JP7486038B2 - Noise reduction device - Google Patents

Description

The present invention relates to a noise reduction device.

Conventionally, in order to keep the interior of a vehicle comfortable, various technologies have been proposed to reduce the intrusion of noise into the vehicle interior. Examples of such technologies include a passive method (see, for example, Patent Document 1) in which the vehicle is equipped with sound-absorbing or sound-proofing materials to suppress the intrusion of noise into the vehicle interior, and an active method (see, for example, Patent Document 2) in which sound-cancelling waves (sound waves of the opposite phase) corresponding to the target noise are emitted to cancel the noise.

JP 2020-106689 A Japanese Patent Application Laid-Open No. 07-199954

In the above passive method, the sound absorbing effect of the sound absorbing material is roughly proportional to its volume, and the sound insulation material is roughly proportional to its mass and sound volume and frequency, so that in vehicles where there is a limit to the space available for installing the sound absorbing or sound insulation material or where weight reduction is required, it is not yet possible to achieve a sufficient sound insulation effect. In the above active method, however, in order to invert the phase of the noise acquired by a sensor or the like and deliver it accurately to the vehicle cabin, it is difficult to control the speed of the calculation and the position and direction of the sound absorbing wave generation, which requires multiple sound absorbing radiators (e.g. speakers), and depending on the location in the vehicle cabin, the sound pressure of the noise is amplified, causing discomfort to the passengers.

The technology disclosed here has been developed in consideration of the current state of the prior art, and aims to provide a new noise reduction device that reduces the discomfort caused by noise entering the vehicle cabin.

One of the purposes of noise reduction in vehicles is to reduce the discomfort felt by passengers due to noise, and typical examples of this noise include road noise, wind noise, engine noise, etc. Although various technologies aimed at muffling these noises have been developed in the past, the inventor has conducted extensive research and found that, for example, it is preferable for passengers to hear a certain amount of noise in order to perceive the driving situation of the vehicle. In other words, the technology disclosed herein provides a noise reduction device. This noise reduction device is a noise reduction device that reduces the discomfort felt by passengers due to noise entering the vehicle compartment, and includes a sound reproduction unit that reproduces a reproduction sound based on a reproduction sound signal for the vehicle compartment, a vibration generation unit that is provided on a plate-shaped vehicle compartment component that defines the vehicle compartment and vibrates the vehicle compartment component, and a control unit that controls the vibration generation unit to vibrate the vehicle compartment component, thereby generating a mitigating sound from the vehicle compartment component to mitigate the noise. The control unit is configured to generate the mitigating sound so as to increase the sound pressure of some of the frequency components of the propagation noise propagating into the vehicle cabin through the vehicle cabin component that overlap with the frequency components of the reproduction sound when the sound reproduction unit is reproducing the reproduction sound.

According to the above configuration, when the sound reproducing unit is reproducing a certain type of reproduction sound, the vibration generating unit generates a mitigating sound from the vehicle cabin component. As a result, the propagation noise propagating into the cabin through the vehicle cabin component is transformed into a sound that blends in with the reproduction sound by the mitigating sound being superimposed on it. In addition, since the mitigating sound is emitted into the vehicle cabin from the same vehicle cabin component that emits the propagation noise, it travels the same path as the noise before reaching the passenger's ears. In other words, while being emitted and propagating within the vehicle cabin, the mitigating sound and the propagation noise are affected by attenuation, reflection, amplification, etc. in exactly the same way. As a result, the mitigating sound is not affected differently from the propagation noise depending on the shape and size of the vehicle cabin, the position and material of the equipment, etc., and the discomfort of the propagation noise can be reduced in the same way at any point in the vehicle cabin.

In a preferred embodiment of the noise reduction device, the control unit is configured to generate the mitigation sound so as to increase the sound pressure of the frequency components between peaks in the frequency spectrum of the propagation noise. Propagation noise usually includes sounds of various frequency components, and peaks of various sizes may appear across a wide frequency range in the frequency spectrum that shows the relationship between the frequency and the sound pressure. The psychological effect of a sound (sound wave) on human hearing differs not only depending on the sound pressure (typically, the loudness of the sound) but also on the waveform of the frequency spectrum. According to the above configuration, the propagation noise is changed to a relatively broad peak by superimposing the mitigation sound, so that the sound pressure between any two peaks in the frequency spectrum is increased (for example, averaged to the same extent as the peaks). This reduces the tonal characteristics of the propagation noise, and the unpleasantness of the propagation noise can be reduced.

