Improving Tone by Understanding Stick-Slip Motion

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String Instrument Physics for Teachers and Parents, Part 1: Improving Tone by Understanding Helmholtz’ Stick-Slip Motion.
How to get a good tone is really easy to understand for students of all ages. This video explains the science behind both good and bad tone.

TRANSCRIPT

Hello, and thank you for watching this Parents as Partners video. We will be exploring one of my favorite topics, String Instrument Physics.

As teachers and parents, one of our main goals is to help our students to become independent learners and ultimately to teach themselves.

My name is Meredith Arksey and I teach violin and viola at Washington State University in Pullman Washington. I’m also a Suzuki teacher, but I am not a physicist. I became really interested in this topic and have researched it extensively, as well as presenting a session on it at the Suzuki conference in Minneapolis and now a shortened version for Parents as Partners.

We will begin with Helmholtz and his stick-slip motion. What exactly is happening with the rosin and the string to make a sound, and what is happening to the string when the tone is bad?

Helmholtz was a 19th century physicist and acoustician and he used strobe lights to discover what happens when the rosin grips the string. For example, on a down-bow the friction of the rosin grabs the string and pulls it to the right, and then the string is released. When it’s grabbing, that’s called the stick phase, and when it is released, that’s called the slip phase. You can go on you tube and look up bowed violin string in slow motion and you’ll be able to see this amazing wave: the grab, and then how it waves and hits the nut then comes back to the bridge again. And it’s so mind-boggling to think that a stick followed by a slip, 440 times per second, results in the A tone, the pitch of the A string. It’s almost as though a pizzicato is going so fast, and that’s what makes our beautiful tone. It’s the stick followed by the slip.

But what happens when the tone is bad? That’s what we’re going to discuss, and that is what is useful to kids.

So, if we were playing with our bow close to the fingerboard where the string is rather spongy, where it’s very flexible, then we need to have a certain bow speed, bow weight, or number of hairs, or tilt of the bow, to make that good stick-slip motion. We call this the sports car lane. We’re going to go out to the sports car lane here, and I’m going to play with light bow, and fast (just like a sports car), and tipped up to the side. And that allows a stick to be followed by a slip.

But let’s say that I was going to play in the middle, which is where we usually play anyway. I’m going to call that the family-car lane, somewhere over the circle on the F hole, and I’m going to be like a car. So instead of a fast, light, sports car, I’m going to be like a family car: a heavier weight, and a slower speed than the sports car, but I’m going to call it a medium speed and medium weight, and also a medium tilt to the bow.

And then let’s say we’re driving in the truck lane (that’s the closest-to-the-bridge lane). My bow has to act like a truck. Remember how I said that it’s spongy near the fingerboard? It is medium tough in the middle, but it is very, very hard next to the bridge. The string is very firm here. So, my bow is going to have to match that. I’m going to do a truck bowing next to the bridge, so I’m going to be slower —trucks are supposed to drive slower than cars (even though we know they don’t always), and heavier and I’m also going to have all eighteen of my wheels down.

So, what happens when we have a bad tone? What happens is that a “stick” might be followed by another “stick”, or a “slip” by another “slip”, instead of “stick-slip, stick-slip”. Let me do an example. Let me drive a truck, but I’m going to swerve out into the sports-car lane. So, I’m heavy and I’m slow. This is going to make too much friction, isn’t it? Bad—very bad.

Now let’s say that I take a sports car and I drive in the truck lane. I’m going to be light and fast, and I end up with a ponticello kind of sound because I don’t have enough friction to get the whole string going.

I call this a “stick, stick, stick” kind of tone because of driving too slowly and too heavily in a spongy lane, out here in the sports-car lane.

Or, this is a “slip, slip, slip” tone, driving too fast and too light in a lane where the string is very hard.

A good exercise is to have the students play in a certain lane. For example you could say “play me a note in the sports car lane, and make sure that your bow is fast and light and that it’s tilted on its side”. Or, “play a note in the family car lane and make sure that your bow is medium weight, medium speed and medium tilt”. Or, “play a note in the truck lane and make sure that you’re driving a truck—slow, heavy, and with all the wheels on”.

When discussing the slip-stick motion we also need to discuss the permitted range. The permitted range refers to the amount that the bow is permitted to swerve around without disrupting the stick followed by the stick, or the stick-slip motion.

Closer to the bridge the permitted range gets narrower and narrower. So, when we’re playing very close to the bridge (in the truck lane), we have to be very, very exact about how far from the bridge we are, how much weight, how much speed and how directly over the hair the stick is. So, we have no wiggle room. It’s as if we are driving on a very, very narrow mountain road, and on either side are these huge cliffs going down, and we have to really keep our eyes focused on the exact piece of winding that we’re playing on, and maintain a constant speed and a constant weight. Any kind of swerve in this very narrow permitted range is going to result in a bad tone. For example, you can hear me as I swerve closer and farther from the bridge, the tone suffers.

The good news is that the permitted range out here, in the family-car and in the sports-car area is quite large. That’s why we start kids on playing in the middle lane because we don’t want them to be having to deal with this very narrow permitted range close to the bridge. So, out here I can swerve a lot and I’m still going to retain my good stick-slip motion. Watch as I swerve. I still have proper tone, and I’m skating all over the place.

I hope you enjoyed this video on how we can use Helmholtz’ stick-slip motion to improve our tone on string instruments. Please check back for more videos on string instrument physics if you are interested. Thank you.

Video by Meredith Arksey

Meredith Arksey

Dr. Meredith Arksey, Associate Professor of Music at Washington State University in Pullman WA, is the coordinator of the string area and teaches studio violin and viola to undergraduate and graduate string majors. In addition to her university teaching, she is an active Suzuki teacher with a studio of fine young players. She received her bachelor’s and master’s degrees in violin performance from the University of Michigan where she was a student of Camilla Wicks, and a string pedagogy graduate teaching assistant under Robert Culver. She received her doctorate in Violin Performance from Michigan State University. She performs frequently as a soloist and chamber musician. She is a contributor to THE STRAD Online Magazine, is an adjudicator for WMEA and National ASTACAP, and is Past-President of the Washington State American String Teachers Association. She is a popular clinician at National ASTA Conferences and Suzuki workshops.

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