Do Bode Plots reflect Output?

[gpdb]

I've noticed that in general, the overall height (in dB) of my bode plots seem to correlate with inductance. The higher the inductance, the higher the chart. When compared to Dimarzio's output readings in mV, they don't always seem to correlate. For instance, my Dimarzio Evo2 has an inductance of 7.5 H, and my Dimarzio Evolution has an inductance of 6.7 H. Dimarzio's website states that the Evo2 has less output than the Evolution - 375mV vs. 404mV. When looking at the bode plot, the Evo2 has more dB overall than the Evolution.


 So, do bode plots not accurately represent a pickup's output? And if they don't, how should I be interpreting the overall height of one pickup's plot compared to others? 

[stratotarts]

Isn't this just a case of, DiMarzio specs being wrong?

[gpdb]

That's essentially my question - Is the plot right or is Dimarzio right? I'm not well versed enough on bode plots to know if they actually mean output or not. Going back to the Evo2 and Evolution, the Evolution has a bigger ceramic magnet, so it should be able to produce more magnetism within the strings, which would make me believe it could produce more output. But it also has less inductance, and generally I've heard that inductance = power (but that could be wrong too). Dimarzio clearly got their reading from somewhere. I can't remember where I heard this, but I recall reading that they excite the A string with something like an eBow and measure the average voltage.

[antigua]

By and large, yes, this test does reflect the output. The reason being that they mitigating factors are small. 

The three main things that determine output 1) coil turns (causes higher inductance) 2) magnetic strength 3) magnetic coupling with the strings. 

Only one of these three is not covered by the exciter coil test, magnetic strength, but it tends to be the case that the guitar string magnetically saturates, and that the degree to which magnetic strength can increase the output maxes out, and the other two factors become more dominant. In a test I did recently, I had a pickup with ceramic bars and no steel, meaning the magnetic coupling was very low but the magnetic strength was very high, and to my surprise, the output of the pickup was overall a lot lower than I have even expected it would be.

So the more important factors, magnetic coupling and coil turns, also cause the test output to be higher, so the test is effectively measuring output potential of the pickup as well. Keep in mind though that the exciter coil is not shaped like a guitar string, so you can't compare a PAF humbucker to a Strat pickup in this manner, since the PAF is a wider pickup with two coils under the guitar string, the magnetic coupling coefficient is different, and the results are not apples to apples, but for pickups of the same form factor the test is valid. 

Keep in mind that moving the exciter coil even 0.5 mm nearer or further changes the output well in excess of 1dBV, so if you do this test, your test rig has to be precise and you have to consider things like how the cover on the pickup is affecting the comparison, because the cover will mean the exciter coil is a millimeter or two farther from the coil than a pickup with no cover. Like if you're comparing Tele neck pickups, it might seem like one pickup is lower output than another, but it turns out there's just a little more of a gap between the top of the cover and the top of the coil that is to blame. 

As for DiMarzio's output chart, it's probably just made up and intended to satisfy customers who ask a question that they probably don't have a good answer for. 

[guitarmd]

I've wondered the same thing. All the lower bode plots were a humbucker I made, tested with different magnets. I was quite confused when I tested a Strat single coil I made and it started plotting all the way up there. I'd like to know what the deal is too. I stopped the plot after having a "wtf?" moment. 19.8dBv higher than the humbucker.

I don't remember the exact inductance for those pickups, but the humbucker was quite a bit higher, at least 1.5 or 2 Henries more.

[antigua]

Nov 12, 2022 12:17:18 GMT -5 guitarmd said:

I've wondered the same thing. All the lower bode plots were a humbucker I made, tested with different magnets. I was quite confused when I tested a Strat single coil I made and it started plotting all the way up there. I'd like to know what the deal is too. I stopped the plot after having a "wtf?" moment. 19.8dBv higher than the humbucker.

I don't remember the exact inductance for those pickups, but the humbucker was quite a bit higher, at least 1.5 or 2 Henries more.

I'd guess the coupling with the exciter coil is different in these two cases. Humbuckers and single coils are apples and oranges in terms of how the exciter coil spatially pairs with their coils, especially given that to measure a humbucker you have to set the exciter at a 90 degree angle in between the two side by side coils.  I don't usually see a difference that large, though. Maybe if I observed your test setup, a cause would present itself.