In a preferred embodiment of the noise reduction device, the control unit is configured to generate the mitigation sound so as to increase the sound pressure of the frequency components between the fundamental frequency in the propagation noise and the frequency of the second harmonic of the fundamental frequency. Natural sounds are composed of a combination of multiple harmonics, and by increasing the sound pressure between the peak of the fundamental frequency and the peak of the second harmonic, the tonal characteristics of the propagation noise can be effectively reduced.

In a preferred embodiment of the noise reduction device, the control unit generates the mitigation sound so as to increase the sound pressure of harmonic frequencies that are integer multiples of the fundamental frequency of the propagation noise among the frequency components of the reproduction sound. Natural sounds are composed of a combination of multiple harmonic overtones, and humans tend to feel that chords of sounds of the same scale that differ by one octave are "pleasant" because there is no frequency deviation. According to the above configuration, the vehicle cabin component reproduces, in addition to the propagation noise, sounds contained in the reproduction sound that are of the same scale as the propagation noise. As a result, the propagation noise and the reproduction sound are reproduced in the vehicle cabin as a consonant sound, reducing the discomfort of the noise.

In a preferred embodiment of the noise reduction device, the vehicle compartment component is at least one selected from the group consisting of door trim, cowl side trim, instrument panel, deck side trim, pillar garnish, floor carpet, and window glass. The vehicle compartment component is generally plate-shaped and is located in a location that is closely related to the causes of typical noises such as road noise, wind noise, and rain noise. Therefore, it is preferred to have these vehicle compartment components function as sub-speakers to effectively reduce vehicle noise.

In a preferred embodiment of the noise reduction device, the vehicle equipped with the vehicle cabin is a land vehicle that includes a road contact member, and the noise reduction unit pre-stores the frequency characteristics of the propagated noise for at least one element selected from the group consisting of road surface conditions, weather, traveling speed, and the degree of deterioration of the road contact member. Vehicle cabin components have a vibration frequency specific to the component depending on their material, shape, and relationship with the noise source, and emit a noise specific to the component into the vehicle cabin. Therefore, by investigating and storing in advance the frequency characteristics of the propagated noise under various conditions for the target vehicle cabin component, the noise reduction unit can generate a more appropriate mitigating sound under each condition. This provides a noise reduction device that can more effectively reduce vehicle noise.

In a preferred embodiment of the noise reduction device, the control unit is configured to measure the frequency characteristics of the propagated noise in real time, and based on the measurement results, to cause the vibration generating unit to generate the mitigating sound from the vehicle compartment component. Depending on the material, shape, and relationship with the noise source, the vehicle compartment component has a vibration frequency specific to that component, and emits a noise specific to that component into the vehicle compartment. Therefore, by examining the frequency characteristics of the propagated noise for the target vehicle compartment component in real time, the noise mitigation unit can generate a more appropriate mitigating sound in real time. This provides a noise reduction device that can more effectively reduce vehicle noise.

The technology disclosed herein can provide a new noise reduction device that reduces the discomfort caused by noise entering the vehicle cabin.

FIG. 1 is a diagram showing a configuration of a vehicle equipped with a noise reduction device according to an embodiment; 1 is a block diagram of a noise reduction device according to an embodiment; Frequency spectrum of door trim vibration caused by road noise A frequency spectrum of the reproduced sound according to one embodiment is superimposed on FIG. Frequency spectrum of door trim vibration when mitigating sound is generated from the door trim during road noise FIG. 4 is a diagram showing a frequency spectrum of the reproduced sound according to another embodiment superimposed on FIG. 3. Frequency spectrum of door trim vibration when mitigating sound is generated from the door trim during road noise FIG. 4 is a diagram showing a frequency spectrum of the reproduced sound according to another embodiment superimposed on FIG. 3. FIG. 4 is a diagram showing a frequency spectrum of the relaxation sound according to another embodiment superimposed on FIG.

<Embodiment>
An embodiment of the technology disclosed herein will be described with reference to Fig. 1 to Fig. 9, taking as an example a noise reduction device 10 mounted on a vehicle 1 as an example of a vehicle. The symbols F, Rr, U, and D shown in each figure indicate the front and rear in the vehicle travel direction, and the upper and lower in the vertical direction (up and down direction), respectively. However, the above directions are merely defined for convenience and should not be interpreted in a restrictive manner.

