The new IP67 waterproof and rugged wireless Bluetooth speaker Philips S4807 is launching on April 15 for $79: http://www.amazon.com/dp/B09QH64LSY/

Philips S4807 is surprisingly powerful, with a 40W capacity. 40 Watts from that little speaker is impressively loud.

So that should create a good feeling of sound even outdoors, and with a 12 hour battery life and rechargeable battery, you might as well use it as much as you possibly can, and with the volume way up high.