This invention relates to a loudspeaker device of a stereophonic
dipole system (hereinafter referred to as " SD system" in which no acoustic short-circuiting
takes place in a case where left side and right side loudspeakers are disposed in
close proximity to each other.
In a conventional loudspeaker device for stereophonic audio
reproduction, left side and right side loudspeakers are disposed in front of a listener
and with a certain distance provided between the two loudspeakers. Such a loudspeaker
device is known from document US 3,892,624.
A loudspeaker device called SD system has recently been
proposed. A brief explanation will be made about the reproduction principle of the
SD system.
The SD system is basically composed of a digital filter
network inserted immediately before an amplifying power amplifier in the reproduction
system and two loudspeakers disposed in front of a listener in close proximity to
each other. The digital filter network corresponds to standard stereophonic, monaural
and binaural sources as their input sources. For these input signals, the digital
filter network has a function of cancelling a crosstalk sound which reaches from
the right channel to the left channel (or from the left channel to the right channel)
and produces two channel outputs after subjecting the input signals to this filtering
processing. By amplifying these outputs and supplying them to the two loudspeakers
which are disposed in front of a listener in close proximity to each other for reproduction,
a virtual reality sound field space is produced in front of the listener. This SD
system is advantageous in that, in comparison with the conventional loudspeaker
device, it has a broader listenable area and a broader allowable range for moving
of the listener's head during reproduction.
Further, as a result of passing through the above described
digital filter network, the output sound reaches the listener's ear with the harmful
component called the crosstalk sound being cancelled, so that a high fidelity reproduction
of music can be realized.
In the above described SD system, however, there occurs
a problem that, since the loudspeakers are disposed in close proximity to each other,
opposite phase components of left and right channel signals are acoustically short-circuited
to cancel each other in the vicinity of loudspeaker units immediately after generation
of these signals and, therefore, these components do not reach the listener's ear.
Particularly, occurrence of this phenomenon in middle and low frequency sound ranges
which have a broad directivity in reproduction prevents propagation of a reproduced
sound over a broad range and also reduces the sound pressure level of a reproduced
sound in the middle and low frequency sound ranges.
It is, therefore, an object of the invention to provide
a loudspeaker device of the SD system in which opposite phase components of left
and right channel signals do not cancel each other.
For achieving the above described object of the invention,
there is provided a loudspeaker device comprising left and right channel loudspeaker
units which are disposed on left and right sides in close proximity to each other,
each unit having a front baffle defining a plane, and a partition member projecting
forwardly in a direction of propagation of sound from the loudspeaker units by a
predetermined distance from a position between the loudspeaker units on said planes
of said front baffles on which the loudspeaker uni ts are mounted.
In one aspect of the invention, in the loudspeaker device,
said left and right channel loudspeaker units are respectively mounted on independent
loudspeaker enclosures and these left and right loudspeaker enclosures which constitute
a pair are disposed adjacent to each other to be integrated together and said partition
member is disposed on a plane on which the loudspeaker enclosures are disposed adjacent
to each other.
In another aspect of the invention, there is provided a
loudspeaker device comprising left and right channel loudspeaker units of a full
frequency range type or a middle and low frequency range type disposed in proximity
to each other on a first front baffle plane, a loudspeaker unit for a low-frequency
sound used commonly for the left and right channels mounted on a second front baffle
plane which is located forwardly in a direction of propagation of sound from the
loudspeaker units from the first front baffle plane, and a partition member disposed
between said first front baffle plane and said second front baffle plane and between
the left and right channel loudspeaker units of the full frequency range type or
the middle and low frequency range type.
The loudspeaker device of the SD system according to the
invention has the following advantages:
- 1. By providing the partition member between the left and right side loudspeakers,
opposite phase components of reproduced sound, particularly those in the middle
and low frequency ranges do not cancel each other in the vicinity of the loudspeakers,
so that the reproduced sound can be propagated over a broader range whereby reproduction
by the SD system can be realized with a high fidelity and a high quality.
- 2. In a case where a loudspeaker cabinet is adopted in which the left and right
side loudspeakers are integrally disposed, the partition member, together with a
Saran (TM) net, increases the mechanical strength of the loudspeaker as a whole
with resulting improvement in the quality of a reproduced sound.
