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?

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    \$\begingroup\$ You'd need the specifications of the phone to determine that. Practically speaking, while no one other than the vendor can make any promises, there's a reasonable chance you would get away with it - a single 16 ohm speaker is a comparable load to two 32 ohm headphones with a Y adapter, for example, and if that broke phones it would seem likely that people would complain. Absent specs from the vendor you could try to identify the headphone amp from a teardown writeup, or look at data sheets of other headphone amps sold for such purposes. \$\endgroup\$ – Chris Stratton May 24 '17 at 18:16
  • \$\begingroup\$ Most probably in the hundreds of ohms. \$\endgroup\$ – winny May 24 '17 at 18:22
  • \$\begingroup\$ 50 Ohms minimum IMO although this test was 16 Ohms Not sure about Pd issues. forum.xda-developers.com/s7-edge/how-to/… \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 24 '17 at 18:38
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    \$\begingroup\$ The headphones that ship with the device have a 32-ohm impedance, it appears. cnet.com/products/… \$\endgroup\$ – Chris M. May 24 '17 at 18:51
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    \$\begingroup\$ @ChrisH-I already made a circuit (in a small box) that is powering the phone from my bike hub dynamo. I would like to put the speaker in there. I don't have a lot of room. It looks like I have to move the circuit in a new box to accommodate the amplifier. \$\endgroup\$ – Ultralisk May 26 '17 at 9:40

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