an antique soviet woofer 5gd-3 from vintage acoustics symphony

symphony acoustics vintage perforation cardboard cap resonant frequency rare antique resistance gray cast case bracket cobalt alnico shielding radio soviet woofer speaker 5gd3 old cases speakers retro 1960s 60s 70s wave announcer recording studio listening audio threeway microphone award interview ussr helmholtz resonator report spy plywood desk voice wooden play loud archive