Ever wondered how exactly your violin bow makes the strings vibrate? Why does your bow sometimes get a beautiful sound, and sometimes a horrifying sound? And why are speed, weight, and contact point so crucial to getting a good sound?
The answer is actually pretty straightforward, if we stick to just the basics of violin physics. If you want get waist-deep into it, scroll to the end for some links. But for the rest of us, here’s a “least you need to know” explanation of:
what goes on between the bow and the string
why that matters
why weight, speed, and contact point are so important in getting a good sound on the violin
What Goes On Between the Bow and the String
The Slip-Stick Process
A violin string and bow work together in something called the “slip-stick process.” It’s a phrase that brings all sorts of colorful images to mind... But when talking about the violin, it just means that the bow is always alternating between slipping across the string and sticking to the string. It’s a process that has a lot in common with plucking a string. So let’s start by looking at a string being plucked in slow motion:
When you pluck a string, your finger grabs it, moves it to the side, then releases it. This starts the string vibrating.
The slip-stick process in the bow is basically a lot of plucks in a row. The bow grabs and releases (“plucks”) the string hundreds of times per second. When the bow “sticks” it uses friction (from the horsehair and rosin) to grab the string, pulling it to the side. Once the sideways tension becomes greater than the friction, the string slips underneath the hair and is free to vibrate for a split second ... until the bow catches hold of it again and repeats the cycle. At normal speeds, this process is invisible. But you can see it clearly in this ultra-slow-motion video:
And with that, we’ve covered all the physics we need for now! So let’s talk about why this matters, and what it means for your sound production.
Why This Matters
This slip-stick process works when everything is in balance: the bow grabs the string just enough to get the string moving, but not so much that it stops the string from slipping (and vibrating). As you can see in the video above, the bow grabs onto the string only during one direction of the string’s vibration, and releases it on the opposite direction of its vibration. If the bow grabs-and-releases at a different rate than what the string wants – say, grabbing onto the string again before the string has finished one cycle of motion back and forth – then the bow and string fight with each other and create all sorts of extraneous vibrations. These are also known as noise, grit, scratch, squeak, “Oops,” and “Oh, $&*%!”
“Oops!”
Why Weight, Speed, and Contact Point Are So Important
You already know that these three factors are key to getting a good sound. But here’s a little bit about why.
The amount of weight you put into the bow affects how much your bow grabs onto the string. Too much weight creates too much friction, so the bow “sticks” too much and squashes the natural vibration of the string during the “slip” portion. This creates a gritty sound. Too little friction, and the bow isn’t able to grab the string enough during the “stick” phase to get it going fully, leading to a glassy or brittle sound.
The speed of the bow also affects how the hair and string interact. Moving it too quickly or too slowly across the string will cause the bow’s slip-stick process to get out of sync with the string’s natural rate of vibration.
Finally, the position of the bow along the string – the “sounding point” or “contact point” – will also affect the functioning of the slip-stick process. The width of the string’s vibration changes along its length. It’s generally narrower near the bridge, and wider as you go away from the bridge. So the balance of weight and speed need to vary with the contact point in order the keep the slip-stick process working optimally. This usually means more weight near the bridge and less weight away from the bridge.
Should you be thinking about the slip-stick process in the middle of a performance? Definitely not! But exploring it a little bit during your practice time, and knowing why weight, speed, and contact point are so important, can give you more confidence in your playing and help you to be a more expressive and resilient violinist.
Additional reading
Joseph Curtin, violin maker
A successful, cutting-edge violin maker who’s challenging just about every assumption in violin making, and making some interesting discoveries. His site includes a lot of articles about the physics and acoustics of great violins – old and modern.
PhysicsCentral: Overview of violin physics
An overview of all the physics of how a violin makes sound, this page is just scratching the surface. As that page says, “The acoustics of the assembled violin body are fantastically complex ...” But this is an accessible introduction to that complexity.
What do you think? I’d love to know. Just leave me a comment below.
I’m a violinist and private teacher in the Chicago area, and in a previous musical life I was in a professional string quartet. Teaching violin and chamber music are dear to my heart. Send me a note or leave a comment on a post — I’d love to hear from you.