JP2007201624A - Modulator for super-directivity speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modulator for a super-directivity speaker for activating a radiator by properly correcting a modulation signal indicating an audible sound modulating a carrier of an ultrasonic wave. <P>SOLUTION: An amplitude modulation section 20 receives an audible sound signal from a sound source 1 to apply amplitude modulation to the carrier of the ultrasonic wave by the audible sound signal, and a correction filter 8 receives the modulation signal from the amplitude modulation section 20 to correct a signal level of a side band at an ultrasonic wave band included in the modulation signal relative to a signal level with the carrier frequency also included in the modulation signal, and outputs the corrected signal to an amplifier 9. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a modulator for a super-directional speaker that causes a radiator to perform super-directional radiation of audible sound.

A conventional superdirective speaker modulator processes a sound signal generated by a modulation signal source with a double integrator, then multiplies it with a coefficient unit, and uses an adder to output the coefficient signal from the coefficient source and the DC source. Add the bias. A square root converter is used to perform square root processing on the output signal of the adder. A multiplier is used to multiply the output signal of the square root converter and the ultrasonic signal generated by the ultrasonic band oscillator to perform amplitude modulation, thereby generating a modulation signal. Thereafter, the modulation signal output from the modulator is amplified by a power amplifier, and the amplified signal is supplied to an ultrasonic emitter, that is, an ultrasonic radiator to generate / radiate ultrasonic waves. This ultrasonic wave self-demodulates into an audible sound by non-linear interaction when propagating in the air, and an audible sound that can be heard only within the ultrasonic radiation range is generated.
The double integrator is such that the sound pressure of the self-demodulated audible sound is proportional to the second derivative of the original modulation signal, that is, the sound pressure level of the audible sound increases in proportion to the square of the frequency. Used to correct sound pressure characteristics. In other words, when a modulated signal is generated after double integration of an audible sound signal in advance, and the sound of the modulated signal is reproduced, the sound pressure is proportional to the original modulated signal (for example, Patent Documents). 1).

FIG. 4 is an explanatory diagram showing the operation of a conventional superdirective speaker modulator. This figure shows the frequency characteristics when a conventional superdirective speaker modulator is operated by being connected to an ultrasonic radiator via an amplifier. The vertical axis of the illustrated graph represents the relative level [dB], and the sound pressure level of the audible sound output from the radiator into the air is expressed in decibels. The horizontal axis represents the frequency [Hz] of the audible sound band expressed using a logarithmic scale.
Since the sound pressure level of audible sound rises in proportion to the square of the frequency as described above when the voltage input to the radiator, that is, the signal between the terminals of the radiator is reproduced and the signal of each frequency is reproduced, theoretically, The sound pressure level radiated from the radiator increases with an increase rate of, for example, +12 [dB / octave] as the frequency of the output sound increases as shown in the characteristic A in the figure.

  Further, when the above-mentioned double integrator is operated under the same conditions as the operation of the above-described radiator, the double integrator has a higher output signal as the frequency becomes higher as shown by the characteristic B shown by the broken line. Since the transmission characteristic has a low level, when a double integrator is used, the sound pressure level radiated from the radiator becomes constant regardless of the frequency. In this way, theoretically, it has a flat sound pressure level / frequency characteristic like the characteristic C shown in the figure.

FIG. 5 is an explanatory diagram showing the frequency characteristics of the ultrasonic band of the superdirective speaker. The vertical axis of the graph shown in FIG. 5 represents the relative level [dB], and represents the sound pressure level of the ultrasonic wave radiated from the radiator into the air by the decibel display. The horizontal axis represents the ultrasonic frequency [Hz] expressed using a logarithmic scale. Hereinafter, the sound pressure level / frequency characteristics will be referred to as frequency characteristics except for those described with an explanation.
The above super directional speaker, more specifically, the ultrasonic radiator, generates ultrasonic waves by an ultrasonic transducer. Therefore, in the ultrasonic band, a flat frequency characteristic as indicated by a broken line F shown in FIG. In fact, it has a frequency characteristic in which a peak occurs in a narrow band like the characteristic G. The modulator that drives the radiator uses the peak frequency of the characteristic G of the radiator as the carrier frequency to increase the generation efficiency of the ultrasonic wave, and an audible sound with a high sound pressure is obtained when the emitted ultrasonic wave is self-demodulated. I am trying to do it.

