Helmholtz double siren
Date: c. 1912
Inventory Number: DW0173
Classification: Siren
Subject:
Maker: J. Lancelot (fl. 1912)
Cultural Region:
Dimensions:
49.2 x 29 x 21.8 cm (19 3/8 x 11 7/16 x 8 9/16 in.)
DescriptionA mahogany base, on which two A-shaped feet were fixed, support the brass double siren. The double siren, of Helmholtz's design, consists of two wind chests linked together on a common, central shaft. Pressurized air is introduced into the wind chests by means of brass angled connectors at the top and bottom.
The air escapes through a circle of holes in the wind chest, turning a rotor. A brass crank at the top of the siren causes the holes in the upper chamber to rotate, thereby chaning the air sent to the rotor. This changes the frequency of the sound. The dial at the crank is divided 0-60 every 1.
The top siren as four, angled, pull stops marked 9, 12, 15 and 16. The lower siren has four more stops marked 8, 10, 12 and 16.
Between the two sirens, there are two silvered counters (or dials). The left one (units) is divided 0-100, counterclockwise by 1. The right counter (hundreds) is divided 0-25, clockwise every 1. Two knurled knobs at the sides of the dial plate allow one to shift it left in order to disengage the dial gears from the sirens' central shaft. The shift is visible in a window on the back. Each siren has a cover divided into two halves. These are held on by screws.
The air escapes through a circle of holes in the wind chest, turning a rotor. A brass crank at the top of the siren causes the holes in the upper chamber to rotate, thereby chaning the air sent to the rotor. This changes the frequency of the sound. The dial at the crank is divided 0-60 every 1.
The top siren as four, angled, pull stops marked 9, 12, 15 and 16. The lower siren has four more stops marked 8, 10, 12 and 16.
Between the two sirens, there are two silvered counters (or dials). The left one (units) is divided 0-100, counterclockwise by 1. The right counter (hundreds) is divided 0-25, clockwise every 1. Two knurled knobs at the sides of the dial plate allow one to shift it left in order to disengage the dial gears from the sirens' central shaft. The shift is visible in a window on the back. Each siren has a cover divided into two halves. These are held on by screws.
In Collection(s)
Signedunsigned
FunctionThe double siren is a device for determining the absolute frequency of a sound and demonstrating the interference of sound waves through beat phenomena. Two sirens are coupled on the same shaft.
A video recordings of a Helmholtz double siren in use were produced by David Pantalony and Stephen Morris and are available on Youtube at these links:
Running the Helmholtz Double Siren
Close-ups of the Helmholtz Double Siren
Starting up the Helmholtz Double Siren
Adjusting the Phase
Adjusting the Stops.
A video recordings of a Helmholtz double siren in use were produced by David Pantalony and Stephen Morris and are available on Youtube at these links:
Running the Helmholtz Double Siren
Close-ups of the Helmholtz Double Siren
Starting up the Helmholtz Double Siren
Adjusting the Phase
Adjusting the Stops.
Curatorial RemarksThough unsigned, this siren is identical with the one depicted in Lancelot's catalogue, the A-shaped feet included.
Primary SourcesJ. Lancelot, Catalogue des appareils d'acoustique pour la démonstration (Paris, 1912), 7, no. 25. Online here at the Virtual Laboratory, MPI.