Mono Playback on TS215 very low using minijack from MacBook straight into the PA

I'm trying to use my laptop for playback directly into the pa using a minijack with a converter plugged into an Alto TS215 PA single speaker. I was only getting one channel so I switched to a mono output on my MacBook. This resulted in a much lower volume. Any Idea why this is happening?

Should I be using a different cable? I know I should ideally use a mixer but its just for a simple setup at home and I don't want to keep setting up my mixer every time.
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