JP-A-4-58758 (pages 2, 3 and 2)

  The conventional superdirective speaker modulator is configured as described above, and the radiator connected to the modulator via an amplifier has the characteristic G shown in FIG. 5 as the frequency characteristic of the ultrasonic band. Thus, it has a peak frequency, that is, a resonance frequency. Further, the frequency characteristic of the audible voice band is actually the characteristic D shown in FIG. 4, and the sound pressure level is in the above-mentioned ratio of +12 [dB / octave] from the low to middle of the audible voice band. It does not increase, and it increases more slowly in the middle and high range above a certain frequency than the above low range, and the rate of increase decreases rapidly, resulting in a generally constant or fine decrease. Therefore, when the frequency characteristic is corrected by using a double integrator, the frequency characteristic of the audible audio band to be radiated is as shown by the characteristic E in FIG. However, the sound pressure is insufficient, and there is a problem that it is difficult to appropriately correct the frequency characteristics of the audible voice band.

  The present invention has been made to solve the above-described problems, and provides a modulator for a super-directional speaker that operates a radiator by appropriately correcting a modulation signal indicating audible sound using ultrasonic waves as a carrier wave. For the purpose.

  A superdirective speaker modulator according to the present invention is a correction filter that receives a modulation signal from an amplitude modulation means, corrects the signal level of the sideband of the ultrasonic band included in the modulation signal, and outputs the signal to the amplification means. It is equipped with.

  According to the present invention, the modulation signal is input from the amplitude modulation means, and the signal level of the side band of the ultrasonic band included in the modulation signal is corrected by the correction filter. The sound pressure level of the sound is increased, and an audible sound that can be heard well by the listener can be emitted in a superdirective manner.

An embodiment of the present invention will be described below.
Embodiment 1 FIG.
1 is a block diagram showing a schematic configuration of a superdirective speaker modulator according to Embodiment 1 of the present invention. The illustrated superdirective speaker modulator includes a sound source 1 for generating an audible sound signal, a coefficient unit 2 for inputting an audible sound signal from the sound source 1, a DC source 3 for generating a signal indicating a bias amount applied to the audible sound signal, An adder 4 for adding a bias amount from the DC source 3 to the audible audio signal output from the coefficient unit 2, a square root converter 5 for performing a square root process on the output signal of the adder 4, and a signal indicating an ultrasonic wave used as a carrier wave. The generated ultrasonic band oscillator 6, the multiplier 7 that multiplies the output signal of the square root converter 5 and the output signal of the ultrasonic band oscillator 6, and the correction filter 8 that corrects the sound level indicated by the output signal of the multiplier 7. . The coefficient modulator 2, the DC source 3, the adder 4, the square root converter 5, the ultrasonic band oscillator 6, and the multiplier 7 constitute an amplitude modulation unit 20 that performs amplitude modulation using an audible audio signal. Has been. In addition, the parametric speaker converter of the present invention is constituted by, for example, the amplitude modulation unit 20 and the correction filter 8 described above. The output signal of the correction filter 8 is input to the amplifier 9, and the output signal of the amplifier 9 is connected to be input to the radiator 10.

