Taming the BASS WOLF

Most conversations about wolf notes focus on the cello, an instrument that is particularly prone to the phenomenon. Violinists and violists tend to only encounter wolf notes when playing in high positions on their lowest string and are usually able to overcome them by creative bowing or fingering. But double basses do suffer, and frequently their wolf notes are right in the thick of their bread-and-butter orchestral range.

what is a wolf note?

A wolf note is characterised by a juddering string which feels like it is fighting the bow and choking the note. The note will often jump into the harmonic an octave above - this yodelling effect presumably giving it its name. It is a complex acoustic phenomenon, but is essentially caused by an interaction between the main resonance of the instrument and the particular frequency of a note (see box, page 32).

Any stringed instrument has a soundbox. Think of a glass bottle: you blow across the top, and it makes a note. Add a bit of water, and the note becomes higher, because you have changed the size of its resonating chamber. A double bass is, of course, more complex than a glass bottle, and part of its construction is to mitigate its favouring one frequency above all others, with elements including its top-plate graduation, soundpost, bass-bar, bridge and tailpiece all working together to even out that sort of response.

how to combat a wolf note

It is important to understand that, even though not all instruments have a distinct wolf note, having one does not imply a poor instrument. In fact, the more resonant an instrument, the more likely it is to have a wolf. That said, it may be possible to fix a wolf, or at least make it more manageable, by asking a bass-specialist luthier to experiment with some adjustments to your instrument. There are also a number of wolf-note suppressor products on the market which are worth considering. They work in different ways but each aims subtly to change the resonance of the instrument enough to discourage the wolf note - ideally without affecting the overall tone.

Reports differ, but it seems the bass wolf tends to appear between F and B flat, with the area around A flat and A a particular trouble spot for 3/4-size basses. The unluckiest location is the G, which in extreme cases can even affect the open string. I chose that as the scenario to present to a range of bass specialists.

Jay VandeKopple (below),director of the VSA/Oberlin Bass Workshop, says that with any wolf note he would first check to see if it only appears high up on the A string. ‘If it is also wolfy on the D string (at the same note) and the G string (again at the same note), then I’ll try adjusting the soundpost. If I only get the wolf on the A string, I’ll start with a different approach.’ His concern is not to sacrifice the resonance of the instrument for the sake of fixing a wolf: ‘What I want to do is to have something on the instrument that will vibrate at the wolf frequency, but not generate sound output. If isolated near that one frequency, it should not mute the instrument. I’ll generally start with one of the wolf suppressors that attaches to the afterlength of a string.’

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His process is to use the suppressor’s position on the afterlength and actually tune it to the wolf. ‘It should have its lowest pitch when centred between the bridge and tailpiece. If we move it either way, the pitch will rise. What I don’t want to do is get into an adjustment that shifts the suppressor close enough to the bridge that it would act as a mute on the sound. If you need a higher pitch, it’s better to go with a lower-mass suppressor.’

VandeKopple suggests it may be possible to draw the bow across the suppressor in place and hear its frequency, but he recommends using a ‘Fuhr tube’ (a thin glass capillary tube) for tuning purposes, and is currently working on an article explaining the process.

Jason Heath (below),double bass player, teacher, and host of the Contrabass Conversations podcast, also recommends adjustment by a luthier as the first port of call. ‘I’ve found that a good soundpost adjustment can often shift the wolf to another note. Most bass players would rather have a wolf on A fiat than on G or A, and this can often be achieved simply by getting a soundpost adjustment. There are a variety of wolf-note suppressors that can be used between the bridge and tailpiece, though these often have the effect of reducing the volume of the instrument or otherwise diminishing the tone. Many players have also noticed some wolf-note improvement by switching to a carbon fibre endpin.’

The more resonant an instrument, the more likely it is to have a wolf

Martyn Bailey (right),a bass-specialist luthier in Essex, UK, says that he would always recommend an instrument with a bad wolf is inspected for obvious structural problems and has its set-up checked over. ‘Then I would start with the simplest and least expensive adjustment, namely the soundpost position and fit sometimes this is very effective and other times not at all.’

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George Martin of Thomas & George Martin(below)in Oxfordshire, UK, also recommends some trial-and- error adjustments before using a suppressor, particularly for very strong wolf notes. ‘If I had a bass that was fighting itself, the first thing I would do is change the tailpiece, the length of the tailwire, or the tailwire material. If you do have a bass with a wolf on an open string, changing some variables might just move it away enough that it won’t bother you if you stay in tune.’ Martin does, however, caution against making soundpost adjustments with only the wolf in mind. ‘The problem with changing the soundpost is that you might lessen the wolf, but you’ve likely done it at the expense of that whole range of the instrument.’

