JPH10271596

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DESCRIPTION JPH10271596
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates
generally to electro-acoustic conversion, and more particularly, emits sound waves of a
predetermined pattern to generate an acoustic image of a sound source to be converted. Relates
to a small loudspeaker system.
[0002]
BACKGROUND ART As background art, U.S. Pat. Nos. 4,503,553 and 5,210,802, and
"Stereophonic Projection Console" (IRE Transactions on Audio Vol. AU-8, No. 1, pp. 13I quote the
document entitled -16 (1/2 month, 1996).
[0003]
SUMMARY OF THE INVENTION An important object of the present invention is to obtain an
improvement in electroacoustic conversion.
[0004]
SUMMARY OF THE INVENTION In accordance with the present invention, a loudspeaker system
comprises an input for receiving an audio electrical signal, a first sound wave oriented in a first
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direction, coupled to the input, and a first sound wave within a first frequency range. , A second
transducer directing a second sound wave, and a third transducer directing a third sound wave
and emitting a third acoustic wave.
A low pass filter couples the input to the second and third transducers and provides a modified
audio electrical signal to the second and third transducers. A delay network delays the emission
of the second and third sound waves, which substantially oppose the portions of the first sound
wave emitted in the second and third directions, in the second and third directions. It
substantially cancels out the first sound wave.
[0005]
In another aspect of the invention, a directional loudspeaker system comprises: a first
loudspeaker having a substantially dipole acoustic radiation pattern in a first frequency range;
and substantially omnidirectional within said first frequency range And a second loudspeaker
having an acoustic radiation pattern. The first and second loudspeakers are configured to
combine radiation in the first and second directions cumulatively and differentially, respectively.
[0006]
In another aspect of the invention, a multi-channel audio playback device is in an enclosure, a
first input for receiving a first audio electrical signal, and in the enclosure, coupled to the first
input, for receiving a first sound wave. A first transducer to emit, a second transducer in the
enclosure to emit a second sound wave, and a first input coupled to the second transducer, the
second sound wave being coupled to the second transducer in a first direction. A first signal
modification configured and arranged to face a first sound wave, a second input receiving a
second audio electrical signal, and in the enclosure, coupled to the second input, for receiving a
third sound wave A third transducer for emitting, a fourth transducer in the enclosure for
emitting a fourth sound wave, and the second input coupled to the fourth transducer, the fourth
sound wave in the second direction; Construction and to 2 waves opposed and a second signal
change portion is located.
[0007]
In yet another aspect of the present invention, a multi-channel audio reproduction system
includes a first input coupled to a first transducer that receives a first audio electrical signal and
emits a first sound wave; A second input coupled to a second transducer receiving a signal and
emitting a second acoustic wave, a first signal modifier coupling the first input to a third
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transducer, and the second input being coupled to the third And a second signal modifier coupled
to the transducer, wherein the third transducer is configured to emit a third acoustic wave
substantially opposite the first acoustic wave and the second acoustic wave in the first direction.
And it is arranged.
[0008]
Other features, objects and advantages will become apparent upon reading the following detailed
description in conjunction with the accompanying drawings.
Throughout the drawings, the same reference symbols identify corresponding elements.
[0009]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and
in particular to FIG. 1, an isometric view of a loudspeaker unit 10 according to the present
invention is shown.
A housing or enclosure 8 supports three electro-acoustic transducers (transducers) or
loudspeaker drivers 12, 14 and 16 pointing in the directions 18, 20 and 22 respectively.
[0010]
Referring to FIG. 2, a schematic diagram of the loudspeaker unit 10 of FIG. 1 in a room audio
reproduction system is shown. The first driver 12 is directed in a space substantially
perpendicular to the second driver 14 and the third driver 16 and is separated by paths 33 and
35 of lengths 11 and 12 respectively.
[0011]
The audio signal source 24 sends the audio electrical signal to the electroacoustic transducers
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12, 14, 16 and emits corresponding sound waves. The network 100 generates the desired sound
field by modifying the signal delivered to the transducers and controlling the pattern of sound
waves emitted by the combination of transducers 12,14,16. In one embodiment, the network 100
modifies the signal so that the radiation pattern of the loudspeaker unit 10 is strongly directional
in the direction 18. In operation, audio signal source 24 transmits an audio signal through
network 100 to first transducer 12, second transducer 14, and third transducer 16, which emit
sound waves. The network 100 is out of phase with the sound wave which the second transducer
14 has arrived from the first transducer 12 when the sound wave emitted in the first transducer
12 reaches the second transducer 14 and the amplitude is the same. Modify the time and
amplitude characteristics of the audio signal to emit a sound wave. As a result, in the direction
20, the sound wave emitted from the second transducer 14 substantially opposes the sound
wave emitted from the first transducer 12. Similarly, the network 100 is out of phase with the
sound waves that the third transducer 16 arrives from the first transducer 12 when the sound
waves emitted by the first transducer 12 reach the third transducer 16, The audio signal is
modified to emit sound waves of similar amplitude. As a result, in the direction 22, the sound
wave emitted from the third transducer 16 will be substantially opposite (opposite) to the sound
wave emitted from the first transducer 12. The sound waves coming from the first transducer 12
are substantially opposite in directions 20 and 22 so that the radiation from the loudspeaker unit
is more directional in the direction 18. Note that a transducer that emits sound in a direction in
which the loudspeaker unit has directivity is defined as a "main transducer", and a transducer
that emits an acoustic wave opposite to the acoustic wave emitted by the main transducer is
"backing transformed. It would be convenient to define a bucking transducer. A single transducer
may be both a main transducer and a backing transducer, and one backing transducer may be
opposed to the acoustic waves emitted by the one or more primary transducers.
