Acoustic couplers; high-frequency apparatus, namely, high frequency switches, high frequency audio crossovers, and high frequency tweeters; loudspeakers; sound reproduction apparatus; sound transmitting apparatus; acoustic conduits; cabinets for loudspeakers; diaphragms acoustics, namely, audio speakers, audio woofers, and audio tweeters; converters, electric; amplifiers; audio- and video-receivers; record players; DVD players; radios; apparatus and instruments for physics, namely, sound level meters