I want to connect an external (passive) speaker (3W/16 ohm) directly to my Samsung Galaxy S6 using the headphone jack. I want to do this on my bicycle using the smallest space possible. Connecting the phone to an active speaker requires extra space (speaker + rechargeable batteries + amplifier pbc) so reusing phone's amplifier will be the optimal solution.
Is the impedance too small? What is the minimum impedance that I can use? Is 16 ohm safe?