Adjustment is also the first choice for the team at the Quantum Bass Centerin Houston, Texas. ‘If you have a wolf on G (and nothing apparently unusual with the neck angle, string length, bass-bar, or plate thickness), you would start by adjusting every possible function. So first examine the bridge fit and placement (perfectly perpendicular to the top, no gap under the feet). Check the soundpost condition and position so the bass plays as easily as possible. Tune the afterlength, trying a couple of consonant intervals to see if one works better than another. Experiment with the tailpiece mass, tailwire material and endpin to see if they affect the wolf. Try a magnetic wolf modulator, particularly on the bass side of the top, about six inches below the f-hole. Make sure the strings are in good condition, and consider experimenting with a different string type.’

‘Most bass players would rather have a wolf on A flat than on G or A, and this can often be achieved by a soundpost adjustment’ - Jason Heath

A LITTLE WOLF SCIENCE

Key to understanding the wolf note are the concepts of phase cancellation and Helmholtz motion. Picture a sound wave, with its smooth peaks and troughs. Now introduce a second identical wave, but slide it along by half a wavelength, so it looks like a mirror image of the first, with each peak corresponding to a trough in the first. Separately, they sound exactly the same, but together they cancel each other out. The phenomenon is known as a phase cancellation and is half the story behind the wolf note. On any note but the wolf, the instrument takes the lead from the string, where all the energy is coming from, and resonates accordingly. But at the wolf frequency the body over-resonates and starts feeding back through the bridge into the string, creating the potential for phase cancellation.

A wolf note is particularly associated with bowed strings, which is crucial. Look up Helmholtz motion on YouTube. When a string is plucked, it does not, as you might imagine, vibrate in a nice rounded wave shape. Instead it forms a sharp peak which travels the length of the string, bounces on the bridge and travels back again. It gradually smooths out as the energy dissipates. However, when you bow a string, you keep putting energy back into it, so this sharp peak remains sharp and, in fact, when it travels back under your bow, it causes the bow to slip across the string a fraction. This is imperceptible to us as it happens so quickly. When coupled with the wolf frequency and potential for phase cancellation, the sharp peak acts as a trigger for the string to jump in and out of phase with the exaggerated body vibration, and causes the bow to skip and slip erratically.

As a side note, this is also why wolf notes tend to be more pronounced when playing notes in high positions on low strings, because the string is operating outside its most efficient state, and is less able to impose its vibration on the instrument.

WOLF ELIMINATORS

The products listed below have a good reputation, but we would always recommend making decisions about your instrument with the help of a luthier

Wolf-Be-Gone

Super-Sensitive Musical String Co /www.supersensitive.comAn example of the most common style of eliminator, with a rubber liner, thumb screw and lock nut. These eliminators are affordable, easy to fit and widely stocked.

Wolf Note Suppressor

New Harmony Music /www.newharmonymusic.comAvailable in 16, 18, 20, 22, and 24g weights for bass, with the recommendation that the lightest weight necessary to eliminate the wolf note is used. The curved notch in the solid brass cylinder means that it is held in place just by the taut string itself. There is no need for a rubber insert or screws that might come loose, and many reports suggest these suppressors are less prone to any muting effect.

Rezx Resonance Modulator

Rezx Inc /www.rezx.bizA pair of strong magnets with a brass weight. One magnet, fed through the f-hole, holds the weight in place on the top plate of the instrument. It has a soft leather pad, so it can be moved around on the plate without damaging the varnish. The device works by altering the vibration characteristics of the instrument and requires a gradual search for a position that discourages the wolf without affecting the overall resonance of the instrument.

Krentz Modulator

Krentz String Works /www.krentzstringworks.comThis product, designed by cellist Kevin Krentz, uses a magnetic piston enclosed in a tube which attaches to the underside of the top plate through the f-hole, and is held in place with a subtle outer magnet. The manufacturer claims that the device alters the vibration pattern rather than just absorbing its extremes, and doesnt dampen the overall resonance of the instrument.

Wolf Terminator

Hideo Kamimoto /www.wolfterminator.comThis wolf eliminator has a tuning screw so it can be precisely matched to the wolf note. It is attached to the top plate with museum putty, a removable adhesive which doesnt damage the varnish, meaning the device can be applied and reapplied many times. The manufacturer claims that, owing to the eliminator’s ability to be tuned to the wolf note specifically, it can remain effective when installed in less resonant areas of the instrument top, thereby reducing or eliminating any effect on overall resonance.