Originally Posted by GregBe
Why is it that in general headphones that are lower in Ohms are easier to drive, whereas, speakers with higher Ohms are eaier to drive?
My take on that:
The typical impedance you find in speakers is 8 ohms. Speakers with low impedance can have 6, 4, or even less ohms.
Notice that zero ohms would be absolute no resistance, meaning, basically a short circuit. Zero ohms would be equivalent (for the amp) to not connecting the speaker wires to the speakers, but simply shorting the red wire to the black wire. The lower the impedance of the speakers, the more the amp sees the load as such a shorted circuit.
Also, the closer-to-shorted-circuit the load is, the more the power supply needs to continuously provide higher and higher amounts of sustained current to provide the same voltage. (After all, V = I*R; notice that the closer to zero R gets in that formula, the higher the I -current- needs to become to yield the same voltage V).
But providing high levels of current (and voltages) in a sustained and reliable manner is not easy, and that is (ultimately) the tough job of the power supplies. Depending on their circuitry and specs, different power supplies have different operational limits. In general, the closer to zero ohms the load gets, the harder the power supply has to work, the closer to its operational limits it gets, and the easier it is for the power supply to attempt to exceed those limits and fail (either by making the amp produce clipped sound waves, by blowing up a fuse, or by shutting off if it has a self-protection mechanism built-in.)
Now, "low impedance" headphones are never as close to a shorted circuit as low impedance speakers. A low impedance headphone is usually around 32 ohms, quite higher than even typical "normal/high" impedance speakers, which as mentioned before, have ~ 8 ohms. Also, the voltage levels required in headphones are in general lower than those required by speakers to produce the desired volume levels from the drivers. So in general, the operational parameters are much more demanding and extreme when driving speakers (in particular, when driving "low impedance" speakers) compared to when driving headphones, whether low or high impedance ones.
This is only my take and understanding. The true knowledgeable electronics gurus here can bring more clarity on this, I'm sure.