how much power do the earphone need?

[nickooeda]

I am going to design a PA for earphone,but i don't know the power that earphone need.
by the way,what is the mean of impedance of earphone? that is AC impedance or other meaning??
thanks a lot!!

 

[vfone]

Earphone usually needs 100mW of power.
Standard impedance for handset earphone is 32 ohms.

 

[nickooeda]

thank u ,vfone. I have anohter question, 32 ohms is the result test at 1khz ?? and 100mw is the max of the min power?? thanks

 

[selvaraja]

that is should be maximum power transfer to load but should consider losses in the filters too

 

[vfone]

The max power is 100mW. But from a PA point of view I think is good to have a little bit more margin (less distortions), and anyway this power is adjustable.
Impedance is tested somewhere between 1 and 3kHz, but the frequency response usually is between 100Hz and 15kHz.

 

[nickooeda]

thanks a lot to vfone and selvaraja
ok,impedance will change with the frequency.32 ohm is constant??I think the max power for headphone or earphone is different.if 3.3v supply,how can i calculate the current (rms) from supply??? )

 

[vfone]

As I said, you measure the impedance only at one frequency (let's say 1kHz).
The power standard is independent from the power supply voltage (3V, 3.3V, 3.6V, etc). Of course, if you design for 100mW @ 3V, increasing the Vcc you will get more power.
For RMS current calculation this link may help you:
**broken link removed**

 

[nickooeda]

thank u ,vfone.