[0012]
In the embodiment of FIG. 2, the acoustic path of the sound waves emitted in the direction 18
and reflected by the acoustic reflection surface 36 to reach the listener 34 at the target listening
position is longer and therefore (transducers 12, 14, The arrival is delayed compared to the
sound waves that arrive directly from other sound sources (such as sound waves that arrive
directly from 16). However, by generating a much larger amplitude sound wave (about 10 dB)
that is emitted in direction 18 and reflected at acoustically reflective surface 36, listener 34
follows the accepted psychoacoustic criteria. Since the sound source is perceived as one or more
"virtual sound sources" in the general direction of the reflective surface 36, an extension of the
perceived sound image results. The virtual source may also be referred to as the position behind
the reflective surface (i.e. between reflective surface 36 and position 13) or between the
loudspeaker unit 10 and the reflective surface 36. This perception, or localization, towards the
reflective surface of the "virtual source" instead of in the source is one of the advantages of the
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present invention.
[0013]
Referring to FIG. 3, a loudspeaker system is shown that includes two loudspeaker units
configured in accordance with the principles of the embodiment of FIG. The stereo audio signal
source 24 distributes the left signal and the right signal to the left loudspeaker unit 10L and the
right loudspeaker unit 10R respectively through the networks 100L and 100R. The loudspeaker
units 10L and 10R may each have an electro-acoustic transducer (12L, 14L, 16L and 12R, 14R,
16R) similar to the loudspeaker unit 10 of FIG.
[0014]
Loudspeakers 10L and 10R emit sound in the directions indicated by arrows 18L and 18R,
respectively, according to the principles of operation outlined in the discussion of FIG. The sound
radiated by the loudspeaker systems 10L and 10R is reflected at the acoustic reflection surfaces
36L and 36R, respectively, and is located in the direction of the reflection surfaces 36L and 36R
as discussed earlier in the discussion of FIG. Create a perception to the listener that it was
emitted by The position of the "virtual sound source" is changed by changing the distance
between the loudspeaker units 10L and 10R and the acoustic reflection surfaces 36L and 36R, or
changing the orientation of the loudspeaker units with respect to the acoustic reflection surface
It is possible to The loudspeaker system according to FIG. 3 is advantageous as it allows the
placement of "virtual sound sources" in locations where it is impractical or impossible to
physically locate the loudspeakers. In addition, the loudspeaker system according to FIG. 3 is
capable of producing a perceived sound image larger than the room in which the loudspeakers
are arranged. The reason is that the first reflections from the acoustic reflection surfaces 36L and
36R can be felt as being emitted by the virtual sound source beyond the acoustic reflection
surfaces 36L and 36R.
[0015]
Referring to FIG. 4, another embodiment of the loudspeaker system of FIG. 3 is shown. System
200 includes stereo acoustic signal source 24 coupled to loudspeaker units 10L and 10R
through networks 100L and 100R, respectively, in a single enclosure. The system of FIG. 4 has
the same elements as the system of FIG. 3 (some of which are not shown in FIG. 4). The system
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according to FIG. 4 has a perceived sound image width similar to, or better than, many
stereophonic systems with two widely separated speakers, typically located remotely from a
stereophonic signal source. It is advantageous because it gives width). When operating system
200 in accordance with the principles of the embodiment of FIG. 3, the radiation patterns of left
loudspeaker unit 10L and right loudspeaker unit 10R have maxima in directions 18L and 18R,
respectively. The sound waves emitted in directions 18L and 18R and reflected by the
acoustically reflective surfaces 36L and 36R towards the listener 34 at the target listening
position respectively are transmitted to the listener by the transducers 12L, 14L, 16L, 12R, 14R,
16R. The amplitude is much greater than that of directly emitted sound waves. As already
discussed in the discussion of FIG. 2, the listener 34 perceives the sound emitted from virtual
sources in the direction of the reflective surfaces 36L and 36R.
[0016]
Referring to FIG. 5, there is shown an alternative embodiment of the loudspeaker system of FIG.
2 adapted to the situation where it is not necessary to block sound waves emitted in the opposite
direction to the intended listening position. This example can include a wall mounted
loudspeaker system or a loudspeaker system mounted in a cabinet such as a television console.
The loudspeaker unit 10 'has a first electro-acoustic transducer 12' pointing in the direction
indicated by the arrow 18 and a second electro-acoustic transducer pointing in the direction
indicated by the arrow 20 orthogonal to the first transducer 12 '. Vessel 14 '. An audio signal
source 24 'is coupled to a first transducer 12' and a second transducer 14 'through a network
100' that modifies the signal from the signal source 24 ', similar to the network 100 of FIG. As a
result, the sound waves emitted from the first transducer 12 face the sound waves emitted by the
second transducer 14 in the direction 20. The sound waves emitted in the direction 18 and
reflected by the acoustic reflection surface 36 and directed to the listener 34 at the target
listening position are much louder than the sound waves radiated directly to the listener 34. This
reflected energy forms a "virtual sound source" in the direction of the acoustic reflection surface
36. The embodiment of FIG. 5 is advantageous when the loudspeaker unit 10 'is near the wall 80.
A similar arrangement can be used if the wall 80 is replaced by a cabinet such as a television
console. The embodiment of FIG. 5 can be implemented as a stereo system by combining the
principles disclosed in the discussion of FIGS. 3, 4 and 5.
