[opus111]

Hey all,
 
I own Beyerdynamic 990's and am considering buying an amp for them.
 
But the Engineer in me is bothered...  Why should high impedance phones need a bigger amp?
 
I can see that you need more voltage for a given volume level.  P = V^2 / R so twice the impedance requires sqrt(2) more voltage.  I can see that you might clip you amp before the phones were loud enough.
 
However, if my current amp is loud enough for me, what does a better amp buy?
 
With speakers, it is low impedance, and reactive impedance that is the problem.  Driving low impedance requires more current, and that requires a bigger power supply.  A reactive impedance also requires an amp with lots of reserve power.  It is easy to understand how a reactive electrostatic or 2 ohm ribbon loudspeaker benefit from a heavy duty amp.
 
However, a high impedance headphone is not very reactive, and does not require large amounts of current-- in fact they need less current for the same volume level.
 
I feel like 600ohm phones should be easier to drive.  What am I missing?
 
Thanks in advance
P

 

[wuwhere]

Impedance matching.

 

[Uncle Erik]

You're right, 600 Ohm headphones are an easy load for most amps.

 

[FallenAngel]

The higher the impedance, the "easier" the load on the amp - as in stability, but as the resistance is higher, more voltage is required to drive the headphones to same loudness than a lower impedance headphone (of course sensitivity plays into the volume at a specific voltage, but we won't get into that as it's not directly relevant to the idea of low vs high impedance loading).