We’ve all seen string players (maybe you’re one yourself) producing beautiful sounds with that fantastic combination of instrument and bow. Have you ever wondered how the bow, a seemingly un-musical length of wood and hair, can coax an instrument into producing such sounds? The answer is both simple and complex.
Bow Stroke Energy
A stringed instrument makes sound when one or more of the strings are vibrating. To start vibrating, the string needs energy. This is the whole purpose of a bow: it adds energy into the system of the instrument to make sound. Short bursts of energy are nice, but they make a sound that quickly dies away (pizzicato notes on a violin, for example, or a plucked guitar). The advantage of a bow is that it provides a continuous source of energy resulting in a sustained sound. The bow’s length of hair continuously excites the strings as it’s pulled across them.
When the bow is pulled across the string, sticky rosin helps the horsehair grab the string. The friction between the hair and the string pulls the string a little to one side. When the string reaches the limit of how far it can stretch, it snaps back. The bow grabs the string again, and back and forth it goes. The string is now vibrating (and therefore producing sound) because of this motion. This cycle of sticking and releasing can happen about 20 times each second.
The physical principal that allows this action to happen is called the stick-slip mechanism. Though you may have never heard of it, you have certainly heard what it does. Every time a shoe squeaks or chalk screeches on a chalkboard, that’s the slip-stick mechanism in action.
Putting It All Together
We all want an instrument that sounds better than a screeching chalkboard. Thankfully, an instrument can create beautiful sounds because of the interacting parts of a very complex system. These components include the wood of the instrument, the air inside it, the bridge, the strings, and–last but not least–the bow hair and stick. Though it may seem that the shaft of material pulling horsehair across the strings wouldn’t matter much, it actually does. Turns out the resonant properties of the material used for the stick feed into that complex system, and have a profound effect on the quality of the sound. We’ll explore the parts and qualities of the bow further in another post.
Violins, violas, cellos, and basses are all played with bows that differ in length and weight. Because a larger string requires more energy to start the string vibrating, we see a general rule in play: the larger the instrument, the heavier the bow. This extra weight usually comes by way of a larger bow stick.
What About Bow Size?
But what about bow length? Smaller instruments and strings require more speed in the bow stroke to produce the same amount of sound. If all bows were short, viola and violin players would have to change bow direction more frequently (making them cranky). The solution: longer bows.
If you are in need of a good quality bow, we highly recommend our Pierre Martin pernambuco bow. These significantly help sound quality production at an affordable price.
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