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Wolf Tones

So you've found a distinctive wah-wah-wah-wah-wah on a note on your instrument and it's all you can think about.
 

It sounds like you've broken your vibrato and your bow stroke feels like you're driving down the rumble strip on the highway.

You have just discovered a wolf tone.

If this is your first experience with this phenomenon, you may be concerned there is something seriously wrong with your instrument. The good (and bad) news is that with enough determined hunting, wolf tones can be found on ALL bowed string instruments. In fact, the better adjusted your instrument is, the higher the likelihood is that you will find a more pronounced wolf tone.

Why Does My Instrument Have a Wolf Tone?



While there are issues that can contribute to a wolf tone that require immediate attention (see the photos to the right), the average player will notice wolf tones when they are playing a well-adjusted instrument or they may find wolf tones that emerge in dry climates or when winter months arrive.


These are very common causes, but you can't stop winter and you don't want to turn your well-adjusted instrument into a poorly-adjusted instrument. To better understand how to adjust a wolf tone, let’s take a look into the very basic mechanics of what causes a wolf tone. 



The issues pictured above require the immediate help of your repair-person/luthier.

What is a Wolf Tone?


There are several different types of wolf tones, but for the sake of simplicity, today we are going to refer to the definition of a wolf tone as a note (or notes) which is, “literally, not absolutely controllable by the player.” (Pickering page 39)

Before we can understand how a note can be out of control, let’s take an elementary look at how sound is created and controlled on a violin, viola, cello, or bass. 

How a Player Creates Sound—Simplified

Although there are many moving parts that contribute to the creation of sound on your instrument, here we will focus on the following parts and how they play a large role in how notes/frequencies are created/excited:




1. The Bow. 
Wolf tones are most easily discovered during sustained notes. On violin (and viol) family instruments, sustained notes are made when the bow is drawn across a string.


As the bow moves along the string, the continuous energy supply coming from the bow causes the string to vibrate side to side.



2. The String(s). 
Once the string begins to vibrate continuously, that energy is transferred from the string to the top of the bridge. 



3. The Bridge.  As the energy from the string excites the top of the bridge, the remainder of the bridge beings to vibrate and move together (or in-phase) with the string. Those bridge vibrations are carried through to the top of the instrument. 
4. The Soundpost. The soundpost—which stands inside of the instrument—quickly transfers the vibrations from the top of the instrument to the back of the instrument. (The bassbar also helps transfer these vibrations along the top of the instrument.)

5. The Instrument Body. 
The sustained energy coming from the bow to the string to the bridge and all the way to the soundpost causes the body of the instrument to vibrate.

Review Time!
Let's review our simple sound concepts.

  • Bow energy makes the string move (vibrate).
  • String vibration makes the top of the bridge move.
  • The entire bridge begins to vibrate, moving in-phase (together) with the string.
  • Sound/vibrations transfer to the top of the instrument.
  • The instrument top vibrates and the soundpost transfers the sound to the back of the instrument.
  • The instrument body begins to vibrate.

 

More Complex Concepts

No Batteries Required for Amplification. 


The body of the instrument (and its reverberations or resonance) is especially important when discussing wolf tones.



For example, if you consider an electric cello like the Yamaha "Silent Cello" (pictured right), this instrument does not project a lot of sound without being plugged into an electric amplifier. As the name implies, Yamaha specifically designed this line of instruments to be virtually "silent" without external amplification.  


Electric instruments don't put out a lot of sound on their own because they have either no body to act as a sound chamber (like the "Silent" Cello) or they have solid bodies which just don't act as a sound chamber. 


However, in the case of acoustic cellos, violas, violins, etc., the body of the instrument—the top, the back, the ribs (sides), and even the air swirling around inside—helps magnify and project the sound of the instrument.








Simply put-- your instrument's body is its amplifier. 

 

The instrument body plays such an important part in how pleasing an (acoustic) instrument sounds that violin, viola, and cello bodies are built to be as resonant as possible.

In fact, when making an instrument, a luthier (string instrument maker) will tap in different places on the top and back plates, listen to the note/frequency made when tapping, and then remove wood in different areas to help fine-tune the top and back plates so that, when tapped, specific notes are created.

The better fine-tuned the top and back plates are, the more easily notes will excite the individual plates and cause them to vibrate.

 





When the top, back, and ribs (and, of course, the other important parts which make up the body) are all glued together, there are certain played notes/frequencies which cause the air inside the body to reverberate/resonate. 







Just as the top and the back each have certain notes/frequencies which cause them to vibrate easily, a fully assembled instrument body will have its own certain resonances.
 
As described on PhysicsCentral.com, a resonance is a frequency (note) "at which the violin naturally tends to vibrate—most of us are familiar with resonances of objects like tuning forks, which, very soon after being struck, vibrate at one frequency and not any other." The body of the instrument has its own resonances.

