An unmanned aerial vehicle (UAV) may emit masking sounds during operation of the UAV to mask other sounds generated by the UAV during operation. The UAV may be used to deliver items to a residence or other location associated with a customer. The UAV may emit sounds that mask the conventional sounds generated by the propellers and/or motors to cause the UAV to emit sounds that are pleasing to bystanders or do not annoy the bystanders. The UAV may emit sounds using speakers or other sound generating devices, such as fins, reeds, whistles, or other devices which may cause sound to be emitted from the UAV. Noise canceling algorithms may be used to cancel at least some of the conventional noise generated by operation of the UAV using inverted sounds, while additional sound may be emitted by the UAV, which may not be subject to noise cancelation.

An apparatus for synthesizing an engine sound according to an embodiment of the present invention comprises: a memory for storing a plurality of explosion sound samples corresponding to a plurality of cylinders included in a cylinder module, respectively; a sound output unit; and a processor for calculating explosion periods of the plurality of cylinders, and overlapping the plurality of samples stored according to the calculated explosion periods on explosion noises of corresponding cylinders, respectively, to output a synthesized virtual engine sound through the sound output unit.

A work machine includes a housing. The housing at least partly houses a machine. The housing has an opening. The work machine includes a path leading into the housing from the opening. The work machine includes a controller and a speaker. The controller is configured to cause a speaker to output a control sound for reducing operating noise. The operating noise is generated in the housing by motion of the machine and propagates in the path from a source of the operating noise to the opening. The speaker is arranged so that the control sound propagates in the path with its wavefront parallel to a wavefront of the operating noise that propagates in the path.

A method for operating a centrifugal separator associated with a prime mover and/or a working machine. The centrifugal separator comprises at least one rotatably mounted rotor that can be rotated at a variable speed via a drive controlled by a control unit. The method is characterized in that the speed of the rotor is controlled according to the sound emissions of the prime mover and/or according to the sound emissions of the working machine.

An active device for attenuating the acoustic emissions of an aircraft turbojet engine includes circulation conduits for a pressurized air flow rate supplying rotary elements each having a pulsation system for the delivered air. The rotary elements are controlled in amplitude and phase and deliver, to outlet diffusers, a pulsed air flow rate with a pulsation at the frequency of the noise to be attenuated having an amplitude and a phase adjusted according to a local feedback law with microphones to attenuate the radiated acoustic power.

An air moving device (AMD) includes a housing that dampens noise and routes airflow. The AMD housing includes a focal-bearing surface that has an associated focal point. The focal-bearing surface routes airflow through the AMD housing and reflects and concentrates noise to the focal point. The AMD housing further includes a noise dampening structure at the focal point to reduce, absorb, and/or dampen the concentrated noise. Because the noise is concentrated, a relatively smaller size noise dampening structure may effectively or adequately reduce or dampen AMD noise. The smaller size noise dampening structure relatively reduces airflow impedance. As such, AMD housing may provide for both reduced AMD noise and relatively reduced airflow impedance therein and/or therefrom.

A noise cancellation system for a vehicle audio system may include at least one input sensor arranged on an engine of a vehicle configured to provide an input signal indicative of acceleration or vibration detected at the engine and a processor. The processor may be programmed to receive a reference signal, apply at least one order tracking to reference signal, generate an error signal based on an output signal, and apply at least one other order tracking filter to the error signal to provide engine order cancelation of the input signal.

The present disclosure provides an active noise reduction method, a system, and a new energy vehicle. The active noise reduction method includes: obtaining a frequency of a high-frequency noise signal in an acoustic environment, constructing and generating a harmonic masking signal according to the frequency of the high-frequency noise signal, where the harmonic masking signal includes a harmonic signal and a masking signal, and the harmonic signal is a subharmonic wave of the high-frequency noise signal, and inputting the harmonic masking signal into a sound playback apparatus for playback to output a noise reduction construction sound, and performing noise reduction on the acoustic environment.

An example audio device includes: communication circuitry configured to receive a first signal representative of an audible sound associated with a welding-type waveform; audio processing circuitry configured to generate, based on the first signal, a welding noise cancellation signal to produce destructive interference to the audible sound; and a transducer configured to output the destructive interference using the welding noise cancellation signal.

An active vibratory noise reduction system includes: a canceling vibratory sound generator; an error signal detector for detecting a canceling error between the canceling vibratory sound and a vibratory noise as an error signal; and an active vibratory noise controller for generating, based on the error signal, a control signal for controlling the canceling vibratory sound generator. The active vibratory noise controller is provided with a stability improving unit including: a correction value generation unit for generating an error signal correction value by multiplying a reaching control sound estimation value by a stabilization coefficient; an error signal correction unit for correcting the error signal by using the error signal correction value to generate a corrected error signal, and a stabilization coefficient updating unit for sequentially updating the stabilization coefficient based on the corrected error signal and the reaching control sound estimation value by using an adaptive algorithm.