Originally Posted by Remior
The more resistance you conect to amplifier the less power it can deliver to it.
It's impossible deliver the same power changing the headphones or speaker you conect for the same quantity of volume gain you set on amplifier, because their resistance to electricity isn't the same.
Low impedance headphones improve with amplifiers deliver a good amount of current (Hifiman's for example).
High impedance headphones improve with amplifiers tat deliver a good amount of voltaje (Sennheiser's for example).
You have converted my first example (eg. 100W in 8 Ohm, 200 into 4, 400 into 2, with V=const, same about headphone amplifiers) into words :)
In reality, I am not able to tell how much power can be supplied to the driver (apart from the power into 1KHz), as the impedance of driver is dependent on the frequency. So, at each frequency there will be different amount of power supplied.
Anyway, we are not talking about speakers, but amplifiers.
For example, if we take Lamm amplifiers, there are ML models, which output power is the same into 8/4/2 Ohms (see their site for proof), which tells us that they supply the same power into any impedance between 2 and 8 Ohms (or even wider impedance brandwich).
But there are also M models, which can supply the same voltage into 8 or 4 Ohms (again, can be seen on their webpage), so we can assume that the voltage across the 4- to 8 Ohm load is constant.
WHY do they differ?
Obviously, to have “uncoloured” sound it is better to have a constant voltage. (Because if you have 10 V going into 20 Hz and, say, 20 V into 200 Hz, 200 Hz will sound 6dB louder, if I am not mistaken. So even if your driver’s frequency response is perfectly flat, your amp will add its own colour, which isn't what we're into ;)
But there are a lot of amplifiers (I would say most of them), which are not able to give us constant voltage.
P.S. I doubt that only high impedance headphones need high voltage, but I agree about current (due to Ohm’s law)