RU2545462C2 - System for active noise reduction with ultrasonic radiator - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: system for active noise reduction with an ultrasonic radiator consists of a microphone, analogue-to-digital converter, a received signal processing device, a digital-to-analogue converter, an ultrasonic radiator, a high-frequency radiation generator with a mixer, a broadband amplifier and an acoustic filter. The generator and the mixer are situated between the signal processing device and the digital-to-analogue converter, and a power amplifier is connected by its input to the output of the digital-to-analogue converter, the output of the amplifier is connected to a piezoelectric transducer and the output of the transducer is connected to the input of the acoustic filter.

EFFECT: wide spectrum of emitted frequencies.

2 cl, 1 dwg

Description

The invention relates to protection against acoustic noise of various origins and can be used in industrial and residential premises, as well as in open areas.

Known devices for actively suppressing noise (see, for example, patents: RU No. 21115960, IPC G10K 11/16, published July 20, 1998; US No. 5848169, IPC: G11K 11/00, published December 8, 1998), the essence of the work of which is that the sound signal of noise received by the microphone is converted into an electric signal and after processing it is fed to a speaker that emits sound waves of the same frequency, but with a phase opposite to the waves incident on the microphone.

The main and fundamental drawback of these devices is their limited radiation over the frequency range, since the acoustic systems (speakers) used in them are resonant oscillatory systems in their structure and do not allow reproducing any broadband signal reliably. The specific mass and dimensions of the components of such systems do not allow equal reproduction of signals from a different frequency range on one speaker, causing phase and amplitude distortions at the edge of the allotted frequency range. The use of several speakers emitting in different frequency ranges requires the use of filters and does not allow summing to obtain a signal shape sufficient for high-quality noise reduction in a wide frequency range.

For uniform suppression, it is necessary that the sound waves of noise and the waves emitted by the device are not only coherent, but that they also coincide in the shape of their surface of the wave front and the direction of their propagation. Otherwise, coherent waves, arriving at different points in space, will have different phases and, depending on the phase difference, will cancel each other in one place and amplify in another.

In addition, the speakers emit a signal generated to suppress noise with a delay of the order of 10 ⁻³ s (the radiation speed of the low-frequency component of the signal by the speaker system). As a result, it becomes necessary to separate the microphone and speaker by a distance of the order of 0.5 m (a noise wave manages to travel such a distance during the time of emission by the speakers of the noise reduction signal). However, the characteristics of the noise wave itself in the new location will be different and, accordingly, the emitted signal will not be effective for its suppression (due to the lack of coherence).

Attempts to eliminate these shortcomings were made in the development of active noise reduction devices (see, RU patent: No. 2363992, IPC G10K 11/178, published on 08/10/2009; No. 2411592, IPC G10K 11/178, published on 02/10/2011), containing the main and control microphones, devices for converting and processing the received signals, a device for generating a noise reduction signal and at least one speaker emitting the generated signal.

The presence in the above devices of the control microphone allows you to slightly correct the phase shifts that occur due to the time delay of the radiation between the noise signal and the noise reduction signal. However, the use of these devices is possible only in a limited amount of space adjacent to the radiation point.

The known system of directional sound Audio SPOTLIGHT (http://www.holosonics.com /products.html ), containing a high-frequency (ultrasonic) radiation generator (sound projector) and a microcontroller that generates a predistortion into the emitted signal.

In this system, the generated high-frequency radiation is pre-modulated by a given sound range signal and then, directionally propagating in space, excites this modulation signal in ambient air, allowing it to be heard in the carrier wave propagation zone.

The fundamentally described system can be used for active noise reduction, however, its capabilities are severely limited by the “cone” of the carrier wave propagation, and its use, which requires high-power ultrasonic signals, is harmful to humans and energy-intensive in operation.

Closest to the claimed technical solution is an active noise reduction system (see US patent No. 5535283, IPC G10K 11/178, published July 9, 1996) containing a microphone located on the path of propagation of a noise wave, an analog-to-digital converter, a device for processing the received signal , digital-to-analog converter with high-pass filter and emitter.