[0017]
Referring now to FIG. 6A, an alternative embodiment of the loudspeaker system shown in FIG. 3
is shown. The left channel of the stereo audio signal source 24 is coupled by the left network
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100 L to the first transducer 72, the second transducer 74 and the third transducer 76. Similarly,
the right channel of the stereo audio signal source 24 is coupled to the fourth converter 78
through the right network 100R.
[0018]
In operation, stereo audio signal source 24 sends the left channel signal to first transducer 72
and to second and third transducers 74 and 76 through network 100L. Similar to the
embodiment of FIG. 2, the network 100 L modifies this signal so that the sound waves emitted by
the second and third transducers 74 and 76 face the sound waves arriving from the first
transducer 72. As a result, the left channel sound field has directivity with respect to the
direction 18L that the first transducer 72 faces. Similarly, the stereo audio signal source 24
sends right channel signals to the fourth transducer 78 and the second and third transducers 74
and 76 through the network 100R. Similar to the embodiment of FIG. 2, the network 100R
modifies this signal so that the sound waves emitted by the second and third transducers 74 and
76 face the sound waves arriving from the fourth transducer 78. . As a result, the right channel
sound field has directivity with respect to the direction 18R that the fourth transducer 78 faces.
In this embodiment, the second and third transducers 74, 76 act to oppose the sound waves
arriving from both the first transducer 72 and the fourth transducer 78. As in the example of FIG.
4, the left and right channels are felt to be emitted from a virtual source in the direction of the
acoustically reflective surfaces 36L and 36R, respectively.
[0019]
Referring now to FIG. 6B, an alternative configuration of the embodiment of FIG. 6A is shown
combining aspects of the embodiments of FIGS. 4, 5 and 6A. In this and the other embodiments,
the radial directions of the main transducers (in the figure, transducers 72 and 78) are oriented
(with respect to the axis of backing transducer 74) at acute angles φ1 and φ2 However, in other
embodiments, it may be in a space substantially perpendicular to this axis. Similar to the
embodiment of FIG. 4, this arrangement is also particularly suitable for mounting the
loudspeaker unit on a wall or in a cabinet such as a television console. In addition, the
embodiment of FIG. 6B can be easily adapted to emit two channels of a multi-channel system.
This will be described below in the discussion of FIGS. 7A-7B and 8A-8C.
[0020]
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Referring now to FIGS. 7A and 7B, another embodiment of the present invention is shown. For
purposes of clarity, the connections between elements are shown in two separate figures. The left
channel of multi-channel audio signal source 95 is coupled to first, second and third transducers
101, 102, 103 by left channel network 100L, as shown in FIG. 7A. The right channel of multichannel audio signal source 95 is coupled to first, second and third transducers 104, 105, 106,
as shown in FIG. 7A. As shown in FIG. 7B, the central channel of multi-channel audio signal
source 95 is coupled to second, third, fifth and sixth channel converters 102, 103, 105 and 106
through central channel network 100C, respectively. And coupled to seventh and eighth
transducers 107 and 108, respectively.
[0021]
The first, second, third and seventh transducers 101, 102, 103 and 107 are in the first
loudspeaker unit 10L and the fourth, fifth, sixth and eighth transducers 104, 105, 106 , And 108
are in the second loudspeaker unit 10R.
[0022]
In the same manner as described above in connection with FIG. 2, the radiation by the second
and third transducers 102, 103 is for the sound waves emitted in response to the left channel
signal (hereinafter referred to as left channel sound waves ) Left channel acoustic wave
substantially faces the left channel acoustic wave emitted from the first transducer 101 in the
directions 20 and 22 facing the second and third transducers 102 and 103, respectively. Is
radiated with directivity substantially in the direction in which the first transducer 101 faces.
The center channel sound waves emitted by the first and seventh transducers 101, 107 with
respect to sound waves emitted in response to the center channel signal (hereinafter "center
channel sound waves") are second converted in the directions 18L and 18LC. It opposes the
central channel sound wave emitted from the vessel 102. Similarly, center channel sound waves
emitted by the fourth and eighth transducers 104, 108 are emitted from the fifth transducer 105
in the directions 18RC, 18R facing the fourth and eighth transducers 104, 108. Face the sound
wave. Thus, the center channel sound wave is emitted with directivity substantially in the
direction 20 that the second transducer 102 and the fifth transducer 105 face. With respect to
sound waves emitted in response to the right channel signal (hereinafter, right channel sound
waves ), the right channel sound waves emitted by the fifth and sixth transducers 105 and 106
reach the right from the fourth transducer 104 Because it is opposed to the channel sound
waves, the right channel sound waves are emitted with directivity substantially in the direction
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18R that the fourth transducer 108 faces. As a result, the left channel sound wave appears to be
emitted at a virtual sound source in the direction of the left acoustic reflection surface 36L, the
right channel sound wave appears to be emitted at a virtual sound source in the direction of the
right reflection surface 36R, and the center channel sound wave is It will be felt to emit at a
virtual sound source that is between the loudspeaker units 10L and 10R. The embodiments of
FIGS. 7A and 7B can also be modified such that the central channel radiates directionally in the
directions 18LC and 18RC. The embodiments of FIGS. 7A and 7B may be useful as components of
a multi-channel system where one of the channels is a center channel or mono.
