How the bow makes sound · From Zero to Mozart

You've been making a sound with the bow since Stage 0. Now it's worth knowing how, because every stroke in this stage is a different way of steering the one thing that's actually happening between the hair and the string.

The one thing that happens

The hair of the bow is coated in rosin, which makes it sticky. Drag it across the string and it catches the string and pulls it sideways. The string stretches, its tension builds, and at some point it snaps back the other way — where the hair catches it again and pulls it back. Catch, pull, release, catch. On the open A string that cycle repeats 440 times a second, and that repeating tug is the note.

The bow doesn't "put sound into" the string so much as keep a swing going — like pushing a child on a swing, one small shove per pass.

40 bpm

Open D, one down-bow and one up-bow, slow. Watch the string itself while it sounds — you can see it blur into a wide band. That blur is the swing the bow is keeping going.

The whole string moves — and wider means louder

The blur is widest halfway between the bridge and your finger (or the nut). The wider that swing, the more the sound carries across a room. And here's the part that catches beginners out: the pitch never changes with the width. Loud and soft are the same 440 swings a second — the string just travels further side to side when it's loud.

40 bpm

Open A loud, then open A soft. Same note, same speed of vibration — only the width of the string's swing changes. Play both and watch the string get narrower for the quiet one.

One note is really a stack of notes

When the string swings, it doesn't only vibrate as one long band — it also vibrates in halves, thirds, quarters, all at once, each adding a faint higher note called a partial (this is Stage 4's harmonic series — the-harmonic-series, why-your-violin-rings). You don't hear them separately; together they're the colour of the sound. Changing where and how the bow meets the string changes which partials come through — which is why the next few lessons are about exactly that.

Try it

Try

On the open D string, play one very slow whole bow and just look at the string. Use more bow (faster) and watch the blur widen; use less bow and watch it narrow. Then try pressing down harder without moving faster — notice the blur gets thinner and the sound gets rougher, not louder. The bow's job is to keep the string swinging freely, not to squash it.

The usual mistake

Believing "louder means press harder." Pressing down works against the sideways swing — past a point it chokes the string and the tone turns scratchy and small. Loudness comes mostly from a wider swing, and a wider swing comes mostly from a faster bow (more bow per note). The next lesson, speed-not-pressure, is entirely about this.