Who’s afraid of the big bad wolf? Part 1

There is probably not a singularly more common nor perplexing problem than a “wolf on my cello”. I work with various cellos and cellists on their “wolves” almost every week. There are thousands of wolves I have tried to tame!

There are a ton of myths, legends and misconceptions about wolfs. In this blog, let’s talk science. While we want the facts, we don’t want them to get in the way of the “truth”. Later I’ll talk about the realities and how wolves operate in the real world.

Here are some excerpts of articles I have found on the web and in string articles.

The Science


A “Wolf tone” is the tendency of a musical instrument to respond at greater amplitude when the frequency of its oscillations matches the system’s natural frequency of vibration (its resonance frequency or resonant frequency) than it does at other frequencies. It may cause violent pitch swaying motions —a phenomenon known as resonance disaster. (We are sure some cellists feel their wolf is a “resonance disaster!)

Some cellos have more than one resonance frequency, particularly at harmonics (multiples) of the strongest resonance. It will vibrate easily at those frequencies, and less so at other frequencies. It will “pick out” its resonance frequency from a complex excitation, such as an impulse or a wideband noise excitation. In effect, it is filtering out all frequencies other than its resonance. In the example above, the swing cannot easily be excited by harmonic frequencies, but can be excited by subharmonics.

Excerpted from Strings Magazine

 

What Is a Wolf, Anyway?
Instrument maker Chris Dungey describes the wolf as “a result of the instability between the vibration of the body of the cello and the vibration of the affected string, which then serve to cancel each other out. The note has barely begun to sound when it disappears. This is repeated, resulting in a stuttering sound. The wolf note is mainly found on the lower strings of the cello. Not the result of a basic structural failure, a faulty repair job, or a misplaced soundpost, it’s characteristic of the instrument. Every properly proportioned cello has a wolf note.”
The process of amplifying the sound of the string through the body of the instrument is imperfect, and can interfere with ideal sound production. Seattle-based maker David Van Zandt says, “In a wolf tone, the air volume and the top, or the air volume and the back, want to cancel each other out. If there are two sound waves going up and down in sync the sound will be twice as loud. However, if the sound waves get slightly out of sync, the wolf note appears—the sound gets louder for a bit and then the waves cancel each other out. There is so much energy when the two notes are slightly out—so at the top of a sound wave the pitch goes up, and at the bottom it goes down.”
Fan Tao of D’Addario Strings mentions that better-sounding instruments tend to have stronger wolf tones. “There is some truth to the belief that good-sounding cellos and wolf tones go together. Powerful resonances are required for good-sounding cellos, but they also increase the likelihood of wolf tones.”

 

OK… so much for the science, my head hurts! In my next post, we’ll find out what to do to chase “The Big Bad Wolf!”

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