- 3. By providing the partition member on the side of the Saran net, the Saran
net can be added or replaced on a loudspeaker device which has no such Saran net
and, accordingly, an acoustic effect produced by mounting the Saran net can be recognized
easily.
Preferred embodiments of the invention will be described
below with reference to the accompanying drawings.
In the accompanying drawings,
- Fig. 1 is a perspective view showing a first embodiment of the loudspeaker device
of the SD system made according to the invention;
- Fig. 2 is a perspective view showing a second embodiment of the loudspeaker
device of the SD system made according to the invention;
- Fig. 3 is a perspective view showing a third embodiment of the loudspeaker device
of the SD system made according to the invention; and
- Fig. 4A is a diagram showing the function of the conventional loudspeaker device
of the SD system; and
- Fig. 4B is a diagram showing the function of the loudspeaker device of the SD
system made according to the invention.
Fig. 1 shows a first embodiment of the loudspeaker device
according to the invention.
In this figure, reference character 1 designates a left
channel loudspeaker and reference character 2 designates a right channel loudspeaker.
These loudspeakers 1 and 2 are of the same construction and description will be
made below with respect to the left channel loudspeaker 1 only. On a front baffle
3 of the loudspeaker 1 is mounted a full range type loudspeaker unit 4. A partition
plate 5 projecting from the front baffle 3 is provided between the loudspeakers
1 and 2. This partition plate 5 is disposed in such a manner that it projects forwardly
from the front baffle 3 to divide the pair of left and right loudspeaker units 4
in the center.
By performing reproduction of music by using the SD system
loudspeaker device constructed in the above described manner, propagation of a sound
wave of an opposite phase component from one loudspeaker 1 (or 2) to the other loudspeaker
2 (or 1) is interrupted and acoustic short-circuiting is thereby prevented. More
specifically, a sound wave which is propagated through the shortest path from the
loudspeaker 1 to the loudspeaker 2 as shown in Fig. 4A is interrupted by the partition
plate 5 as shown in Fig. 4B. This prevents occurrence of an acoustic short-circuiting
phenomenon and thereby prevents decrease in the sound pressure level due to short-circuiting,
so that the sound wave can accurately reach a listening point.
For realizing the first embodiment of the loudspeaker device
in a specific form, two independent loudspeaker enclosures may be provided adjacent
to each other and a partition plate 5 may be mounted in the center thereof, i.e.,
on a plane on which these loudspeaker enclosures are disposed adjacent to each other.
According to this construction, a loudspeaker device of the SD system can be readily
provided by utilizing an existing loudspeaker device. Alternatively, it is possible
to combine cabinets of two loudspeaker devices together in such a manner that they
share a common side plate and extend this common side plate forwardly to form a
partition plate 5. Further alternatively, left and right channel loudspeaker units
may be mounted on an integrally formed cabinet and a partition plate 5 may be provided
so that the left and right channel loudspeakers share a common partition plate 5
provided in the center. According to this construction, mechanical strength of the
cabinet of the loudspeaker device can be improved and the manufacturing cost can
be reduced because the number of component parts and manufacturing steps can be
reduced.
Fig. 2 shows a two-way loudspeaker device which is the
second embodiment of the invention.
In this figure, reference characters 1 to 3 and 5 designate
the same component parts as those shown in Fig. 1. Reference character 6 designates
a tweeter which is a loudspeaker unit for a high frequency sound (hereinafter simply
called "tweeter") and reference character 7 designates a woofer which is a loudspeaker
unit for a low frequency sound (hereinafter simply called "woofer"). In a case where,
as shown in this figure, a loudspeaker of each unit consists of plural loudspeaker
units, it is preferable that a partition plate 5 is provided between each pairing
loudspeaker units so as to prevent interference of sound waves in each pairing loudspeaker
units. In this embodiment also, various structures similar to those described with
respect to the embodiment of Fig. 1 may be adopted.
