BrightKidz Library
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Why a Drum Has No Tune

About 10 minutes

Ask someone to hum the note a guitar string makes and they can do it. Ask them to hum the note a drum makes and they will look at you strangely, because a drum does not really make one.

This is odd when you think about what the two things are. A guitar string is a stretched thing that wobbles. A drum skin is a stretched thing that wobbles. Same idea, entirely different result.

A string never wobbles only one way

Pluck a string and you set off the obvious wobble: the whole length swinging up and down as one long arch.

But that is not the only wobble happening. At the same time the string is quietly wobbling in two halves, and in three thirds, and in four quarters, all at once, all on top of each other. Each of those is a faster wobble, so each one makes a higher sound.

Here is the important part. Two halves wobble exactly twice as fast as the whole. Three thirds, exactly three times. Four quarters, exactly four.

A string's tidy ladder beside a drum's untidy list Two halves divided by a faint upright line. On the left, three short strings are stacked one above the other, each pinned at both ends by a small upright mark. The top string bulges into a single arch, the middle one into two, the bottom one into three, and beside each is a plain whole number: one, two, three. On the right, three circles stand for a drum skin seen from above. The first circle is plain, the second is split down the middle by a straight line, and the third has a smaller circle drawn inside it. The numbers under them are not whole numbers at all: one, one point six, two point one. The string's extra notes climb a tidy ladder and the drum's do not, which is why one sings a note and the other only thuds. 1 2 3 1 1.6 2.1
The same string, wobbling three ways at once. The extra wobbles land on exact whole numbers — two times, three times — because a string is a line and a line divides evenly. The circles on the right are the same idea on a drum skin, and its numbers are nothing like as tidy.

Whole numbers. A ladder with even rungs. And your ear does something remarkable with a ladder like that: it stops hearing separate sounds and hears one note instead, with the extra rungs turning into the difference between a guitar and a violin rather than into extra notes.

A drum skin has no such ladder

Now do the same to a drum. Tap it and the whole skin domes up and down together — that is the obvious wobble, the same as the string's.

Underneath it, other wobbles start up too. But a skin is not a line. It is a disc, and a disc does not divide into halves and thirds the way a length of string does. It splits down the middle, or into rings, or into four quarters like a pie, and each of those patterns wobbles at its own awkward speed.

Those speeds are roughly 1.6 times, 2.1 times, 2.3 times the main one.

Not two. Not three. Nothing your ear can build a ladder out of.

So it never fuses them into a single note. It hears a crowd of sounds arriving together and reports what a crowd of sounds actually is: a thud.

Every one of these makes a sound by wobbling. Which ones hand your ear a whole-number ladder, and which hand it a crowd?

  • A plucked guitar string
  • A blown recorder
  • A struck tuning fork
  • A tapped cardboard box
  • A snare drum
  • A slammed door

Look at the two lists. Everything in the first one wobbles along a length — a string, a column of air, the prongs of a fork. Everything in the second wobbles across a surface or a whole lump. That is the split.

Test it with a finger

You can prove the string's ladder is really there, and you only need a rubber band or a guitar.

Pluck the string normally and listen. Now touch it very lightly at the exact halfway point — do not press it down, just rest a fingertip on it — and pluck again.

The low sound vanishes and a clear, thin, much higher note is left. That note was already there. Your finger did not create it; it just stopped the whole-length wobble and let the halves keep going on their own.

Move your fingertip to a third of the way along and you will find another one, higher still. These are the rungs of the ladder, and you can pick them off one at a time.

Try the same trick on a drum skin. Rest a finger anywhere on it and tap. You do not get a clean higher note. You get a deader thud, because there was no ladder to isolate.

A xylophone bar is a flat slab, yet a xylophone plays proper tunes. What does that suggest instrument makers have to do to a slab?

What to listen for now

Next time a piece of music is playing, try separating it into the two lists. The parts you could hum are coming from lengths. The parts you could only tap along to are coming from surfaces.

Once you have heard that split you cannot stop hearing it, and it explains why a drummer is doing a completely different job from everybody else on the stage.