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P pickups angled/ flat

I play and use my ears and keep adjusting until the response feels as even as possible across all 4 strings.

The split-coil design is handy IMO because you can adjust to each string.
right.

you should end up with the D-G coil closer to the strings and about the same distance from each string, and the E-A coil a little further away, maybe dropped on the low E a pinch.

it's totally an "adjust by ear" thing; when all 4 strings are loud enough and are the same volume as each other, with no strings smacking into the pickup poles when you dig in, you're done.
 
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The angled setup is generally due to the attempt to follow the string height which should be following the fingerboard radius. That puts the "A" and "D" further from the pickup than the "E" and "G". All advice above is just as good. I've measured pickup output on a digital vu meter and it takes a great deal of distance change to make much difference in output. About the only problem you will encounter is getting the pup to close to the string. That can create some strange overtones and string muting issues due to magnetic damping of the string travel.
 
The angled setup is generally due to the attempt to follow the string height which should be following the fingerboard radius. That puts the "A" and "D" further from the pickup than the "E" and "G". All advice above is just as good. I've measured pickup output on a digital vu meter and it takes a great deal of distance change to make much difference in output. About the only problem you will encounter is getting the pup to close to the string. That can create some strange overtones and string muting issues due to magnetic damping of the string travel.

That's interesting about the VU meter. How far did you have to change the height to get a 3dB difference? (3dB being the smallest increment that most people can clearly distinguish)
 
What I've used are VU meters on recording equipment to try to balance string output. I really wasn't trying to see maximum or minimum output; I was trying to get balanced output across all strings. (short answer is that I don't know how much pickup height change is required to get a 3 db change, but there seems to be enough adj. range on a P bass pup).
I quickly found out that is not the way to set-up pickups anyway. Balanced output of an "E" string vs a "D" string does not equal the same perceived volume of each out of the amp, since amplifiers are more efficient at amplifying certain frequencies over others. Ears are as good or better at setting the pup height by listening to the perceived volume coming out of the amp. Jazz or P pups that have individual (or dual) adjustable pole pieces will allow you to get the output level very close on a meter, but when you plug in the bass, it's usually nowhere near balanced for string to string volume. A decibel meter with a mike three feet away from the speaker would probably be a better measurement of volume level for balancing string volume by pup height. Then you get into string guage, plucking force, etc. Ears win and everyone already has a pair. I'll repeat that "too close" is the bigger problem & you have to take into account that a string fretted at the 12th fret or higher will get about 3/16ths closer to the pup.
 
Yeah, I definitely wouldn't use a VU meter to set my pickup height. Better to use your ear, like you say. The catch is that a lot of time our minds and eyes overrule our ears, because we think we ought to be hearing this or that for one reason or another. That's why I think it's good to understand the physics of what's going on, so that your mind isn't overruling your ears based on a faulty understanding. Getting the science right liberates your ears to hear what they're really hearing.

That's why this VU thing is interesting. It would be cool to measure how height affects volume -- so you can know what to expect when you adjust your pickups.
 
It would be nice to have a meter or software that would averege the input level. It would help eliminate the string plucking difference. One thing I did notice while playing with a meter; the max output from a pickup is not always at a point closest to the string. It not the magnetic damping issue either. It seems there are "sweet spots" in the magneticc field of a pickup where it seems to read or detect the vibration of the string the best. It might be where the fundamental is strongest, I don't really know the answer.
 
It would be nice to have a meter or software that would averege the input level. It would help eliminate the string plucking difference. One thing I did notice while playing with a meter; the max output from a pickup is not always at a point closest to the string. It not the magnetic damping issue either. It seems there are "sweet spots" in the magneticc field of a pickup where it seems to read or detect the vibration of the string the best. It might be where the fundamental is strongest, I don't really know the answer.

I think the string pluck would need to be taken completely out of the equation to get meaningful results. A tuning fork has similar properties as a bass string and rings at a pretty constant level. You could hold it over the pole piece and move it in and out and watch the meter move. I think that would give a pretty good sense of the relationship between distance and volume. The 3dB change is what you'd be looking for since that's the smallest change that most people can clearly hear. 1 dB would also be interesting since that's what a trained ear can detect when listening closely.

I tried something similar the other day with a screwdriver (couldn't find my tuning fork), holding the tip near the pickup while tapping on the shaft with another screwdriver. It worked pretty well but I think a tuning fork's continuous note would make it easier to judge the volume change versus discrete taps - and of course I didn't have a VU meter to measure the change.

The effect on volume is a little tricky to predict because you've got two response curves interacting. There's the magnetic field (whose strength determines the signal voltage) and then there's your ear. I have a feeling the field is going to cause the voltage to drop exponentially as you move away, but then your ear's logarithmic response is going to counteract the exponential curve somewhat, making it flatter.

Someone who's better at math could probably say what that would look like, but I think the result would be a shallow curve that would give more change the closer you're in to the pickup but not radically more. I think this is what I heard with my tap test. It was a crude test but just to take a stab at it I'd say the 3dB distance was 1/8" and the 1 dB distance was 1/16".
 
We have to be careful here or we'll end up in the PUP forum. I made a mistake that got us off on another subject. What I intended to say was that it would be nice to have a meter or software to average the OUTPUT signal. If you had something that would take the peak or average of the output, it would take care of variations on input. Then you could use string pluck for input and that's what you want. A tuning fork or E-Bow doesn't have the harmonic content of a string. To get back on track with the orignial post, the P-Bass pups are angled to attempt to keep each pickup pole equal distance from each string which should get the string to string output volume close to balanced.