Standard Control Methods
Most wolf eliminators attempt to control the wolf note in one of three methods, with adjustments and setup constituting a fourth. There are advantages, disadvantages and trade-offs for each.
1. The first, and probably oldest method, is what could be called the “brute force method”. In this category, the wolf is diminished through a small weight attached to the top, or through damping the top vibration by wedging a cork or other semi-soft material between the tailpiece and the top. In a pinch, a regular mute can be used, either on the bridge in the normal fashion or pushed partially back from the bridge. Most players would agree that using a mute as a wolf eliminator is not a real solution. For cello players, squeezing the the lower bout of the instrument with your knees (carefully – this is literally brute force) can help. For bass players, this is not an option!
Each of these methods will diminish the response of the top to vibrations transmitted from the string/bridge to the top (this reduces the amplitude and/or changes the frequency of the Main Body Resonance) and in so doing, the interaction between the string and the body resonance at the wolf frequency is reduced. With enough weight or pressure, this can reduce or eliminate the wolf. Unfortunately, because this method is not selective, the overall tone will be noticeably affected.
Tuning The Afterlength Of The String
2. The second method relies on selectively tuning the string running between the bridge and the tailpiece (typically the G string on the cello and the A string on the double bass) by attaching a small weight to the string. The afterlength of the string is then tuned to the wolf note region by adjusting the weight and position of the device. This is the method (a single resonator) proposed by Schelling (2) in the mid-sixties and wolf eliminators based on this method are perhaps the most popular because of their simplicity and reasonable cost.
Most commercial wolf eliminators of this type consist of a metal tube lined with rubber on the inside. When fitted to the string it is tightened just enough to prevent it from accidentally moving. The relative loose fit and the interior rubber lining broaden the frequency response of the device and make it effective over a wider frequency range. By moving the device along the string and listening to the string while tapping it, the string can be tuned to the approximate pitch of the wolf note. A consideration when using this type of wolf eliminator is that popular mutes which slide on the G and D strings can’t be used.
A major obstacle is that this device cannot be easily adjusted for the amount of suppression. If the device is moved closer to the bridge, suppression will be introduced to the entire range of the cello (the effect is similar to a mute) and the tuning of the string to the wolf note cannot be maintained. In the lab, the weight of the wolf eliminator can be adjusted, and thus the amount of suppression can be adjusted while maintaining the tuning. This is difficult to achieve in the real world by real players.
Another problem with this method goes back to the physics of the wolf note, the interaction between the vibrating string and the Main Body Resonance. By introducing another tuned resonance (the string with wolf eliminator attached) in addition to the vibrating string and the resonance of the body, the practical net effect is to push the offending wolf note away from the desired note. If the original wolf note is not too strong, pushing the wolf note away from the intended note and away from the Main Body Resonance can be enough to diminish the interaction between the string and body resonance and allow a clean note to be played. With strong wolfs which span two adjacent notes, moving the wolf note around doesn’t solve the problem.
Because the wolf note is not actually eliminated but pushed away from the desired note, this inherently unstable condition makes it hard to maintain this adjustment over a long period of time. If the wolf note is severe, affecting two adjacent notes, it will be difficult (if not impossible) to eliminate the wolf from both notes. In addition, changes in strings or in the setup of the instrument – anything that affects the string/bridge relationship with the resonances in the body – will almost certainly alter the effectiveness of this type of eliminator. For mild wolf note problems, this method might be “good enough”. There are better ways to control the wolf. Because the afterlength of the string between the bridge and the tailpiece is a particularly sensitive area for tone production, many players notice a degradation in tone when using this device.
3. A third type of wolf eliminator makes use of an independent resonant element within the device to counteract the wolf note. One make, which is available in three tuning ranges is affixed to the instrument top. This “resonator” type of wolf eliminator is broadly tuned and even though its tuning is not specific to the exact frequency of the wolf note, this device appears to work more effectively than the type 2 devices described above. Since this device is attached to the top and not the string, it is not affected by changes to the string or bridge, nor does it interfere with the use of a mute. On the other hand, the non-specific tuning is relatively insensitive to the vibrations of the instrument and requires attachment to the most sensitive areas of the top, affecting the overall tone of the instrument. And as with the wolf eliminators above, this single resonator type of wolf eliminator works by pushing the wolf away from the intended note. As with the wolf eliminators above, this type of wolf eliminator can help with mild wolf problems but is ineffective when a severe wolf affects two adjacent notes.
Setup And Adjustment
4. The overall setup and adjustment of the cello will affect wolf notes on the cello. That is, since adjustment of the bridge, choice of strings, and adjustment of the soundpost and tailpiece, all interact with the many resonances of the instrument (including the Main Body Resonance) the setup of the instrument will affect the severity of the wolf. In some instruments, using a lighter string can help minimize the wolf, at the potential expense of volume and/or tone. There is a difference of opinion as to whether or not adjustments in the instrument setup to specifically minimize the wolf is advisable. Adjustments which can minimize a wolf note can run counter to adjustments which enhance the best tone. While you would probably want to consult with your violin repair shop before having anything done, it would seem that setting up your instrument for the best tone quality should receive the highest priority. Further adjustments to reduce the wolf note should not be done at the expense of tone.
As you can see, each of the common methods used to control the wolf note has advantages and disadvantages. Each can work when the wolf note is not severe, but all lack consistent and predictable results. All fall short whenever the instrument has a really strong wolf.