"Power hungry" speakers

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.

Capacitors have varying levels of dielectric absorption and thermal losses as frequency is varied. Their transfer characteristics ( linearity ) can be measured and compared over a given frequency range. None of this is new technology and studying these factors along with many others is what have led to the breakthroughs in higher resolution / lower loss circuitry. This is part of why newer gear has the potential to sound better than older gear i.e. improvements in passive parts. Some capacitors that were believed to be "excellent" in the past are actually quite horrid in performance. Most electrolytics are amongst that group along with several others.

In order to get around this problem, some have experimented with using two different types of capacitors wired in parallel i.e. "bypasses". The non-linearities of one cap offset those of the other, summing together to improve the transfer characterstics of the circuit on the whole. This can be a VERY tricky business though as you can end up with two ( or more ) non-complimentary distortions, resulting in even poorer performance. This is why some folks say that "bypasses work well" and "bypasses create other problems". Sean
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I am running b+w 801s which are said to be power hungry.I can tell you that I tried a 170 watt bryston amplifier and it drove the speakers to earth shattering levels.You must remember that 99% of the time your speakers are only using a few watts(usually less then 20 to be sure).I think this "POWER" thing has been very much over stated.99.9% of the time a 25 watt amp would do the job.However it is when the large dynamic swings take place that one could use more power...the differnce between a 300 watt amp and a 600 watt amp is only 3 db (for every 3 db increase then double the power is required)...so the difference between a 150 watt amp and a 300 watt amp is miniscule...