In fact, there are certain frequencies that cause the instrument to react more strongly than it does with other notes/frequencies. This strong response is also known as a strong body resonance. (Artist rendering of a Strong Body Resonance pictured left. **Remember this guy--he'll be back.)














Fun Fact:  As described in the post "How Does a Violin Work?" by Professor Joe Wolf at the University of New South Wales, the air inside the instrument can, "vibrate a little like the air in a bottle when you blow across the top. In fact if you sing a note near D4 close to the violin (or the second lowest string on a viola, cello, or bass), and then hold your ear close to the f-holes, you may hear the air in the body resonating. This is called the Helmholtz resonance.” 

So try singing into your instrument's F Hole! If you have a violin, sing the same note as the D string. If you have a viola or cello, sing the same note as the G string. Then listen for the Helmholtz resonance!

Here’s What a Renowned Engineer Can Teach Us

In his article titled, “The Wolf Tone,” which originally appeared in Volume 37, Number 3 of Bass World, musician and renowned engineer, Norman Pickering, goes into great detail on what a wolf tone is and offers some suggestions on correcting the issue.

We won’t go through the entirety of his article here, but let’s touch on a few of the more important points he makes regarding the most common causes of wolf tones.

Played Note vs. Strong Body Resonance: Competing Frequencies

Mr. Pickering says, “In the case of an instrument with a strong body resonance close to the string frequency, the (strong body resonance) can steal energy from the string and oscillate strongly enough to overwhelm the bowed note.”

This means that when a bowed note is close in frequency to the strong body resonance of the instrument, the excited, super-strong body resonance fights back and creates interference or a note which is “not absolutely controllable by the player.”

Recap.

Similar Bowed Note/Frequency + Similar Strong Body Resonance = Wolf Tone!

Why Does the Bow Feel Out of Control During a Wolf Tone?

Many players complain that when they try to play the note which creates/excites a wolf tone, it feels as if they cannot control their bow.

Mr. Pickering explains that when the musician is bowing a note which occurs below the strong body resonance, “the string and bridge are moving in-phase (together).”

Later he continues, “At the start of the (problem) note, the string forces the bridge to move in the same direction as the force it exerts. Coupling (the note played combined with the body resonance) can cause the bridge motion suddenly to reverse phase, opposing the string force. Bridge motion is suppressed, and the tone drops abruptly.”

Remember what we learned about the creation of sound?

When a note that doesn’t have a wolf tone is bowed on the string, the string and the bridge move together. The body of the instrument then happily resonates and acts as an amplifier of sound.







When a note that does have a wolf tone is bowed and the bridge is excited, the body of the instrument begins to vibrate and activates a strong body resonance that essentially fights back!






 





The strong body resonance causes the bridge to reverse the direction it is vibrating.


Because the bow is still providing energy to the string, the string vibrations continue to try to move the bridge while the strong body resonance is trying to do the same thing.







 

With both forces pushing the bridge in opposite directions, the bridge motion will temporarily be stifled and the tone of the note will drop abruptly.

Once the note drops, the strong body resonance is no longer being excited and the player is able to regain “control” of the note through continued bowing. Then the cycle begins again.

Bowing through a wolf tone becomes even more difficult the quieter (or further from the bridge) the note is bowed.

Other Wolf Predictors

Mr. Pickering also lists the following elements which can help in the prediction of a wolf tone:

“The frequency difference between a major… resonance in the instrument and a desired musical note. Less is worse.”

Translation: The closer the bowed note is to a strong body resonance, the worse the wolf tone is.

 

“The amount of energy available from the string. More is worse.”
Translation: Higher tension strings can increase the energy provided to the bridge/instrument body and are more likely to excite wolf tones.

Why are Wolf Tones More Prominent in Higher Fingerboard Positions?

Many cello players notice a more pronounced wolf tone on/between the E3 to G3 when playing on the G string than when they play the same note in first position on the D string.

“Derived from the string tension and distributed mass, (the string parameter known as wave impedance) … indicates how much energy the string imparts to the bridge. Typically, violin D strings have nearly twice and G strings more than three times the driving energy of the A string. A similar relationship exists between the lower three strings of the viola and cello.”

Using the violin as an example, Mr. Pickering explains why this happens:

"The same note played in higher positions on a lower string transfers much more energy to the body of the instrument, and explains why wolf tones often show up only on those lower strings.”

Put simply, wolf tones become more obvious in higher positions because lower strings provide more energy to the instrument body which excites strong body resonances.

So there you have it!

The most common wolf tones are created when a bowed note is similar in frequency to a strong body resonance. And the higher up on the fingerboard you play that trouble note, the stronger the wolf tone may be.

