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Phase Cancellation and Pickup Spacing.

A

Aka Nameless

Oct 24, 2006
155
1
#1
This came up in another thread, and i'm really curious about this issue.

Phase cancellation is pretty much 1 note picked up by 2 pickups or microphones at different locations, making the waveform's crests and valleys not line up correctly when both signals are summed together, in turn cancelling out some of the sound, giving you a phasing effect, or if both waveforms (one from each pickup/mic) are 180 degrees out-of-phase (one waveform is at the highest peak of it's crest while at the same time the other is at the lowest dip in it's valley) with eachother there will be no sound.

I'm wiring up a bass that I made with 2 single coils and it will be wired like a Jazz Bass. I'm forseeing many many phase cancellation issues, with the fact that both pickups are picking up the same note but at different spots on the string, in turn, making the signals from each pickup slightly or completely out of phase.

Am I overlooking something? I'm thinking I should have considered this when I was figuring out the pickup spacing..
 
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#2
Two Pups, one say wired "clockwise" w/magnet tops you can see being north polarity (just a guess could be south) and the other arranged vise versa. This was a way that Leo Fender could get two pups (for sound variations) to cancel out NOISE from radio stations etc... In the process, the sound is somewhat cancelled out as well, but most comes thru. This why I like many others favor one pup or another to allow current/signal to flow w/out being cancelled out too much. I personally turn the bridge pup down from 7/8 to about 1/2 to get a deep sound, but w/some J-growl tone. When I have both pups up it sounds alright, although the sound is a bit compressed and less open. I have a 74 j w/very good Lindy Fralins which where designed to give more low end by having a fatter winding. Lindy winds his j pups just to the point before they lose their good tone and became blurry. Just some info. that may/may not be. helpful.
 
#3
RW/RP pickups allow you to receive the signal through both pickups and cancel the 60 cycle hum *when they are wired in phase*. You can also wire pickups out of phase, which cancels much of your low end signal (just like listening to a pair of speakers wired out of phase), and IIRC wiring RW/RP pickups out of phase defeats their 60 cycle noise cancelling. When wired properly, it shouldn't be an issue...
 
#4
I think the dude who came up with this thing in a past thread was me. Something I may have forgot to mention, play your fat B string and check out the wave it does when you hit it, detune it even to see it move even more. Examine that wave and then do it again but fretted on the 14th 15th whatever, notice how it gets smaller? so even if you could perfectly align your pups, it would work only on open, 12th and 24th. all the rest would have some sort of cancelation... no? someone wanna elaborate on this theory? Im curious
 
#6
Just like T2W said, you can get the spacing so there is no cancellation for a note of your choice, E for example, so when you play an E anywhere on the fretboard there should be no phase cancellation, but with any other note... it's all up to lady luck.

With a true humbucker this wouldn't be a problem because both coils are picking up the same note at almost the same location. But, i'm seeing a problem with wiring up my dual single coils like a jazz bass, there will be phase cancellation everywhere, no?
 
#7
Hi Y'all...

This is a nice little link with a (strictly theoretical) Java applet
that will calculate cancellation and response for a given
pickup configuration.

http://www.till.com/articles/PickupResponseDemo/

Interesting variables include the pickup width ("aperture"),
scale length, and open string frequency.
You can drag the pickups around with the mouse, and
see the resulting (again, strictly theoretical) freq. response.

Enjoy!

Peace,
Martin
 
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#8
Aka Nameless said:
This came up in another thread, and i'm really curious about this issue.

Phase cancellation is pretty much 1 note picked up by 2 pickups or microphones at different locations, making the waveform's crests and valleys not line up correctly when both signals are summed together, in turn cancelling out some of the sound, giving you a phasing effect, or if both waveforms (one from each pickup/mic) are 180 degrees out-of-phase (one waveform is at the highest peak of it's crest while at the same time the other is at the lowest dip in it's valley) with eachother there will be no sound.

I'm wiring up a bass that I made with 2 single coils and it will be wired like a Jazz Bass. I'm forseeing many many phase cancellation issues, with the fact that both pickups are picking up the same note but at different spots on the string, in turn, making the signals from each pickup slightly or completely out of phase.

Am I overlooking something? I'm thinking I should have considered this when I was figuring out the pickup spacing..
Click to expand...

I have bought basses with numerous pickup combinations and have preferred the tone on basses with one pickup. My favourite basses for tone are my pre EB Music Man StingRay and my Fender Precisions. I have two. I was surprised my G&L 2000 did not sound as good as my StingRay because I thought with two wide humbuckers the extra string sensing area would sense more overtones. The sound is compressed when both pickups are selected. The explanation of signal cancellation from peaks and valleys from the two signals is plausible and could explain what I was hearing. Any explanation is a rationalization that may or may not be true. It is difficult to predict complex relationships but reality makes itself evident.

I have observed the tone with the fullest set of frequencies, and most consistent volumes come from single pickup basses and there is more to be gained from finding ways to make the bass more rigid, shielding cavities and anchoring strings. I have noticed instruments with string through body sound better. I have replaced necks with necks that have reinforcement rods and they have improved tone and eliminated dead spots. My basses with two pickups" Jazz, G&L 2000 and Rickenbacker 4003, spend a lot of time sitting in their cases. I tend to reach for my Music Man StingRay or one of my single pickup Precisions.
 
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#10
As a solid body, that would be 1952, with the original Les Paul. They had multi-pickup hollow body guitars before that though.

The first production Fender with multiple pickups was the Broadcaster (Telecaster) in 1950. It did have a pickup selector but the original switching was neck with treble cut in the first position, neck with no treble cut in the second, and neck blended with bridge (blend controlled by the Tone knob) in the third.

I'm in the middle of reading The Birth Of Loud, so all this is very fresh in my memory!
 

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