SPL levels are actually easier to hit with separates, and easier to control.
My point is that unless one needs very high spls, that amp power becomes a non factor, except for possibleaverage SETs. My 20 watter handles my two ways to 100db spl.
And blending separate subs is actually real easy if done right. It really has little to do with different types of amps. The difference really comes from driver speed. The difference in damping factors of the amps is nothing compared to the moving mass of the drivers in most cases.
It has everything to do with different amplifiers and their differing sonic characters. As an example, try combining a bright sounding amplifier (for the tweeter) with a full sounding amplifier (for the woofer). It is quite easy to perceive a disjointed quality in the sound.
Driver speed is not that much of a problem. Often the cause of "slow" vs "quick" "speed" is the phase relationship between the fundamental and harmonics of said driver.
For higher frequency drivers, check the FR and cone resonance properties, as well as the Qs. For the woofer, again check the cone resonance properties and the Qs. If one is having "energy storage" problems, either the drivers have a problem to begin with, or the cabinet/design is problematic and the final Qs of the system is incorrect.
I have a control to adjust the Q of my woofer at resonance. I believe in controls on speakers.
For instance take a mini-monitor or small floor standing speaker and try to match the speed (and by speed I mean settling time) with a large and heavy low frequency driver . That's where you get the mis-match, and poor blending.
That is a function of the phase relationship between the fundamental and harmonics. The smaller mini will have the harmonics slightly ahead of the fundamental due to its lack of low frequency respone, which gives a steeper slope, thus "faster" time. It can be too "fast". The trick is to obtain the proper rise time (attack time) for said instruments.
Another issue that I didn't mention earlier is that the larger voice coil of the bigger driver can create a large back EMF that effects (negatively) everything else. So when driven by the same amp they tend to muddy the output of other drivers. They can sound blended or more smeared together but not in a good way.
That is where the proper xover design comes in. I have no problems with such, demonstrated by the fact that I am dealing with 1 part in 300,000 (resistor value). In other wards, I am dealing with FR etc changes so small they equate to -110db down from the fundamental. The ear is that sensitive. One will not obtain that precision of blending using a typical subwoofer amp xover controls etc. Sounds like you are discussing a problem with a total Q that is too high.
Another point is that the typical xover, whether reg speaker or subwoofer, does
not have the fine tuning necessary to seamlessly blend different drivers.
If you want to spend a little time with wire and listening comparisons then you will find that the geometry of the wire, quality of the wire, and dielectric material to have a much greater effect then the gauge of the wire.
I have dealt with several types of wire, and as you point out, a variety of factors influence the sound. Included in the list are your generalities; to be more specific, materials used, solid or stranded, total gauge and paralleling of individual wires. Here is a quote from a previous post I made addressing the high frequency response of one vs paralleling wires. I altered the quote slightly, an update.
Inductance is frequency dependent. For comparison, below is the DC resistance, the straight wire inductance, and inductive reactance for 5 feet of single wire and parallel wires at 20khz:
Single Single Single 10 parallel
18 gauge wire 13 ga. ~9 ga. 18 ga.
.0325 .0104 .0066 .0065 DC resistance
2410 nh 2232 nh 2162 nh 240 nh Inductance
.30 ohms .28 ohms .27 ohms .03 ohms Inductive reactance at 20khz
Notice the 10 parallel 18 gauge wires equate to an approximate 9 gauge wire in DC resistance, but the inductive reactance is only 1/9 that of the 9 gauge wire.
(You may have heard the past arguments over the small wire parallel with the large wire improving the highs. The highs were increased because the inductance of the two wires was about 1/2 that of a single wire.)
Remember, this is for a single 5 foot lead, not both leads. Multiply this by 2 for the total 10 feet speaker lead length. I would say .54 ohms is quite a bit in series with a 4 ohm, or 8 ohm speaker, although the impedance of a speaker at 20khz is higher. One could easily be about half a db down at 20khz, a couple of tenths at 10khz and even a tenth at 5khz. Whether one notices a difference will depend upon some factors. I and friends perceived a difference between 8, 10,, and 12 parallel wires per lead. Bass resonance is also affected and perceived.
Concerning low frequencies, multiple actions occur.
1) The damping of the woofer resonance via reduced resistance to the output of the amplifier is enhanced by larger gauge wire (comparison using same material wire).
2) All drivers are influenced by the gauge of the wire due to the combination of wire resistance (and impedance) and varying impedance of each driver. Of course this does not occur with constant impedance speakers, such as magnepans etc.
One final point. The effect of one's personal tastes will also affect perception. As at Audio Fest's, one hears a variety of tonal balance in the different rooms. The range I have observed are from very full sounding to that of sterile. As such, the fuller sounding rooms will probably have little problems with matching drivers, even using different sounding amplifiers. The opposite will occur with the sterile sounding rooms, where different amplifiers and their characteristics will be perceived more easily.
The last point is that I am not personally attacking any of your products Danny. I have heard great things about your speakers. I am just providing information, responding to the OPs question, and your question; why I use one amplifier for both drivers in my speakers. I addressed multiple problems that need addressing.
cheers
steve