Drew covers a lot of excellent points. I can tell that he's really been doing his homework as his contributions to these forums continues to grow in quality. Kudo's to him for learning as much as he has AND for sharing his knowledge in a very useful manner : )
Having said that, i've ALWAYS promoted the benefits of "direct drive" i.e. amplifier to driver using active crossovers. The increase in clarity, liquidity, transient response, dynamics, etc... is STAGGERING compared to an equivalently designed passively crossed over speaker. Even with speakers using the simplest crossovers possible ( 6 dB / octave aka "first order" ), one can EASILY hear the benefits.
The drawback to active crossovers / going "direct drive" is that you increase the number of channels of amplification required and end up with at least one more chassis in the rack ( active crossover ) for most designs. Depending on whether or not one uses one multi-channel amp or several two channel amps can also make for a big difference in the amount of real estate that your system takes up in the room.
By bandwidth limiting the amp PRIOR to feeding it the signal to be amplified, the amp can now concentrate all of the available power to a much narrower frequency range. As such, efficiency is increased and so is headroom. As taken from Audio magazine September 1975 in an article entitled "Bi-Amplification - Power vs Program Material", it was demonstrated that an actively crossed two way with 30 watts on the tweeter and 60 watts on the woofer clipped at appr the same point as a 175 wpc amp driving the same speaker full range with a passive crossover. Since 60 + 30 = 90 and 175 is almost twice that, we can see that actively crossing pretty much doubles our effective power rating. This is done by reducing the thermal losses that one would normally incur when running the capacitors, coils, resistors found in a typical passive crossover.
In the case of the Orion's, that "measly" ( and it IS measly ) 60 watts would be equivalent to appr 360 watts if fed into a typical passively crossed speaker design. Even with 360 wpc into that passively crossed design, it still wouldn't have the same transient response, control, transparency or liquidity that the active design is able to achieve.
If it is not apparent by now, i'm a BIG fan of actively crossed multi-amp speakers. My mains are 3 way actively crossed designs using 12 channels of amplification ( 6000 watts rms ), my bedroom system is actively crossed with multiple amps ( 400 watts rms ), my office system is "direct drive" ( no passive crossovers ) with about 1500 watts rms, my Brother's system is actively crossed and quad-amped ( 1700 watts rms ), etc... Bare in mind that these are factory power ratings, not the "effecive" power ratings that one gains from actively crossing over.
With all of that in mind, the more power that you have, the LESS chance that you have of "slapping" or "bottoming out" the driver due to a lack of control. That's because as the driver takes a longer excursion, it produces a greater amount of reflected EMF ( electromotive force or "voltage" ). In order to maintain control over the driver, the amplifier not only has to generate enough power to overcome that reflected voltage that the driver itself has produced, but it has to have even more power on reserve in order to "muscle" the driver according to the intensity of the music signal that it's being fed. With some very long throw ( long excursion ) drivers that have massive ( big voice coil / magnets ) motor structures, this can equate to several HUNDRED watts of reflected EMF. Bob Carver discusses this in detail in his white papers for the Sunfire subs if anyone is interested.
As such, the "beefier" the drivers that you're using and the louder and lower in frequency that you want them to play, the more power that you have to have to maintain control. If you don't have the power to maintain control, the driver is more likely to "overshoot" or "over-extend" its' own mechanical suspension, resulting in damage. This is completely different than what Linkwitz is discussing though, as he's talking about feeding too much power into the driver, which results in over-excursion but for different reasons.
The difference here is that with this type of over-excursion, the driver is still being controlled by the amplifier, which has plenty of power and headroom to push it beyond the mechanical limits. In effect, too little power is equivalent to "understeer" in a car i.e. you turn the wheel and the car slides forward instead of turning due to a lack of control. Too much power is equivalent to "oversteer" or "torque steering" i.e. where the excess power applied actually increases the amount of steering input that one used.
Having said that, it has been my experience that high quality drivers can take GOBS of power beyond their power rating. That is, so long as the power remains clean ( non-clipped ) AND the music that one is listening to is "dynamic" in nature. By "dynamic", i'm talking about music that has a lot of dynamic range. That's because the less dynamic range ( more compression ) that the music has, the higher the average power levels will be. The higher the average power levels, the more continuous heat each driver has to dissipate. As such, listening to hard rock / heavy metal type music is FAR more demanding of both amplifiers and speakers, because the average power levels are much higher than with Classical, Jazz, Blues, Country, etc...
If one encounters EXTREMELY dynamic recordings and is running gobs of power, the initial dynamic bursts can cause the driver to over-extend beyond reasonable excursion levels. Such is the case with the cannon blast on the 1812 overture. This is the kind of "over excursion" that Linkwitz is worried about with "big power" and justifiably so.
As a side note, vented ( ports, passive radiators, slot loaded, etc... ) speakers are FAR more likely to be damaged from over-excursion / lack of control as compared to a sealed design. That's because the air trapped inside the box of a sealed design acts as an equal but opposite "air spring", sucking the driver back into the box as it tries to take a longer excursion. At the same, this same "air spring" pushes the driver back out as it tries to compress the air in the box on the "back-stroke". This is why sealed and stuffed designs are called "acoustic suspension" i.e. the air pressure in the box acts as a linear suspension for the driver. Vented designs lack a linear suspension as the opening used for the vent allows the driver to become "undamped" in either direction. The fact that sealed boxes typically have a much lower impedance at resonance also means that the amp can deliver more power into the woofer. As stated above, more power transfer equals more amplifier control over the driver.
Hope this helps clarify some things and answers your questions. Sean
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PS... 22 wpc without passive crossovers would be equivalent to 40 wpc. Fourty wpc on a speaker that is 104 dB's efficient would surely roar. As it is, about half of the 22 wpc capabilities of that amp would be lost in the crossover network. Factor in that the speaker that the 22 watts was going to be run on has a 4 ohm woofer, which means that it needs a lot more current, and you'll see where the reduced power might not be enough. On top of that, most tubed amps don't do ANYWHERE near their rated power with "low" distortion.
If tubed amps were rated with less than .1% THD, their power ratings would be WAY lower than what they are currently being rated at by most manufacturers. If such were the case, that 22 wpc tubed amp would probably be rated at something around 5 - 8 wpc or so.
If you doubt this, go back and look at the
first BAT amplifier that Stereophile reviewed. While the VK-60 is rated at 60 wpc, if the power output of this amp was rated at .1 THD ( which is pretty high for an SS design ), the VK-60 could only deliver 2.5 watts @ 8 ohms and 1 watt @ 4 ohms. That's a far cry from the rated 60 wpc. Then again, Stereophile did comment that this was a very noisy / highly distorted amplifier, so using it as an example to represent all other tubed amps may be a bit extreme.