[0023]
Referring to FIGS. 8A-8C, an alternative embodiment of the multi-channel system of FIGS. 7A-7B
is shown. For the sake of clarity, the connections between the elements of the left, right and
center channels are shown in three separate figures. As shown in FIG. 8A, the left channel of
multi-channel signal source 95 is coupled by a left channel network 100L to a first transducer
72, a second transducer 74 and a third transducer 76. As shown in FIG. 8B, the central channel
of multi-channel signal source 95 is coupled by a central channel network 100C to a first
transducer 72, a second transducer 74 and a fourth transducer 78. The right channel of multichannel signal source 95 is coupled by a right channel network 100R to a second converter 74, a
third converter 76, and a fourth converter 78.
[0024]
The first, second and third transducers 72, 74, 76 operate in the same manner as the transducers
101, 102, 103 of FIGS. 7A and 7B, substantially in the direction 18L in which the first transducer
72 faces. Directly radiate left channel sound waves. The first, second and fourth transducers 72,
74, 78 operate in the same manner as the transducers 101, 102, 107 of FIGS. 7A and 7B or the
transducers 108, 105, 104 of FIGS. 7A and 7B. A central channel sound wave is emitted, with
directivity substantially in the direction 20 that the second transducer 74 faces. The second, third
and fourth transducers 74, 78, 76 operate in the same manner as the transducers 105, 104, 106
of FIGS. 7A and 7B, substantially in the direction 18R facing the fourth transducer 78. Directly
radiate left channel sound waves. In the embodiments of FIGS. 8A, 8B and 8C, the first, second
and fourth transducers 72, 74, 78 are used as main transducers and as backing transducers.
[0025]
Although the embodiments of FIGS. 2-8C primarily show the main transducer and the backing
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transducer oriented substantially orthogonally in space, the invention can be practiced with other
relative orientations.
[0026]
Referring now to FIG. 9, a block diagram showing the network 100 of the loudspeaker unit 10 of
FIGS. 1 and 2 in more detail is shown.
Network 100 includes an input 25 coupled to a first transducer 12. Also, the input 25 is coupled
to the second converter 14 through the phase shifter 27a, the attenuator 29a and the low pass
filter 32a, and the phase shifter 27b, the attenuator 29b and the low pass filter It is also coupled
to the third converter 16 via 32b.
[0027]
In operation, an audio signal from audio signal source 24 enters audio signal input 25 and then
proceeds to first transducer 12. The audio signal from the audio signal input 24 powers the
second transducer 14 after attenuation and phase shift. The amounts of attenuation and phase
shift are similar in amplitude to the sound waves that the second transducer 14 arrives from the
first transducer 12 when the sound waves emitted by the first transducer 12 reach the second
transducer 14. Then, we decide to emit sound waves that are out of phase. Similarly, the audio
signal on the audio signal input 24 powers the third converter 16 after attenuation and phase
shift. The amounts of attenuation and phase shift are similar in amplitude to the sound waves
that the third transducer 16 arrives from the first transducer 12 when the sound waves emitted
by the first transducer 12 reach the third transducer 16. In order to emit sound waves out of
phase. As already mentioned in the discussion of FIG. 2, if the out-of-phase sound waves emitted
by the second transducer 14 and the third transducer 16 are similar in amplitude to the sound
waves arriving from the first transducer 12, the direction At each of 20 and 22, substantially
cancellation occurs, and a significant reduction of about 10 dB or more occurs in the transmitted
sound, thereby achieving the effects described above in the discussion of FIG.
[0028]
The phase shift amount Δφ1 given by the phase shifter 27a is typically -180 ° -k1f, where f is
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the frequency and k1 separates the first converter 12 and the second converter 14 (see FIG. 2) is
a constant determined by the length of the acoustic path l1. The phase shift amount Δφ 2 given
by the phase shifter 27 b is typically −180 ° −k 2 f, where f is the frequency and k 2 separates
the first converter 12 and the third converter 16 (see FIG. 2) is a constant determined by the
length of the acoustic path l2. The amount of attenuation for the second and third transducers 14
and 16 is sufficient for the sound waves arriving from them to reach their vicinity to be of similar
amplitude.
[0029]
The constant k is determined by the length of the acoustic path between the main transducer and
the backing transducer, or in other words it is determined by the time it takes for the sound wave
emitted from the main transducer to reach near the backing transducer, In general, it is
expressed by the following equation.
[0030]
Where l is the length of the acoustic path between the backing transducer and the main
transducer, and c is the speed of sound for the phase shift measured in degrees.
As an example, in the embodiment of FIG. 2, if the length of the acoustic path l1 (FIG. 2) between
the main transducer 12 and the backing transducer 14 is 5 inches (about 0.4167 feet), the speed
of sound is 1130 Assuming feet per second, it is determined as follows.
