JP2000209691A - Parametric speaker - Google Patents

Abstract

(57) [Abstract] [Purpose] In a parametric speaker that demodulates a modulated signal in a medium such as air using the parametric effect, the noise mixed with the demodulated reproduced sound is reduced, and the natural sound quality is easy to hear. Provide speakers. [Constitution] A filter that cuts a low frequency range of a modulated signal, a filter that passes through a predetermined frequency range of an audible sound frequency band, and a switch that appropriately selects these filters are provided. By pre-cutting the inaudible frequency components, modulating the ultrasonic waves and radiating them into the air, eliminating the difference sound of each frequency component that causes noise,
At the same time, the low frequency range of the cut frequency components is reproduced by the audible range speaker, thereby compensating for the low frequency range lacking in the reproduced sound due to the parametric array effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave propagation path obtained by radiating an ultrasonic wave amplitude-modulated by an audible sound signal or the like to a medium (for example, in the air) by a parametric array effect. The present invention relates to a parametric speaker utilizing a phenomenon that a modulated signal is demodulated as an audible sound along the line.

[0002]

2. Description of the Related Art In the field of information transmission by voice, controlling the transmission range and direction of voice is one of important issues. For example, in an event venue where many people gather, it is necessary to convey audio information to many people at once,
In the guidance of an exhibit such as an art museum or a museum, it is sufficient if audio information can be transmitted to persons existing in a limited area, and transmitting audio to persons in an unnecessary area leads to noise. In the case of a cash dispenser such as a bank, the range is further limited, and it is desirable to transmit information to one user. Therefore, a parametric speaker has been conventionally proposed as a device for generating an audible sound in a specific range of space. This parametric speaker emits ultrasonic waves, amplitude-modulated by an audible range signal, from a transducer such as an ultrasonic transducer into the air, resulting in the non-linear propagation characteristics of sound waves in air (parametric array effect), The modulated signal is self-demodulated along the path.

[0003]

In the above parametric loudspeaker, when a modulated signal having a spectrum as shown in FIG. 5A is amplitude-modulated by using, for example, an ultrasonic wave of 40 kHz as a carrier wave, FIG. Ultrasonic waves having the spectrum shown in b) are emitted into the air. At this time, if the amplitude of the ultrasonic wave is large enough to be regarded as a finite amplitude level, the carrier component and the upper and lower sideband components cause a nonlinear interaction in the air, and the difference sound is generated along the ultrasonic propagation path. Occur. That is, an audible sound of 10 kHz is generated by the 50 kHz component of the upper sideband and the 40 kHz component of the carrier, and a 10 Hz sound wave is similarly generated by the 40.01 kHz component and the carrier component. The modulated signal is demodulated. As described above, if only the difference sound between the carrier component and the sideband component is reproduced, the modulated signal is reproduced, and the audible sound with high sound quality can be heard. However, in practice, a difference sound occurs between all the frequency components included in the upper sideband and the lower sideband, and also a difference sound occurs in the same sideband, and these difference sounds are different from the modulated signal. It was a different noise. That is, there is a problem that noise is mixed in as the sideband (frequency band of the modulated signal) is wider.

In general, when the frequency characteristics of a music signal are examined, the lower the tone range, the higher the volume level. Therefore, when a music signal is used as a modulated signal, an ultrasonic wave rich in a low tone range is radiated. become. However, in the parametric array effect, since the conversion efficiency from ultrasonic waves to audible sound decreases as the sound range becomes lower, the actual audible sound lacks the low frequency range and a high pitch sound can be heard. However, in practice, low-frequency and high-frequency components, which are hard to hear to the human ear, are also modulated into ultrasonic waves and radiated into the air, so frequency components generated between both sidebands and in the same sideband The difference sound between them becomes noise having a high sound pressure level in proportion to the output level of each frequency component, resulting in deterioration of the sound quality of the reproduced sound. In addition to the fact that the bass sound has a particularly high volume level, the Q (Quality Factor) of the ultrasonic vibrator is also large.
r) peaks at the carrier frequency and decreases rapidly as the frequency departs from the carrier frequency. Therefore, when amplitude modulation is performed, the lower the tone range of the modulated signal, the more efficiently the signal is radiated, which is a major factor in generating noise. Under these circumstances, there has been a problem that an audible sound that is inaudible and mixed with noise is generated on a high pitch.

