If it is truly mono the music in the right and left channel is identical, so it’s still mono. In the days when mono was the only way to get music home the source (record or tape) only had one channel and the mono electronics were connected to one speaker. Now that stereo is the rage, everyone has two (or more) speakers. So if you bought a mono LP, CD or download and the signal was only in one channel then it would only play on one speaker. I don’t think that would go over to good with the finicky consumer. So they put the same signal in both channels. It plays on two speakers, but it is mono. The only difference of one speaker versus two is two can produce a center image, but none of the right/left soundstage artifacts that a good stereo can.
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