Acoustic couplers; electronic devices being remote control apparatus for remotely controlled headset and sound receivers; audio- and video-receivers; audiovisual teaching apparatus in the nature of digital devices, namely, sound insulation headsets and sound receivers; cordless telephones; wearable digital devices in the nature of connected bracelets; measuring instruments, namely, instruments for measuring acoustic levels; measuring apparatus, namely, apparatus for measuring acoustic levels; measuring devices, electric, namely, electric devices for measuring acoustic levels; tape measures; flowmeters; camcorders; video telephones; answering machines; hands-free kits for telephones; loudspeakers; dictating machines; protective masks; mouth guards for sports; sound alarms; sound reproduction apparatus; sound recording carriers; sound recording apparatus; sound transmitting apparatus; acoustic conduits; data processing equipment, namely, readers; distance recording apparatus; megaphones; portable media players; mobile telephones; headphones; intercommunication apparatus, namely, intercoms, microphone, telephones; speaking tubes; video recorders; record players