Siren Disc (3C20.30)

Description:

A disc with eight rings of uniformly spaced holes and a ninth ring of randomly spaced holes. The disc is spun by a motor and an air jet is directed at the holes. Puffs of air through the disc as a hole passes the air jet produce pressure variations, and thus sound. Different musical notes are heard from different rings of regularly spaced holes but noise is heard from the ring of randomly spaced holes.

Procedure or Operation Notes:

The disc is driven by a motor at 1,725 rpm. From the outermost ring, the hole count and audible frequency are:
48 holes, 1,380 Hz
45 holes, 1,294 Hz
40 holes, 1,150 Hz
36 holes, 1,035 Hz
32 holes, 920 Hz
30 holes, 862 Hz
27 holes, 776 Hz
24 holes, 690 Hz

The innermost ring has 16 holes randomly spaced and produces noise at approximately 460 Hz.