As shown in FIG. 1, a vehicle 1 includes wheels 2, 2 that are driven to rotate and run the vehicle 1, a floor panel 3 that forms part of the vehicle 1's framework and forms the floor surface of the passenger compartment, a roof panel 4 that forms the ceiling surface, and pillars 5 that support the ceiling surface against the floor surface. Vehicle doors 6, window glass 7, and the like are attached to these vehicle frameworks to define a passenger compartment space inside the vehicle 1. The passenger compartment is equipped with vehicle interior materials such as cowl side trim 2A, floor carpet 3A, roof trim 4A, pillar garnish 5A, door trim 6A, an instrument panel (not shown), and deck side trim to improve livability and design. These vehicle interior materials surround the passenger compartment to form the design surface of the passenger compartment, and also function as passive sound absorption and insulation materials to increase the heat retention of the passenger compartment.

Here, the members (e.g., vehicle interior materials, etc.) that define the passenger compartment are formed into various shapes and vibrate when shocks and vibrations are transmitted when the vehicle 1 runs on land, and the vibrations are radiated into the passenger compartment as noise. For example, in the vehicle 1, the vibrations and contact sounds (road noise) generated when the tires 2B (one example of a road contact member) attached to the wheels 2, 2 come into contact with the road surface are easily radiated into the passenger compartment through the cowl side trim 2A, floor carpet 3A, door trim 6A, deck side trim (not shown), etc. In addition, engine sounds are easily radiated into the passenger compartment through the instrument panel (not shown) arranged between the gasoline engine room at the front of the vehicle 1 and the passenger compartment. And wind noises and rain noises caused by air and rain hitting the vehicle 1 while it is running are easily radiated into the passenger compartment as noise through the door trim 6A, pillar garnish 5A, window glass 7, etc. The vibration behavior of cabin components may vary depending on the vehicle structure, the shape and material of each cabin component, etc., but as a typical example, the frequencies of the cabin components shown below due to external shocks and vibrations are approximately as follows:

Therefore, the vehicle 1 is equipped with a noise reduction device 10 to reduce the discomfort caused by such noise. This noise reduction device 10 is generally configured with an audio device 12 (an example of a sound reproduction unit), a vibration control unit 14, and a vibration generating unit 16, and causes the above-mentioned vehicle interior components to function as sub-speakers, and when playing music or other sounds from the audio device 12, the vehicle interior components also generate mitigating sounds that mitigate noise propagating into the vehicle cabin through the vehicle interior components (hereinafter referred to as propagating noise). Each component of the noise reduction device 10 and its operation are described below.

The audio device 12 is a device that can reproduce sound into the vehicle cabin based on a digital or analog reproduction sound signal, and the audio device 12 in this example can be configured with a general acoustic device (also called a stereo device, etc.) as shown in FIG. 2, for example. Although not limited to this, the audio device 12 typically includes a conversion unit 12A that converts the sound to be transmitted into an electrical signal that can be digitally processed, a processing unit 12B that processes the converted electrical signal as necessary, an amplifier 12C that amplifies the processed or unprocessed electrical signal, a speaker unit 12D that converts the electrical signal amplified by the amplifier into acoustic vibrations and radiates them into the vehicle cabin, and a control unit 12E that controls each of these units to reproduce sound.

The conversion unit 12A is an element in the audio device 12 that generates an electrical signal corresponding to the sound that is to be transmitted (radiated) to the outside, and may be a microphone that converts various sounds into an electrical signal, a player that converts sound information including a playback sound signal into an electrical signal by playing media that records the sound information, or a receiving device that receives a playback sound signal sent by wire or wirelessly from an external device, etc., and converts it into an electrical signal as necessary.

The processing unit 12B has, for example, a gain function that amplifies the sound components of the multiple input electrical signals (reproduced sound signals in the form of electrical signals) divided by sound quality (for example, frequency), a mixer function that mixes them, an equalizer function that performs tone correction, etc., and a panning function that outputs electrical signals to multiple speakers and changes the ratio. The processing unit 12B can convert the multiple reproduced sound signals sent in the form of electrical signals from the conversion unit 12A into, for example, a sound quality preferred by the user.

The amplifier 12C is an element that amplifies the electrical signal processed by the processing unit 12B or the unprocessed electrical signal, and amplifies the electrical signal so as to achieve the sound pressure level desired to be output from the speaker unit 12D. The amplifier 12C may be integrated with the speaker unit 12D, or may be separate from the speaker unit 12D. The speaker unit 12D is an element that returns the electrical signal amplified by the amplifier 12C to raw sound and radiates it into the vehicle cabin, and one or more of the amplifiers may be provided in one audio device 12.

