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.
Philips Fidelio AS140 Bluetooth Android
65% have it
8. 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.