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Picture of the Month (September 2010)
Dedicated User Captions:
1. Rare item of noodle street view or of noodle maps?
2. Fork bent by Uri Geller (by GeorgS)
3. A fork to eat cable salad. (by Electric Avenue)
Blow tube for siren disks (schematic illustration)

Sirens are simple devices to produce sounds. Blowing a stream of air onto a row of holes of a rotating perforated disk interrupts this flow periodically and therefore creates a tone whose frequency is dependent of the rotating speed of the disk and the distances between the holes. To produce more complex sounds more than just one row of holes may be used at the same time, using either multiple pneumatic tubes or an attachment like the one above to distribute the air of one tube to different streams.

Sirens have been widespread in the field of acoustic research; they were affordable, easy to maintain and quite versatile in their usage.

Picture Source:
Spindler & Hoyer. 1908. Apparate für psychologische Untersuchungen. Preisliste XXI. Göttingen (Collection Jirí Hoskovec)

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