Left side is inputs from power amplifier and right side 8 ohm is speaker system. Relay needs DC coil resistance of 100 ohms and pull in voltage 2 volts less than required for speaker system or hearing level protection.
Diodes and capacitors rated two times peak voltage of current passing through them. Bottom 50 ohm resistor can be 50 to 100 ohm. Bypass for bottom resistor for 4 watt speaker range.
As rms voltage on audio builds switching happens automatically.
