Abstract: A loudspeaker includes a cylindrical sound case provided with a plurality of radial ribs thereby dividing interior of the cylindrical sound case into a plurality of chambers and a common circular space at a central portion and therefore forming a plurality of resonance chambers, a sound coil assembly including cylindrical member which is open at one side and formed with a curved surface at another, the curved surface having a center through hole, the cylindrical member being dimensioned so that the cylindrical member will be tightly engaged with the ribs when fitted into the sound case thus forming a plurality of resonance chambers, a collar having a tubular reel at one end and a curved diaphragm at another end being arranged inside the cylindrical member, and a magnet assembly including a circular iron member having a central recess in which is fitted a magnet and a magnetism permeable disc.

Abstract: A feed-back noise-eliminating microphone circuit is provided. The circuit includes a positive-phase pick-up circuit to pick up sound source signal for amplification through a positive-phase amplifier for further output through a balance adjusting circuit and a power amplifier. The circuit further includes a reverse-phase pick-up circuit to pick up feedback signals from the loudspeaker for amplification through a reverse-phase amplifier, wherein feedback noise from the reverse-phase amplifier is offset at said balance adjusting circuit by the output signal from the positive-phase amplifier.

Abstract: This invention relates to a type of "multi-purpose traffic director's stick", featuring the composition of a bar tube, flashlight handle, lamp element, speaker and control circuit board, to achieve multiple purposes with a single director's stick without sophisticated equipment but the functions provided by a director's stick, police club, trouble alarm lamp, flashlight and a whistle.