JPH02224498A - Active noise canceler - Google Patents

Abstract

PURPOSE:To prevent production of howling in an audible range and to improve the noise eliminating performance by arranging a monitor microphone to a position of a side face of a noise eliminating speaker and a position where a cancel tone radiating from a positive pressing face of the noise eliminating speaker and a cancel tone radiating from a negative pressing face are canceled together. CONSTITUTION:A monitor microphone 2 is placed to a position close to the side face of the noise eliminating speaker 1 and a position where a cancel tone radiating from a diaphragm surface 1e (positive pressing face) of the noise eliminating speaker 1 and the cancel tone radiating from a housing surface 1f (negative pressing face is canceled with each other. When the active noise canceler is used in a place such as a cockpit of an aircraft having external noise, the external noise is inputted by the monitor microphone 2, a noise cancel circuit 3 generates a cancel tone generating signal of the opposite phase to the input signal, the cancel tone radiates toward the ear shell E of the user from the noise eliminating speaker 1 based on the signal and the external noise listened to by the user is eliminated through the canceling action of the opposite phase by the cancel tone.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an active noise canceller having a function of actively canceling external noise.

(Prior Art) Conventionally, one known active noise canceller is one described in US Pat. No. 4,455,675, for example. This active noise canceller consists of a monitoring microphone that inputs a synthesized sound of external noise and cancellation sound, a silence speaker that generates the cancellation sound, and a cancellation sound that is in the opposite phase of the input sound picked up by the monitoring microphone. The noise canceling circuit outputs a canceling sound generation signal to be generated by the muffling speaker, and the external noise is muffled by canceling the canceling sound of three phases opposite to the external noise.

(Problem to be solved by the invention) However, such conventional active noise
In the canceller, the monitoring microphone manually collects both the external noise and the canceling sound to form a closed loop, which causes the following problems.

That is, the monitor speaker is placed opposite to and immediately in front of the muffler speaker in order to input the canceling sound emitted from the muffler speaker evenly. Therefore, this monitor microphone and its support member,
The sound field radiated from the muffled speaker was disturbed, particularly the sound field of short wavelengths, for example, high frequencies of 1000 Hz or more. Therefore, the amount of silencing in the high frequency range was reduced, making the silencing unstable.

Furthermore, in order to prevent the disturbance of the sound field as mentioned above, to prevent the vibration of the diaphragm of the muffled speaker from being disturbed, to prevent it from being affected by the magnet of the muffled speaker, and to prevent the muffled speaker from being affected by external noise. In order to avoid getting in the way of the intrusion route.

between the silencer speaker and the monitor microphone.

It becomes necessary to provide a certain amount of space. For this reason, a phase delay occurs when the canceling sound emitted from the muffled speaker propagates through the air and is input to the monitoring microphone, which causes howling at audible frequencies.
Sound deadening performance deteriorates.

By the way, as a solution to the above-mentioned conventional problems, it is conceivable to provide a monitoring microphone dedicated to inputting external noise at a position away from the muffling speaker. However, in this case, the monitoring microphone is also separated from the user's ear cavity, and the sound input to the microphone differs from the sound actually heard by the user.

This results in poor silencing performance. Therefore, in order to improve silencing performance, it is necessary to install a feedback microphone near the user's ear cavity in addition to the external noise monitoring microphone to perform feedback control. becomes complicated.

The present invention has been made in view of the above-mentioned problems, and aims to prevent the occurrence of howling.

The goal is to develop an active noise canceller that prevents disturbances in the sound field, provides stable and high sound deadening performance, and has a simple structure.

(Means for Solving the Problems) In order to solve the above problems, the active noise canceller of the present invention includes a muffling speaker that generates and radiates a predetermined canceling sound into the user's ear cavity, and a system that manually eliminates external noise. It is equipped with a monitoring microphone and a noise canceling circuit that outputs a canceling sound generation signal to the silencing system 5-force to generate a canceling sound with a phase substantially opposite to that of the input sound of the monitoring microphone. In an active noise canceller that muffles external noise by canceling the phase canceling sound, the monitoring microphone is placed at a side position of the muffling speaker, and is connected to the canceling sound emitted from the positive pressure surface of the muffling speaker. The means is characterized by being arranged at a position where the canceling sound radiated from the negative pressure surface cancels out each other.

