JPH0331320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a directional microphone that utilizes the parametric effect of a sound field.

FIG. 1 shows the configuration of a conventional parametric directional sound receiving system.

An oscillator 1 generates a frequency ₁ in the ultrasonic range. This passes through power amplifier 2 to transmitter 3.
The ultrasonic waves are supplied to the ultrasonic waves and are emitted in the direction of the wave receiver 4 as ultrasonic waves. Here, when an audio signal of frequency ₂ arrives from the direction of the transmitter 3, if the ultrasonic output is sufficiently large, these two waves will cause nonlinear interference, and as a result, in addition to ₁ and ₂ , ₁ ± ₂ secondary waves are generated. Therefore, after amplifying these signals with a preamplifier 5, a signal wave can be obtained by demodulating PM or FM with a demodulator 6 using ₁ as a carrier and ₁ ± ₂ as a sideband. In addition, the smaller the angle θ of incidence of the signal wave with respect to the transducer axis, the greater the interference distance, so the detection output increases, and as the angle increases, the output decreases, and theoretically becomes zero in the 180° direction. . A directional microphone is thus obtained. However, as can be seen in FIG. 1, since signals arriving from the direction of the transducer are detected, the dimensions of the transducer must be sufficiently small. For example, if the distance between the transducer and receiver is 50 cm, and you are trying to detect the incoming signal frequency up to 15 KHz, the size of the transmitter must be kept to about 5 cm in diameter, but currently, transmitters of this size are not enough. It does not reach the sound pressure level that causes air nonlinear phenomena. In other words, in the conventional configuration, the maximum output is obtained when the signal arrives from the transmitter side, so there is a limit to the size of the transmitter and the signal-to-noise ratio deteriorates. We were connected.

The present invention is designed to eliminate the above-mentioned drawbacks. In other words, means is provided so that the maximum detection output can be obtained when the signal arrives from the receiver side. FIG. 2 shows a main part of an embodiment of the present invention.
The signal wave ₂ enters the receiver 4 side, is reflected by the transmitter 3, causes nonlinear interference with the ultrasonic wave ₁ from the transmitter, and is captured by the receiver 4. The receiver 4 can be of sufficiently small dimensions so that the incoming signal is not masked by it. On the other hand, since the signal coming from the transmitter side is an unnecessary signal, the transmitter can be made large enough to generate ultrasonic waves of the required level. On the contrary, the size of the transmitter is required to be large because it determines the lowest frequency of the signal to be detected. Specifically, in order to reflect sound waves of a certain wavelength, a reflecting surface with a diameter about 1/2 the wavelength is required, so for example, when considering reproduction up to 300 Hz (wavelength of about 1 m),
A minimum diameter of 50cm is required. FIG. 3 shows another embodiment of the present invention in which the transmitter 3 is curved to increase the ultrasonic level at the receiver position and the efficiency of collecting incoming sound waves. Since it is difficult to realize this curved wave transmitter with a single element, a plurality of elements may be arranged in a curved shape and used.

As described above, the present invention has a means for obtaining the maximum detection output when a signal arrives from the receiver side in a parametric directional sound receiving system. It can be made large enough to obtain the necessary acoustic power, and a directional microphone with a good signal-to-noise ratio can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example of a parametric directional sound receiving system, and FIGS. 2 and 3 are principle diagrams of essential parts of an embodiment of the parametric directional sound receiving system according to the present invention. 1 is an oscillator, 2 is a power amplifier, 3 is a transmitter,
4 is a receiver, 5 is a preamplifier, and 6 is a demodulator.

Claims (1)

[Claims] 1. A transmitter that generates ultrasonic waves, a receiver that receives the ultrasonic waves generated by the transmitter by nonlinear interference with the incoming sound waves facing the transmitter, and the sound waves that arrive from the received signal. and a demodulator for demodulating the waveform, and the surface on the transmitter side is a reflecting surface having a diameter of approximately 1/2 or more of the wavelength of the received sound wave among the sound waves arriving from the receiver side. Parametric array microphone.