Magnetic pickups, both single-wound and humbucker, are becoming a more and more popular addition to a CBG build. Both are now inexpensive and offer several advantages in terms of tone and absence of unwanted box noise.
Installation is relatively easy: Cut a slot in the neck for the pickup (assuming you aren’t already building stepped neck assemblies), reinforce the cutout slot, cut a hole in the box and you’re good to go.
……….or are you?
Most of us are aware of the significant differences in the tone and volume of a piezo pickup depending on the location and method of mounting. So, is location of a magnetic pickup also important to the sound quality?
Recently, two of your number (Uncle Fred and Tom T) corresponded and collaborated on this question. Using the instant gratification of email and the free-for-all recording software “Audacity” we were both able to perform independent tests and compare results.
Using 3-string CBGs, built to 25" and 25.5” scales and tuned to GDB, we set out to try to determine the position of the pickup along the length of the neck that would provide the cleanest and most balanced sound. Tests were performed with both single-wound and humbucker pickups.
To simplify testing, both guitars were tested with the tops removed. Pickups were secured to the offset neck with rubber bands to allow for quick movement up and down the neck. Tests were performed with pickup positioned down the neck as close to the bridge as possible then moved up the neck in one inch increments to as much as seven inches from the bridge.
The test procedure was to perform single “plucks” of each string at different fret locations using the bare thumb followed by a strum test. Tests were recorded using Audacity so that results could be shared and compared for consistency.
As might be expected, locating the pickups close to the bridge subdued the bass notes and produced an amplified, penetrating treble. The strong treble tones produced a sound similar to a typical piezo without any tone control applied.
Moving the pickup toward the neck in one inch increments gradually dampened the treble and amplified the bass. Locating the pickup far up the neck (in the six to seven inch area) produced an overpowering, bass and less intense treble.
The Sweet Spot:
Realizing that the clear, balanced tone lay somewhere between the extremes, we carefully tested, recorded and compared information at each location from one inch north of the bridge to six inches north of the bridge. Sound quality was compared using Audacity files emailed back and forth.
Gradually, the range was narrowed and agreed upon. Both the single-wound pickup and the humbucker produced the most balanced base/treble tone and the cleanest tone when centered approximately 3 ¾” from the bridge.
Location matters. While tone controls on amplifiers, effects devices or pre-amps might be able to adjust the tone when the pickup is located at a position other than that noted, it was our feeling that starting with the cleanest best balanced tone possible is an advantage allowing more creative use of external tone-modifying devices. So, as with real-estate, it’s all about location.
TomT & Uncle Fred
Very interesting information about harmonic points and mag pickup response.So, would the best mag response be the midpoint between a node and the bridge?
The 24th fret position on a 25" scale would be 6.250" from the bridge.
The midpoint between the bridge and this node would be 3.25" from bridge.
There is some evidence that the "sweet spot" for good, clean tone from a mag pickup is around 15% of the scale length from the bridge. This comes to about 3.75" from the bridge. Very close to the midpoint between the 24th and the bridge. Again, very interesting.
This seems logical for an open string. But, don't the harmonic nodes for a string shift as the string is fretted up the neck? Were are the harmonic nodes for the string while the string is fretted at the 2nd fret or 3rd fret?
-- Uncle Fred
Oooooh......That is a sticky thought. You are, of course, correct. The nodes will move with each change in scale length (fret). Given that reality, it seems that no matter where you put the pickup, there will be some fret which puts the node right on top of the pickup with the attendant tonal losses........
Why not mount the pick-up on a small rack inside the box so you could slide it back and forth as you play? You could fix strips of burlap on either side with wood strips glued to it for a roll-top desk effect to cover the "window". Hmmmm.. OK, headed to the shop now :)
You could mount the pickup on a slider above the strings for test purposes.
Alternatively, you can mount the pickup fully inside the box and make it "slidable"