As the third embodiment of the invention, a loudspeaker
device having a monaural subwoofer for enhancing a low frequency sound is shown
in Fig. 3. This embodiment is suitable for use in a situation in which the sound
wave interference prevention effect by the partition plate in the above described
embodiments is still insufficient in a low frequency range. In this embodiment,
as left and right channel loudspeaker units, a loudspeaker unit of a full range
type or a loudspeaker unit of a middle and high frequency range type such as a multi-way
type may be effectively used. This system has a first reproduction unit which is
disposed in the upper portion of the system for reproducing mainly middle and high
frequency sounds through left and right stereophonic channels and a second reproduction
unit which is disposed in the lower portion of the system for monaurally reproducing
a low frequency sound or a super-low frequency sound. Tweeters 9 and woofer-squawkers
10 which are loudspeakers of the first reproduction unit are mounted on a first
baffle plane, i.e., front baffle 8 in the upper portion of the system and a subwoofer
12 which is a loudspeaker of the second reproduction unit is mounted on a second
baffle plane which is disposed forwardly of the first baffle plane, i.e., front
baffle 11 in the lower portion of the system. The front baffle 11 is formed with
bass-reflex ports 13. A partition plate 14 projects from the front baffle 8. A decorative
and protective Saran net 15 is detachably mounted on the two front baffles 8 and
11 by means of fitting devices 16 and 17 as illustrated which can be fittedly engaged
with each other.
In this example, the subwoofer 12 addes left and right
channel signals together and reproduces the added signal as a monaural signal so
that a partition member for dividing the left and right loudspeaker units is not
necessary. In the first reproduction unit, in the same manner as in the above described
embodiments, there is provided the partition plate 14 projecting forwardly in the
direction of propagation of sound from the loudspeaker unit by a predetermined distance
from a position between the loudspeaker units on a plane of baffles on which the
loudspeaker units are mounted. The length of projection of this partition plate
14 is adjusted so that the front end of the partition plate 14 is made flush with
the second baffle plane, i.e., the front baffle 11 of the second reproduction unit.
In the present invention, it is not essential that the length of projection of the
partition plate 14 should be adjusted in this manner. However, by adjusting the
length of projection of the partition plate 14 in this manner, an advantage to be
described in C below will be derived.
By adopting the structure having the first and second reproduction
units and having the front baffles 8 and 11 positioned on the first and second baffle
planes, the following advantages will result:
- A. In a case where sound wave interference is prevented sufficiently in middle
and high frequency sound ranges by providing a partition plate between left and
right channel loudspeakers which are driven by the SD system but a sufficient sound
wave interference prevention effect cannot be achieved in a low frequency sound
range due to bypassing of sound wave and, as a result, the sound pressure level
of a reproduced sound is insufficient, the sound pressure level of a low frequency
sound can be enhanced by the provision of the subwoofer in the system.
- B. By suitably setting the degree of the step formed between the first reproduction
unit and the second reproduction unit, a hypothetic point sound source of a middle
or high frequency sound which is mainly produced by the first reproduction unit
and a hypothetic point sound source of a low frequency sound which is produced by
the second reproduction unit can be matched to cause phases of the respective sound
waves to coincide with each other whereby matching of the reproduction characteristics
can be realized.
- C. By adjusting the length of projection of the partition plate 14 so that the
front end of the partition plate 14 is made flush with the front baffle 11, the
Saran net 15 which covers the entire front surface of the loudspeaker device is
supported in its upper middle portion with resulting increase in the mounting strength
of the Saran net 15. Particularly in the third embodiment in which the left and
right channel loudspeakers of the first reproduction unit are received in a single
system cabinet, the area of the front baffle is about double that of the conventional
loudspeaker device which consists of separate left and right channel loudspeakers.
By further integrating the second reproduction unit, a Saran net of a large size
is required. The arrangement of matching the length of projection of the partition
plate 14 with the height of the front baffle 11 is effective for maintaining the
mechanical strength of such a large size Saran net.
In the above described embodiments, the partition plate
is supported on the baffle plane of a loudspeaker cabinet or enclosure. In a case
where a Saran net is provided further forwardly of the baffle plane, the partition
plate may be supported on the Saran net side. If such a structure is used on a loudspeaker
device of the SD system which has no partition plate on its baffle plane, the advantages
of the present invention can be achieved without changing the design of the system
itself such as a cabinet.