(Function) When used under external noise, a canceling sound is emitted from the muffling speaker into the user's ear cavity, and the external noise that the user hears is canceled out by the opposite phase of this canceling sound. Ru.

By the way, in the canceling sound emitted from the muffling speaker, the sound from the positive pressure side and the sound from the negative pressure side of the muffling loudspeaker are out of phase with each other. Therefore, at a position acoustically equidistant from the positive pressure surface and the negative pressure surface, that is, at the position where the monitoring microphone is provided in the present invention, the canceling sounds from both the positive pressure and negative pressure surfaces cancel each other out.
It becomes 0.

Therefore, when used in an environment with external noise, ideally only the external noise will be input to the monitor microphone. Howling can be prevented from occurring.

Moreover, the monitor microphone does not disturb the sound field of the muted speaker.

Further, the position where the canceling sounds from the positive pressure side and the negative pressure side cancel each other out and become zero can be a position close to the muffling speaker as long as it is acoustically equidistant from both sides.

Therefore, it is possible to input only the same external noise that the user hears at a position close to the silencer speaker.

(Example) Embodiments of the present invention will be described below based on the drawings.

First, the configuration will be explained.

FIG. 1 is an overall diagram showing the configuration of an active noise canceller according to a first embodiment of the present invention, and in the figure, 1
2 is a muffling speaker that generates and emits a predetermined canceling sound into the ear cavity of the user; 2 is a monitoring microphone that inputs external noise; and 3 is a canceling sound that is approximately in opposite phase to the input sound of the monitoring microphone. 6. The noise canceling circuit outputs a canceling sound generation signal to the silence speaker l so that the noise canceling circuit outputs a canceling sound generation signal to the silence speaker l. The silence speaker l is supported by a housing la,
Equipped with diaphragm ib, magnet lc, coil ld^
ing. That is, the surface 1e of the diaphragm lb is the positive pressure surface of the silencing speaker l, and when a canceling sound generation signal is applied to the coil ld, the diaphragm lb generates and radiates a canceling sound into the ear cavity E of the user. ing.

Note that the space between the diaphragm 1b and the ear cavity E as well as the muffling speaker 1 are covered with a cover (not shown) in the form of a so-called headphone.

Further, the surface If of the housing la is a negative pressure surface of the muffling speaker l, and emits sound having an opposite phase to the sound emitted from the diaphragm lb.

The monitoring microphone 2 is located close to the side surface of the muffling speaker 1, and is configured to separate the canceling sound emitted from the diaphragm surface 1e (positive pressure surface) of the muffling speaker 1 and the canceling sound emitted from the housing surface if (negative pressure surface). It is placed in a position where the sound cancels out each other. Note that the position where the monitoring microphone 2 is provided is not limited to a position close to the muffling speaker I, but is preferably within a distance equal to or less than the diameter of the diaphragm Ib.

The noise canceling circuit 3 includes a preamplifier 3b that pre-amplifies the input sound of the monitor microphone 2, a filter circuit 3C that removes unnecessary frequency ranges from the canceled sound,
It is formed to include a power amplifier 3d and an inversion circuit 3e that shifts the phase of input sound by 180 degrees.

Next, the effect will be explained.

When used in an environment with external noise such as inside the cockpit of an aircraft, the external noise is input by the monitor microphone 2, and the noise canceling circuit 3 forms a canceling sound generation signal with a phase opposite to that of the input signal. Based on this, a canceling sound is emitted from the muffling speaker I toward the user's ear cavity E, and the external noise that the user hears is canceled out by the opposite phase of the canceling sound.