The correction filter 8 is, for example, a digital filter that can easily set an arbitrary frequency characteristic. Since the correction filter 8 handles a signal indicating an ultrasonic band, the correction filter 8 can operate at a frequency of about 20 kHz to 100 kHz. A personal computer equipped with software that operates as a digital filter, a board equipped with a DSP, Any form may be used. Moreover, you may comprise by the analog filter which has the characteristic similar to said digital filter.
The radiator 10 is, for example, a parametric speaker provided with a large number of piezoelectric ceramic elements as a vibrator, and is an ultrasonic radiator that generates ultrasonic waves by vibrating each of the piezoelectric ceramic elements according to an input modulation signal. .

Next, the operation will be described.
For example, the modulator shown in FIG. 1 operates as follows. The coefficient unit 2 receives an audible audio signal v (t) generated by the sound source 1 and multiplies this signal by a coefficient m set in advance as the degree of modulation. The adder 4 adds a bias amount indicated by a signal generated by the DC source 3, for example, a bias value 1 to the output signal m · v (t) of the coefficient unit 2. The square root converter 5 performs square root processing on the output signal 1 + m · v (t) of the adder 4 to obtain {1 + m · v (t)} ^1/2 . The multiplier 7 multiplies the signal indicating the ultrasonic wave generated by the ultrasonic band oscillator 6 by the output signal {1 + m · v (t)} ^1/2 of the square root converter 5 to generate a modulation signal.

The amplitude of the audible sound signal v (t) generated by the sound source 1 in this way is modulated, and self-demodulates from an ultrasonic wave to an audible sound when radiated into the air, that is, represents an audible sound using the ultrasonic wave as a carrier wave. A modulation signal is generated. This modulation signal is input to the correction filter 8, and the signal level is corrected as described later.
The amplifier 9 receives the modulation signal level-corrected by the correction filter 8 and amplifies it to a power level that can drive the radiator 10. The radiator 10 generates an ultrasonic wave according to the modulation signal amplified by the amplifier 9 and radiates it into the air.

Generally, when amplitude modulation is performed, a frequency band around the carrier frequency, that is, a side band is generated together with the carrier frequency. Sidebands are also generated in the modulation operation of the superdirective speaker modulator of the present invention, and the generated modulation signal includes sideband frequency components.
The modulator described here amplitude-modulates the ultrasonic wave of the carrier wave with an audible audio signal. When such modulation processing is performed, sidebands are formed on both the upper and lower sides of the carrier frequency, that is, the carrier frequency. Occurs. In normal amplitude modulation, for example, if the carrier frequency is any one of 30 kHz to 50 kHz, the sideband is in a range of about ± 20 kHz with respect to the carrier frequency.

The signal level of the sideband affects the level of an audible audio signal that is amplitude-modulated by an ultrasonic wave having a carrier frequency. In other words, since the ultrasonic wave is self-demodulated into an audible sound by the interaction between the carrier frequency component and the sideband component, when the ultrasonic wave is radiated from the radiator 10 based on the amplitude-modulated modulation signal, the modulation signal The sideband component included in the sound affects the sound pressure level of the demodulated audible sound.
When the sideband signal level is half of the carrier frequency signal level, that is, the sideband signal level is −6 [dB] relative to the carrier frequency signal level, the modulation rate becomes 100% and the optimum modulation signal is obtained. can get. When the level of the audible audio signal to be modulated is lowered, the sideband signal level is −6 [dB] or less, and the modulation rate is lowered. When the level of the audible audio signal is high, the sideband signal level is -6 [dB] or more, and the modulation rate exceeds 100%. Thus, if the modulation rate exceeds 100%, the distortion component increases in the audible sound, which is not preferable.
However, even if the carrier frequency component and the sideband component are adjusted so that the modulation factor becomes 100% as described above and a modulation signal is generated and supplied to the radiator 10, the frequency of the radiator 10 as will be described later is used. Depending on the characteristics, the emitted ultrasonic wave may not be demodulated into an audible sound that can be heard well.

