The invention relates to a damper for reducing pulsations in a gas turbine, which includes an enclosure, a main neck extending from the enclosure, a spacer plate disposed in the enclosure to separate the enclosure into a first cavity and a second cavity and an inner neck with a first end and a second end, extending through the spacer plate to interconnect the first cavity and the second cavity. The first end of the inner neck remains in the first cavity and the second end remains in the second cavity. A flow deflecting member is disposed proximate the second end of the inner neck to deflect a flow passing through the inner neck. With the solution of the present invention, as a damper according to embodiments of the present invention operates, flow field hence damping characteristic in the second cavity constant regardless the adjustment of the spacer plate in the enclosure.

This application describes an apparatus (300) for monitoring for blockage of an acoustic (110) port of a microphone device (100). The apparatus has a spectrum peak detect block (301) for receiving a microphone signal (S.sub.MIC) and determining, from the microphone signal, a resonance frequency (f.sub.H) and a quality factor (Q.sub.H) of a resonance (202) associated with the acoustic port. A condition monitoring block (302) is configured to determine any change in resonance frequency and quality factor and to determine a blockage status for the microphone based on said detect changes. The condition monitoring block identifies a change in blockage status if there is a change in quality factor.

The present disclosure provides an acoustic output device. The acoustic output device includes a first acoustic assembly and a second acoustic assembly. The first acoustic assembly may comprise a first diaphragm, and the first diaphragm vibrates to produce a first sound. The second acoustic assembly may comprise a second diaphragm, the second diaphragm vibrates to produce a second sound, wherein at least a portion of the second diaphragm may be disposed around the first diaphragm. Vibrational phases of the first diaphragm and the second diaphragm may be opposite in a target frequency range, and the second sound may interfere with the first sound to produce a directional acoustic field pointing to a target direction.

A microphone includes a microphone case having an opening in front of the microphone case accommodating a microphone unit in the opening; a piece of double-sided adhesive tape whose back side is attached along the opening of the front side of the microphone case; and a filter adhered to a front side of the piece of the double-sided adhesive tape so as to cover the opening of the microphone case, wherein the piece of the double-sided adhesive tape is provided with sound introduction holes which introduces sound waves to the microphone unit through the filter. This configuration enables to provide a microphone easily and in a short time having desired frequency response characteristics without raising costs.

Examples are disclosed herein that relate to avoiding mechanical noise from operation of a vibrational output device. One example provides a computing device including a processor and a storage device storing instructions executable by the processor to vary a drive voltage applied to a vibrational output device, receive acoustic data, and from the acoustic data detect a noise signal from the vibrational output device as the drive voltage is varied. The instructions are further executable to, based upon the detected noise signal, select an operational drive voltage for the vibrational output device, and operate the vibrational output device using the operational drive voltage.

A speaker apparatus includes a sound guide and a pair of speakers mounted to the sound guide. The sound guide includes a first guide portion configured to guide a sound generated from any one of the pair of speakers in a first direction; and a second guide portion configured to guide a sound generated from the other speaker in a second direction that is plane-symmetric with respect to the first direction. Each of the first and second guide portions includes an opening forming portion formed in an end portion of the corresponding portion and including an opening configured to output a sound generated by the pair of speakers, and a slit forming portion including a slit configured to output a sound, together with the opening, wherein the slit is extended from one side of the opening.

A noise control system for a ducted rotor assembly, the ducted rotor assembly including a hub, a duct, and two or more blades coupled to the hub and supported by the duct. The noise control system including a microphone configured to receive a sound input generated by the ducted rotor assembly, the microphone configured for association with the hub; a speaker unit configured to generate a cancellation noise, the speaker configured for association with the hub; and a controller operably connected to the microphone and the speaker unit, the controller configured to selectively adjust harmonics of the cancellation noise to reduce an acoustic signature of the ducted rotor assembly. In another aspect, there is provided a rotorcraft with a ducted rotor assembly in a tail portion including a noise control system. In a third aspect, there is a method of reducing an acoustic signature of a ducted rotor assembly.

A microphone transducer is provided, the microphone transducer comprising a housing and a transducer assembly supported within the housing and defining an internal acoustic space. The transducer assembly includes a magnet assembly, a diaphragm disposed adjacent the magnet assembly and having a front surface and a rear surface, and a coil attached to the rear surface of the diaphragm and capable of moving relative to the magnet assembly in response to acoustic waves impinging on the front surface. The transducer assembly further includes a primary port establishing acoustic communication between the internal acoustic space and an external cavity at least partially within the housing, and a secondary port located at the front surface of the diaphragm.

A free-standing, portable speaker system including (1) at least a first cabinet enclosure of a first size generally rectangular in shape and having six sides; wherein the at least first cabinet enclosure includes at least a first driver and at least a second driver; and a planar partition soundboard member; wherein the partition soundboard member is adapted for enhancing the quality of sound from said first cabinet enclosure; and (2) at least a third driver releasably attached to the first cabinet enclosure; wherein the at least third driver in combination with the at least first and second drivers enclosed in the at least first cabinet enclosure enhances the quality of sound from said speaker system.

A device includes a coil and magnetic mass movable next to the coil in response to vibrations to generate a back electromotive force signal. An amplifier generates, from the back EMF signal, a vibration signal. A processing device converts the vibration signal to time-frequency domain signal as two-dimensional matrix of frequencies mapped against time slots. Pre-process voiced data of the time-frequency domain signal to generate a reduced-noise signal. Average signal values within a frequency window, and that exist at a first time slot, of the reduced-noise signal to generate a complex frequency coefficient. Shift the frequency window across the frequencies to generate multiple complex frequency coefficients that identify speech energy concentration. Replicate signal values at a fundamental frequency within the voiced data to multiple harmonic frequencies to generate an expanded voice source signal. Combine the speech energy concentration with the expanded voice source signal to recreate original speech.