The Keystone has a long-excursion 4-inch woofer in an acoustic suspension enclosure and a wide-dispersion 1-inch soft dome tweeter. Together, they combine for smooth, wide-range response that does full justice to even the most demanding program material. Keystone can also stream music wirelessly from any Bluetooth device, and it’s powered by a long-lasting internal rechargeable battery. Other features include a built-in 40-watt (peak) amplifier, an embedded solar panel that keeps the battery charged, and the ability to link the two speakers together wirelessly. It’s also IPX4 water-resistant.