A playback device comprises an electroacoustic transducer; an acoustic waveguide in fluid communication with the transducer; and a housing delimiting an opening of the waveguide, the opening extending around an axis passing through the transducer. The opening may have a radial distance from the axis that varies with an azimuthal angle about the axis. An acoustic path length within the waveguide, between the transducer and the opening, is substantially constant and independent of azimuthal angle about the axis.

Active noise control (ANC), including active and adaptive noise cancellation (ANC) with non-voice-coil transducers having highly linear transfer functions, such as planar transducers, planar magnetic transducers, electro-static transducers, and piezo-electric transducers. This active and adaptive noise cancellation (ANC) may be used with: planar transducer headphones and earphones; open-backed and closed-back headphones and earphones; in-ear earphones, and phase plugs.

Active noise control (ANC), including active and adaptive noise cancellation (ANC) with non-voice-coil transducers having highly linear transfer functions, such as planar transducers, planar magnetic transducers, electro-static transducers, and piezo-electric transducers. This active and adaptive noise cancellation (ANC) may be used with: planar transducer headphones and earphones; open-backed and closed-back headphones and earphones; in-ear earphones, and phase plugs.

Phase plugs (70) and related audio devices (100, 105) and methods comprise various compression members (2), and guides (120) extending from the compression members (2) to tips (84), are configured such that central axes (93, 99) defined perpendicular to compression members (2) and/or diaphragms (94) are asymmetric and/or non-axisymmetric to the central axes (93, 99).

Phase plugs (70) and related audio devices (100, 105) and methods comprise various compression members (2), and guides (120) extending from the compression members (2) to tips (84), are configured such that central axes (93, 99) defined perpendicular to compression members (2) and/or diaphragms (94) are asymmetric and/or non-axisymmetric to the central axes (93, 99).

A sound sensing device may include a housing having a dome-shaped shell and a baseplate. The housing may have a symmetrically shaped perimeter. The dome-shaped shell may have an arcuate cross section characterized by tangent lines that monotonically increase in slope from a top of the dome-shaped shell toward a bottom of the dome-shaped shell. At least three sound ports may be provided between an interior volume of the housing and an exterior surrounding of the housing, and disposed symmetrically and peripherally about the perimeter of the housing. The sound ports may be located at most 1 cm above the support surface.

Non-axisymmetric and horn-free phase plugs [70] and related audio devices [100, 200] include various compression members [2] such that central axes [93, 99] are defined perpendicular thereto; and such that a guide [120] extends from a compression member [2] to a phase plug tip [84], wherein the guide [120] is non-axisymmetric to the central axes [93, 99].

Non-axisymmetric and horn-free phase plugs [70] and related audio devices [100, 200] include various compression members [2] such that central axes [93, 99] are defined perpendicular thereto; and such that a guide [120] extends from a compression member [2] to a phase plug tip [84], wherein the guide [120] is non-axisymmetric to the central axes [93, 99].

A display apparatus for visual and audio multiplexed display may include a directive display unit configured to display a plurality of pieces of visual information toward a corresponding plurality of locations, wherein each of the plurality of pieces of visual information is output toward a specific location of the plurality of locations. The display apparatus may also include a directive speaker unit configured to transmit a plurality of pieces of audio information toward the plurality of locations, wherein each of the plurality of pieces of audio information is output toward a specific location of the plurality of locations, and a central control unit configured to control the directive display unit and the directive speaker unit.

A display apparatus for visual and audio multiplexed display may include a directive display unit configured to display a plurality of pieces of visual information toward a corresponding plurality of locations, wherein each of the plurality of pieces of visual information is output toward a specific location of the plurality of locations. The display apparatus may also include a directive speaker unit configured to transmit a plurality of pieces of audio information toward the plurality of locations, wherein each of the plurality of pieces of audio information is output toward a specific location of the plurality of locations, and a central control unit configured to control the directive display unit and the directive speaker unit.