Loudspeaker system

The present invention includes a loudspeaker system in which sound radiation axes of two speakers in a single loudspeaker unit form an angle with respect to each other in a horizontal plane to increase the size of a listening area. The horizontal angle can be formed by orienting the sound axes of speakers in the loudspeaker unit at an angle in the range of 15 to 45 degrees from each other. The system also includes a phase adjustment system which adjusts the phase of the speakers in each loudspeaker unit so that the phase of the sound from each speaker in each loudspeaker unit is properly adjusted throughout the increased listening area to provide increased sound presence or spread.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a loudspeaker system which increases the 
size of the best listening area and, more particularly, to a loudspeaker 
system which broadcasts sound into a broader sonic cone by angling the 
speakers with respect to each other and which is particularly suitable for 
a television. 
2. Description of the Related Art 
A conventional loudspeaker 10, as illustrated in FIG. 1, includes a speaker 
cabinet 12 and one or more speakers 14 and 16 having a sound radiation 
axis extending forwardly and generally perpendicular to the front face 18 
of the cabinet 12. Such a loudspeaker 10 produces a relatively narrow 
sonic cone in which the sound can be adequately heard. When a pair of 
loudspeakers 10 is incorporated into a television system 20 including a 
television 22, the sound radiated from each speaker 10 in the system 
produces a pattern, as illustrated by the one-dot chain lines of FIG. 3. 
The best listening area in such a system is the shaded area where the 
sound patterns from the right and left speakers overlap. When a person is 
positioned in the shaded listening area, the sound image is properly 
localized with respect to the television 22, that is, the person hears the 
sound from the television as if it were radiated from the screen of the 
television. In such a conventional system, the shaded area of FIG. 3 is 
very narrow, requiring that everyone watching the television be crowded 
into the narrow listening area to obtain the best sound localization. If a 
person is positioned outside the shaded area, the person hears only the 
sound radiated from the closest speaker, and, as a result, the sound image 
is separate or dislocated from the television screen. Such a dislocation 
is annoying to the viewer. In addition, because the broadcast pattern for 
an individual speaker is different for high and low frequency sound, the 
perceived spread or presence of the sound is not good, particularly on the 
edges of the best listening area. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a loudspeaker system 
which increases the size of the listening area where the sound from a pair 
of speakers overlaps. 
It is another object of the present invention to increase the best 
listening in front of a television set so that an increased area will be 
provided in which sound image and picture image will be properly 
localized. 
It is an additional object of the present invention to increase the sound 
spread or presence produced by a speaker system. 
The above objects can be accomplished by a loudspeaker system in which the 
sound radiation axes of two speakers in a single loudspeaker unit form an 
angle with respect to each other in a horizontal plane. The use of two 
speakers in a single loudspeaker unit that are angled with respect to each 
other increases the area of the sound cone produced by the speaker unit. 
when two speaker units with the broadened sound cone are used, the best 
listening area, where the cones overlap, is increased dramatically. This 
angle between the speakers in a single unit can be formed by orienting the 
sound axis of each speaker in the loudspeaker unit at an angle in the 
range of 15 to 45 degrees from each other. The system also includes a 
phase adjustment system which adjusts the phase of the speakers in each 
loudspeaker unit so that the phase of the sound from the loudspeaker unit 
is properly adjusted throughout the increased listening area, so that the 
sound spread or presence of the sound is increased along with the increase 
in the size of the best listening area. 
These together with other objects and advantages which will be subsequently 
apparent, reside in the details of construction and operation as more 
fully hereinafter described and claimed, reference being had to the 
accompanying drawings forming a part hereof, wherein like numerals refer 
to like parts throughout.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A loudspeaker unit 30 which will increase the size of the sound projection 
area or cone in accordance with the present invention, as illustrated in 
FIG. 4, includes a cabinet 32 with speakers 34 and 36 mounted in a front 
face 38 of the cabinet 32. Upper speaker 36 is mounted in such a manner 
that its sound projection axis 40 forms an angle, in a horizontal plane 
with respect to the front face 38 of the cabinet 32 and with respect to 
the sound projection axis 42 of lower speaker 34. 
FIG. 5 illustrates a pair of speakers 30 incorporated into a television 22. 
