... Using the world's advanced technology, low-voltage, low-power amplifier IC7.Power supply:USB power, Build-in Li-battery, longer time ... Yellow, Blue, Green, Black, Purple,etc., Main SPEC:1.Loudspeaker Output: 2W 40mm/4Ω,Antimagnetic speaker unit2.Frequency response: 100hz-20Khz3 ... to noise: ≥80db4.THD: ≤1.0%5.Battery voltage/capacity: 200mAh6.Battery Charging voltage: 4.7V±0.05V7.Battery charge time: 5V ...