Details of working through things:
I've been having fun trying to figure this out--with email help from a luthier here who may tune in. I have not had it down to my luthier, who also did the extension work, but planned when available. This has mostly been an interesting trial and error in figuring out the issue and interesting interactions--Any "I" ideas below were definitely collaborative with these other minds.
The bass is young, November 2017, and played arco primarily. C Extension was installed in January 2019. Issues began in late February/early March 2020. Bass wolf is just south of A.
My open C string began to be tricky to start and maintain--the string wasn't reliably oscillating on C and would falter often. I first noticed when prepping Beethoven 5 in school.
At first, I thought it was an issue with the string (Perm), so I swapped it for another I had handy, but it also was present. Swapped it for a Spiro, Evah, and Passione--Same issue. Through this, I made sure the extension and nut were secure, I've had the sound post adjusted, and tail-piece moved). All of these resulted in more volume, tone, and response, except for the C string--as all of these improved, the C issue became more obvious.
I noticed that the first overtone (octave harmonic) made the issue more obvious, sounding very wolf-life, slower in its oscillation--I tried various things, including detuning other strings to reduce downward pressure on the top--which didn't help. For the hell of it, I detuned my C to B, and to Bb, the issue remained until just south of Bb, which I think was more to do with the loss of power/energy in such a soft string.
I looked back at the extension and thought perhaps the break angle behind the nut was too low, not creating a clean enough node/stop. I grabbed the scroll, pressing down on the length behind the nut, and the issue vanished! I assumed I had it, and we had a plan.
Thinking about it, this introduced more variables... I wasn't only increasing break angle, but my hand was ultimately dampening.
My extension has an adjustable/tunable nut, so I maxed it out--no change in the stability of the open/harmonic C.
Wanted a simple and temporary means of testing things--put some felt furniture pads on a few different styles of clamps--some smaller 2-ounce trigger clamps and 7-ounce spring clamps. Boom more stability in the open string and harmonic—the heavier clamp made the octave harmonic/node cleaner and less diffuse feeling under hands, a more defined node—with the 2-ounce clamp, there wasn’t the faulting of the string, but the node felt fuzzy under my finger. All other harmonics on the instrument also seem to be clearer and have more sustain.
I imagine this is what is happening at the nut as well… ultimately, the extra mass near/past the nut increases the stability of the anchor point/node of the vibrating length, creating a more stable string vibration—an inertial anchor of sorts… Other mechanisms at play could be related to constructive/deconstructive frequency responses of the neck assembly changing with the added mass in a more favorable direction in this case.
The larger mass also seems to increase fundamental/first partial—a deeper and clearer tone. Notes across the bass and in all registers are also more even and full sounding.
Beginning to think of potential more permanent solutions, brainstorming places to hide mass—behind the extension, pegbox, etc.… began using the clamps to test different placements.
Placement seems important. At the very top of the scroll is most effective—moving behind the scroll, on the body of the extension, and pegbox is all less effective in both the vibrating string stability and the perceived improvement in tonal response.
To refine this, I tried applying some small, ¼ ounce tire weights with removable mounting putty. I quickly realized that the localized weight was less effective than the large, extended clamps, which are A) vibrating along their length and B) acting with some mechanical advantage… again.. either more potential energy dampening or frequency interaction.
The 2-ounce clamp gets me a minimized vibration/string stability issue. Using a clamp around 9.5 ounces seems to give me the best response without any real volume loss. Starting the string, even at the most ppp, is easy and effortless to maintain, and I can play much closer to the bridge before I lose contact/resistance from the string.
Using the smaller profile/localized and incremental tire weights, adding ¼ ounce at a time gets me: around 6 ounces, the fundamental begins to develop more, but the instability is still present. Around 12 ounces, the instability begins to subside, similar to the 2-ounce clamp—slightly diffuse node at the harmonic. Around 13.5 ounces, the node begins to feel more stable but not as solid as the 9.5-ounce clamp. I ran out of weights at 14 ounces. I’ll pick up some more tomorrow and do some consistent side-by-side recording to post along with any suggestions or requests.
This all feels a little counter-intuitive… and adding nearly a pound to the scroll seems less than exciting. The scroll and extension aren’t particularly petite.
An additional complication, as the stability and tonal improvements, seem to peak, the string feels more difficult to close with my left hand—Not that moving the string to the fingerboard takes more energy, but there is enough vibration that keeping the string closed feels like it takes more effort and is pretty tiring.
