**Siren Discs**

**What it shows**:

Demonstrate musical intervals, the relation of pitch to frequency, and autocorrelation in psycho-acoustics.

**How it works**:

A 25 cm diameter metal disk has a number of concentric rows of regularly spaced holes. When rotated at a uniform speed while blowing air at a row of holes, a musical note is produced by the sequence of regular puffs of air issuing from successive holes. The frequency is determined by the speed of rotation and the known number of holes.

The numbers of holes in the successive rows are 24, 27...

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