JP2014149455A - Space muffler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a space muffler that is free from trouble in that there is a place where "large sound is heard" in a space apart from a muffle area α, by muffling only the muffle area α.SOLUTION: A space muffler comprises: an ultrasonic frequency loudspeaker 1 configured to generate ultrasonic wave toward a muffle area α; a microphone 2 configured to detect a sound wave reaching the muffle area α; inverse phase signal generating means 3 configured to generate an inverse phase signal for nullifying a sound wave β to be muffled; ultrasonic wave modulating means 4 configured to modulate an inverse phase signal to ultrasonic frequency; and a power amplifier 5 configured to drive an ultrasonic loudspeaker by the ultrasonic modulation signal. Sound wave β to be muffled, which reaches the muffle area α, is nullified by at least inverse phase pressure change γ', which is included in an ultrasonic wave, or inverse phase sound pressure change γ, resulting from demodulation of inverse phase pressure change γ' in air. Thus, only the muffle area α can be muffled using ultrasonic wave having intense directivity.

Description

  The present invention relates to a spatial silencer that silences a predetermined area (silence area α) in a space.

As a technique for silencing a predetermined silencing area α set in a space, a technique disclosed in Patent Document 1 is known.
This spatial muffler eliminates this “silence target sound wave β (for example, noise)” that has reached the silence area α, and cancels this “silence target sound wave β” with an “anti-phase sound pressure fluctuation γ ( A dynamic speaker that directly generates sound waves of an audible frequency as a means for generating “anti-phase sound pressure fluctuations γ”. D is used.

Problems of the prior art will be described with reference to FIG.
3 indicates a sound source of “silent sound wave β”. Further, “the sound wave β to be muffled” and “the sound pressure fluctuation γ in the opposite phase” in FIG. 3 represent a dense wave.

The “anti-phase sound pressure fluctuation γ” generated by the dynamic speaker D is emitted not only in the silence region α but also around the dynamic speaker D. For this reason, in the space outside the silencing area α, “the sound wave β to be silenced” and “the sound pressure fluctuation γ in the opposite phase” are synthesized, and many places where the sound becomes loud are generated. In FIG. 3, “the sound wave β to be silenced” and “the sound pressure fluctuation γ of the opposite phase” are combined and indicated by “hatching where the sound is reduced”, and conversely “× where the sound is increased” It shows with.
As described above, in the conventional technique, it is not possible to mute only the muffling region α, and in a space outside the muffling region α, there is a problem that “a place where the sound can be heard” is created.

Japanese Patent Laid-Open No. 08-123447

  The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a space that can mute only the silencing area α and avoid the problem that a “sound can be heard loudly” in a space outside the silencing area α. The object is to provide a silencer.

The spatial silencing device of the present invention is configured to transmit the “sound wave β to be silenced” that reaches the silencing region α.
(A) “Anti-phase pressure fluctuation γ ′ (inaudible to humans)” included in “Ultrasonic waves obtained by modulating an anti-phase sound pressure fluctuation γ (cancellation sound) into an ultrasonic frequency”,
(B) or “anti-phase pressure fluctuation γ ′” included in the ultrasonic wave is demodulated in the air “anti-phase sound pressure fluctuation γ (sound to humans)”,
It cancels out by at least one of the above.

Specifically, “an ultrasonic wave obtained by modulating a sound pressure fluctuation γ (cancellation sound) having an antiphase to an ultrasonic frequency” includes “an antiphase pressure fluctuation γ ′” even if it cannot be heard by the human ear. This “anti-phase pressure fluctuation γ ′” cancels “the sound wave β to be silenced”.
Also, like a parametric speaker that utilizes the nonlinearity of air viscosity, “anti-phase pressure fluctuation γ ′” contained in the ultrasonic wave is demodulated in the air, and “anti-phase sound pressure fluctuation γ” that can be heard by humans. Even in this case, since the ultrasonic wave has high directivity with high straightness, it is possible to limit the arrival range of the “anti-phase sound pressure fluctuation γ” only to the silencing region α.