[0005]

According to the present invention, there is provided an oscillation circuit for oscillating a carrier wave in an ultrasonic frequency band, and a carrier wave in the ultrasonic frequency band is modulated by a modulated signal. A modulating unit that modulates, a first filter that blocks a predetermined frequency or less of a modulated signal input to the modulating unit,
An ultrasonic transducer that emits a signal output from the modulation unit as an ultrasonic wave into a medium, a second filter that cuts off a predetermined frequency or more of the modulated signal, and a signal that passes through the second filter. A parametric speaker characterized by comprising an audible sound range speaker that reproduces an audible sound is proposed.

(2) An oscillation circuit for oscillating a carrier wave in the ultrasonic frequency band, a modulator for modulating the carrier wave in the ultrasonic frequency band with a modulated signal, and a predetermined frequency of the modulated signal input to the modulator. A first filter that passes a band, an ultrasonic transducer that emits a signal output from the modulation unit as ultrasonic waves into a medium, and a second filter that blocks a predetermined frequency or more of the modulated signal, An audible range speaker that reproduces an audible sound of the signal that has passed through the second filter is proposed.

(3) An oscillation circuit for oscillating a carrier wave in the ultrasonic frequency band, a modulator for modulating the carrier wave in the ultrasonic frequency band with the modulated signal, and a predetermined frequency of the modulated signal input to the modulator. A first filter that blocks the following, a second filter that passes a predetermined frequency band of a modulated signal input to the modulation unit, a switch that switches the filters, and a signal that is output from the modulation unit. An ultrasonic vibrator for radiating ultrasonic waves into a medium as ultrasonic waves, a third filter for cutting off a predetermined frequency or more of the modulated signal,
And an audible range speaker that reproduces an audible sound of the signal passed through the filter.

(4) Further, in the parametric speaker proposed above, a filter is proposed in which each filter includes a volume switch for appropriately adjusting a cutoff frequency or a pass frequency band.

[0009]

According to the proposal of (1), it is possible to modulate the carrier by cutting the low frequency range of the modulated signal and generate a reproduced sound as a parametric speaker. Therefore,
It is possible to greatly reduce noise caused by unnecessary components below the audible sound. Further, since only the low-frequency range of the cut modulated signal is reproduced by the audible range speaker, a parametric speaker having sharp directivity and good sound quality can be provided.

According to the proposal (2), only the audible sound frequency band required as the reproduced sound in the modulated signal is modulated, and the reproduced sound can be generated as a parametric speaker. Therefore, it is possible to greatly reduce noise caused by components unnecessary for reproduction of a voice message or the like. Furthermore, since only the insufficient bass range is reproduced by the audible range speakers, a parametric speaker having sharp directivity and good sound quality can be provided.

According to the proposals of (3) and (4), the modulated signal is modulated via a filter, and the type of the filter or the cutoff frequency and the cutoff frequency are determined according to the noise mixing state of the reproduced sound generated by the parametric array effect. Pass frequency band can be selected and adjusted. In addition, the cutoff frequency of the filter connected to the audible sound range speaker can be adjusted.
Therefore, it is possible to effectively reduce noise and adjust sound quality according to the type of the modulated signal (audio signal, music signal, etc.).

