This clip on YouTube below by 'Minty GT', simulates the sound of the Cuckfield Siren using the YouTube contributor's own identical siren. It's a truly spine-chilling sound wail - which must have been terrifying for children and adults alike.
The siren has one or more fans rotating at high speed, causing air to be forced outwards by centrifugal force, creating a high pressure at the impeller's circumference. The high pressure air is unable to flow continually due to the chopper projections at the end of the blades. There are an equal number of blades and holes in the sound box. Air can only escape when the choppers uncover the openings in the surrounding sound box.
Typically, a British air raid siren rotates at 2850-2900 revs per minute, one end has 10 openings and 10 blades, the other has 12 of each. This creates two tones harmonically related to each other as a minor third. The tone in Hertz can be calculated by multiplying the rotation speed in R.P.M. by the number of openings and dividing by sixty. For example, at 2850 r.p.m. the two tones are 475 Hz and 570 Hz.
To prevent the siren fans freezing up with ice and snow, each end has a 1000 Watt heater, with an element similar to those in an electric kettle. These are controlled by a thermostat mounted near to the siren The heater plates on the siren you hear on the YouTube clip has the heater plates removed.
These sirens can be heard up to 0.75 to 1 mile away. In a series of heavy bombing raids there was a danger that the power supply might get cut and the warning for the next raid could not be given.
The UK-wide early warning system was largely dismantled around 1992, and so there is no longer a national coverage of sirens. Maybe Cuckfield can count itself fortunate. I wonder how many times it was sounded. Can anyone give us some idea perhaps?
If you don't want to frighten your neighbours - turn down the sound!!
Contributed by Malcolm Davison.
Steve Turner very kindly added the following additional information on Cuckfield Gossip Facebook group:
Connected to a system called WB400 [seepic below), later WB1400 (wideband). Connected via a telephone line back to the telephone exchange and linked nationally via the speaking clock network.
On a Monday the system 'self tested' , at 9.30am when the announcement was "at the 3rd stroke' there were actually 4, the 4th stroke was to test the connections.
I can remember in the 60s and 70s when the sirens were given a test run, to a child it was fun but then we didn't realise what their true purpose was !
A magazine article below from 1944 showing how the air siren early warning network operated across Britain.
We are fortunate to have this piece of history still - the majority were removed after the Home Office ordered them to be scrapped in 1999. It's probably been up there since 1938.
Minty GT's YouTube clip: https://youtu.be/0ARqhLBkf2U?si=QeMq_MlRZ-Gi1HWN
data from http://www.ringbell.co.uk/ukwmo/Page216.htm
Visit Cuckfield Museum, follow the link for details https://cuckfieldmuseum.org.