Wah Pedals and Neck Pickups vs. Bridge Pickups

Last Updated 10/28/05
By Paul J. Marossy

I have been pondering about this subject for a while. Just why is it that with wah pedals that you get a much stronger wah effect using the bridge pickup and then it almost disappears when using the neck pickup?! This is especially noticeable with humbucking pickups. Aside from the type of amp you use and what your guitar is constructed of, the pickups are the largest factor in how an electric guitar sounds. Anyone who is knowledeable about guitar pickups knows that there are a wide variety of pickups out there, each with its own unique characteristics. Some are quite "hot" and some are more "mellow". It should stand to reason then that the type of pickups that are in a particular guitar will have the largest influence on how that guitar will sound with a wah pedal. Other factors in the sound characteristics of pickups are not only the physical nature of pickups employed, but also where they are physically located on the guitar.

The other side of the coin is the wah circuit itself. There are a shocking amount of different wah circuits out there, and each wah will have its own unique characteristics. A wah circuit will have a "sweep frequency" that gives it a characteristic sound in conjunction with the how the wah circuit is designed, and there are several methods to accomplish a wah wah sound. Some wahs are inductor based and others do not use an inductor at all, but rather a "twin-T" arrangement that uses capacitor and resistor networks to accomplish a wah sound. Still others use a different method. The actual type of wah circuit can have as much of an effect on the sound as does the pickups. What they all have in common is that they all employ some method to create a resonant peak/variable comb filter sound.

So then, with so many variables, how can one explain why a wah pedal can sound dramatically different with the bridge pickup vs. the neck pickup? The answer is fairly simple. It comes down to the physics of a vibrating guitar string. A bridge pickup will simply produce fewer harmonics when compared to a neck pickup because of its position beneath the strings. Usually, the neck pickup produces more complex harmonics than a bridge pickup for a given output. But, because the bridge pickup is close to the bridge, the strings aren't able to vibrate as far as those near the midpoint of the strings. This means that you will get proportionally more higher harmonics, and fewer lower harmonics. When adjusted for the same output, a bridge pickup will sound brighter than a neck pickup. It is the attenuation of frequencies in the mid-high range which gives wah pedals their sweep and vocal qualities. This is one reason why they most often sound better when using with a bridge pickup. This is made even more apparent by humbuckers that are designed for use on the bridge, to have a high output (and DC resistance) and generate a lot of harmonics.

This brings me to a fork in the road. Anyone who is into wah pedals I'm sure has heard about the magic virtues of this inductor over that inductor. I'm sure that some of this is hype and some of it is true. What I want to point out is that, first of all, is that this is a highly subjective topic. One person will like they way a certain inductor sounds and the next person will not care for it. These people will then jump to a conclusion that "this inductor sucks", when in fact, there is a vast array of variables involved in how a wah will sound with a certain inductor - from the player to the speaker(s) in the amplifier and everything in between. If you are going to compare, please compare apples to apples! Maybe I am stating the obvious here, but it seems like a lot of people do not take all of these things into account when speaking of wah pedals and inductors. With all things being equal, many times we are talking about subtleties that the average non-musician will never hear.

One thing that I have not mentioned yet, is that where you put the wah in your chain of effects is just as important as what kind of wah it is, what magical inductor it uses, etc. Don't get me wrong, the old Clyde McCoys and certain vintage Vox wah pedals do sound great, as many can attest. All I am saying is to exercise common sense when you hear certain things about wah pedals in general. Of course, personal experience is valuable as well. Not all wah pedals will appeal to all guitar players for many different reasons. This is just a fact of life. Well, back to the original topic. At least now I have a better understanding as to why a wah pedal sounds the way it does with different pickup locations and types. I hope it was of some help to you as well.

If you want to learn more about the physics of a vibrating guitar string, check out this page. To learn more about how wah pedals work, check out "The Technology of Wah pedals" at www.geofex.com.

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