that can be done.
Brief description of the drawings
FIG. 1 is an explanatory view showing the deviation between the speaker system and the
listening point in the vertical direction, FIG. 2 is a block diagram showing an example of a
conventional multi-uni-node speaker system, and FIGS. Fig. 8 is a block diagram showing one
embodiment of the present invention, Fig. 9 is a graph showing frequency characteristics in the
vertical direction of the same, and Fig. 13 is a block diagram showing another embodiment of the
present invention. FIG. 14 is a block diagram showing a modification thereof.
In the figure, 5 is a multi-unit speaker system, 7 is a speaker unit, 8 is an arc line, and Pe is a
listening point. Applicant: Fujitsu Ten Ltd. Attorney Attorney Atsushi Ayanagi
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