JPH0550196B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a speaker with sharp directivity that 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 interaction effects 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, and the diameter is
11.5cm, center frequency 40KHz, efficiency 1m on axis,
When inputting 10V, it is 113dB. A parametric array speaker 2 is constructed by arranging 547 of these transducers into an array as shown in the figure.
The signal from the audio signal source 3 is converted into AM by the modulator 4.
The signal is modulated and input to the parametric array speaker 2 via the power amplifier 5. The frequency of the carrier wave (primary wave) is 40KHz. 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 the secondary waves of this parametric array speaker 2. a is
For 1KHz, b is for 5KHz. In this way, the higher the frequency, the sharper the directivity, and at 5KHz, the half-reduction angle of sound pressure was approximately 4°. This is considered to be too narrow considering actual usage conditions. Furthermore, such a large change in directivity has the disadvantage that even a slight change in the listening position changes the auditory sensation, resulting in an extremely unnatural sound.

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 for a diameter of 150 mm, b is for a diameter of 450 mm, and the frequency is 1 KHz. In this way, as the diameter increases, the directivity becomes sharper.

Next, FIG. 4 shows the sound pressure frequency characteristics of a conventional parametric array speaker. In a parametric array speaker, if the sound pressure frequency characteristics of the primary wave are flat, the sound pressure frequency characteristics of the secondary wave are
It increases with frequency at 12dB/octave. Since the transducer currently in use has a narrow band of 40±2KHz, the sound pressure rises almost as expected up to 2KHz, but beyond that it becomes uneven due to the sound pressure frequency characteristics of the primary wave. It has become a certain characteristic.

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 with little change in directivity characteristics and sound pressure frequency characteristics depending on frequency.

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

Description of Embodiments 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. 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, the array is divided into multiple concentric areas, with the entire frequency band in the center.
Also, by inputting only the low range to the surrounding area,
A flat sound pressure frequency characteristic and uniform directional characteristics can be achieved.

FIG. 5 shows the configuration of an embodiment of the present invention. 127 transducers in the center of the array (diameter 180
mm) is region A, and the outside thereof is region B. The audio signal is separated into areas A and B, and area A has the conventional
A signal is input through a modulator 4 and a power amplifier 5. 2K in area B by low pass filter 6
Components higher than Hz are cut off, and the signal is input 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, area B is mainly used for low frequency input.
Raise the input level and modulation depth for region A than for region A. Increasing the input level or modulation degree causes an increase in distortion, but since low-frequency distortion is less noticeable than high-frequency distortion, there is almost no problem in terms of hearing. The sound pressure frequency characteristics of this embodiment are shown in FIG. 6, and the directivity characteristics are shown in FIG. 7. Figure 7a shows the case of 1KHz, and b shows the case of 5KHz. When compared with the conventional figures 4 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 directional characteristics can be flattened by inputting mainly the high range to the center and mainly the low range 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 depending on each region (for example, increasing the modulation degree in the lower range).

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of a conventional example, and Figure 2 is a diagram showing the configuration of a conventional example.
Figure 3 is a diagram showing the relationship between the diameter and directional characteristics of a conventional parametric array speaker. Figure 4 is a diagram showing the sound pressure frequency characteristics of the conventional example. FIG. 6 is a diagram showing the same sound pressure frequency characteristic, and FIG. 7 is a diagram showing the same directional 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.

Claims (1)

[Claims] 1. An ultrasonic transducer array consisting of a plurality of substantially concentric regions, and a plurality of modulators for driving each region with ultrasound modulated with audio frequency, A parametric array speaker characterized in that finite amplitude ultrasonic waves are emitted into the air from a transducer array and audio frequencies are reproduced by 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 array 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. speaker. 4. Among the plurality of regions, at least one of the input level and the modulation degree is made smaller in the region where the high frequency range is mainly input, and the region where the low frequency range is mainly input is made larger. Section 1,
Parametric array speaker according to item 2 or 3.