[0031]
The phase shifter 27a shifts the phase by -180-0.133f, as k = (360 x 0.4167) / 1130, that is,
0.133. Therefore, when the frequency is 500 Hz, the phase shift amount is −180− (0.133 ×
500) = − 246.5 °.
[0032]
Referring now to FIG. 10, an alternative embodiment of the loudspeaker system of FIG. 9 is
shown. Network 100 includes an input 25 coupled to a first transducer 12. Also, the input 25 is
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coupled to the second converter 14 through the phase shifter 27a ', the attenuator 29a, and the
low pass filter 32a, and the phase shifter 27b', the attenuator 29b and the low It is coupled to the
third converter 16 via the pass filter 32b. + In the first converter 12 and − in the
second converter 14 and the third converter 16 are such that the converters 14 and 16 are
driven in the opposite phase to the first converter 12 Indicates This drive configuration
effectively achieves a -180 ° phase shift, thus achieving a dephasing relationship between the
sound waves arriving from the first transducer 12 and the second transducer 14 near the second
transducer 14 The phase shift amount .DELTA..phi.1 given by the phase shifter 27a 'is -k1f. Here,
k1 is a constant determined by the length of the acoustic path separating the first transducer 12
and the second transducer 14. Similarly, in the vicinity of the third converter 16, the phase shift
amount Δφ 2 provided by the phase shifter 27 b ′ to achieve an out-of-phase relationship
between the sound waves arriving from the first converter 12 and the third converter 16 is , K 2
f, where k 2 is a constant determined by the length of the acoustic path separating the first
transducer 12 and the third transducer 16. The determination of the constants k, k1, and k2 in
this and the following embodiments are as described above in the discussion of FIG. In an
example in which the distance l between the first (main) converter 12 and the second (backing)
converter 14 is 0.4167 feet, the value of k1 is 0.133 and the phase shifter 27a 'is Taking an
example of an amount .DELTA..phi.1 equal to .133 f, i.e. a frequency of 500 Hz, the phase is
shifted by -66.5 DEG. The required -244.5 ° (as taught in the discussion of Fig. 9) is the -180 °
phase shift obtained by the reverse polarity connection, and the -66.5 ° obtained by phase
shifters 27a 'and 27b'. Achieved by
[0033]
Referring now to FIG. 11, another alternative embodiment of the loudspeaker system of FIG. 9 is
shown. In the loudspeaker system of FIG. 11, the + in the first transducer 12 and the −
in the second and third transducers 14 and 16 show the same relationship as described above in
the discussion of FIG. . The network 100 of FIG. 11 is coupled to the first transducer 12 and
coupled to the second and third transducers 14 and 16 via the common phase shifter 27,
attenuator 29 and low pass filter 32. Contains the input 25 being In the present embodiment, the
length of the acoustic path between the first transducer 12 and the second transducer 14 and the
length of the acoustic path between the first transducer 12 and the third transducer 16 are
substantially equal. The phase shift amount Δφ generated by the phase shifter 27 is −kf, where
k is a constant determined similarly to the constants k1 and k2 of FIG. The embodiment of FIG.
11 can be implemented with appropriate connections to the phase shifter of FIG. 9 and the
second and third converters 14, 16.
[0034]
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Referring to FIG. 12, another alternative embodiment of the loudspeaker system of FIG. 9 is
shown. An audio signal input 25 is coupled to the first transducer 12. Also, the input 25 is
coupled to the second converter 14 via the delay network 28a, the attenuator 29a, and the low
pass filter 32a, and the delay network 28b, the attenuator 29b and the low pass filter 32b. Are
also coupled to the third converter 16. In the loudspeaker system of FIG. 12, the + in the first
transducer 12 and the − in the second and third transducers 14 and 16 exhibit the same
relationship as described above in the discussion of FIG. . The amount of time delay .DELTA.t
generated by the delay network 28a is the amount of time it takes for the sound wave emitted by
the first transducer 12 to reach the second transducer 14, i.e. l1 / c. Here, l1 is the length of the
acoustic path between the first transducer 12 and the second transducer 14, and c is the speed
of sound. Thus, for example, if the distance 11 is 0.4167 feet and the speed of sound is 1130 feet
per second, then the delay Δt = 0.4167 / 1130 or 369 microseconds. The embodiment of FIG.
12 can be implemented with a common attenuator, delay, and low pass filter as in FIG.
[0035]
Referring to FIG. 13, graphs of signal waveforms at different frequencies are shown to help
explain the relationship between the phase shifters of FIGS. 9-12 and the delay network of FIG. At
frequency f 0 (waveform 30), the time delay of interval Δt is equivalent to a 90 ° phase shift
Δφ (waveform 40). At frequency 1.5f0 (waveform 42), the time delay of interval Δt is
equivalent to a phase shift of 135 ° (waveform 44). That is, 1.5 times the phase shift indicated
by the waveform 40. At frequency 2f0 (waveform 46), the time delay of interval Δt is equivalent
to a 180 ° phase shift Δφ (waveform 48). That is, twice the phase shift indicated by the
waveform 40. Similarly, at other frequencies, it can be shown that the time delay of interval Δt is
equivalent to a phase shift Δφ proportional to the frequency.
