"Power hungry" speakers

I believe the motor magnet affects efficiency.
The stronger the magnet, the louder the speaker will play with x amount of power.
The size of the drivers is also a factor. Tiny drivers cannot move enough air (to go loud) with average power.

Dazzdax, maybe I have an explanation about the crossover of the Sonus being simple, and yet, why of their consuming such a large amounts of current? Last year, I was experimenting with an old Pioneer receiver from the 70s I have picked up from the garbage as well as a small midi JVC system (2002 model) that I had imported from Asia. I was trying to make them run with a pair of EPOS ES11, 87 db efficiency, no crossover, just one cap between the wires and the doomed metal tweeter. This load was supposed to be very benign...and yet, the sound was very distant, muddied, with both...I was running them with a pair of old radioshack wires I had both for non essensial duties...had chopped some and had decided to "solder" them together again.

Later, I ran the same set of wires to my powered sub and guess what, the same muted sound. I swapped cables and there the sub was, reproducing loud, clear volumes and programs.

The point is this, even with copper wire and simple solder, there can be a major hampering in the power and delivery of the signal to some drivers. Eventhough Sonus might have what it seem to the naked eyes as a "few" components, they still might be robbing the drivers of the "original" watts that were intended for them.

Do not get me wrong, people swear by Sonus Faber and other of these rather power hungry speaker manufacturers, but maybe it was the intention of the company to make somehow demanding speakers in order to get clientele who are moneyed, AKA: can afford to have monster amps, rather than some tube loving, hi efficiency owners of SET amps.

To make my speculation into conclusion, you will simply need to have the same pair of speakers, Sonus with one tweeter and one 6-7 inch midwoofer and another of the same type of set up, one tweeter and midwoofer, play the same source or selections for about 2 hours at medium volume. Then, touch the crossovers of the X brand of speaker and the Sonus. If the Sonus crossover components are warmer than the other speakers, then you will be able to determine that the Sonus Fabers soak up the watts and current converting them into heat rather than sound waves. Inefficient, even with a group of smaller crossover components!

JM Labs originated as a speaker manufacturer (JM= Jacques Mahul, the designer of said speakers). Allegedly, Focal acquired the speaker manufacturer who now operates as the finished (consumer) products division of Focal. So it wasn't quite a matter of fitting the drivers into a speaker enclosure -- at least, not in the beginning...
As a general rule, efficiency in drive units is a function of moving parts mass vs. magnet strength. High strength magnets are expensive.
Efficiency in the speaker system, as has been noted, is also a matter of how much energy is used by the filters (x-over, notches, zobels, etc, you name it).
Hence, average magnets with heavy filters, do not a dynamic speaker make! Ultimately, small level info is lost to our perception as Sean notes -- and the result can be pleasant, flat across the critical range, etc, and "laid back".

Re, Sonus Faber & others: don't forget that, while the x-overs may be capacitor-less, it doesn't mean they are simple (1st order, etc) all over (I don't know if they are...). Also, the drivers used, like the expensive Scanspeak woofs on some models, are not that sensitive to begin with... some are ref'd at 86-87db...

First let me state that I have seen improvements in the sound of many speakers through use of more powerful amplifiers. In particular, my MG 1.6 now enjoy 600 watts.
However, it is very obvious (a simple voltage measurement will do) that the power actually drawn by the speakers is nowhere near the amplifier's capability. There are other amplifier characteristric that come with high power capability that do the magic.

Crossover networks may have a lot to do with speaker performance, but they don't "eat up" power. If they did they would get very hot, which they don't, and could not be mounted inside a wool (or fiberglass) insulated box.

The first thing you learn in EE101 is that the power dissipated in a capacitor is zero.

The woofer inductor will generate a little heat because the woofer amps flow through the inductor. However, crossover inductors generally have low resistance compared with the driver, so most of the heat will end up in the driver voice coil.

A crossover without any capacitors means that the tweeter must have an inductor in parallel with it. To avoid a near dead short on the amplifier at low frequency a resistor must be put in series. This resistor, and the inductor will draw power, and will get hot. This "capacitorless" crossover is essentially a series crossover, with the woofer and its parallel capacitor replaced by a resistor.

Eldartford, thanks for the clarification.