JPS60150399A - Parametric array speaker - Google Patents

Abstract

PURPOSE:To offer a parametric array speaker with less change in the directivity characteristic and sound pressure versus frequency characteristic due to frequencies by separating an ultrasonic wave transducer array into plural regions of nearly concentric form and driving them independently. CONSTITUTION:A part comprising 127 pieces (180mm. in diameter) of a transducer at the center of the array is used as a region A and the outer part is used as a region B. A sound signal is used separately for the regions A, B and the signal is inputted to the region A through a modulator 4 and a power amplifier 5 as a conventional speaker. The signal is fed to the region B while the component over 2kHz is cut off by a low pass filter 6 through a modulator 4' and a power amplifier 5'. The input voltage or modulation to each region is selected so that the sound frequency characteris is made flat as much as possible. The input level or modulation of the region B inputted with low frequency is increased mainly more than that of the region A in order to improve the low frequency sound pressure concretely. Although the increase in the input level and modulation incurs increase in the distortion, since the distortion at low frequency is not sensed easily in comparison with that at high frequency, there is no listening problem.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a speaker with sharp directivity, which is particularly suitable for explaining exhibits at exhibitions, broadcasting information on station platforms, and the like.

Conventional configurations and their problems Conventionally, horn speakers have been used in loudspeaker systems where sharp directivity is required. However, the directivity of a horn speaker is strongly related to its length and diameter, and when sharp directivity is required, especially in the low frequency range, the horn itself has to be extremely large.

On the other hand, in recent years, speakers using parametric effects, which are nonlinear interactions of ultrasonic waves, have been attracting attention because they can provide much sharper directivity than in the linear region. First, a conventional example will be explained with reference to FIG. 1 is an ultrasonic transducer using a ceramic piezoelectric vibrator with a bimorph structure, which has a diameter of 11.5 mm, a center frequency of 40 KHz, an efficiency of 1 m on the axis, and 113 dB when inputting 10 V. A parametric array speaker 2 is constructed by arranging 547 of these transducers into an array as shown in the figure. A signal from the audio signal source 3 is subjected to AM modulation by a modulator 4, and is input to the parametric array speaker 2 via a power amplifier 5. The frequency of the carrier wave (primary wave) is 4
It is 0KHz. The primary wave and sideband waves emitted from the speaker interfere with each other due to the nonlinearity of the air, and a modulated wave (secondary wave) with sharp directivity is generated in the air. FIG. 2 shows the directivity characteristics of secondary waves of this parametric array speaker. a is for IKHz, b is for 5KHz.As shown above, the higher the frequency, the sharper the directivity, and at 5KHz
In this case, the sound pressure half-reduction angle was approximately 4°. This is considered to be too narrow considering actual usage conditions. Further, such a large change in directivity has the disadvantage that the auditory sensation changes due to a slight change in the listening position, which is extremely unnatural.

On the other hand, FIG. 3 shows the relationship between the array diameter and the directivity of secondary waves in a conventional parametric array speaker. A is a diameter of 150 m, b is a case of 450 m, and the frequency is IKHz.As the diameter becomes larger, the directivity becomes sharper.

Next, FIG. 4 shows the sound pressure frequency characteristics of the same conventional parametric array speaker. In a parametric array speaker, if the sound pressure frequency characteristic of the primary wave is flat, the sound pressure frequency characteristic of the secondary wave increases with frequency at 12 dBloCt. Since the transducer currently in use has a narrow band of 40±2KHz, the sound pressure rises almost as expected up to 2KHz, but above that the sound pressure increases due to the sound pressure frequency characteristics of the primary wave. It has certain characteristics.

OBJECTS OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned conventional drawbacks and to provide a parametric array speaker whose directional characteristics and sound pressure frequency characteristics change little with frequency.

Structure of the Invention The present invention comprises a parametric array speaker consisting of a plurality of regions separated approximately concentrically, and a plurality of modulators, filters, and power supplies for supplying inputs with different frequency characteristics and modulation degrees to each region. Consists of amplifiers, etc.