[0036]
Referring to FIGS. 14-17, examples of polar patterns of the sound field generated by a full range
transducer at frequencies of 250 Hz, 500 Hz, 1000 Hz and 2000 Hz, respectively, are shown as
an example. . The patterns of FIGS. 14-16 serve to illustrate the low pass filter 32b of FIGS. 9, 10
and 12 and the low pass filter 32 of FIG. FIG. 14 is an approximation of the sound field polar
pattern in an octave with a frequency of about 177 Hz to 354 Hz (hereinafter referred to as a
250 Hz octave). The first converter is virtually virtually omnidirectional in this frequency range.
That is, the sound radiated in either direction from this transducer is equal in amplitude to the
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sound radiated along the transducer axis in direction 18. FIG. 15 shows a polar coordinate
pattern in an octave of frequency about 354 Hz to 707 Hz (hereinafter referred to as a 500 Hz
octave). This sound field polar coordinate pattern is totally omnidirectional, but more directional
than in the frequency range shown in FIG. In the direction indicated by arrows 20 and 22 and in
the direction opposite to the direction of arrow 18, the sound field is about 1 db weaker. FIG. 16
shows a sound field polar coordinate pattern in an octave of frequency about 707 Hz to 1414 Hz
(hereinafter referred to as 1 KHz octave). In this frequency range, the first transducer 12 is
somewhat directional. In the direction indicated by arrows 20 and 22 and in the direction
opposite to the direction of arrow 18, the sound field is about 5 dB weaker. FIG. 17 shows the
sound field at an octave of frequency about 1.4 Khz to 2.8 Khz (hereinafter referred to as 2 Khz
octave). In this frequency range, the first transducer 12 is more directional. In the direction
indicated by arrows 20 and 22 and in the direction opposite to the direction of arrow 18, the
sound field is more than 5 dB weaker.
[0037]
Referring again to FIG. 2, above the predetermined frequency (about 1 Khz in the above
example), the transducers 12, 14 and 16 point substantially along the axis of the transducer (in
this case, direction 18) Have sex. As a result, acoustic energy from transducers whose axes are
generally orthogonal does not interact as well at high frequencies as at low frequencies. As a
result, the sound wave having the predetermined frequency or higher is directly emitted to the
listener 34 by the second transducer 14 or emitted by the third transducer 16 and reflected by
the rear reflecting surface 37 to reach the listener 34 , And may be stronger (and faster to reach)
against sound radiated in direction 18 and reflected back to the listener. Thus, the listener 34
can determine (localize) the sound on the second transducer 14.
[0038]
The features of the present invention are typically the frequency range in which the main
transducer emits acoustic waves substantially omnidirectionally, and the backing transducer
operates in a narrower frequency range of the frequency range from the main transducer It is to
let The low pass filters 32a and 32b (FIGS. 9, 10 and 12) or the low pass filter 32 (FIG. 11)
significantly attenuate the spectral components of the audio signal above a predetermined cutoff
frequency. , And embody one method to achieve this feature.
[0039]
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14
The frequency range in which the transducer emits sound essentially omnidirectionally is
typically related to the dimensions of the emitting surface of the transducer. At frequencies
where the wavelength of the sound waves approaches the dimensions of the emitting surface of
the transducer, the directivity of the sound emitted by the transducer begins to increase. For
example, for the 2-1 / 4 inch diameter transducer used in the above-described exemplary
embodiment, the transducer is essential at a frequency of 1 Khz (wavelength is about 13 inches,
about twice around the transducer). It radiates sound in a directional manner. Thus, using a low
pass filter with a cutoff frequency of about 1 Khz, the backing transducer will operate in the
frequency range up to about 1 Khz while the main transducer will operate to a much higher
frequency than this .
[0040]
By changing the parameters of the delay network 28, the phase shifter 27, the attenuator 29 or
the equalizer 26, or by changing the frequency response of the low pass filter 32 or different
converters By using it, it is possible to generate a variety of different sound fields.
[0041]
Referring to FIG. 18, a circuit implementing phase shifter 27, attenuator 29, and low pass filter
32 of network 100 of FIG. 11 is shown.
The first terminal 50 of the audio signal input 24 is connected to the positive terminal 52 of the
first transducer 54. The negative terminal 56 of the first converter 54 is coupled to the first
terminals of bipolar capacitors 66 and 76 and also to the negative terminals 68, 70 of the second
and third converters 60, 64. Each is coupled. The second terminal 74 of the audio signal input 24
is coupled to the second terminal of the bipolar capacitor 76 and also to the first terminal of the
inductor 78. The positive terminals of the converters 60, 64 are coupled to the second terminal
of the bipolar capacitor 66 and to the second terminal of the inductor 78. The first converter 54
corresponds to the first converter 12 of FIG. The second and third converters 60, 64 correspond
to the second and third converters 14, 16 of FIG.
[0042]
10-05-2019
15
In one embodiment of the present invention, transducers 54, 60, 64 are 2-1 / 4 inch full range
electro-acoustic transducers, the radiation planes of which are separated by a distance of about 5
inches. In a network where the first capacitor 66 is 47 μF, the second capacitor 76 is 94 μF,
and the inductor 78 is 0.5 mh, the relative amplitude and phase responses of the transducers 60,
64 to the transducer 54 are shown in FIGS. It will be shown. This will be described below.
[0043]
Referring to FIG. 19, the audio signals (equivalent to the graph of the cancel converters 14 and
16 in FIG. 11) input to the second and third converters 60 and 64 and the first converter 54 are
input. The phase difference between the audio signal is shown as a function of frequency. Curve
67 represents the theoretically ideal relationship between phase difference and frequency for an
acoustic path of about 5 inches (0.4167 feet), according to the equation Δφ = −180 ° -kf.