  In this way, it is possible to mute only the silencing region α by at least one of “antiphase pressure fluctuation γ ′” and “antiphase sound pressure fluctuation γ” generated by ultrasonic waves with strong directivity, and the silencing area α It is possible to avoid the disadvantages of the prior art that can create “a place where the sound can be heard loudly” in a space outside the distance.

(A) It is explanatory drawing of the silence in space, (b) It is a block diagram of a spatial silencer (Example 1). (A) Characteristic diagram of “actual sound pressure of pressure fluctuation γ ′ to mute” and “sound pressure actually heard by human ear”, (b) explanatory diagram of the measuring device (Example 1). It is explanatory drawing of the muffling in space (conventional example).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The following examples show specific examples, and it goes without saying that the present invention is not limited to the examples.

[Example 1]
A first embodiment will be described with reference to FIGS.
The space silencer of this embodiment performs a silence of a predetermined silence area α in the space, and is mounted on a vehicle in this embodiment.
Specifically, the spatial silencer of this embodiment sets a silencing area α near the head of an occupant (driver or the like) sitting on a seat (specifically, a spatial area including the left and right ears of the occupant). The “silence target sound wave β (noise etc.)” that reaches the silencing area α is silenced.

  The space silencer of this embodiment has, for example, “when the window glass is opened (that is, when external noise or wind noise intrudes)”, “sound pressure of vehicle interior noise (sound pressure at the passenger's ear, etc.). It is activated when “exceeds a predetermined value” or “when the occupant desires to mute (when manually operated)”.

The spatial silencer is configured to transmit a “sound wave β to be silenced” that reaches the silence area α.
・ "Antiphase pressure fluctuation γ '" included in the ultrasonic wave,
・ Or “anti-phase pressure fluctuation γ ′” included in the ultrasonic wave demodulated in air “anti-phase sound pressure fluctuation γ”,
It cancels out by at least one of the above.

A schematic configuration of the space silencer will be described with reference to FIG.
The space silencer installed in the vehicle
(A) an ultrasonic speaker 1 for generating an ultrasonic wave toward the silence area α;
(B) a microphone 2 (abbreviation of microphone) that converts a sound wave that reaches the silencing region α into an electrical signal (audio signal);
(C) an anti-phase signal generator 3 for generating an anti-phase signal (an electric signal of an anti-phase sound pressure fluctuation γ) for canceling the “sound wave β to be silenced” based on the electric signal detected by the microphone 2; ,
(D) an ultrasonic modulation means 4 for modulating the antiphase signal generated by the antiphase signal generating means 3 into an electric signal having an ultrasonic frequency;
(E) a power amplifier 5 (for example, a class B amplifier or a class D amplifier) that drives the ultrasonic speaker 1 with an electrical signal having an ultrasonic frequency modulated by the ultrasonic modulation means 4;
It is configured with.

  The ultrasonic speaker 1 is an ultrasonic generator that generates a sparse wave having an ultrasonic wavelength toward the silencing region α (specifically, the ear of the occupant sitting on the seat), and an electric signal (drive of the power amplifier 5). Signal) is converted into air vibration, and air vibration having a frequency (20 kHz or higher) higher than the human audible band is generated.

The structure and type of the ultrasonic speaker 1 (ultrasonic generator) is not limited. However, when a specific example is disclosed, a plurality of piezoelectric elements capable of generating ultrasonic waves are collectively arranged in an array. It is arranged with the direction of ultrasonic irradiation directed toward the passenger's head (occupant's ear).
The mounting position of the ultrasonic speaker 1 is not limited, but is set in advance when the sound source A of “the sound wave β to be silenced” is set in advance (for example, when a window glass is opened and noise enters). The ultrasonic speaker 1 is disposed between the sound source A and the occupant's head, and the direction of ultrasonic irradiation is directed toward the occupant's head (ear).

