Abstract: A duct filter bag used in connection with a heating and air conditioning vent, the duct filter bag including a filter body constructed of a material that is air permeable yet catches particles exiting the vent, the filter body having a perimeter; an attachment assembly connected to the filter body; where the filter body is extendable outward relative to the attachment assembly to define a filter volume; the attachment assembly being adapted to attach the filter body such that the filter volume is in registry with the vent.

Abstract: An exterior duct filter retainer used in connection with a heating and air conditioning vent, the duct filter retainer including a filter body constructed of a material that is air permeable yet catches particles exiting the vent, the filter body having a an attachment assembly connected to the filter body; the attachment assembly being adapted to attach the filter body such that the filter is against and/or in registry with the vent. The filter body can be flat, and the attachment assembly can use a variety of means to attach the filter body in registry with the vent.

Abstract: An exterior duct filter retainer used in connection with a heating and air conditioning vent, the duct filter retainer including a filter body constructed of a material that is air permeable yet catches particles exiting the vent, the filter body having a an attachment assembly connected to the filter body; the attachment assembly being adapted to attach the filter body such that the filter is against and/or in registry with the vent. The filter body can be flat, and the attachment assembly can use a variety of means to attach the filter body in registry with the vent.

Abstract: A duct filter bag used in connection with a heating and air conditioning vent, the duct filter bag including a filter body constructed of a material that is air permeable yet catches particles exiting the vent, the filter body having a perimeter; an attachment assembly connected to the filter body; where the filter body is extendable outward relative to the attachment assembly to define a filter volume; the attachment assembly being adapted to attach the filter body such that the filter volume is in registry with the vent.

Abstract: A twisting ring control for a compact speaker is rotatably mounted on a speaker encircling the speaker baffle. When the ring is rotated in one direction, the ring causes the speaker to be switched off, and when the ring is rotated in the opposite direction, the ring causes the speaker to be switched on. A volume control can be integrated into the same mechanism, and arranged such that, after the speaker is switched on, when the ring is rotated in one direction the volume is increased and when the ring is rotated in the opposite direction the volume is decreased.

Abstract: A system and method for enhancing the stereo sound effect produced by speaker systems having two or more speakers fed by two or more channels or audio, respectively. Second-order high pass filtering is applied to first and second audio signals of a stereo signal. A phase shift of approximately 180 degrees is applied to the resulting signals. A mixer mixes the processed first audio signal with the original second audio signal and mixes the processed second audio signal with the original first audio signal, whereby an expanded stereo sound field effect is created.