The control unit 12E is an element that controls the operation of each part of the audio device 12, and is mainly composed of a microcomputer having, for example, a CPU, RAM, ROM, etc., and is connected to the above-mentioned parts 12A to 12D so that they can communicate with each other via wires or wirelessly. The control unit 12E is basically configured to convert the playback sound signal into an electric signal by the conversion unit 12A, amplify the electric signal by the amplifier 12C so that a predetermined sound pressure (volume) can be realized, and radiate the amplified electric signal in the speaker unit 12D as acoustic vibrations into the vehicle cabin to reproduce the sound. Note that, for example, when the sound reproduction unit 13 includes multiple speaker units 12D, the control unit 12E can, for example, divide the playback sound signal into multiple sound components for each sound quality in the processing unit 12B, and then change the type and ratio of the sound components to be output for each of the multiple speaker units 12D. The control unit 12E can also change the sound pressure of the sound to be output, in other words, the amplification rate of the amplifier 12C, for each of the multiple speaker units 12D. Furthermore, the control unit 12E may be configured to store the processing contents of the processing unit 12B and the sound quality and sound pressure of the reproduced sound radiated from each speaker unit 12D as multiple control modes in advance so that, for example, high-quality sound can be radiated according to the size, shape, configuration, etc. of the vehicle interior, and to reproduce sound from each speaker unit 12D based on the control mode selected by the user.

The vibration generating unit 16 is an element provided in a plate-shaped vehicle compartment component that defines the vehicle compartment and vibrates the vehicle compartment component, and is an example of a control unit in the technology disclosed herein. Examples of the vehicle compartment component include, but are not limited to, the vehicle interior materials surrounding the vehicle compartment described above (typically, the cowl side trim 2A, floor carpet 3A, roof trim 4A, pillar garnish 5A, door trim 6A, instrument panel, deck side trim, and window glass 7, etc.). In addition, as the vibration generating unit 16, for example, a vibration generating device that can generate mechanical vibrations based on an electric signal can be used. As such a vibration generating unit 16, for example, a piezo film speaker, an exciter, a vibration motor, an electromagnetic vibration device, etc. that can convert electric energy into kinetic energy can be used. The vibration generating unit 16 vibrates the vehicle compartment component to which it is attached, allowing the vehicle compartment component to function as a speaker. The vibration generating unit 16 may be attached to any one of the vehicle interior materials, or to each of two or more vehicle interior materials. If the vehicle interior component is a vehicle interior material, the vibration generating unit 16 should be attached to the back side (the surface facing the outside of the vehicle interior) of the vehicle interior material. If the vehicle interior component is a window glass 7, the vibration generating unit 16 should be attached to the mounting frame of the window glass 7 or inside the frame panel (a position that is not exposed to the outside, such as the part between the inner panel and the outer panel).

The vibration control unit 14 is an element that controls the operation of the vibration generating unit 16 to vibrate the vehicle compartment components, and provides the vibration generating unit 16 with an electrical signal corresponding to the mitigation sound for mitigating the above-mentioned propagation noise. The vibration control unit 14 may be provided inside the audio device 12, or may be provided in a position other than the audio device 12 (for example, near the vibration generating unit 16). When the vibration control unit 14 is provided inside the audio device 12, the vibration control unit 14 may be an element of the control unit 12E. When the vibration control unit 14 is provided separately from the audio device 12, the vibration control unit 14 is mainly composed of, for example, a microcomputer having a CPU, RAM, ROM, etc., and is connected to the vibration generating unit 16 and the audio device 12 via wired or wireless communication. The vibration control unit 14 sends, for example, an electrical signal corresponding to the mitigation sound to the vibration generating unit 16, which causes the vibration generating unit 16 to vibrate the vehicle compartment components, and the sound corresponding to the above-mentioned electrical signal (i.e., the mitigation sound) is reproduced from the vehicle compartment components together with the propagation noise. When creating an electrical signal corresponding to the relaxation sound, the vibration generating unit 16 may appropriately use the conversion unit 12A, processing unit 12B, amplifier 12C, etc. of the audio device 12.

