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 eavesdropping strut varnished song hit broadcasting fm helmholtz resonator system wooden audiophile spy interview mass media entertainment archive listen singer broadcast art