How Do I Get Rid of My Wolf Tone?

There are a few things your luthier may want to check on your instrument to see if they are causing your wolf tone.

Gluing  
Anything which can vibrate that isn’t normally supposed to vibrate on its own can create a new wolf tone. Your luthier will want to make sure everything is properly glued (seams, fingerboard, the fret on your tailpiece, your bassbar, the label inside your instrument, etc.).

Tonal Adjustments  
Your luthier will want to make sure that parts which can be fit are well-adjusted and well-fit.
      
Bow Hair

They may ask how old your bow hair is because older bow hair (with lots of rosin build-up) can sometimes highlight wolf tones.

String Age
       
  • Are your strings old? Older strings require more tension to get up to pitch and can bring attention to wolf tones.
  • Are your strings a different brand of string than your last set? If they are a higher tension than your previous strings, they may be providing more energy to the bridge/body and causing trouble.

Soundpost 
Has your soundpost shifted or been moved recently? This can change the speed that vibrations are transferring from the top to the back of the instrument and might be highlighting your wolf tone.

Humidity
If it is winter or you are in a dryer climate than you were before, your luthier may ask if you are humidifying your instrument. This is because a drop in humidity causes the wood cells in the instrument to shrink and therefore increases the speed of sound transmission. An increase in the speed of transmission will highlight wolf tones that may otherwise be more muted in months that have higher humidity. 

 

Wolf Eliminators (Suppressors)


If your luthier has gone through all of the items on the list above, but you still have a troublesome wolf, they may suggest a wolf suppressor. 

Wolf suppressors are more commonly known as "wolf eliminators" but that term is a bit of a misnomer because, and we cannot stress this enough— wolf eliminators do not eliminate the wolf on your instrument.

A wolf eliminator's job is to simply move the wolf to a note which you do not play often or, even better, between two notes.

Imagine you were jumping on a trampoline with your friend. If you find that special sweet spot, when you jump, you can send your friend flying into the air. If you move just a little bit to the left and jump again, you may not be able to launch your friend with the same force.

In a rough, metaphorical nutshell that is what your wolf eliminator is doing; just moving your jump a little bit to the left so you don't upset your friend. 

The most common wolf suppressors available today are on-string wolf suppressors. They fit on your string between the bridge and the tailpiece. The weight they provide to your string changes how your string, bridge, tailpiece, instrument body, etc. vibrates together which slows (or impedes) the movement of sound throughout your instrument.

On-string wolf suppressors come in different weights and styles. We recommend going with the lightest wolf suppressor that effectively suppresses your wolf tone(s).

These styles of wolf suppressors typically require seasonal adjustments and some occasional sleuthing to see where they work best on your instrument, but they tend to work well for most musicians because they are easy to adjust and fairly affordable.

Other Wolf Suppressor Alternatives

Due to their affordable price and easy use for the average string player, on-string wolf eliminators work well for a large number of musicians, but they are not without fault.  

In String Magazine's article, "How to Tame Annoying Howling Wolf Tones," instrument maker, David Van Zandt notes, “Wolf eliminators take care of the wolf tone, but they also act as filters and can dampen the sound of the instrument. Just about any good instrument has a wolf. Any solution takes away from the voice of the instrument in one way or another to a lesser or greater degree.” 

For that reason, there are other alternatives to more traditional on-string wolf suppressors. There are models which can safely attach by a magnet to the top of your instrument. There are also models of suppressor resonators that can be glued inside the instrument by a trusted luthier. 

Finally, there are some players who prefer no wolf eliminators at all. These players will choose to play through the note by hugging their cello a little tighter with their knees at the lower ribs of the instrument or by silencing the same note from resonating on another string by placing a (spare) left finger on that note. 

Final Thoughts


Our best advice is to approach this process with patience. Wolf suppression requires experimentation to determine what the best solution will be for you and your instrument.

You may try a number of wolf suppression options and eventually land on an option that works well only to decide to use a different brand of strings and then have to go back to a former wolf suppression option. That is ok! Your instrument is your voice and, at the end of the day, you need to feel comfortable with any changes to your instrument. 


Works Cited

Norman Pickering. "The Wolf Tone." Volume 37, Number 3 Bass World Magazine.
Recently reprinted in The Scroll. (The membership magazine for The Violin Society of America.) Volume 1, No 1, Pages 37-43. Summer 2016.

PhysicsCentral. "Fiddle Physics." Physicscentral.com

Prof. Joe Wolf at the University of New South Wales. "How Does a Violin Work?" Newt.phys.unsw.edu

Sarah Freiberg. "How to Tame Annoying Howling Wolf Tones." May 12, 2005. Stringsmagazine.com

Posted on 20 March, 2021