The Bobwire SPK1 is a high-power handling two channel (stereo) speaker level A/B switch. The SPK1 will automatically switch between two audio amplifiers and send the audio signal on to one pair of speakers (2 IN & 1 OUT). The Mode switch determines whether the SPK1 will operate by audio sensing or by a 12V trigger input. An alternative setup would have a single audio amplifier and the SPK1 will switch between two pairs of speaker outputs (1 IN & 2 OUT) but this is only possible in 12V trigger mode. The double thick copper circuit board traces and the highest quality gold contact relays ensure the purest audio signal path. The ultra-sensitive audio detection circuit is 100% analog & remains out of the signal path at all times.  See website for more details www.bobwireaudio.com.  Ships from San Francisco, CA.