FIG. 2 is an explanatory diagram showing transmission characteristics of the correction filter of the superdirective speaker modulator according to the first embodiment. This figure shows the transmission characteristic of the correction filter 8 shown in FIG. 1, that is, the frequency characteristic of the relative level of the output signal relative to the input signal. The vertical axis shown is the relative level [dB], and the horizontal axis is the logarithmic scale. The frequency [Hz] indicated by using.
The frequency at which the resonance peak occurs in the frequency characteristic of the radiator 10, that is, the resonance frequency of the radiator 10 is shown in FIG. Note that the characteristic G shown in FIG. 2 does not necessarily represent the actual sound pressure level of the ultrasonic wave radiated from the radiator 10. The resonance frequency fp is the carrier frequency of the ultrasonic band generated by the ultrasonic band oscillator 6.

The radiator 10 includes a piezoelectric ceramic element as described above and generates ultrasonic waves. A mechanical resonance type vibrator such as a piezoelectric ceramic element has a frequency characteristic in which a single resonance peak occurs at a specific resonance frequency. Therefore, it is difficult to remove the resonance peak from the frequency characteristics of a parametric speaker constituted by a large number of piezoelectric ceramic elements.
The radiator 10 has a frequency characteristic like a narrow-band bandpass filter like the characteristic G shown in FIG. 2 or the like when generating ultrasonic waves, and when the resonance frequency fp is used as the carrier frequency. The sideband level becomes −6 [dB] or less when the level of the resonance frequency fp is 0 [dB]. Therefore, the modulation rate is 100% or less, and the sound pressure level of the audible sound that is self-demodulated is also reduced.

  In order to compensate for the frequency characteristic of the radiator 10 as described above, the correction filter 8 has a transmission characteristic such as the characteristic H in FIG. The transmission characteristic of the correction filter 8 is such that, for example, a signal with a relative level of 0 [dB] between the input signal and the output signal is output at the resonance frequency fp, and the signal level in the peripheral frequency band on both the upper and lower sides of the resonance frequency fp, ie, the carrier frequency It amplifies larger than the signal level of the carrier frequency. That is, level correction is not performed on the carrier frequency, and the sideband signal level is increased to increase the sideband signal level to the peak carrier frequency signal level, preferably −6 [dB. ], For example, the modulation rate is adjusted so as to approach 100%. When the modulation rate of the modulation signal generated by the amplitude modulation unit 20 is less than 100%, the correction filter 8 amplifies the signal level of the carrier frequency and the signal level of the carrier frequency amplified as described above. Are amplified so that the signal level of the sideband becomes −6 [dB].

  FIG. 3 is an explanatory diagram illustrating frequency characteristics of the superdirective speaker modulator according to the first embodiment. In this figure, the vertical axis represents the relative level [dB], and the horizontal axis represents the frequency [Hz] indicated using a logarithmic scale. A characteristic G indicated by a broken line in FIG. 3 is the same as the characteristic G shown in FIG. 5, and the modulation signal generated by the amplitude modulation unit 20 is amplified by the amplifier 9 without using the correction filter 8, and this signal is It is a frequency characteristic when converted into ultrasonic waves by the radiator 10. The characteristic D shown by the broken line in FIG. 3 is the frequency characteristic of the audible sound that is self-demodulated in the air when the ultrasonic wave radiated from the radiator 10 is the characteristic G, and the characteristic D shown in FIG. It is similar.

  When the modulation signal that has passed through the correction filter 8 having the transmission characteristic such as the characteristic H in FIG. 2 is amplified by the amplifier 9 and the radiator 10 is driven to generate an ultrasonic wave, the frequency of the ultrasonic band generated at that time is generated. The characteristic is like the characteristic K shown in FIG. The characteristic K has the same peak value as the characteristic G shown in FIG. 3, but the peripheral frequencies on both the upper and lower sides of the carrier frequency at which the peak value is obtained, that is, the signal level of the sideband is increased. When such a frequency characteristic of the ultrasonic band is obtained, the frequency characteristic of the audible sound that is self-demodulated from the ultrasonic wave is as shown by a characteristic L in FIG. As described above, as the sideband component increases, the demodulating action increases and the sound pressure level of the audible sound increases. Further, when comparing the characteristic D and the characteristic L, the sound pressure level in the audible voice band is generally higher in the characteristic L, and the sound pressure level in the low sound range is high without impairing the high sound range. The audible sound that can be heard can be emitted in a super-directional manner.

