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A siren with two rows of ports is known as a dual tone siren. By placing a second stator over the main stator and attaching a solenoid to it, one can repeatedly close and open all of the stator ports thus creating a tone called a pulse. If this is done while the siren is wailing (rather than sounding a steady tone) then it is called a pulse wail.
The most common siren type is the electromechanical KM Europ eight-port single-tone siren. These sirens have a very characteristic sound: a very fast wind-up and a lower pitch than most sirens (the pitch is comparable to a Federal Signal STL-10 on a lower frequency). A recording of these sirens was used in the movie Silent Hill. [citation needed]
The sirens were able to produce these tones: Alert - A steady siren tone [3]; Attack - A wailing siren tone [4]; Alternating Steady - An siren tone alternating between a high and low frequency, at half-second intervals, akin to a typical European emergency vehicle siren.
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The Federal Signal 3T22 was originally designed as the 2T22 in 1952 or 1954. The 2T22 has the same number of ports and cones. It can produce two main signals (it can produce more but the other signals are rarely used), hence the name "2T22" (the 2 at front representing the 2 choppers, and the 22 representing the amount of horns).
This siren is similar to Federal Signal's Thunderbolt series. Only a single unit remains in service in Milwaukee, WI. Screamers Electro-Mechanical 2, 5, 7.5, 10 8, 9, 9/12, 10/12 1968–1994 Omni Directional 102–115 dB at 100 ft. Series of small vertical sirens, comparable to Federal Signal Corporation's vertical sirens. Sentry 95
The Hurricane 130 was a supercharged electro-mechanical siren utilizing an air compressor to produce a high output similar to the Thunderbolt siren. It was available in dual tone 8/10, 10/12, 8/12 port, or single tone 8, 10, or 12 port configurations, most models however came equipped with an 8/10 chopper port ratio (similar to a Major Third ) .
Duke typically tests sirens around Shearon Harris between 10 a.m. and 11 a.m., with the alarms sounding between five and 30 seconds. Emergency alert that went out to many Wake County residents ...