Amplifiers have an internal series resistor for each side to limit the
current to the headphones. Lower impedance headphones will have a greater
load after the limit resistor, thus reducing the voltage across the drivers.
This will force the user to turn up the volume higher in order to listen to
them.

Most amplifiers that work from the AC power for operation were designed for
8 ohm headphones. Portable devices that run on batteries are usually
designed to use headphones of at least 32 ohms or greater. This will offer
less load on the output circuits, and thus save some battery energy. The
internal bias resistor value was chosen to allow for a lower current drive.
This is why an 8 ohms headphones will be lower sounding on most portable
devices.

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JANA
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"andrew_h" wrote in message
oups.com...
Why is it that the lower the impedance for headphones, the harder it is
to drive????

Thinking about speakers ..... say connected to an 8ohm rated amp. If
they were 32 ohms, then the amp's possible power would be was less
(than if the speakers were 8 ohm)....

So why is it so?