FIG. 5 illustrates that the top speaker 36L in the left speaker 30L is 
angled toward the right, while the top speaker 36R in the right speaker 
unit 30R is angled toward the left. The resulting sound patterns of the 
two loudspeaker units 30 are in mirror symmetry with each other and 
overlap. 
The sound pattern produced by the speaker system of FIG. 5 is illustrated 
in FIG. 6. In the left speaker unit 30L, the bottom left speaker 34L forms 
a projection pattern with an angle defined by L1A-01-L1B while the upper 
left speaker 36L forms a projection pattern L2A-01-L2B. the right hand 
speaker 30R creates a mirror symmetric pattern with the bottom right 
speaker 34R producing the pattern R1A-02-R1B and the top right speaker 36R 
producing the pattern R2A-02-R2B. Since the lower speakers 34L and 34R 
radiate sound generally forwardly of the television 22 and the upper 
speakers 36L and 36R radiate sound generally across the television 22, the 
created sound radiation area or cone is larger than that of the 
conventional loudspeaker illustrated in FIG. 1. If a person is watching 
the television set 22 while sitting in the enlarged shaded area depicted 
in FIG. 6, the sound image is localized in the television picture because 
the right and left loudspeaker sound areas overlap each other. 
FIGS. 7(a)-7(e) illustrate the result of experiments to determine the 
preferred angle between the sound projection axes 40 and 42 of the upper 
and lower speakers 34 and 36, respectively. In the experimental system, 
two all band type speakers ten centimeters in diameter are arranged 
vertically with the sound radiation axis 42 of the lower speaker fixed in 
a direction perpendicular to the face 38 of the cabinet 32 and the sound 
radiation axis 40 of the upper speaker oriented to form angles of 
0.degree., 15.degree., 30.degree., 45.degree. and 60.degree. with respect 
to the sound radiation axis 42 of the lower speaker. At each of the 
angles, sound energy measurements were carried at a constant distance from 
the speaker unit 30 using sound broadcast frequencies of 6 kHz and 12 kHz. 
The results of the measurement with 6 KHz are indicated by the solid line 
in the polar diagrams of FIGS. 7(a)-7(e) and the results of the 12 kHz 
signal measurement by the broken line. As can be seen by reviewing FIGS. 
7(a)-7(e), the polar plots for 15.degree., 30.degree. and 45.degree. 
appear to provide the broadest and most uniform sound pattern at both 
frequencies. The results of the experiment to determine the preferred 
angle between the speakers when a -10 dB sound pressure level degradation 
is used as the cutoff level are summarized in Table 1 below: 
TABLE 1 
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EXPERIMENTAL DATA 
Angle width with which 
Angle between -10 dB is obtained with 
sound radiation 
respect to the forward 
Sound radiation angle 
axes Frequency 
direction (0.degree.) 
of loudspeaker unit 
Remarks 
__________________________________________________________________________ 
0.degree. 
6 kHz about 73.degree. 
front direction (0.degree.) 
12 kHz 
about 45.degree. 
front direction (0.degree.) 
15.degree. 
6 kHz about 87.degree. 
in a direction of about 10.degree. 
12 kHz 
about 68.degree. 
in a direction of about 10.degree. 
30.degree. 
6 kHz about 95.degree. 
in a direction of about 20.degree. 
12 kHz 
about 97.degree. 
in a direction of about 15.degree. 
45.degree. 
6 kHz about 120.degree. 
in a direction of about 30.degree. 
12 kHz 
about 102.degree. 
in a direction of about 20.degree. 
60.degree. 
6 kHz 125.degree. or more 
in a direction of about 35.degree. 
12 kHz 
about 40.degree. and about 48.degree. 
Null point, in a direction of 
Lobe, split 
into two 
parts 
__________________________________________________________________________ 
As is apparent from FIG. 7 and Table 1, when the angle between the sound 
radiation axes of the speakers is from 15 to 45 degrees, the directional 
patterns are relatively broad and satisfactory at both the 6 kHz and 12 
kHz frequencies. However, when the angle reaches 60.degree. and the 
measurement frequency is 12 kHz, the sound pressure lobe is divided into 
two parts. In the directional pattern obtained when the angle is 
45.degree. and the sound frequency is 12 kHz, the sound pressure lobe 
tends to split into two lobes at an angle of 20.degree.; however, the 
single partial split in the lobe causes no apparent problem for the user. 
