[zero the hero]

At the risk of over-simplifying a more complex problem: wouldn't the equasion for "high efficiency bookshelf" basically be "high efficiency driver (full-range to avoid crossover loss) combined with a large enclosure (likely ported) to provide as little resistance as possible"?

what is "crossover loss"? The 1/5th of an ohm resistance from an inductor?

 

[zero the hero]

Actually: I was thinking that since not all drivers are equally efficient at a given range, that there had to be equalization in the crossover to "driver match". Since that cannot introduce new power (increase the power going to the less effcient driver), it must reduce power to the more efficient by converting it to heat: hence "loss".

But I've not built a crossover: perhaps I'm missing some basic physics. How do you prevent one driver from being unequal to another without selective reduction in the power flowing to it?

Tweeters are generally padded down because they are inherantly more efficient than woofers. There are some efficient full range drivers, but they have rediculously low xmax and therefore cancel out any gains obtained from the efficiency gains.
Multi-driver is the way to go if youre looking for SPL.

The bigger the better also, but if you're using a sub you can sacrifice extension for efficiency...