Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Mounting or support feature of housed loudspeaker
Reexamination Certificate
1999-02-22
2003-04-29
Barnie, Rexford (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Mounting or support feature of housed loudspeaker
Reexamination Certificate
active
06556687
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a loudspeaker using an ultrasonic wave and more particularly, to a super-directional loudspeaker having electro-acoustic transducer elements arranged on a curved surface to converge on a point, which makes it possible for a listener to listen anytime a sound emitted from the loudspeaker at a high sound pressure.
2. Description of the Prior Art
Conventionally, it has been known that a loudspeaker system with high directivity can be realized by using an ultrasonic wave.
For example, the Japanese Non-Examined Patent Publication No. 3-159400 published in July 1991 discloses a super-directional loudspeaker system comprising a super-directional loudspeaker using a parametric array, an ultrasonic wave receiver for receiving an ultrasonic wave beam which is emitted from the loudspeaker and reflected by a listener, and a controller for selecting sound sources on the basis of the reflected ultrasonic wave beam received by the receiver and for applying the selected sound source to the loudspeaker.
A first input signal, which is produced in a first one of the sound sources selected by the controller, is modulated and amplified to produce a first output signal. The first output signal is then applied to the super-directional loudspeaker, thereby emitting an ultrasonic wave beam. At this time, a first audible sound (e.g., a background music) according to the first input signal is emitted from the loudspeaker along with the ultrasonic wave beam thus emitted.
If a listener exists at a position in front of the loudspeaker, the listener can listen to the emitted first sound and at the same time, a part of the emitted ultrasonic wave beam is reflected by the listener and received by the ultrasonic wave receiver. If the level of the received ultrasonic wave beam is greater than a specific threshold value, a second one of the sound sources is selected by the controller instead of the first sound source. Then, a second input signal produced in the second sound source is modulated and amplified to produce a second output signal. The second output signal is applied to the super-directional loudspeaker, thereby emitting an ultrasonic wave beam containing a second audible sound (e.g., a shopping information) according to the second input signal. In this case, the listener listens to the emitted second sound.
If the level of the reflected ultrasonic wave beam is equal to or less than the specific threshold value or no reflected ultrasonic wave beam exists, the first sound is kept being emitted and the listener keeps listening to the first sound.
As described above, in the conventional super-directional loudspeaker system disclosed in the Japanese Non-Examined Patent Publication No. 3-159400, an ultrasonic wave beam is used as a carrier for an audio input signal of an audio frequency. Specifically, a high-frequency signal of an ultrasonic frequency is modulated by an input signal of an audio frequency. The modulated high-frequency signal is applied to electro-acoustic transducer elements of the loudspeaker, thereby emitting high-directional ultrasonic waves containing an audible sound according to the input signal. The ultrasonic waves thus emitted propagate in the air as a super-directional ultrasonic wave beam. The electro-acoustic transducer elements of the loudspeaker are arranged on a flat surface and as a result, the emitted ultrasonic waves propagate in parallel in the air.
Moreover, the Japanese Non-Examined Patent Publication No. 3-296399 published in December 1991 discloses a parametric loudspeaker system comprising a loudspeaker unit having ultrasonic oscillators arranged on a plate- or rod-shaped base, and a rotating means for rotating the loudspeaker unit around a specific rotation axis while the ultrasonic oscillators are located to face the rotation axis. The loudspeaker unit is rotatable so as to keep an angle with respect to the rotation axis acute, where the angle can be adjusted by the rotating means as necessary.
A high-frequency signal of an ultrasonic frequency is modulated by an input signal of an audio frequency and amplified. The modulated and amplified signal is then applied to the ultrasonic oscillators of the loudspeaker unit, thereby emitting high-directional ultrasonic waves containing an audible sound according to the input signal. Since the ultrasonic oscillators of the loudspeaker unit are arranged on the plate- or rod-shaped base, the emitted ultrasonic waves propagate in parallel in the air as a beam.
Further, the loudspeaker unit is rotated around the rotation axis to form a circular cone. Therefore, the ultrasonic waves emitted from the ultrasonic oscillators are converged on a point where a listener is located in front of the loudspeaker unit. If the acute angle between the loudspeaker unit and the rotation axis is changed in value by the rotating means, the focusing point of the ultrasonic waves can be changed so as to follow the change of the point of the listener.
As described above, in the conventional parametric loudspeaker system disclosed in the Japanese Non-Examined Patent Publication No. 3-296399, similar to that disclosed in the Japanese-Non Examined Patent Publication No. 3-159400, an ultrasonic wave beam is used as a carrier for an audio input signal of an audio frequency. Specifically, a high-frequency signal of an ultrasonic frequency is modulated by an input signal of an audio frequency. The modulated high-frequency signal is applied to electro-acoustic transducer elements arranged on a flat surface, thereby emitting ultrasonic waves containing an audible sound according to the input signal. However, unlike the case of the Japanese-Non Examined Patent Publication No. 3-159400, the ultrasonic waves emitted from the loudspeaker unit propagate to be focused on an optional point.
FIG. 1
is a block diagram showing the common basic configuration of the above-described two conventional loudspeaker systems.
As shown in
FIG. 1
, an audio signal source
110
generates an electric audible signal S
101
of a variable audio frequency. A high-frequency oscillator
150
generates an electric high-frequency signal S
102
of a fixed ultrasonic frequency. An amplitude modulator
120
amplitude-modulates the high-frequency signal S
102
by the audio signal S
101
, thereby producing a modulated ultrasonic signal S
103
. A power amplifier
130
amplifies the modulated ultrasonic signal S
103
to produce an amplified ultrasonic signal S
104
.
An electro-acoustic transducer unit (i.e., a loudspeaker unit) comprise a plurality of electro-acoustic transducer elements
145
arranged on a flat surface of a suitable supporting member (not shown). The transducer elements
145
convert the amplified ultrasonic signal S
104
to acoustic vibrations of the same ultrasonic frequency as that of the high-frequency signal S
102
. The acoustic vibrations of the same ultrasonic frequency, which are produced by the transducer elements
145
, generate high-directional ultrasonic waves USW and emit them into the air. The ultrasonic waves USW thus emitted propagate in the air as an ultrasonic wave beam with a super directivity.
While the ultrasonic waves USW propagate in the air, a nonlinear interaction occurs between the ultrasonic waves USW and the air, resulting in demodulation operation of the ultrasonic waves USW. As a consequence, an audible sound according to the audio signal S
101
of the audio frequency is generated in the air and transferred by the beam of the ultrasonic waves USW. In other words, a super-directional audible sound wave is generated in the air. This phenomenon has been termed the “parametric array effect”.
If a listener is located at any one of locations in the propagation direction of the beam of the ultrasonic waves USW, the listener can listen to the audible sound. However, if the listener is located out of the propagation direction, the listener is unable to listen to the audible sound because of its super directivity.
With the conventional loudspeaker system having the conven
Barnie Rexford
Dabney Phylesha
NEC Corporation
Whitman, Curtis & Christofferson P.C.
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