Years ago, we always had an old car stereo and 2 or 4 speakers wired up on our old honda 3 wheelers. Usually 2 6x9 alone or paired with 2 4" speakers. But they were mounted in the wooden cargo boxes we assists built for the bike. You need the solid surface, plastic flexes too much with very little air pressure and sounds like crap. The only way to make it sound decent would be to sandwich the baffel with plywood where the speaker is mounted, and actually enclose a small area around the rear of the speaker with wood.
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