In the following, the dampening sound generated by the vibration control unit 14 will be described using as an example a case in which the vehicle compartment component is a door trim 6A as shown in FIG.
3 is a schematic diagram showing a frequency spectrum of the vibration of the door trim 6A caused by the shock and vibration of the vehicle 1 while it is running, where the horizontal axis shows the frequency in octave bands, and the vertical axis shows the sound pressure level. The door trim 6A generates a propagation noise over a frequency range of about 100 to 1000 Hz, for example, as shown in Table 1, due to the vibration of the door trim 6A itself based on the impact between the tire and the road surface while the vehicle is running. Here, the door trim 6A has a natural frequency, and the center frequency of the vibration of the door trim 6A when the vehicle 1 runs on a general paved road surface (in other words, the road noise propagating into the passenger compartment via the door trim 6A) is about 160 Hz. Note that natural sounds including propagation noise are composed of a combination of a fundamental tone and its overtones, and it can be confirmed that the door trim 6A of this example also contains a fundamental tone (scale: Re# (D#3)) of about 160 Hz and a second overtone (scale: Re# (D#4)) of about 315 Hz. In this technology, when we simply say "the vibration frequency of the door trim 6A," it means the frequency of the fundamental tone. In addition, since the loudness of a sound sensed by a human is not proportional to a multiple of a reference sound pressure but is proportional to its logarithm, the unit of sound pressure on the vertical axis in Figures 3 to 9 is decibels [dB] (logarithmic display).

Here, in a known active noise canceller (ANC), a canceling vibration (cancelling sound) that cancels such road noise is applied to, for example, the door trim. In contrast, the present inventor has noted that road noise does not necessarily need to be eliminated because it includes information related to the operation of the vehicle 1, such as the surface condition of the road surface and tires, the installation condition, and the driving speed. However, for example, when listening to music or the like through the audio device 12 of the vehicle 1, the road noise may interfere with the music and the road noise may be felt as unpleasant. Therefore, when listening to music or the like through the audio device 12, the present inventor has prepared a mitigating sound that reduces the discomfort of the noise propagating through the door trim 6A for each vehicle compartment component to which the vibration generating unit 16 is attached (here, for example, the door trim 6A), and by playing the mitigating sound together with the noise from the door trim 6A, the noise reaches the ears of the occupants as a reduced discomfort. For example, music is played from the speaker unit 12D of the audio device 12, and the door trim 6A is used as a sub-speaker, so that a mitigating sound is played from the door trim 6A (sub-speaker) in addition to the propagation noise. The mitigating sound played from the door trim 6A (sub-speaker) in addition to the propagation noise may contain only a sound corresponding to a frequency component that mitigates the noise (the mitigating sound itself), or it may contain the mitigating sound and the music to be played. The technology disclosed herein proposes a new technological concept that has never been seen before, from the viewpoint of reducing discomfort from noise, rather than eliminating noise.

More specifically, when the audio device 12 is reproducing some kind of reproduced sound, the vibration control unit 14 generates a mitigation sound by increasing the sound pressure of some of the frequency components of the propagation noise propagating into the vehicle cabin through the door trim 6A that overlap with the frequency components of the reproduced sound. The solid line in FIG. 4 is a schematic representation of the frequency spectrum (relationship between frequency and sound pressure) of the music (reproduced sound) reproduced by the audio device 12. This reproduced sound generates a sound with a frequency that includes the frequency range of the propagation noise from the door trim 6A (approximately 100 to 1000 Hz). As shown in FIG. 4, for example, when the sound pressure of the music reproduced by the audio device 12 is greater than the sound pressure of the road noise, the mitigation sound can be such that the sound pressure of the frequency components between the peaks in the frequency spectrum of the propagation noise is increased, as shown in FIG. 5. The mitigating sound can be, for example, a sound that has the effect of increasing the sound pressure (hatched portion) of the frequency components (i.e., about 160 to 315 Hz) between the fundamental frequency of the propagation noise (here, about 160 Hz) and its second harmonic frequency (here, about 315 Hz) in the frequency spectrum of the road noise. Such a mitigating sound has the effect of smoothly filling the gap between the fundamental frequency and the second harmonic of the propagation noise with white noise or various colored noises with a roughly constant sound pressure. This can reduce the discomfort of the noise.

For example, as shown in FIG. 6, when the sound pressure of the music reproduced by the audio device 12 is smaller than the sound pressure of the propagation noise, the mitigation sound can be a sound that includes frequency components (i.e., about 160 to 315 Hz) between the fundamental frequency of the propagation noise (about 160 Hz in this case) and its second harmonic frequency (about 315 Hz in this case) in the frequency spectrum of the road noise, and has increased sound pressure (hatched portion) to fill the low sound pressure region formed in a valley between the fundamental frequency and the second harmonic. In addition, the mitigation sound may suppress a sudden drop in sound pressure in the high-frequency portion of the spectrum of the propagation noise, and compensate for the sound pressure to drop smoothly inversely proportional to the frequency. Such a mitigation sound has the effect of smoothly filling the sound at the high-frequency end of the spectrum of the propagation noise with colored noise such as Brownian noise. Such propagation noise and mitigation sound are reproduced in the vehicle cabin from the door trim 6A as sounds having frequency components that follow the outline shown in FIG. 7. This eliminates the discord between the noise and the playback sound, making the noise less unpleasant.