  Here, the correction filter 8 having a transmission characteristic such as the characteristic H shown in FIG. 2 has been described as an example. However, the transmission characteristic of the correction filter 8 is not limited to the above, and the frequency characteristic of the radiator 10 is not limited. The correction filter 8 may be configured by setting the transmission characteristics so as to be suitable and to make the audible sound have a desired sound quality. Thus, the correction filter 8 is suitable as a digital filter that can easily set the transmission characteristic, and can accurately correct the frequency characteristic of the audible voice band that self-demodulates from the ultrasonic wave radiated from the radiator 10. it can. In addition, as parameters for setting the transmission characteristics of the correction filter 8, for example, a side band in a frequency band lower than the carrier frequency and a side band in a frequency band higher than the carrier frequency are determined, and the level of these side bands is individually corrected. The correction filter 8 may be configured to do this. Further, when configured in this way, it is configured to have a function of correcting the level of only one of the low frequency band sideband or the high frequency band sideband, and further adjusting the level to be corrected, The setting may be changed / adjusted to have an arbitrary transmission characteristic.

  As described above, according to Embodiment 1, the modulation signal generated by the amplitude modulation unit 20 is input, and the radiator 10 exceeds the signal level of the sideband with respect to the signal level of the carrier frequency included in the signal. Since the correction filter 8 for correcting the sound wave according to the frequency characteristic when the sound wave is generated is provided, the sound pressure level of the audible sound is changed by changing the frequency characteristic of the audible sound band to be self-demodulated from the ultrasonic wave emitted from the radiator 10. Therefore, there is an effect that the audible sound that can be heard by the listener can be emitted in a super-directional manner.

It is a block diagram which shows schematic structure of the modulator for superdirective speakers by Embodiment 1 of this invention. 6 is an explanatory diagram showing transmission characteristics of a correction filter of the superdirective speaker modulator according to Embodiment 1. FIG. 6 is an explanatory diagram illustrating frequency characteristics of the superdirective speaker modulator according to Embodiment 1. FIG. It is explanatory drawing which shows operation | movement of the modulator for conventional superdirective speakers. It is explanatory drawing which shows the frequency characteristic of the ultrasonic band of a super-directional speaker.

Explanation of symbols

1 sound source, 2 coefficient unit, 3 DC source, 4 adder, 5 square root converter, 6 ultrasonic band oscillator, 7 multiplier, 8 correction filter, 9 amplifier, 10 radiator, 20 amplitude modulation unit.

Claims (4)

An audible sound signal is input from a sound source, and amplitude modulation means for generating a modulation signal by amplitude-modulating an ultrasonic carrier wave with the audible sound signal is provided. In the superdirective speaker modulator to be operated,
Superdirectivity comprising a correction filter that receives a modulation signal from the amplitude modulation means, corrects the signal level of the sideband of the ultrasonic band included in the modulation signal, and outputs the signal to the amplification means. Modulator for speakers.   2. The modulator for superdirective speakers according to claim 1, wherein the correction filter corrects the sideband signal level in correspondence with the signal level of the carrier frequency included in the modulation signal.   The modulator for a super-directional speaker according to claim 2, wherein the correction filter amplifies the signal level of the sideband of the ultrasonic band included in the modulation signal. The superdirectivity according to any one of claims 1 to 3, wherein transmission characteristics of an ultrasonic band included in the modulation signal are arbitrarily changed / adjusted in the correction filter. Modulator for speakers.

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