The bow-hair and the string

Understanding Bow Technique in String Instruments

An interesting question to ask, and really the first question to ask, is: What exactly does the hair of the bow do to the string?

The Function of Bow Hair

Most people answer that the hair makes the string vibrate. But then the next question is: What does "make the string vibrate" mean?

The answer is that the friction of the bow makes the string swing from side to side, a bit like that on the down bow.

• The hair catches the string and pulls it sideways to the right.
• You can see the string bending.
• As it does so, the tension of the string naturally increases.

This sideways bending can only go on for so long before the tension is so great that the string springs back in the opposite direction to the left. It's then caught again by the hair, pulled to the right again, and the next cycle begins. Millions of these cycles make up one single bow stroke.

And of course, the reverse happens on the up bow:

• The bow hair pushes the string to the left.

The Catch, Pull, Click Sequence

I just made those clicks with the bow in my fist and my thumb on the bridge. It's very easy like that.

However, it takes much more control to do it using a normal bow hold. You can make this catch, pull, click sequence into an excellent exercise.

• Therefore, the string moves sideways under the bow, to and fro.
• This sideways movement is called the amplitude.

Understanding Amplitude

The amplitude is the blur that you can see around the string and is widest at the middle point between the bridge and the nut, or between the bridge and the finger (which is a movable nut, if you like).

• The wider the amplitude, the more carrying the tone.
• But the pitch of the note remains the same.

Whatever the amplitude, the note A vibrates.

• In other words, the string swings from side to side 440 times each second, whether it's played pianissimo or fortissimo.
• The distance the string swings from side to side is narrower when it's quieter and wider when it's louder.

The Importance of Bow Pressure

This is 440, and so is this. But the sound is different because of the different amplitude.

If the downward pressure of the bow into the string is too much, it prevents the string from swinging freely side to side.

• It's like the string is trying to swing, but you're inhibiting its movement.
• Then, although you're pressing hard and it feels as though you should be getting a lot of sound and projection, you actually get more if you release the pressure slightly and let the string go.

The First Rule of Tone Production

This leads to the first rule, if you like, of tone production: To base everything on speed of bow, not pressure.

• Think of lifting or pulling the sound out of the string rather than trying to press it out.
• Even in a strong, sustained passage, you can easily hear the difference.

Using bow speed, you can draw the sound out even in forte. When using pressure, it's as though you're trying to drive the sound down in the direction of your feet instead of up and out.

You can see it as clearly as you can hear it. If you look at the width of the vibrating string, try alternating between over-pressing with the bow and lightening.

• Look just here, midway between the finger and the bridge.
• I'll over-press and see how narrow the amplitude is.
• And now look at this! So much wider.

The Secret to Rich Tone

Lifting the sound out of the instrument so that it sings and resonates is one of the secrets of playing with a tone that is big, warm, rich, and yet soft, sweet, and unforced.

Pressing or pushing the tone out produces one that is smaller, thinner, and harder.

It's significant anyway that we speak of bow strokes, not bow pressers.