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a driving circuit according to an embodiment of the present invention. Reference numeral 1 denotes an oscillation circuit that oscillates a carrier wave (for example, 40 KHz) of an ultrasonic wave radiated from an ultrasonic transducer. Is a modulator for modulating the audio signal output from the audio signal generator 2 to the carrier output from the oscillation circuit 1. Reference numeral 4 denotes an ultrasonic transducer amplifying circuit for amplifying an output signal from the modulator 3, and drives the ultrasonic transducer 5. Reference numeral 6 denotes a high-pass filter that cuts the audio signal output from the audio signal generator 2 below the low frequency range. The cut-off frequency is set to 300 Hz, for example. By the way, the range of audible sound is generally 30 Hz to 16K.
However, in practice, sounds below 300 Hz are hardly audible, and the efficiency of demodulation, that is, conversion to reproduced sound is very low in a parametric speaker. However, music signals generally contain a lot of these low-frequency components, and if they are modulated as they are as a modulated signal, the sound quality will be degraded as noise rather than as reproduced sound when demodulated. Therefore, in this embodiment, the cutoff frequency is set to 300 Hz as an example. Reference numeral 7 denotes a band pass filter whose passing frequency band is 3 as an example.
00 Hz to 10 KHz. These filters are connected to the modulation unit 3 via the switch 8. 9
Is a low-pass filter that cuts a low frequency range or higher of the audio signal output from the audio signal generator 2, and its cutoff frequency is set to 200 Hz as an example. Reference numeral 10 denotes an audible sound range speaker amplifier circuit that amplifies an output signal from the low-pass filter 9, and drives an audible sound range speaker 11.

Next, the operation of the present invention will be described. When the high pass filter 6 is selected by the switch 8, the audio signal output from the audio signal generator 2 is 300H
An ultrasonic wave having a spectrum as shown in FIG. 2A is radiated into the air by cutting a low frequency range below z, and FIG.
Is demodulated. As described above, since the frequency components of 300 Hz or less that are hard to hear when demodulated are cut, noise generated as a difference sound from the cut frequency components can be significantly reduced. This will be described in more detail with reference to FIG. For example, a carrier wave of 40 KHz has 300 Hz and 15 KH.
When the signal z is amplitude-modulated and radiated from the ultrasonic vibrator into the air, the difference sound of each signal component is A: 300 Hz B: 14.7 KHz C: 1
5KHz and three kinds of sounds are demodulated. That is, 30
A signal of 14.7 KHz, which is a difference sound between 0 Hz and 15 KHz, is generated as unnecessary noise. Moreover, this 14.7 KHz signal is 300 Hz and 15 KH
Since it is proportional to the output level of z, the noise becomes very high in sound pressure. Therefore, if the signal of 300 Hz which is hardly heard as the demodulated sound is cut, no difference sound B is generated, and the noise can be eliminated.

Next, when the band pass filter 7 is selected by the switch 8, only the frequency components of 300 Hz to 10 KHz are modulated in the audio signal output from the audio signal generator 2, and the spectrum as shown in FIG. Is radiated into the air, and a reproduced sound having a frequency characteristic as shown in FIG. 3B is demodulated. Thus, a frequency component of 300 Hz or less that is almost inaudible when demodulated,
Since high frequency components having high conversion efficiency to reproduced sound are cut, noise generated as a difference sound from the cut frequency components can be greatly reduced.

On the other hand, the low-pass filter 9 outputs a frequency component of 200 Hz or less in the audio signal output from the audio signal generating section 2 to the audible-range speaker amplifier circuit 10. Only the components are directly reproduced as audible sounds. Therefore, the low-frequency components cut by the high-pass filter 6 and the band-pass filter 7 can be complemented by the audible-range speaker 11.

Although the present invention is configured as described above, the present invention is not limited to the above-described embodiment, but is applied to a case where the audio signal has a fixed content or is only a voice message. Each of the above filters may be provided with a volume switch capable of appropriately adjusting a cutoff frequency and a pass frequency band, and set to the most appropriate value while checking the reproduced sound. For example, setting the cutoff frequency of the high-pass filter to 500 Hz,
When the cut-off frequency of the low-pass filter connected to the audible range speaker is set to 400 Hz, narrow directivity is somewhat lost as a parametric array effect, but a remarkable noise reduction effect is obtained for music reproduction, and the sound quality is dramatically improved. It was confirmed. Instead of selecting each of the filters with a switch, a dedicated filter may be fixedly provided when the content of the audio signal is determined.

