An acoustic panel is provided that includes a perforated first skin, a second skin and a corrugated structure. The corrugated structure is between and is connected to the perforated first skin and the second skin. The corrugated structure includes a first baffle, a first septum, first material and second material that is configured with the first material. The first baffle is formed by an uninterrupted portion of the first material. The first septum is formed by a portion of the second material that is exposed through an interruption in the first material.

An earphone system comprises at least one earphone configured to be inserted in an ear of a user, wherein each of the at least one earphone comprises at least one sound reproduction unit, and a remote unit that is separate from each of the at least one earphone, wherein the remote unit comprises at least one microphone configured to capture ambient sound. The remote unit is configured to evaluate, analyze and/or process the ambient sound captured by the at least one microphone, to determine one or more of at least one ambient sound parameter, at least one control parameter, and at least one control command, based at least on the evaluation, analysis and/or processing of the ambient sound, and to send the at least one ambient sound parameter, the at least one control parameter and/or the at least one control command to the at least one earphone.

A silencer comprises a main air guide tube provided with an air guide channel; the main air guide tube comprises an air inlet end and an air outlet end; both ends of an assistant air guide tube are connected with an outer wall of the main air guide tube, and the assistant air guide tube comprises a guide section and a reflux section; the guide section is provided with an air inlet, and the air inlet is communicated with the air guide channel; the reflux section is provided with an air outlet, and the air outlet is communicated with the air guide channel.

A speaker comprises a housing, a transducer residing inside the housing, and at least one sound guiding hole located on the housing. The transducer generates vibrations. The vibrations produce a sound wave inside the housing and cause a leaked sound wave spreading outside the housing from a portion of the housing. The at least one sound guiding hole guides the sound wave inside the housing through the at least one sound guiding hole to an outside of the housing. The guided sound wave interferes with the leaked sound wave in a target region. The interference at a specific frequency relates to a distance between the at least one sound guiding hole and the portion of the housing.

A speaker comprises a housing, a transducer residing inside the housing, and at least one sound guiding hole located on the housing. The transducer generates vibrations. The vibrations produce a sound wave inside the housing and cause a leaked sound wave spreading outside the housing from a portion of the housing. The at least one sound guiding hole guides the sound wave inside the housing through the at least one sound guiding hole to an outside of the housing. The guided sound wave interferes with the leaked sound wave in a target region. The interference at a specific frequency relates to a distance between the at least one sound guiding hole and the portion of the housing.

A speaker comprises a housing, a transducer residing inside the housing, and at least one sound guiding hole located on the housing. The transducer generates vibrations. The vibrations produce a sound wave inside the housing and cause a leaked sound wave spreading outside the housing from a portion of the housing. The at least one sound guiding hole guides the sound wave inside the housing through the at least one sound guiding hole to an outside of the housing. The guided sound wave interferes with the leaked sound wave in a target region. The interference at a specific frequency relates to a distance between the at least one sound guiding hole and the portion of the housing.

A speaker comprises a housing, a transducer residing inside the housing, and at least one sound guiding hole located on the housing. The transducer generates vibrations. The vibrations produce a sound wave inside the housing and cause a leaked sound wave spreading outside the housing from a portion of the housing. The at least one sound guiding hole guides the sound wave inside the housing through the at least one sound guiding hole to an outside of the housing. The guided sound wave interferes with the leaked sound wave in a target region. The interference at a specific frequency relates to a distance between the at least one sound guiding hole and the portion of the housing.

A noise suppression unit is provided and configured to reduce noise generated by gas flow, where the suppression unit includes a body including an inlet port and an outlet port, a central passage structure extending between a first end and a second end of the body, at least one layer of a first absorbing material on the central passage structure and at least one layer of a second absorbing material on the central passage structure, where the first absorbing material and the second absorbing material are different. Sound waves generated by gas flow through the suppression unit passes through the central passage structure and the at least one layer of the first absorbing material and the at least one layer of the second absorbing material to reduce the sound waves and thereby the noise generated by the gas flow.

A takeoff location and a landing location are received for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors. An autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle is determined based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function. A set of one or more desired forces or moments is determined for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory. A plurality of motor control signals is determined for the plurality of rotors based at least in part on the set of one or more desired forces or moments.

A takeoff location and a landing location are received for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors. An autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle is determined based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function. A set of one or more desired forces or moments is determined for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory. A plurality of motor control signals is determined for the plurality of rotors based at least in part on the set of one or more desired forces or moments.