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. Weather sealed
Device is protected with extra seals to prevent failures due to any kind of weather.
16% have it
11. audio output power
Audio output power is based on the number of speakers and their power in watts. High audio output power results in loud, clear sounds.