Patent Application
20200193955
The present invention relates to a noise cancellation device, and in particular, to an active noise cancellation device, a circumaural earphone, and an in-ear earphone.
According to a most common conventional noise suppression technology, noise suppression is implemented in most cases by passively absorbing noise energy by using various sound absorption materials. However, in a low frequency status, a wavelength of a sound is far greater than a thickness of a general sound absorption material. For example, a sound whose frequency is 100 Hz has a wavelength about 3.4 meters at sea level and under the normal atmospheric temperature. Therefore, transmission of a low frequency sound can be effectively blocked only by using a very thick and heavy sound absorption material. However, for general application, this passive noise cancellation technology is not ideal for a capability of isolating a low-frequency noise. Therefore, during practical application, according to a passive noise cancellation method, a balance often needs to be achieved in a problem of contradiction between effective cancellation of a low-frequency noise and a sound absorption material, wherein the sound absorption material may occupy very large space and have a large size and a high cost.
To be capable of effectively resolving the foregoing problem, an active noise control (ANC) theory using an extra sound source to cancel a noise has been widely studied and developed in depth for years. A basic principle of an active noise control system is mainly using a waveform synthesis principle to generate an anti-noise sound wave having a waveform the same as a waveform of an original noise, the intensity equal to the intensity of the original noise, and a phase difference of 180 degrees from the original noise, so that the anti-noise sound wave has destructive interference to the original noise, thereby achieving an objective of reducing noise amplitude.
Taiwan patent number I609363 discloses an active noise cancellation correction system and a speaker apparatus. Referring to
However, a main noise cancellation range of the general active noise cancellation earphone is a medium and low frequency range of 50 Hz to 2 KHz, and a reduction effect for a high frequency noise is not good. In addition, even if a sound in an environment can be heard, the related art does not mention that only some frequency band is heard. Therefore, in a noisy environment, to filter out most noises and hear a voice or even a sound in a particular frequency band, usually digital signal processing needs to be performed. The cost is high for the protecting a general explosive sound is implemented through high-speed digital signal processing in circuit designs.
Therefore, it needs to provide an active noise cancellation device having an acoustic filter, to resolve the foregoing problem.
An objective of the present invention is to provide an active noise cancellation device having an acoustic filter, and the active noise cancellation device combines an active noise cancellation unit and the acoustic filter.
To achieve the foregoing objective, the present disclosure discloses an active noise cancellation device having an acoustic filter includes: a casing including a first channel and a second channel, wherein a channel length of the first channel is greater than a channel length of the second channel; an active noise cancellation unit including an external microphone, disposed outside the casing, and configured to detect an ambient noise, wherein a location of the external microphone corresponds to a location of the first external end of the first channel; a speaker disposed at a second external end of the second channel, and configured to output a phase-inverted signal of the ambient noise; and a noise cancellation processor electrically coupling to the external microphone and the speaker; and an acoustic filter, disposed inside the first channel.
The active noise cancellation device having an acoustic filter in the present invention combines the active noise cancellation unit (including the external microphone, the speaker, and the noise cancellation processor) and the acoustic filter to form a band pass filter, so that a sound in a particular frequency domain can pass through the casing to enter the auditory canal of the listener. For a noise passing through the first channel of the casing and to the auditory canal, the active noise cancellation unit evenly reduces noise intensity based on a frequency when the frequency is less than 1 KHz. In addition, for the noise passing through the first channel of the casing and to the auditory canal, the acoustic filter enhances a noise cancellation effect as the frequency increases while the frequency is greater than 1 KHz.
To make the foregoing objective, feature, and characteristic of the present invention clearer and easier to be understood, related embodiments of the present invention are described in detail in the following with reference to the drawings.
The active noise cancellation unit includes: an external microphone 111, a speaker 112, and a noise cancellation processor 113. The external microphone 111 is disposed outside the casing 10, and is configured to detect an ambient noise, wherein a location of the external microphone 111 corresponds to a location of the first external end 1012. For example, the location of the external microphone 111 is close to the location of the first external end 1012. The speaker 112 is disposed at the second external end 1021, and is configured to output a phase-inverted signal of the ambient noise, wherein the second external end 1021 is a closed end. The noise cancellation processor 113 is electrically coupled to the external microphone 111 and the speaker 112, and is configured to perform phase-inverted processing on the ambient noise detected by the external microphone 111, and then transmit the ambient noise to the speaker 112. The speaker 112 outputs the phase-inverted signal of the ambient noise through the second channel 102, so that the ambient noise transmitted into the auditory canal 81 of the listener 8 through the first channel 101 can be reduced.
