[lattesurf]

XTransbus , in general, normal earphones for end-users range from about 12 to 32ohms, with 16ohms being the most common. The higher the impedance of the earphones, the better the response of the lower frequencies (ie bass). Some high-end headphones used in music industries have impedances as high as 300ohms.

With regards to the battery life, just think of the ohms law V=IR. Assuming a fixed output voltage of 100mV across the earphone, and a 16ohm earphones, we get an output current of 6.25mA. Whereas with a 32ohms earphones, we get an output current of 3.125mA.

The power output for a 16ohm earphone is P=VI=100mV*6.25mA=625uW
and for a 32ohm is 100mV*3.125mA=312.5uW.

With these 2 values, we can see for a 16ohm earphone, it draws 625uW of power from the player, and 32ohms earphone draws 312.5uW. If you think of the power output as the sound being heard on the earphones, we get half the power output for a 32ohm as compared to a 16ohm.

So to level the sound-level, we theorectically need to increase the voltage output for the 32ohms by 2 times. This increases to 200mV for the 32ohms earphones. The higher the voltage output, the more current the audio amplifier needs to produce and this drains the battery life faster.

It is all a trade-off, for better bass-response, you require higher impedance but shortens battery life.

Hope this helps.