Note that while the frequency of the propagation noise propagating from the door trim 6A is low, i.e., a low-pitched sound, the music (sound) reproduced by the audio device 12 may be high-pitched and high-frequency sound, as shown in FIG. 8, compared to the road noise. Although not specifically shown, the music (sound) reproduced by the audio device 12 may not include sounds corresponding to a wide frequency range, as shown in FIG. 4 and FIG. 6. Furthermore, in the chord relationship between two different sounds, it is known that the fundamental tone and its overtones are in best harmony to form a consonant sound. Therefore, among the sounds constituting the music reproduced by the audio device 12, the frequency of the road noise (about 160 Hz in this case) may be set as the fundamental tone, and the sound corresponding to at least one of the fundamental tone and its overtones may be set as the mitigation sound. For example, specifically, as shown in FIG. 9, the sound of the frequency component (about 630 Hz in this case) that is the overtone of the road noise among the reproduced sounds may be set as the mitigation sound. At this time, the vibration control unit 14 extracts the frequency component of the fundamental tone or the harmonic tone (here, about 630 Hz component) of the sound corresponding to the reproduction sound signal of the music to be reproduced by using the fundamental tone of the sound (here, about 160 Hz) of the noise propagating into the vehicle interior through the door trim 6A as the fundamental tone, and can generate an electric signal corresponding to the relaxation sound, and can output this electric signal to the vibration generating unit 16 to reproduce it. If the relaxation sound is only a harmonic tone (for example, only a sound with a frequency of 630 Hz), such a sound is artificial and gives a strange feeling to the human ear, so the relaxation sound may be, for example, a sound over a frequency range having a width of about ±10 Hz of the harmonic tone frequency (see FIG. 9). In this case, the sound pressure of the relaxation sound is not particularly limited, but it is preferable that it is 0.5 times or more (for example, 0.7 times or more) and 1.5 times or less (for example, 1.2 times or less) the sound pressure of the fundamental tone of the noise. Such noise and relaxation sound are reproduced in the vehicle interior from the door trim 6A as a sound having a frequency component shown by the outline of FIG. 9. This makes the noise and the playback sound harmonious, reducing the discomfort caused by the noise.

Such a mitigating sound can be easily created by the vibration control unit 14 using the audio device 12. That is, the audio device 12 has a function of extracting and processing a specific frequency component from the sound corresponding to the playback sound signal. Therefore, the vibration control unit 14 may be configured to send a mitigating sound including at least one of the frequency components of the frequency F1 of the propagation noise propagating into the vehicle cabin through the vehicle cabin component, a signal component of the same frequency F1, and a signal component of a harmonic frequency F2 that is an integer multiple of the frequency F1 of the propagation noise, as an electric signal to the vibration generating unit 16 described later, and generate the mitigating sound from the vehicle cabin component. Although not limited to this, the vibration control unit 14 in this example may be functionally realized by the above-mentioned control unit 12E controlling the operation of the processing unit 12B. In that case, the control unit 12E is configured to generate an electric signal corresponding to the mitigating sound in the vibration control unit 14 and send the generated electric signal corresponding to the mitigating sound to the vibration generating unit 16.

Such a mitigating sound harmonizes the music etc. reproduced by the audio device 12 with the road noise, and is a sound of the reproduced music (i.e., a sound corresponding to the reproduced sound signal) that includes a harmonic frequency F2 (here, about 630 Hz) of the fundamental frequency F1 (here, about 160 Hz) of the road noise propagating into the vehicle interior through the door trim 6A. By reproducing such a mitigating sound from the door trim 6A, the propagation noise propagating through the door trim 6A and the music are harmonized by the action of the mitigating sound, and the discomfort of the noise perceived by the occupants is alleviated. In addition, at this time, the noise and mitigating sound emitted from the door trim 6A follow the same path, in other words, are equally affected by alteration such as reflection and attenuation, and are delivered to the ears of the occupants. As a result, it is also preferable in that the balance between the noise and mitigating sound is maintained equally at any position in the vehicle interior.

