Ok, thanks bassbenj, I understand, really it,s very good your explanation, but, and about my "why"?
You wrote: "...The down-side of split-coil and other hum-canceling Jazz pickups is that they DO NOT sound as good as single coils...". Why? Technically, what makes them sounds like humbuckers?
I understand stack or side-by-side singles are Humbuckers, for my poor knowledge they "seem" like humbuckers, but "in line" splits (I use Aguilars HC splits) sounds to me like "authentic" singles, or should. Thanks again.
No, it's not necessarily that they "sound like humbuckers". Note that one reason humbuckers have a fatter different tone from jazz pickups is that the area of the strings that is producing signals is much less narrow (because you have two pickups spaced at a distance) than a single jazz pickup.
So you ask, well, doesn't a side by side "split coil" humbucker (like say your Aguilars HC which are humbuckers) solve that problem by only having a single line of poles picking up the sound? And the answer, of course is "yes it does...to a degree". It is the "degree" thing that is the problem.
One of the "split coil" problems is that because the magnets in one half must be reversed from the other half to make it cancel hum, that distorts magnetic field at the top of the pickup from a single coil. Note that a P-bass has the same problem but minimizes it by moving the two coils off-set from each other. That moves the magnetic field distortion away to a degree, but the price you pay is that now the two halves are looking at two different spots relative to the total length of the string. Still, it is a decent compromise and works pretty well.
And there is more. Because you are winding two coils side by side there is a space limitation for winding wire. This causes coils to be underwound, and changes the impedance and inductance and capacitance and hence the "tone" of the pickup. The "art" of all this is trying to get those two coils to approximate the sound of a larger single coil. Nordiy big splits, for example, use the P-bass idea of angling the coils to each other to attempt to gain more winding space. Seems to work pretty well, but again you can see it's a compromise. Hence the tone of hum-canceling pickups can be quite good, but you can see just from the geometry problem of fitting wire, compromises occur. The skill of the pickup maker is to find how to make the pickup sound as good as possible while keeping hum canceled.
The last solution is simply to use real single coil pickups, but rather than just letting them hum, you add an other coil just for the purpose of picking up hum. You electronically mix that hum into the pickup output to cancel your single coil hum. Alembic has had this system for years. Now Audere is offering a "phantom coil" system like this for jazz basses as well. Haven't tried it, but seems like a good idea. Downside, of course is bass now must be active and hence electronics is much more complex.
Bottom line is that if your pickups cancel hum and sound good to you, then that's good enough. My PJ has a Dimarzio Ultrajazz (split coil humbucker) that sounds good enough to me. So that means it's good enough. My Jazz V deluxe has two SCN pickups I installed. They happen to be stacked coil which in the past (Carvin) did not impress me, but I totally LOVE the sound of SCNs and LOVE the fact that single coil hum is gone. So if I'm happy, they I guess that is good enough for me! The reason the SCNs were installed was because the bass originally had Fender "noiseless" pickups which were side by side split coils and I HATED the tone! Didn't sound anything like a single coil to me.
So like I said, pickup makers are working on this, but it is really about getting the right combination of things going. If it sounds good to you then it IS good! If not, then try something else.
