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What causes that Jazz Bass Scoop?

So then it seems like with series wiring there doesn't seem to be the same effect (perhaps it's just not as noticeable). Is that because in parallel the signals from each pickup are averaged, and in series the signals are more-or-less summed?

No - that just changes the total resistance and loading characteristics.
 
You're way over-thinking this. It's phase cancellation, plain and simple.

I gave an example of why I thought that right after what you quoted. You can isolate your pickup signals using resistors.

1960s Jazz Bass - Isolated Dual Stacked Vol/Tones - How does it affect tone?

Basically, if comb-filtering is solely responsible for the scoop, why does it go away when using resistors to isolate the pickup signals?

You can do the same thing by rolling down the pickup volumes on a Jazz bass, e.g. set the bridge and neck volume both to 90%. Compare that tone to both volumes at 100%.
 
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Loading happens but it does other things.

From a math perspective it's just plusses and minuses cancelling each other out. One pickup hears a particular harmonic on the upswing of the wave and the other hears it on the downswing. The result is no sound for that harmonic.

And that is the answer. Algebra II, sinewave math.
 
Phase cancellation as has been said. I THINK also that the distance between the coils determines (at least in part) the frequency of the scoop.

In a humbucker when the coils are side by side you lose a bit of the highs. On a typical jazz bass you lose some mid-mids (maybe 500-700hz I'm guessing). On a bass where one pickup is really close to the neck and one is really close to the bridge I believe that what you get is a lower mids scoop (say 300-500 hz).

The scoop generally sounds pleasing on bass but you have to be careful not to scoop too much in a live setting. Using both pickups and then also scooping with the amp can cause the bass tone to lose definition. I usually solo one pickup when playing live.

Would love to see the scoop frequency proved. I have tried to use the various freeware out there but can't figure it out. Just going by ear with my triple pickup basses.

View attachment 875432

View attachment 875433
There's this cool applet that shows this :
Guitar Pickup Response Demonstration

Here's what I'm getting with the 2 pickups at 100% (circles = harmonics for the first G played on the E string) :

Both_Pups.PNG


For reference, I've added a few other captures (neck only, bridge only, neck with a bit of bridge blended).

Neck_Pup.PNG Bridge_Pup.PNG Mostly_Neck_Pup.PNG
 
It's what they said. Phase cancellation. Plain and simple. Some of the harmonics over one pickup will be 180 degrees out of phase when over the other pickup. Combine them and those frequencies cancel. Gone. Can't be heard.

Probably damages them psychologically. Support group for canceled frequencies might be helpful.
 
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There's this cool applet that shows this :
Guitar Pickup Response Demonstration

Here's what I'm getting with the 2 pickups at 100% (circles = harmonics for the first G played on the E string) :

View attachment 875579

For reference, I've added a few other captures (neck only, bridge only, neck with a bit of bridge blended).

View attachment 875577 View attachment 875578 View attachment 875580

Cool! I may have seen this before. Very curious what happens when the pickups are moved closer and pushed apart. Will need to play with it.

Thanks!
 
Interesting. Still like the sound with the pickups and tone control all the way up and I don't have any trouble being heard in the mix with it that way.

However, to be entirely truthful and candid, I compensate somewhat at my amp where I boost the low-mids centered on about 250Hz about 2 clicks because my amp gives me the flexibility to do so. In any case, it works great for me!
 
Phase cancellation that's it. Same on a Strat with the selector on 2 and 4.

Eh, not really. In the case of the strat, they pickups are wired "out of phase", so they get that odd tone that is actually so cool. Do that with a J bass and it will sound... really thin. I know. I've done it.

But the term is correct - one is electrically "out of phase", in the case of the J bass you get phase cancellation when the two signals combine. All can be seen with a good scope or doing an FFT. SOME of us quite like that "J-bass scoop".
 

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