Here, k = 0.133, and f is a frequency. The curve 67 has a constant slope, since the phase
difference is proportional to the frequency. Curve 69 represents the actual phase difference
obtained by the circuit of FIG.
[0044]
Referring to FIG. 20, with respect to the circuit of FIG. 18, an audio signal input to the second and
third transducers 60 and 64 (equivalent to the canceling transducers 14 and 16 of FIG. 11); A
graph of a time difference curve 73 between the audio signal input to (which is equivalent to the
main converter 12 of FIG. 11) is shown as a function of frequency. Curve 71 represents the
length of time it takes for the sound to travel 5 inches (0.4167 feet), assuming that the speed of
sound is 1130 feet per second.
[0045]
Referring to FIG. 21, the first converter 54 (the main converter 12 of FIG. 11) of the voltage
between the terminals of the second and third converters 60 and 64 (equivalent to the cancel
converters 14 and 16 of FIG. 11). The ratio of terminal voltage to terminal voltage is shown as a
function of frequency. The circuit of FIG. 18 acts as a low pass filter with a corner frequency of
about 1 Khz. This low pass filter significantly reduces the sound directly radiated by the second
and third transducers, in the frequency domain which is directional along their axes, so that the
listener 34 The acoustic waves emitted by the reflector 12 and reflected by the acoustic
10-05-2019
16
reflection surface 36 are localized.
[0046]
Referring to FIGS. 22-27, sound field polar coordinate pattern measurements (converters 12, 14,
16) averaged over one octave frequency range, obtained from the system of the embodiment of
FIG. 4 as implemented in FIG. In the plane of the axis of In each of FIGS. 22-27, the directions
indicated by arrows 18L, 18R, 20 and 22 correspond to the similarly numbered directions in FIG.
Curves 130 and 131 represent the intensity of the sound emitted from the loudspeaker units 10L
and 10R of FIG. 4 in dB, respectively. Each concentric circle in the graph represents a difference
of -5 dB. For each octave band, the difference between the amplitude of the sound in directions
18L and 18R and the amplitude of the sounds in directions 20 and 22, respectively, is -10 dB or
more.
[0047]
Referring to FIG. 28, there is shown a graph of the measured amplitude of sound emitted in
directions 18L and 20 by the loudspeaker unit 10L of FIG. 4 as a function of frequency in dB.
Curve 210 represents the amplitude of the sound field emitted in direction 18 L, and curve 212
represents the amplitude of the sound field emitted in direction 20.
[0048]
Referring to FIG. 29, there is shown a graph of the measured amplitude of sound emitted in
directions 18R and 20 by the loudspeaker unit 10R of FIG. 4 as a function of frequency in dB.
Curve 214 represents the amplitude of the sound field emitted in direction 18R, and curve 216
represents the amplitude of the sound field emitted in direction 20. In both FIGS. 22 and 23, at
substantially all frequencies, the amplitude of the sound field is at least 10 dB greater in each of
the directions 18L and 18R than in the direction 20.
[0049]
Referring to FIGS. 30A and 30B, front and rear perspective views of another embodiment of the
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17
present invention are shown. The first transducer 217 is enclosed in an enclosure and radiates
acoustic waves omnidirectionally in the low and intermediate frequency ranges. The second
transducer 218 faces in the same direction as the first transducer 217 and is, for example,
disposed above the first transducer 217 in close proximity to the first transducer 217. The
second transducer 218 is an open-backed dipole and emits sound waves in a direction 18 and a
direction 23 opposite to the direction 18. The first and second transducers 217 and 218 are both
coupled to an audio signal source, not shown in this figure.
[0050]
Referring to FIG. 31, a top view of the polar coordinate pattern of the sound field emitted by the
arrangement of FIG. 30 is shown. The first transducer 217 emits sound substantially
omnidirectionally, as shown by the sound field polar pattern 220. A second transducer 218
(shown as a dotted line in this figure) emits sound waves with directivity characterized by a
figure eight polar pattern 222 of the sound field. The sound fields 220 and 222 add together in
the direction 18 and are opposite in the direction 23 and have no contribution from the sound
field 222 in the directions 20 and 22. As a result, combined sound field 224 is approximately 6
dB greater than sound field 220 in direction 18 and identical to sound field 220 in direction 18
in directions 20 and 22 and nothing in direction 23. This corresponds to a heart-shaped pattern.
[0051]
Refer again to FIG. If the configurations of FIGS. 30 and 31 are incorporated into the embodiment
of FIG. 2, for the listener 34 of FIG. 2 to determine the localization of the sound radiated in the
direction 18 and reflected by the reflecting surface 36, the direction 20 and Attenuation at 22
would be sufficient at 6 dB in many situations.
