[estreeter]

Hi All,
 
   I get a little frustrated that there doesnt seem to be a 'standard' for expressing output power for a headphone amp. For speaker amps, it seems to be the number of Watts into an 8ohm load (sometimes 4ohm), but you will see various figures quoted for headphone amps.
 
     For example, if the Fiio E9 has a rating of '1 Watt' ('16 ohm loaded') and the iBasso P4 has a stated output of 600x600mW into 32 ohms, what is the conversion from the Fiio figure into something I can compare with the P4 32 ohm figure ? Help
 
     It gets worse on the Meier Audio site - here are some numbers for the Corda Swing:
 
Maximum output voltage 11V
Maximum peak output current 250 mA
Power uptake 2 Watts
 
      Granted, it would help if I knew something about electronics, but they dont make it this hard to determine the impedance on a pair of headphones - why does it have to be this hard for amps ?
 
Thanks,
 
estreeter
 

 

[Szadzik]

These four values are interconnected and having them you can do the math and get any one of them.
 
Voltage (Volts/E), Wattage (Watts/Power/P), Resistance (Ohms/R), Current (Ampers/I)
 
Having two of these values you can always get the third one.
 
It is all based on Ohm's law:
 
OHM'S LAW
BASE FORMULAS P=I*E E=I*R
TO FIND VOLTAGE E=P/I E=I*R E=SQR(P*R)
TO FIND CURRENT I=P/E I=E/R I=SQR(P/R)
TO FIND POWER P=I*E P=E2/R P=I2*R
TO FIND RESISTANCE R=E2/P R=E/I R=P/I2

P = Power in Watts
E = Electromotive Force in Volts
I = Electrical Current in Amps
R = Electrical Resistance in Ohms
SQR = Square Root
 
Check these links to have a better understanding:
 
http://www.bcae1.com/ohmslaw.htm
http://www.kc9aop.net/Doc/link_pages/Ohms_Law.htm
http://www.sengpielaudio.com/calculator-ohm.htm
 
 
I was reviewing this myself recently for the same reason you are doing it now

 

[lbj]

Quote:

     For example, if the Fiio E9 has a rating of '1 Watt' ('16 ohm loaded') and the iBasso P4 has a stated output of 600x600mW into 32 ohms, what is the conversion from the Fiio figure into something I can compare with the P4 32 ohm figure ? Help
 
 

Deferring of course to Ohm's law, there are some generalizations you can make.  As the load impedance doubles, output power will roughly halve.  In the case of the E9, if it delivers 1000mW into 16 ohm, it will likely deliver 500mW into 32 ohm.