The effects of the present embodiment will be described. The noise reduction device 10 in this embodiment reduces the discomfort of the occupants caused by noise entering the vehicle cabin (carriage room), and includes an audio device 12 (sound reproduction unit) that reproduces music (reproduced sound) based on a reproduced sound signal into the vehicle cabin, a vibration generating unit 16 that is provided on a plate-shaped door trim 6A (one example of a vehicle cabin component) that defines the vehicle cabin and vibrates the door trim 6A, and a vibration control unit 14 (control unit) that controls the vibration generating unit 16 to vibrate the door trim 6A to generate a mitigating sound for mitigating noise from the door trim 6A. The vibration control unit 14 is configured to generate a mitigating sound so as to increase the sound pressure of some frequency components that overlap with the frequency components of the music among the frequency components of the propagation noise propagating into the vehicle cabin through the door trim 6A when the audio device 12 is playing music. With this configuration, the mitigating sound generated from the door trim 6A by the vibration generating unit 16 is superimposed on the noise propagating into the cabin through the door trim 6A, so that the road noise can be transformed into a sound that blends in with the reproduced sound. In addition, since the mitigating sound is emitted into the cabin from the same door trim 6A as the road noise, it travels the same path as the road noise before reaching the passengers' ears. In other words, while being emitted and propagating inside the cabin, the mitigating sound and the road noise are affected by attenuation, reflection, amplification, etc. in exactly the same way. As a result, the mitigating sound is not affected differently from the noise depending on the shape and size of the cabin, the position and material of the fixtures, etc., and the discomfort of the road noise can be reduced in the same way at any point in the cabin.

In the above embodiment, the vibration control unit 14 is configured to generate a mitigation sound so as to increase the sound pressure of the frequency components between the peaks in the frequency spectrum of the propagation noise. The vibration control unit 14 preferably generates a mitigation sound so as to increase the sound pressure of the frequency components between the fundamental frequency in the propagation noise and the frequency of the second harmonic of the fundamental frequency. In such a configuration, the space between the frequency component with the highest sound pressure and the frequency component with the second highest sound pressure in the propagation noise is filled with a mitigation sound that partially increases the sound pressure of the reproduced sound corresponding to that frequency range. The propagation noise is changed to have a relatively broad frequency peak. This reduces the tonal characteristics of the propagation noise, making it possible to reduce the discomfort of the propagation noise.

In the above embodiment, the vibration control unit 14 is configured to generate mitigating sounds so as to increase the sound pressure of harmonic frequencies that are integer multiples of the fundamental frequency of the propagation noise among the frequency components of the reproduced sound. Natural sounds are composed of a combination of multiple harmonics, and humans tend to feel that chords of sounds of the same scale that differ by one octave are "pleasant" because there is no frequency deviation. According to the above configuration, the vehicle compartment components such as the door trim 6A reproduce, in addition to the propagation noise, sounds of the same scale as the propagation noise that are included in the reproduced sound. As a result, the propagation noise and the reproduced sound are reproduced in the vehicle compartment as a consonant sound, reducing the discomfort of the noise.

<Other configurations>
The technology disclosed herein is not limited to those disclosed in the above embodiments, and for example, the following aspects are also included in the scope of the technology disclosed herein. Furthermore, the technology disclosed herein can be embodied in various modified aspects without departing from its essence.

(1) In the noise reduction device 10 of the above embodiment, the vibration control unit 14 is functionally realized by the control unit 12E of the audio device 12 (sound reproduction unit) controlling the operation of the processing unit 12B, or is mechanically configured by a microprocessor. However, the configuration of the vibration control unit 14 is not limited to this, and may be mechanically realized by other structures such as a digital signal processor (DSP).
(2) In the above embodiment, the door trim 6A as a vehicle compartment component is configured to reduce noise with a frequency of approximately 160 Hz that is based on vibrations and noise caused by the tires 2B of the vehicle 1 traveling on land contacting the road surface, but the technology disclosed herein is not limited to this configuration. The noise reduction device 10 may, for example, be configured to generate a mitigating sound using a vehicle compartment component other than the door trim 6A as a sub-speaker, or may be configured to generate a mitigating sound suitable for each vehicle compartment component using two or more vehicle compartment components as sub-speakers.