If the lobe splits more than once, the tone characteristics of the signal 
will be degraded. Thus, it can be seen that the sound quality will be 
acceptable when the angle between the speakers is in the range of 
15.degree. to 45.degree. with 30.degree. being the most preferable. 
As can be seen by reviewing FIGS. 7(a)-7(e) and Table 1, when the broadcast 
frequency is low, the sound directional pattern is broad and when the 
broadcast frequency is high, peaks and dips tend to occur in the pattern. 
In addition, the sound radiation angle (the average sound projection axis) 
of the speaker unit shifts as the broadcast frequency changes. To smooth 
or remove these deviations in the sound pattern and to prevent sound 
radiation angle shifting, the present invention includes a correction 
circuit 50, as illustrated in FIG. 8. The correction circuit 50 includes 
two band dividers 52 which cause a band division at approximately 400 Hz 
and 12 KHz. This causes higher sound frequencies to be conducted 
throughout the lower speaker 34 while more of the lower frequencies are 
emitted by speaker 36. The band division frequencies or the cutoff 
frequency of a band divider type filter must take into consideration the 
frequency characteristics of the speaker being used which includes the 
range of frequencies which need to be phase shifted to correct the 
variations in sound projection by the speakers as illustrated in FIG. 7. 
Typical portions of a band divider circuit which will provide high 
frequency cutoff or low frequency cutoff are respectively illustrated in 
FIGS. 9(a) and 9(b). One of ordinary skill in the art can select the 
appropriate component values based on the speakers used in the system. 
In addition to the band dividers 52 an all frequency pass phase shifter 56 
is connected between band divider 54 and the top speaker 36. This phase 
shifter 56 provides an average preferred phase shift of 90.degree. at 2 
KHz as compared to the sound waves produced by speaker 34. FIGS. 10(a) and 
10(b) illustrate typical phase shift circuits for the right 30R and left 
30L speaker units. The object of the phase shifting is to make the 
distance from one speaker and the listener and the other speaker and the 
listener correspond to a phase shift of 90.degree.. That is, the phase 
shift should obey the following equation: La-Lb-wavelength/4, where La and 
Lb are the distances from the speaker units 30L and 30R to the listener. 
An appropriate phase shift pattern for the left 30L and right 30R speakers 
is illustrated by the curves 78 and 80 in FIG. 11. One of ordinary skill 
in the art can provide appropriate components to adjust each phase shifter 
56 to provide the above preferred amount of phase shift for the speakers 
actually used. The use of such a phase shifting arrangement compensates 
for the small lobes and dips in the sound pattern and provides a more 
uniform increased size listening area. The phase shifter 56 not only 
corrects the dips and lobes in the sound pattern but increases the 
perception of the spreading of the sound out over the picture or the 
presence feeling provided by the sound. 
In FIG. 13, a phase shifter 56 is connected to the speakers. In this 
embodiment, speakers 36 and 34 have substantially the same reproducible 
frequency band. On the other hand, according to the embodiment shown in 
FIG. 8, the speakers have partially the same reproducible frequency band. 
The band divider 54 is a high-pass filter capable of reproducing 
frequencies greater than 400 Hz. The band divider 52 is a low-pass filter 
capable of reproducing frequencies lower than 12 KHz. With this structure, 
sounds in a range of 400 Hz and 12 KHz are reproduced through the speakers 
36 and 34, so that audible range can be effectively enlarged with respect 
to vocal band. 
The many features and advantages of the invention are apparent from the 
detailed specification and thus, it is intended by the appended claims to 
cover all such features and advantages of the invention which fall within 
the true spirit and scope thereof. Further, since numerous modifications 
and changes will readily occur to those skilled in the art, it is not 
desired to limit the invention to the exact construction and operation 
illustrated and described, and accordingly, all suitable modifications and 
equivalents may be resorted to, falling within the scope of the invention. 
For example, the discussion indicates the top speaker 36 in each speaker 
unit 30 is the angled speaker; however, it is possible to angle the bottom 
speaker 34 instead of the top speaker 36 and produce the increased size 
best listening area. In addition, it is possible to provide different 
amounts of phase shift and to band divide at different points and still 
obtain a high quality, high presence, well localized sound image. It is 
also possible to have two or more speakers in a speaker unit each having a 
different frequency band.