An active noise reduction system (2) comprising an electroacoustic plasma transducer (5) for mounting in an installation structure and an acoustic sensing system (11). The electroacoustic plasma transducer comprises a plasma electrode arrangement (6) including a collector electrode (8) and a corona electrode (9), and a control system (7) connected to the plasma electrode arrangement for supplying power to the plasma electrode arrangement. The control system comprises a controller (12), and a amplification circuit (13). The acoustic sensing system is connected to the control system providing a measurement signal of an environmental sound to control the output of the electroacoustic transducer for reducing noise. The control system comprises a filter implementing a control transfer function θ(ω) based on a model of the electroacoustic plasma transducer.

Recording, manipulating, distributing and creating sound pressure waves in one or more media by employing an apparatus that transfers the energy between photons and particles of the media is disclosed. An exemplary apparatus comprises one or more lasers and an isotropic or anisotropic medium for photon processing and distribution. An exemplary method comprises determining the target locations for sound pressure wave recording, manipulating or creation; transmitting photons to the target locations; transferring photon energy to media particles to create or manipulate a sound pressure wave; or transferring energy of media particles to photons for recording or manipulating a sound pressure wave.

Methods and apparatus to communicate via a welding arc are disclosed. An example welding-type power supply includes a power converter, a weld monitor, and an arc modulator. The power converter outputs welding power to sustain a welding-type arc at a welding-type torch. The weld monitor monitors one or more aspects of a weld performed using the welding-type arc and the welding-type torch, and selects an audio message based on the one or more aspects. The arc modulator configured to modify the welding-type arc to output the selected audio message as a plasma speaker.

Methods and apparatus to communicate via a welding arc are disclosed. An example welding-type power supply includes a power converter, a weld monitor, and an arc modulator. The power converter outputs welding power to sustain a welding-type arc at a welding-type torch. The weld monitor monitors one or more aspects of a weld performed using the welding-type arc and the welding-type torch, and selects an audio message based on the one or more aspects. The arc modulator configured to modify the welding-type arc to output the selected audio message as a plasma speaker.

One example configuration may include one or more ionizing electrodes, one or more receiving electrodes, the one or more ionizing electrodes and the one or more receiving electrodes are exposed to a fluid to generate ions and movement in the fluid within an electric field, and the configuration also includes one or more position adjustment mechanisms to adjust an inter-electrode distance gap between the one or more ionizing electrodes and the one or more receiving electrodes.

One example configuration may include one or more ionizing electrodes, one or more receiving electrodes, the one or more ionizing electrodes and the one or more receiving electrodes are exposed to a fluid to generate ions and movement in the fluid within an electric field, and the configuration also includes one or more position adjustment mechanisms to adjust an inter-electrode distance gap between the one or more ionizing electrodes and the one or more receiving electrodes.

Methods and apparatus to communicate via a welding arc are disclosed. An example welding-type power supply includes a power converter, a weld monitor, and an arc modulator. The power converter outputs welding power to sustain a welding-type arc at a welding-type torch. The weld monitor monitors one or more aspects of a weld performed using the welding-type arc and the welding-type torch, and selects an audio message based on the one or more aspects. The arc modulator configured to modify the welding-type arc to output the selected audio message as a plasma speaker.

Methods and apparatus to communicate via a welding arc are disclosed. An example welding-type power supply includes a power converter, a weld monitor, and an arc modulator. The power converter outputs welding power to sustain a welding-type arc at a welding-type torch. The weld monitor monitors one or more aspects of a weld performed using the welding-type arc and the welding-type torch, and selects an audio message based on the one or more aspects. The arc modulator configured to modify the welding-type arc to output the selected audio message as a plasma speaker.

A speaker (10) comprises an enclosure (8) defining an internal volume (11); and at least one sound generator (7), the sound generator (7) comprising one or more surfaces defining an air-path conduit (15) through which air operably passes in and out of the internal volume. The sound generator (7) further comprises a plurality of electrodes comprising at least one air-exposed electrode (1, 4) and at least one insulated electrode (2, 3). A voltage source (6) is configured to generate an electrical field between the at least one air-exposed electrode (1, 4) and the at least one insulated electrode (2, 3, 70) to operatively generate a plasma proximal (100) to the plurality of electrodes and within the air-path conduit (15).

An electroacoustic transducer for generating an audible acoustic signal includes a base, a cathode having a plurality of cathode discharge elements arranged into an array of cathode discharge elements disposed around an axis associated with the cathode and mounted on the base, and an anode having a plurality of anode discharge elements arranged into an array of anode discharge elements disposed around an axis associated with the anode and mounted on the base. An inter-electrode space separates the cathode and the anode. A first circuit portion connects the cathode to a voltage source, and a second circuit portion connects the anode to the voltage source. The cathode and anode discharge elements extend from the base toward the inter-electrode space. Respective arrays of the cathode and anode are opposite of each other with respect to the inter-electrode space and axisymmetric such that the cathode axis is aligned with the anode axis.