The microphone 2 is a converter that converts sound waves into electrical signals (audio signals).
(I) It may be one that is arranged inside the silencing area α (for example, one that is arranged in a “headrest” or the like close to the ears of the passenger)
(Ii) For those arranged outside the muffling area α (for example, “between the sound source A and the ultrasonic speaker 1”, “near the ultrasonic speaker 1”, “a ceiling or seat close to the head of the passenger”, etc. It may be arranged).
Note that the type of the microphone 2 (dynamic microphone, condenser microphone, etc.) is not questioned, and an acoustic wave having an audible frequency that causes noise for the passenger can be converted into an electric signal. Further, the directivity of the microphone 2 is not questioned.

An example of the antiphase signal generating means 3 will be described.
As described above (i), when the microphone 2 is disposed inside the silencing area α and the microphone 2 is disposed between the ultrasonic speaker 1 and the head of the occupant, the microphone 2 is “the sound wave to be silenced”. Since the sound pressures of both “β” and “sound wave generated by the ultrasonic speaker 1” are received, an electric signal synthesized from the microphone 2 is output.
In this case, the anti-phase signal generating means 3 outputs an electric signal (an anti-phase signal) so that the electric signal output from the microphone 2 is minimized.

On the other hand, as described in (ii) above, when the microphone 2 is disposed outside the silencing area α, the microphone 2 detects only the “sound wave β to be silenced”, and the microphone 2 detects “electricity of the sound wave β to be silenced”. Signal "is output.
In this case, the anti-phase signal generating means 3 converts the electric signal of the “sound wave β to be silenced” detected by the microphone 2 into an electric signal having an anti-phase (an anti-phase signal) and outputs the electric signal. If there is a phase shift between the “sound wave β to be silenced” and the “anti-phase pressure fluctuation γ ′” due to a distance difference between the microphone 2 and the ultrasonic speaker 1, the phase shift is corrected. A delay circuit (such as a simple CR circuit) is provided to eliminate the phase shift.

The ultrasonic modulation means 4 modulates (ultrasonic modulation) the antiphase signal generated by the antiphase signal generation means 3 to an ultrasonic frequency (frequency of 20 kHz or higher).
In addition, the ultrasonic modulation technique in the ultrasonic modulation means 4 is not limited. For example,
-AM modulation (amplitude modulation) that modulates the anti-phase signal generated by the anti-phase signal generating means 3 into "amplitude change at a predetermined ultrasonic frequency (voltage increase / decrease change)" may be used.
Even if PWM modulation (pulse width modulation) is used to modulate the antiphase signal generated by the antiphase signal generating means 3 to “pulse width change (pulse generation time width) at a predetermined ultrasonic frequency”. good.

(Effect 1 of Example 1)
The operation of the spatial silencer will be described.
In the situation where the spatial silencer operates, when “sound wave β to be silenced” is generated from the sound source A toward the silence region α (in the direction of the occupant's head), the “silence” is directed from the ultrasonic speaker 1 toward the silence region α. Ultrasonic waves obtained by modulating the “anti-phase sound pressure fluctuation γ” that cancels the target sound wave β to the ultrasonic frequency are applied.
As a result, “anti-phase pressure fluctuation γ ′” that is not audible to the human ear contained in the ultrasonic waves cancels “the sound wave β to be silenced”. In FIG. 1A, “a portion where the sound is reduced is indicated by hatching”.

  Also, like a parametric speaker that uses the nonlinearity of air viscosity, the “anti-phase pressure fluctuation γ ′” contained in the ultrasonic wave is demodulated in the air, and the “anti-phase sound pressure fluctuation γ” is Even if it is provided so that it can be heard, since the ultrasonic wave has high directivity with strong straightness, it is possible to limit the reach range of the “anti-phase sound pressure fluctuation γ” only to the silencing region α (the silencing target range).

