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Back in November, John Ericson answered a question about “wolf” notes on a natural horn crook.
Here is the question once again, but answered by our contributing writer Dave Weiner.
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Pierre-Antoine asks:
My question is why a natural horn instrument with a certain crook might have a bad note. What is the explanation, the physic behind it? … For example, on my Courtois horn, the top G on the C-crook is terribly sharp in pitch, and has a very poor tone quality.
My first thought was that it might not be clean inside (after all, it’s more than 200 years old!), or maybe a dent was interfering with the vibrations. But I got both the crook cleaned and the dents removed, and the “wolf” note is still there.
Dave replies:
First, a disclaimer: I am not an acoustician, and I only have a technician’s practical understanding of the physics. I am willing to be corrected by those more learned than I.
The physics of producing a vibrating air column is all about pressure. When you vibrate the air column with your lips, a wave of pressure moves down through the trapped air column in the horn, and back again. It happens over and over at hundreds of cycles per second.
As the vibrations and pressure increase, certain points in the air column will equalize as the pressure from one direction equals the pressure from the other direction. At the moment, the length of the vibrating air column will shorten and produce a higher pitch. More pressure produces more and differing points of equalization, and even higher pitches.
As it turns out, to produce notes in tune the diameter of the tubing has to be in proper and precise ratios. As the air column pushes back it also pushes against the wall of the tubing. If the tubing wall is not the precisely the diameter it needs to be then one segment of the vibrating air column will “want to be” longer or shorter than it needs to be. As you struggle to vibrate the air column to play in tune at the proper pitch, your horn is working to play out of tune. Hence, the “wolf” note.
The problem may not be the C-crook itself on you horn, but the combined taper of the crook and corpus. Even so, I would strongly urge you to consider the coupler as a possible source of the difficulty. If it is leaking or worn or bulged in some way, that could cause your problem.
Otherwise, consider trying a new crook.
