Wolf Terminator

The Physics Of The Wolf Note

Table of Contents

Cello and bass players are not concerned with why a wolf note occurs, but in how to get rid of it without otherwise harming the tone. But before getting into the “how-to” part, it would be instructive, though, to explore some of the basic principles behind the occurrence of the wolf note because these principles underlie success or failure of any device meant to suppress this problem. In this way, you will be able to assess the probabilities of success of any of the wolf eliminator devices or cello setup strategies you may be considering. The basic physics are not hard to understand and we’ll keep the scientific jargon to an absolute minimum. If you are interested in further readings on your own, the bibliography at the end of this section will be useful.

As mentioned on the home page, the wolf note is a stuttering or warbling (pulsing) note typically found on the cello G and C string (and sometimes the D string) in the range from D3 to G3. The wolf note on the double bass is found primarily on the A and D string in the range from F2 to B2.

The wolf note is likely to occur under the following conditions.

1. The wolf occurs at or very near the frequency of the *Main Body Resonance (MBR) – also called the Main Wood Resonance (1,2,3,4). The Main Body Resonance is the frequency at which the entire body of the instrument vibrates as a whole and is the strongest of the many body resonances occurring in the instrument. In the cello, the frequency of the Main Body Resonance can vary from D3 at around 147 hz (cycles per second) to G3 at around 196 hz. For the double bass, the Main Body Resonance varies from E2 at around 82 hz to A#2 at around 117 hz. The shape of the response curves for the bass will be similar to the cello response curves shown in figures 1 and 2.

(Fig.1) The Main Body Resonance On A String Instrument


On this cello, the Main Body Resonance is slightly above F (at 178 hz).

2. When the frequency of the vibrating string approaches the resonant frequency of the Main Body Resonance, the strong resonance of the body attempts to push the vibrating string frequency away from the body resonance frequency (3,4). Finally, the string splits into two frequencies of roughly equal amplitude on either side of the body resonance (2,3,4). These two frequencies are separated by a frequency interval (in most instruments) by three to ten hz. This then is what we hear when a wolf note is being produced – two notes at the fundamental frequency, separated by a few hz, with the beating or pulsing sound between the two frequencies giving rise to the typical wolf.



This is the same cello as above: the curve with the double peaks at 174 hz and 182 hz represents the wolf note. The separation of 8 hz between the peaks shows that the characteristic stutter or pulsing sound will occur eight times per second. You can see the relationship to the Main Body Resonance in the display above. On this cello, the wolf note shows strongly on the F and partially on the F#.

3. The wolf note is more likely to occur with heavier strings (2,3,4,5). For example, the intensity of the wolf note will be much more prominent when played on the C string than when played on the G string. Conversely, the wolf note on the D string will be much weaker or absent. You have probably noticed these differences on your own cello (the A and E for basses).

4. Double bass players will notice the same responses, with the wolf weak or absent on the G and D strings, but prominent on the A string and especially strong on the E string. Some basses may also have difficulties producing clean notes an octave below the wolf because the wolf note is the second harmonic of the fundamental played an octave below.

5. Going in the opposite direction, viola and violin players seldom experience serious wolf problems. Although if you go looking for them you can probably find a wolf on the fourth string on the occasional instrument.

6. The wolf note is less likely to occur on instruments built with heavier and stiffer wood (2). Putting it another way, student instruments with coarsely graduated wood in the body will tend to have fewer wolfs than fine handmade instruments with meticulously graduated tops and backs.

Instrument Resonance Terminology

*The important instrument body resonance which is called the Main Body Resonance or MBR on this website is also called the T1, the B1, and Main Wood Resonance. In modern terminology, the B1 resonance is further separated into B1+ and B1. The wolf note originates in the vibration of the top of the instrument (the B1) but for the sake of simplicity this resonance is called the MBR.

The Robust Solution To Wolf Note Suppression