An amplifier is integrated into the device. An audio amplifier takes a small signal and makes it bigger without making any other changes in it which results in better sound, so any sound source can be connected to speakers.
65% have it
10. has an AUX input
An auxiliary input allows you to play other audio sources by connecting them through a simple audio connection like a 3.5mm jack, i.e for MP3 or portable DVD/CD player.
84% have it
11. Weather sealed
Device is protected with extra seals to prevent failures due to any kind of weather.
16% have it
12. maximum bluetooth range
The device can connect at a greater distance via bluetooth / infrared to another device.