For example, the channel length of the first channel 101 is greater than the channel length of the second channel 102, and the location of the external microphone 111 is close to the location of the first external end 1012. Therefore, the noise cancellation processor 113 can perform signal and phase adjustment based on a difference between a time taken by the phase-inverted signal of the ambient noise output by the speaker 112 to pass through the second channel 102 and a time taken by the ambient noise to pass through the first channel 101. In this way, a preferable superposition effect is achieved for the ambient noise and the phase-inverted signal of the ambient noise in an area outside exits of the first internal end 1011 of the first channel 101 and the second internal end 1021 of the second channel 102, thereby achieving a preferable effect of noise cancellation.
The acoustic filter 12 is disposed inside the first channel 101. Referring to
For example, the acoustic filter 12 includes a thin film therein, and the thin film can attenuate intensity of an incoming sound. The acoustic filter 12 can apparently enhance an attenuation effect for an over 1 KHz high-frequency noise passing through the first channel 101 of the casing 10 and to the auditory canal 81 of the listener 8.
Therefore, the active noise cancellation device 1 having an acoustic filter in the present invention combines the active noise cancellation unit (including the external microphone 111, the speaker 112, and the noise cancellation processor 113) and the acoustic filter 12 to form a band pass filter, so that a sound in a particular frequency domain can pass through the casing to enter the auditory canal 81 of the listener 8. For a noise passing through the first channel 101 of the casing 10 and to the auditory canal 81, the active noise cancellation unit evenly reduces noise intensity based on a frequency when the frequency is less than 1 KHz. In addition, for the noise passing through the first channel 101 of the casing 10 and to the auditory canal 81, the acoustic filter 12 enhances a noise cancellation effect as the frequency increases while the frequency is greater than 1 KHz.
In particular, the active noise cancellation unit can have a relatively low noise cancellation effect in a range of 80 Hz to 520 Hz, enabling a main frequency of a voice of a person to pass through the active noise cancellation unit. If a noise whose frequency is over 1 KHz is greatly reduced by using the acoustic filter together, loudness of the voice of the person can be highlighted when a design is performed in coordination with an equal loudness contour (for example, ISO 226).
The active noise cancellation device having an acoustic filter in the present invention combines the active noise cancellation unit and the acoustic filter, so that a degree of freedom for adjusting a noise cancellation curve is increased, reducing development costs of processing software and hardware of the active noise cancellation. For a general active noise cancellation unit, noise cancellation processing in a low frequency domain is easy, but noise cancellation processing in a high frequency domain is difficult. However, for a general acoustic filter, a sound filtering effect is relatively good at the high frequency. Therefore, a band pass filter can be formed by combining the two, to allow a voice or an alarm sound to pass through in a noisy environment.
Referring to
In still another embodiment, the active noise cancellation unit 11 further includes a sound signal component 115. The sound signal component 115 (such as a wireless signal receiver) is electrically coupled the noise cancellation processor 113, and is configured to receive an external sound signal (such as music or a voice) and provide the external sound signal to the noise cancellation processor 113.
Similarly, the active noise cancellation device having an acoustic filter in the present invention combines the active noise cancellation unit (including the external microphone 111, the speaker 112, and the noise cancellation processor 113) and the acoustic filter 12 to form a band pass filter, so that a sound in a particular frequency domain can pass through the casing to enter the auditory canal 81 of the listener 8. For a noise passing through the first channel 101′ of the casing 10 and to the auditory canal 81, the active noise cancellation unit evenly reduces noise intensity based on a frequency when the frequency is less than 1 KHz. In addition, for the noise passing through the first channel 101′ of the casing 10 and to the auditory canal 81, the acoustic filter 12 enhances a noise cancellation effect as the frequency increases when the frequency is greater than 1 KHz.
The active noise cancellation device having an acoustic filter in the present invention combines the active noise cancellation unit and the acoustic filter, so that a degree of freedom for adjusting a noise cancellation curve is increased, reducing development costs of processing software and hardware of the active noise cancellation. For a general active noise cancellation unit, noise cancellation processing in a low frequency domain is easy, but noise cancellation processing in a high frequency domain is difficult. However, for a general acoustic filter, a sound filtering effect is relatively good at the high frequency. Therefore, a band pass filter can be formed by combining the two, to allow a voice or an alarm sound to pass through in a noisy environment.
The active noise cancellation device 1′ having an acoustic filter in the second embodiment of the present invention can alternatively be applied to the circumaural earphone or the in-ear earphone.
The foregoing descriptions are only preferred implementations or embodiments for presenting technical means used for resolving a problem in the present invention, and are not used for limiting the implementation scope of the patent in the present invention. In other words, all equivalent changes and modifications complying with a literal meaning of the patent application scope of the present invention or performed based on the patent scope of the present invention fall within the patent scope of the present invention.
