Abstract: A normally open reed switch mounted on a door jamb is closed by a magnet in a chain-lock keeper when the door is closed. A pole piece, which functions as a bolt on the end of the chain, engages in the keeper and shunts the flux of the permanent magnet so that the reed switch is not effected by the flux, and assumes its normally open condition if the bolt is seated home in the keeper.

Abstract: A loudspeaker system makes use of a closed cubic enclosure the front of which is a square baffle having tapered edges, the intersections of which fit the outline of an imaginary sphere which substantially encompasses the enclosure. Wide dispersion of audible acoustic waves of low frequency with a minimal amount of diffraction from a woofer loudspeaker mounted in the baffle at the convergence of the tapered edges occurs. A tweeter is mounted in substantially freely spaced relationship with the enclosure to provide also for wide dispersion of acoustic waves of high frequency. The enclosure is tuned to enhance the low end of its frequency response. A semirigid foam front panel having beveled edges is disposed on the baffle over the woofer and acts as an acoustically transparent front grill for the system. The tweeter is encased in acoustically transparent material mounted on the top of the enclosure.