By the way, when a canceling sound is emitted from the muffling speaker l, as shown in FIG.
At the same time, a canceling sound is also emitted from the housing surface (negative pressure surface) If, and both canceling sounds a and b have opposite phases to each other as shown in the figure. Therefore, this is the position where the monitor microphone 2 is provided.
At a position acoustically equidistant from the diaphragm surface (positive pressure surface) le and the housing surface (negative pressure surface) If, both surfaces 1e
, the cancellation sounds a and b from 1f cancel each other out, and the result is 0.
becomes.

Therefore, with the monitor microphone 2, the external noise C(
(Fig. 2) is input. This prevents the occurrence of howling that occurs when the original signal and the feedback signal of an integral multiple of 360° are added, and prevents the deterioration of silencing performance due to the occurrence of howling. The effect of being able to do this is obtained.

Moreover, the monitor microphone 2 has a diaphragm 1.
Since it is placed on the side, away from the front surface of the emission of the canceling sound from speaker b, it does not disturb the sound field of the muffling speaker l, so that stable sound muffling performance can be obtained up to the high frequency range.

Moreover, since the monitoring microphone 2 is placed close to the side of the muffling speaker 1, it is possible to input only the same external noise that the user hears. Therefore, stable sound deadening performance can be obtained.

A second embodiment of the present invention, shown in FIG. 3, will be described next.

This second embodiment has three muffled speakers 21°21.2
1 are arranged on the same circumference and attached to the support frame 4, and the monitor microphone 2 is arranged at the center of the circumference. Note that the silencer speaker 21 is of a type having a cone 21b as a vibrating membrane.

In this way, the number of mute speakers may be one or more.

Although the embodiment has been described above based on the drawings, the specific configuration is not limited to this embodiment, and even if there is a design change within the scope of the gist of the present invention, it is included in the present invention. .

For example, a mixer for manually inputting other microphones and external signals may be provided to the noise canceling circuit, and necessary conversation sounds, ejection sounds, etc. may be output from a muffled speaker.

(Effects of the Invention) As explained above, in the active noise canceller of the present invention, the monitoring microphone is placed at a side position of the muffling speaker, and the canceling sound emitted from the positive pressure surface of the muffling speaker is Since it is arranged at a position where the canceling sound radiated from the negative pressure surface and the canceling sound emitted from the negative pressure surface cancel each other out, the following effects can be obtained at the same time.

■ Monitoring microphones can input only external noise without inputting canceling sound, which has the effect of preventing howling from occurring and improving silencing performance.

(2) The monitoring microphone and its supporting member do not disturb the sound field of the muffling speaker, which provides the effect of stably muffling external noise up to a high frequency range.

■ By placing a monitoring microphone close to the silencer speaker and the user's ear cavity, it is possible to input external noise that is equal to the external noise that the user can hear, thereby eliminating the need for feedback control microphones and circuits. This has the effect of simplifying the configuration.

[Brief explanation of the drawing]

Fig. 1 is an overall diagram showing the configuration of the active noise canceller according to the first embodiment of the present invention, and Fig. 2 shows the positive pressure stage and negative pressure stage of the silencing speaker and external noise by the active noise canceller according to the first embodiment. FIG. 3 is a perspective view showing the main structure of an active noise canceller according to a second embodiment of the present invention. le...Diaphragm surface (positive pressure side) If...Housing surface (negative pressure side) 2...Monitoring microphone 3...Noise canceling circuit 21...Muffling speaker

Claims (1)

[Claims] 1) A muffling speaker that generates and radiates a predetermined canceling sound into the user's ear cavity, a monitoring microphone that inputs external noise, and a cancellation that is in opposite phase to the input sound of the monitoring microphone. In an active noise canceller, the active noise canceler is equipped with a noise canceling circuit that outputs a canceling sound generation signal to a silencing speaker to generate a sound, and is configured to muffle external noise by canceling the canceling sound that is in the opposite phase to the external noise. The active device is characterized in that the monitoring microphone is disposed on a side of the muffled speaker at a position where the canceling sound emitted from the positive pressure side and the canceling sound emitted from the negative pressure side of the muffled speaker cancel each other out.・Noise canceller.