(3) In the noise reduction device 10, the vibration control unit 14 may check in advance the noise frequencies determined for each vehicle compartment constituent member for each environmental condition, such as road surface conditions, weather, traveling speed, and the degree of deterioration of the road contact surface members, and may store the noise frequencies for each environmental condition as a frequency table or the like. Furthermore, these environmental conditions may be composite environmental conditions that combine the above elements in various ways. In this case, a more appropriate noise frequency for the vehicle compartment constituent member can be obtained according to the environmental conditions of the vehicle 1, and the discomfort caused by the noise can be more effectively reduced.
(4) The noise reduction device 10 may additionally include a vibration sensor that measures the vibration frequency of the vehicle compartment constituent member. The vibration control unit 14 may be configured to measure the frequency characteristics of noise caused by vibration of the vehicle compartment constituent member in real time, generate an electrical signal corresponding to a mitigating sound that alleviates the discomfort of the noise based on the measurement result, and cause the vibration generating unit 16 to generate the mitigating sound from the vehicle compartment constituent member. This makes it possible to constantly obtain a more appropriate noise frequency for the vehicle compartment constituent member in accordance with the environmental conditions of the vehicle 1, and to more effectively reduce the discomfort of the noise.
(5) Although the vehicle exemplified in the above embodiment is a car, the noise reduction device 10 is not limited to being provided for cars, but may be provided for various other vehicles. For example, the noise reduction device 10 can be applied to vehicles such as trains and recreational vehicles as ground vehicles, airplanes and helicopters as flying vehicles, and ships and submarines as marine and underwater vehicles.

1...vehicle, 2...wheel (road contact member), 6...vehicle door, 6A...door trim (vehicle compartment component), 10...noise reduction device, 12...audio device, 14...noise mitigation section, 16...vibration generating section

Claims (6)

A noise reduction device for reducing discomfort felt by occupants due to noise entering a vehicle cabin, comprising:
a sound reproducing unit that reproduces a reproduction sound based on the reproduction sound signal for the vehicle cabin;
a vibration generating unit provided on a plate-shaped vehicle compartment constituent member that defines the vehicle compartment and vibrates the vehicle compartment constituent member;
a control unit that controls the vibration generating unit to vibrate the vehicle compartment component to generate a mitigating sound for mitigating the noise from the vehicle compartment component;
Equipped with
The control unit is configured to generate the mitigation sound so as to increase the sound pressure of a part of frequency components that overlap with the frequency components of the reproduction sound among frequency components of the propagation noise that propagates into the vehicle cabin through the vehicle cabin constituent member when the sound reproduction unit is reproducing the reproduction sound ,
The control unit generates the mitigation sound so as to increase the sound pressure of frequency components between peaks in a frequency spectrum of the propagation noise . The noise reduction device according to claim 1 , wherein the control unit generates the mitigation sound so as to increase a sound pressure of a frequency component between a frequency of a fundamental tone in the propagation noise and a frequency of a second harmonic of the fundamental tone. A noise reduction device for reducing discomfort felt by occupants due to noise entering a vehicle cabin, comprising:
a sound reproducing unit that reproduces a reproduction sound based on the reproduction sound signal for the vehicle cabin;
a vibration generating unit provided on a plate-shaped vehicle compartment constituent member that defines the vehicle compartment and vibrates the vehicle compartment constituent member;
a control unit that controls the vibration generating unit to vibrate the vehicle compartment component to generate a mitigating sound for mitigating the noise from the vehicle compartment component;
Equipped with
The control unit is configured to generate the mitigation sound so as to increase the sound pressure of a part of frequency components that overlap with the frequency components of the reproduction sound among frequency components of the propagation noise propagating into the vehicle cabin through the vehicle cabin constituent member when the sound reproduction unit is reproducing the reproduction sound,
The control unit generates the mitigation sound so as to increase the sound pressure of harmonic frequencies, which are integer multiples of a frequency of a fundamental tone in the propagating noise, among the frequency components of the reproduced sound. 4. The noise reduction device according to claim 1 , wherein the vehicle compartment component is at least one selected from the group consisting of a door trim, a cowl side trim, an instrument panel, a deck side trim, a pillar garnish, a floor carpet, and a window glass. The vehicle having the vehicle compartment is a land vehicle, the vehicle including a road contact member,
5. The noise reduction device according to claim 1, wherein the control unit pre-stores the frequency characteristics of the propagation noise for at least one element selected from the group consisting of road surface conditions, weather, driving speed , and a deterioration level of the road contact surface components. 6. The noise reduction device according to claim 1, wherein the control unit measures frequency characteristics of the propagation noise in real time, and causes the vibration generating unit to generate the mitigation sound from the vehicle cabin component based on the measurement results.

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