Friday, June 24, 2011

Violin Open E String Whistling Problem (Part 3)

Let us explore some common beliefs about whistling E-strings.

"The open E whistles easier if you play a D natural right before it." False. The D natural has no effect on the whistling; it just happens to be the most common note played before the open E.

"The open E whistles easier on a down bow." False. The E will whistle on an up bow just as well. It has so happens that crossing from the D to E string is most commonly done on a down bow.

"The bow hair needs more rosin, or needs to be rehaired." There is some truth to this. If the bow hair is in poor condition or lacks rosin, this will make it harder to start a normal note and make it easier to whistle. However, if your bow hair has enough rosin, adding more will not prevent whistling.

"Gold plated E strings are easier to whistle." There is some anectodal evidence to support this, but no proof. If true, it might be due to the smoothness of the gold plating, which reduces torsional damping due to the string rubbing against the bridge string notch and nut.

Certain types of plastic sleeves or string notch covering may make whistling easier. I recently encountered violins with bad whistling problems that had a very smooth and shiny bridge string notch covering material instead of the traditional parchment.

Any adjustments to violin setup that changes the response of the E-string can affect whistling. However, there is no single violin adjustment that will prevent whistling in all cases. Therefore, luthiers might go through a lengthy list of adjustments, including soundpost, bridge setup, changing the shape of string notches, the tailpiece assembly, etc. in hopes of finding a cure. The only remedy that will work all the time is to use a string like our Kaplan Solutions non-whistling E (KS311W 4/4M).

Wednesday, June 1, 2011

Violin Open E String Whistling Problem (Part 2)

When I designed the Kaplan Solutions non-whistling E-string (KS311W 4/4M), I spent hours trying to make an E string whistle so I could take some measurements. This after years of trying to achieve just the opposite!

Last summer at the VSA-Oberlin Acoustics Workshop, Aaron Boyd, concertmaster of the Tucson Symphony Orchestra, taught me a very reliable way to whistle an open E. Start the bow moving above the string first, then contact the E string. This works equally well down or up bow! I then remembered a talk by acoustics researcher Knut Guettler where he showed that quick and clean starts of (normal) bowed notes required just the right amount of bow acceleration. I finally realized why preventing an E string from whistling is so difficult.

The normal bowed string vibrates in a transverse (side-to-side) motion, producing a saw-tooth shaped waveform. This motion is called the Helmholtz motion after the great 18th century German physicist Hermann Helmholtz who discovered it. Only certain combinations of bow speed, acceleration and pressure produces a stable Helmholtz motion.

When the bow contacts the string while it is already moving (such as crossing to the open E string from the A string), conditions are favorable for the start of torsional vibrations, and unfavorable for the start of normal transverse vibrations. One rarely whistles an open E-string when starting a note with the bow already on the string, or after changing bow directions, or when playing repeated notes because in these situations the bow starts each note with zero velocity, which favors the start of normal transverse vibrations over the torsional.

Therefore, the way to prevent the whistling E using bowing technique is to stop or slow the bow before it contacts the E-string. In addition, an increase in bow pressure on the E will favor the transverse motion over the torsional, and that is typically what players try to do. However, this usually fails because the increase bow pressure is often accompanied by an increase in bow speed, which is the exact opposite of what is needed! Unfortunately, the bowing conditions required to prevent the whistling may be undesirable musically.

In part 1, I discussed how wound E-strings can solve the whistling problem. In the next part, I will explore some common beliefs about whistling E-strings, and what might be done to minimize the problem through instrument setup.