>> Huh?  You are saying that they deliberately make speakers less efficient 
>> so that a higher voltage can be used to drive them?  I've never heard 
>> that before.
>
> Yes.

Interesting, how do they do that?  Most speakers (electrically speaking) 
seem very simple to me, just a cross-over network and then a coil of wire. 
Hard to see how you could deliberately make the system less efficient 
without just plonking a huge 50W resistor in series (which would totally 
screw up the quality of the sound).

> Hmm, I think my amplifier (nothing special) is rated at 60 W per channel. 
> (IIRC, into 8 ohms at 1 kHz.)

And what happens when you actually output 60 W in your room?  BTW on most 
amplifiers you need to get the input signal at the right level (not too high 
or too low) to get the quoted maximum output power.  I guess also your ears 
work on a logarithmic scale, so 60 W is probably not as much "louder" than 
20 W as you would think just by looking at the numbers.

> Wait... the *voltage* changes depending on how much you use it? That's 
> odd. I thought that potential difference was always constant, and it's 
> only *current* that changes...

That's only true if all the cables in the whole system have precisely zero 
resistance, which they don't.

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