Audio signal amplifiers; audio pre-amplifiers; audio equalizers; audio signal compressors; audio mixing apparatus devices; sound recording apparatus devices; sound reproduction apparatus devices; audio power amplification apparatus devices; sound studio control room playback systems, namely, powered loudspeakers including electronic amplifiers and crossovers and non-powered passive loudspeakers for music, sound and voice playback and critical monitoring; sound studio audio monitor and control apparatus; audio combining networks, namely, analog and digital passive and active mixing and recording and playback consoles, audio mixers for use in sound recording studios, radio and TV broadcast facilities, audio post production studios including music and film sound mastering studios and live sound reinforcement applications