Wolf Notes and Beats
Main C note and Partials
Before we can understand the idea behind a wolf note we must first learn what makes up a note. "When we hear the sound from a vibrating object (such as a musical instrument) we hear a complex sound that contains many different frequencies or pitches called partials. This collection of frequencies, pitches or partials is called the harmonic series or overtone series. This series is based on a fundamental frequency or pitch (first partial) with the series of harmonics or overtones comprising the remaining frequencies or partials. The fundamental is usually the strongest frequency to the ear and defines the pitch of that sound. The intensity (or volume) of the overtones or remaining partials provide the " tone color " or " timbre " of the sound which explains why a middle C on a trumpet sounds different from a middle C on a trombone or tuba. Many factors enter into the strengths and weaknesses (intensity or volume) of the partials. either the fundamental or an overtone in the harmonic series" Source file .
The Following article was written by Roger Siminoff (1) It should give you a good understanding of wolf Tones and of what is going on when you play your instrument. If you are planning to learn Violin Repair you will need to have a grasp of these basic concepts, as you are working on an instrument.
" It is the order of partials and the intensity of each partial that makes up a tone or sound that we here. ( By "order," I mean the arrangement or sequence of them within a sound.) We can adjust the intensity of various partials to make low pitched notes sound bright and dynamic, or we can adjust them to sound warm and regal. Likewise, we can do the very same alterations to high pitched notes.
In other words, by altering the arrangement of partials, we can effect a change in the tone "color" of a sound. Strange as it might seem, we can place the same steel string on several acoustic instruments, and it will develop a unique tone on each one.
A number of things will help alter the strings vibrations: the resonant frequency of the instrument as a whole; the resonant frequency of the air chamber, or of one particular member of the system that is very sensitive and responsive to a particular frequency; the stiffness of the mechanism as a whole, and how that stiffness will help to support the strings vibrations; the frequencies that the player demands from adjacent strings; and so on. The bridge and soundboard play a very important part in helping the string to continue generating its energy. If one or both of these members is very flimsy, or made of very soft wood, it will tend to absorb ("damp") the string's vibration until its energy is gone. On the other hand, if one or both of these members is stiff and has great resilience, that factor will give the string a good springboard to leap from, toward the next vibrational mode.
This supportive force, coming from another member of the acoustical system, is called a "restoring force." It does exactly what the name implies. It restores energy to the vibrating member.
Sometimes the strings can be fooled. Sometimes the exchange of vibrations is not favorable, resulting in one of two negative qualities. The first is the" wolf note"; the second is the pulsating tone.
The wolf note, although virtually always present, is rarely perceived in plucked musical instruments because substantial continuous energy must occur to produce it- and that continuous energy is only found in the bowed members of the acoustic instrument family.
The phenomenon occurs when the string is played at a pitch identical to that of the resonant frequency of a major member of the acoustical system, such as the soundboard or the backboard. When the string is played, the soundboard ( or other member) begins to vibrate+ in sympathy with the string, and in so doing absorbs the string's vibration at that frequency. Then the string - devoid of the stolen frequency (or frequencies) - vibrates with greater intensity in its other partials (or modes). What happens next is that the soundboard, unable to find more of the energy that set it in motion ( the string's vibrations at the affected frequency) in the first place, ceases to vibrate at that frequency.
That puts the string back in business at that frequency - which then starts the cycle all over again. The exchange continues over and over as the instrument produces a howling sound - fondly termed the wolf tone,or wolf note.
The pulsating tone is produced when a string is played at a frequency that is close to, but not identical with, the same pitch as the resonant frequency of one of the major acoustical members. When the string and the similar resonant frequency note are vibrating together they produce "beats" a sound that is the difference of the two frequencies.
For example, if an A440Hz note is played, and the air chamber of the instrument is tuned to an A445Hz pitch, the difference of the two frequencies is 5Hz and beats, or pulsating sounds, of 5Hz (five cycles per second) will be heard along with the the string's vibrations.
Other tone-color qualities that are perceived in string instruments are the "combination" and " difference" tones. Like beats, these tones are created by the difference between two frequencies . But unlike beats, they usually aren't unpleasant qualities. A combination tone is produced by the union of two other tones, and it is a note whose frequency is the sum of the two frequencies that produced it. For example, if an A440Hz note is played along with a D2293.66Hz note, a note will also be perceived that has a frequency of 733.66Hz ( just flat of a fifth - octave F#)
A difference tone is one that is perceived as having a frequency that represents the difference between two other frequencies. If we use the example above, a difference tone created between the two notes I mentioned would be 146.34Hz, or almost a third-octave D (146.832Hz).
Some interesting points about this last pair of tone types: First, although they are an inescapable phenomenon of acoustics, they are kept from bothering us thanks to to the magic of our hearing system - since we tend to hear only what we want or expect to hear, and usually filter out these other tones. Second, our sense of hearing is capable of producing its own set of aural harmonics, and aural combination and difference tones. Third, notice how close the frequencies are to frequencies that are already part of our scale."
There are different types of wolf note eliminators on the market that will help to combat this problem. One common type of eliminator will clip on to your string behind the bridge. If you have a wolf note say on a Cello D string, you would not put the eliminator on the D string but on the string next to it. Maybe the C string or the G string which ever one would help to stop it the most. Sometimes you must move it up and down the string closer to or further away from the bridge till you find the best spot. You also have the type that is fastened to the top of the instrument through the "F" hole. There are many varieties to work with.
(1) Siminoff, Roger. "Tracking Beats and Wolf Tones." Frets. January 1984: Page 64. Print.