As described above, the spatial silencer can silence only the silencing region α by at least one of “anti-phase pressure fluctuation γ ′” and “anti-phase sound pressure fluctuation γ” generated by ultrasonic waves having strong directivity. In addition, it is possible to avoid the disadvantages of the prior art that can make “a place where the sound can be loudly heard” in a space outside the silencing area α.
That is, it is possible to silence only the occupant to whom the ultrasonic speaker 1 is directed without causing discomfort to other occupants.

(Effect 2 of Example 1)
Here, the solid line X in FIG. 2A indicates the frequency characteristic of “pressure fluctuation γ ′” that is included in the ultrasonic wave and silences, and the solid line Y in FIG. 2A “is actually audible to human ears”. The frequency characteristics of “sound pressure of demodulated sound” are shown.
The “sound pressure of the demodulated sound that can actually be heard by the human ear” is measured using the measuring apparatus shown in FIG. That is, the solid line Y uses a dummy head H having an earlobe H1 and an external auditory canal H2, and a diaphragm of the measurement microphone H3 is disposed in the back of the ear canal (the eardrum position), and the ultrasonic speaker 1 is disposed in front of the dummy head H. Then, the “sound pressure of the demodulated sound that can actually be heard by the human ear” was measured.

As indicated by the solid line X, the attenuation of the “pressure fluctuation γ ′” that mutes at a low frequency is small.
On the other hand, as indicated by the solid line Y, the demodulated sound is less likely to be heard by humans as the frequency is lower. This is because the shape factor due to the human ear canal, etc., and the lower the frequency, the longer the distance is required to demodulate (self-modulation of the antiphase pressure fluctuation γ 'contained in the ultrasound becomes an audible sound in the air) Is due to.
As is clear from comparison between the solid line X and the solid line Y, the lower the frequency of the sound, the higher the effect of performing the mute without being heard by the occupant.

  One ultrasonic speaker 1 may radiate ultrasonic waves to the left and right ears of one occupant, and two ultrasonic speakers 1 may radiate ultrasonic waves to the left and right ears of one occupant. .

  The spatial silencer may be used in combination with another device (for example, a device that gives “sound information useful for driving” to the driver).

  The space silencer may be equipment equipment fixed to the vehicle, or equipment detachable from the vehicle.

  The space silencer may be combined with the handsfree of the mobile phone, and only the sound different from the call may be silenced by the space silencer.

α Sound deadening region β Sound wave to be silenced γ Sound pressure fluctuation in opposite phase γ 'Pressure fluctuation in opposite phase

Claims (3)

In a spatial silencer that silences a predetermined silencing area (α) in space,
In this spatial silencer, the sound wave (β) to be silenced that reaches the sound deadening region (α) has a reverse phase pressure fluctuation (γ ′) included in the ultrasonic wave, or a reverse wave included in the ultrasonic wave. A spatial silencer characterized in that the phase pressure fluctuation (γ ′) is canceled out by at least one of the reverse phase sound pressure fluctuations (γ) demodulated in the air. In the space silencer according to claim 1,
This space silencer
An ultrasonic speaker (1) for generating ultrasonic waves toward the silencing region (α);
A microphone (2) that converts a sound wave that reaches the silencing region (α) into an electrical signal;
An antiphase signal generating means (3) for generating an antiphase signal for canceling the sound wave (β) to be silenced based on the electric signal detected by the microphone (2);
Ultrasonic modulation means (4) for modulating the anti-phase signal into an electric signal of ultrasonic frequency;
A power amplifier (5) for driving the ultrasonic speaker (1) by an electric signal having an ultrasonic frequency modulated by the ultrasonic modulation means (4);
A spatial muffler characterized by comprising: The space silencer according to claim 2,
This space silencer is mounted on a vehicle,
The ultrasonic speaker (1) irradiates ultrasonic waves toward the head of an occupant sitting on a seat.

Images