[0017]

As described above, according to the present invention, a reproduced sound can be generated as a parametric speaker by preliminarily cutting a low-frequency range that is hardly heard during demodulation by the parametric array effect and modulating the carrier. Therefore, noise generated at a high sound pressure level as a difference sound between a frequency component necessary for the reproduced sound and an unnecessary frequency component can be significantly reduced. Meanwhile,
Since the lost bass range is directly reproduced as audible sound by the audible range speaker, it is possible to provide a parametric speaker with good sound quality rich in bass range while having narrow directivity as a whole.

Further, at the time of demodulation by the parametric array effect, a high frequency range near the upper limit of the audible sound, which is not particularly necessary but has a high conversion efficiency to a reproduced sound, and a low frequency range which is a major cause of noise generation are cut in advance. Since at least only the audible sound frequency band necessary for the reproduced sound is modulated, noise of a high sound pressure level caused by unnecessary frequency components for reproducing a voice message or the like can be greatly reduced. On the other hand, the lost bass is directly reproduced as audible sound by the audible range speaker, which can complement the low range of a parametric speaker that tends to produce high-pitched sound. It is possible to provide a parametric speaker with noise and natural sound quality.

Further, the modulated signal is modulated via a filter, and the type of filter or the cutoff frequency / pass frequency band can be selected and adjusted according to the noise mixing state of the reproduced sound generated by the parametric array effect.
In addition, the cutoff frequency of the filter connected to the audible sound range speaker can be adjusted. Therefore, it is possible to effectively reduce noise and adjust sound quality according to the type of the modulated signal (audio signal, music signal, voice + music signal, etc.).

[Brief description of the drawings]

FIG. 1 is a block diagram showing a driving circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a spectrum of a modulated wave and a reproduced sound according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a spectrum of a modulated wave and a reproduced sound according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a state where two types of signals are amplitude-modulated on a carrier wave.

FIG. 5 is an explanatory diagram showing a modulated signal and a spectrum after modulation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oscillation circuit 2 Audio signal generation part 3 Modulation part 4 Ultrasonic vibrator amplifier circuit 5 Ultrasonic vibrator 6 High pass filter 7 Band pass filter 8 Switching device 9 Low pass filter 10 Audible sound range speaker amplifier circuit 11 Audible sound range speaker

Claims (4)

[Claims] An oscillator circuit for oscillating a carrier wave in an ultrasonic frequency band, a modulating unit for modulating a carrier wave in an ultrasonic frequency band with a modulated signal, and blocking a modulated signal input to the modulating unit below a predetermined frequency. A first filter that performs the operation, an ultrasonic transducer that emits a signal output from the modulation unit via the first filter as ultrasonic waves, and a second filter that blocks a predetermined frequency or more of the modulated signal. And an audible sound range speaker for audibly reproducing a signal passed through the second filter. 2. An oscillation circuit for oscillating a carrier wave in an ultrasonic frequency band, a modulator for modulating the carrier wave in the ultrasonic frequency band with a modulated signal, and passing through a predetermined frequency band of the modulated signal input to the modulator. A first filter that performs the operation, an ultrasonic transducer that emits a signal output from the modulation unit via the first filter as ultrasonic waves, and a second filter that blocks a predetermined frequency or more of the modulated signal. And an audible sound range speaker for audibly reproducing a signal passed through the second filter. 3. An oscillation circuit for oscillating a carrier wave in an ultrasonic frequency band, a modulating section for modulating a carrier wave in an ultrasonic frequency band with a modulated signal, and blocking a modulated signal input to the modulating section below a predetermined frequency. A first filter, a second filter that passes through a predetermined frequency band of the modulated signal input to the modulation unit, a switch that switches the filters, and the filter via the filters and the switch. An ultrasonic transducer that emits a signal output from the modulator as an ultrasonic wave, a third filter that cuts off a predetermined frequency or more of the modulated signal, and an audible sound that reproduces an audible signal from the third filter. A parametric speaker comprising a range speaker. 4. The parametric speaker according to claim 1, wherein each filter includes a volume switch for appropriately adjusting a cutoff frequency or a pass frequency band.