3. Description of Embodiment In a parametric array speaker, the higher the frequency of the secondary wave, the smaller the sound pressure of the primary wave required to produce a constant sound pressure of the secondary wave.3. That is, it can be seen that the number of transducers is small and the diameter of the array is small. Also, the smaller the diameter, the broader the directional characteristics. Therefore, by dividing the array into concentric solid r (multiple regions) and inputting the entire frequency band to the center and only the low frequency range to the periphery, a flat sound pressure frequency response and uniform directivity can be achieved. Possible 0 Figure 5 shows the configuration of an embodiment of the present invention.127 transducers (diameter 1ao+n+n) in the center of the array
is region A, and the outside (till is region B.

The audio signal is separated into areas A and B, and area A has the conventional
Modulator 4. A signal is input through the power amplifier 5. In region B[, components of 2 kHz or more are cut off by a low-pass filter 6, and the signal is inputted through a modulator 4' and a power amplifier 5'. The input voltage or modulation degree to each region is selected so that the sound pressure frequency characteristics are as flat as possible. Specifically, in order to improve the sound pressure in the low range, the input level and modulation degree of area B, where low frequency input is mainly input, are increased compared to area A.Increasing the input level and modulation degree increases distortion. However, the distortion in the low range is harder to notice than the high range, so the auditory sense is -1.
- There are almost no problems. The sound pressure frequency characteristics of this example are shown in No. 6N, and the directivity characteristics are shown in FIG. Figure 7a is I
In the case of KHz, b is the case of 5 KHz. Conventional 4th
When compared with Figures 1 and 2, it can be seen that there is a clear improvement. In this embodiment, the array is divided into two regions, but it goes without saying that by dividing the array into more regions, both the sound pressure and the directivity characteristics can be further improved.

Effects of the Invention As described above, the present invention provides the following effects by dividing the ultrasonic transducer array into a plurality of substantially concentric regions and driving them independently.

(1) The directivity characteristics can be flattened by inputting mainly the high frequency range to the center and the low frequency range as a co-occurrence to the periphery.

(2) The sound pressure frequency characteristics can be flattened by changing the modulation degree, input level, and frequency characteristics of the modulated wave for each region (for example, by increasing the phase modulation degree in the bass range).

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of a conventional example, Fig. 2 is a diagram showing the directional characteristics of the secondary wave, Fig. 3 is a diagram showing the relationship between the diametrical directional characteristics of a conventional parametric array speaker, and Fig. 4 5 is a diagram showing the sound pressure frequency characteristic of a conventional example, FIG. 5 is a configuration diagram showing an embodiment of the IJ Sockley speaker, FIG. is (2) which indicates the same directivity characteristic. 1... Ultrasonic transducer, 2...
・Transducer array, 3...-Audio signal source, 4, 4'...Modulator, 5, 5'...
Power amplifier, 6...Low pass filter, A,
B... area. Name of agent: Patent attorney Toshio Nakao and 1 other person 41
Figure No. 4 rzJ m renga 0-1z) Challenge 5 Figure No. 6 Gangyohakyo (/h)

Claims (4)

[Claims] (1) The transducer array consists of an ultrasonic transducer array consisting of a plurality of substantially concentric regions and a plurality of modulators that drive each region with ultrasound modulated with audio frequency. A parametric array speaker characterized by emitting finite amplitude ultrasonic waves into the air and reproducing audio frequencies using the nonlinearity of the air. (2) The parametric array speaker according to claim 1, wherein at least one of the level of the input signal, the degree of modulation, and the frequency characteristic of the modulated wave is independently controlled in each region. (3) The parametric system according to claim 1 or 2, characterized in that the inner region of the plurality of regions is input with mainly the high range of audio frequencies, and the outer region is mainly input with the low range of audio frequencies. array speaker. (4) Among the plurality of regions, the input level or the degree of modulation is made smaller in the region where mainly the high frequency range is input, and the region where the low frequency range is mainly input is made larger. A parametric array speaker according to the first, second or third range.