[0052]
Referring to FIGS. 32A and 32B, perspective and partial front views, respectively, of another
embodiment of the present invention comprising a loudspeaker unit 55 of triangular cross
section are shown. Unit 55 supports front transducer 55 and left transducer 51 and right
transducer 52, respectively. When the bottom surface 56 of the loudspeaker unit 55 is arranged
adjacent to the wall or table-like interface 57, the interaction with the surface 57 of the
loudspeaker unit 55 is that of the virtual source of the loudspeaker unit 55 '. It can be modeled
10-05-2019
18
by mirror image. As would be known to one skilled in the art, mirror image transducers 50 ', 51'
and 52 'simulate the initial reflection behavior of transducers 50, 51 and 52 at surface 57,
respectively. Thus, the sound waves emitted by transducers 50, 51 and 52 and reflected at
surface 57 are felt to originate from virtual transducers 50 ', 51' and 52 'respectively. Similarly,
the reflected sound from virtual transducer 50 'opposes the sound waves emitted by virtual
transducers 51' and 52 ', respectively, in directions 22 "and 20". Thus, the combined acoustic
radiation from the first transducer 50 and the virtual transducer 50 'is preferentially emitted in
the direction 18 and is substantially canceled in all directions orthogonal to their axes. Thus, this
loudspeaker unit behaves the same whether it is placed in the horizontal plane or in the vertical
plane. This embodiment is useful in applications where diversity of placement is desirable, such
as one-way sound emission, or surround sound loudspeakers for home theaters.
[0053]
Other embodiments are within the scope of the following claims.
[0054]
Brief description of the drawings
[0055]
1 is an isometric view of a loudspeaker system according to the invention.
[0056]
2 is a schematic diagram of the loudspeaker system of FIG. 1 in a room audio reproduction
system.
[0057]
FIG. 3 is a schematic view of a second embodiment of a loudspeaker system according to the
invention.
[0058]
4 is a schematic view of a third embodiment of an indoor loudspeaker system according to the
invention.
[0059]
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19
5 is a schematic view of a fourth embodiment of an indoor loudspeaker system according to the
invention.
[0060]
6 is a schematic view of a fifth embodiment of a loudspeaker according to the invention.
[0061]
FIG. 7 shows generally a sixth embodiment of a loudspeaker system according to the invention.
[0062]
FIG. 8 shows generally a seventh embodiment of a loudspeaker system according to the
invention.
[0063]
9 is a more detailed diagram of the network of the loudspeaker system of FIG. 2;
[0064]
10 is a diagram showing the network of the loudspeaker system of FIG. 2 in more detail.
[0065]
11 is a diagram showing the network of the loudspeaker system of FIG. 2 in more detail.
[0066]
12 is a diagram showing the network of the loudspeaker system of FIG. 2 in more detail.
[0067]
13 is a graph showing the relative phase versus time delay of the network as in FIGS. 9-12. FIG.
[0068]
14 is a polar coordinate diagram of the sound field of a transducer as used in an embodiment of
the present invention.
10-05-2019
20
[0069]
FIG. 15 is a polar coordinate diagram of the sound field of a transducer as used in an
embodiment of the present invention.
[0070]
FIG. 16 is a polar coordinate diagram of the sound field of a transducer as used in an
embodiment of the present invention.
[0071]
FIG. 17 is a polar coordinate diagram of the sound field of a transducer as used in an
embodiment of the present invention.
[0072]
18 is a block diagram of a circuit for implementing the network portion of the embodiment of the
present invention.
[0073]
19 is a graph showing the phase difference as a function of frequency for the circuit of FIG.
[0074]
20 is a graph of delay as a function of frequency for the circuit of FIG.
[0075]
21 is a graph of amplitude as a function of frequency for the circuit of FIG.
[0076]
22 is a polar coordinate diagram of the sound field of the embodiment of the present invention.
[0077]
23 is a polar coordinate diagram of the sound field of the embodiment of the present invention.
10-05-2019
21
[0078]
FIG. 24 is a polar coordinate diagram of a sound field according to an embodiment of the present
invention.
[0079]
25 is a polar coordinate diagram of the sound field of the embodiment of the present invention.
[0080]
26 is a polar coordinate diagram of the sound field of the embodiment of the present invention.
[0081]
27 is a polar coordinate diagram of the sound field of the embodiment of the present invention.
[0082]
FIG. 28 is a graph of the intensity of sound emitted in two different directions by the loudspeaker
system according to the invention as a function of frequency.
[0083]
Figure 29 is a graph of the intensity of sound emitted in two different directions by the
loudspeaker system according to the invention as a function of frequency.
[0084]
FIG. 30 is an isometric view of another loudspeaker system according to the invention.
[0085]
FIG. 31 is a graph by polar coordinates of the sound field of the loudspeaker according to FIG.
[0086]
FIG. 32 is a perspective view of another embodiment of the present invention.
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22
FIG. 32B is a partial front view of another embodiment of the present invention.
[0087]
Explanation of sign
[0088]
8 Housing 10 Loudspeaker Unit 10L Left Loudspeaker Unit 10R Right Loudspeaker Unit 10
'Loudspeaker Unit 12, 14, 16 Loudspeaker Driver 12L, 14L, 16L, 12R, 14R, 16R Electroacoustic
Transducer 12 '1st electroacoustic transducer 14' 2nd electroacoustic transducer 24 audio signal
source 24 'audio signal source 25 input 27a, 27b phase shifter 27a', 27b 'phase shifter 29a, 29b
attenuator 32a, 32b low Path filter 34 Listener 36 Acoustic reflection surface 36L, 36R Acoustic
reflection surface 100 Network 100L Left channel network 100C Central channel network 100R
Right channel network
10-05-2019
23

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