In a known system, acoustic noise is picked up by a microphone, and then converted into a digital code using an analog-to-digital converter. The data obtained are corrected in the signal processing device (pre-emphasis is made, phase shifts are made, etc.) and then fed to the digital-to-analog converter. The analog output signal obtained as a result of the conversion passes through a high-pass filter, in which its high-frequency component is cut off, emitted, and, being added to the noise wave, suppresses it.

The above system allows quite efficient noise reduction in the mid-frequency region of the sound spectrum (from about 100 to 6000 Hz). However, outside the designated frequency range, phase and amplitude distortions also occur, as a result of which it is impossible to suppress noise in the high and low frequencies with its help.

The problem to which the invention is directed is to obtain a device capable of providing effective noise reduction in the entire range of sound frequencies in a given volume.

The technical result of the invention is the possibility of high-quality noise reduction in the frequency range from 20 to 20,000 Hz in the region up to 10 m ³ .

The claimed technical result is achieved due to the fact that the active noise reduction system with an ultrasonic emitter, consisting of a microphone located on the propagation path of the noise wave, an analog-to-digital converter, a device for processing the received signal, a digital-to-analog converter and a radiator, further comprises a high-frequency radiation generator and a mixer located in the system between the signal processing device and the digital-to-analog converter, a broadband power amplifier, located sequentially behind the digital-to-analog converter and an acoustic filter of ultrasonic frequencies located after the emitter, while the emitter in the system is ultrasonic.

A piezoelectric transducer can be used as an ultrasonic emitter in the system.

The invention is illustrated in the figure, which shows a diagram of an active noise reduction system with an ultrasonic emitter.

The active noise reduction system contains a microphone 1, an analog-to-digital converter (ADC) 2, a signal processing device 3, a high-frequency radiation generator 4 with a mixer 5, a digital-to-analog converter (DAC) 6, a power amplifier 7, an ultrasonic emitter 8, and an ultrahigh-frequency acoustic filter 9.

The system operates as follows.

The acoustic noise of the sound range (from 15 to 25000 Hz) is captured by the microphone 1 and converted into a digital code using an analog-to-digital device 2, the digital code data is sent to a signal processing device 3, in which the original signals are processed (frequency correction of the electronic path is performed, predistortions necessary for the subsequent addition with a noise signal), and after a predetermined interval, the delays are applied to mixer 5. In the mixer, the high-frequency pulses of the the range of 250-350 kHz coming from the generator 4. Next, the modulated pulses are fed to a digital-to-analog converter 6. In this case, the signal processing device real-time controls the operation of the generator 4 and adjusts the characteristics of the generated pulses. The high-frequency analog signal from the DAC output is fed to a broadband power amplifier 7, where it is amplified to the required level and then emitted by the ultrasonic emitter 8 in the form of an acoustic signal. The acoustic filter of ultrahigh frequencies 9 limits the output of the ultrasonic component (carrier wave) and passes into the surrounding space the sound component (modulation wave), which fully corresponds to the noise acoustic signal and is reproduced in antiphase to it.

At the same time, since the speed of emission of an acoustic signal by an ultrasonic emitter (for example, a piezoelectric emitter) is significantly higher than that of resonant dynamic acoustic systems and amounts to about 10 ^-5 s, the distance between the microphone and emitter can be minimized, which further improves the quality of noise reduction and expands the amount of space in which it is produced.

The proposed technical solution allows for high-quality noise reduction in the entire range of sound frequencies in a given volume.

Claims (2)

1. The active noise reduction system with an ultrasonic emitter, consisting of a microphone located on the propagation path of the noise wave, an analog-to-digital converter, a device for processing the received signal, a digital-to-analog converter and a radiator, characterized in that it further comprises a high-frequency radiation generator and a mixer located in the system between a signal processing device and a digital-to-analog converter, a broadband power amplifier located in series behind the digital tax transducer, and an ultrasonic frequency acoustic filter located after the emitter, and the emitter in the system is ultrasonic. 2. The active noise reduction system with an ultrasonic emitter according to claim 1, characterized in that a piezo emitter is used as an ultrasonic emitter.