Hello,

I think JBL Flip 3 - http://www.jbl.com/bluetooth-speakers/JBL+FLIP+III.html could be a good option in this case as it has dual radiators for amplified sound output. Also it has Bluetooth as you require that. In addition this is one of the best weather proof speaker for using outdoor.

Link replaced by moderator.

Hope you will find this product useful.

Best Regards