What you see pictured above is a Chrysler Air Raid Siren, the most powerful siren in the world. It's the size of a car, measuring near 12-feet in length and standing more than 6-feet tall. It also weighs twice as much as today's typical car. This gigantic siren is powered by an 180-HP Chrysler Industrial V-8 HEMI® gasoline engine. The super-duty engine directly drives a three-stage compressor that blows 2,610 cubic feet of air a minute, at nearly 7 PSI, into a giant siren rotor. The compressed air screams through the chopper and out through six giant horns with an exit velocity of 400 miles per hour. The result is an incredibly loud 138 dB sound (measured 100 feet from the siren). The loudness of this siren is unmatched by any other warning device ever sold, ever. It's also considerably louder than the largest steam whistle or horn. As if that were not dramatic enough, the whole unit, engine and all, slowly rotates one and one-half times a minute on its iron turntable base.
Chrysler Air Raid Siren - Specifications
Years of Manufacture:
1952 - 1957
Marine and Industrial Division of the Chrysler Engine Division of the Chrysler Corporation of Trenton, Michigan
Chrysler Industrial 20A 480 Engine
Part Number 1487028
Serial Number 6225
90 degree inclined V-8
4-cycle gasoline converted to propane
331.1 cubic inch displacement
hemispherical cylinder heads
180 HP @ 4000 RPM
312 foot pounds torque @ 2000 RPM
7.5 to 1 compression ratio
Bore 3-13/16 inches / Stroke 3-5/8 inches
Stellite faced exhaust valves
Idle speed 650 RPM
Running speed 4600 RPM
13 inch Gyrol fluid coupling
11 inch friction type single plate, dry disc clutch
Three stage centrifugal type compressor stiff shaft unit
43 inch OD cast iron housing
22-3/4 inch OD cast aluminum heat treated alloy impellers
Rated speed 4,600 RPM
Discharge volume 2,610 CFM
Discharge pressure 6.95 psig
Six throated cast aluminum
Directional beam exponential type
Length 25-1/2 inches (group)
Height 37-1/2 inches (group)
Width 19 inches (group)
138 dBC at 100 feet
Single Tone, 460 Hz
[ Coverage Area ]
Size & Weight:
Assembly overall length 135 inches
Assembly overall width 45 inches
Assembly height 62 inches
Assembly height with exhaust 71 inches
Total weight 5,543 pounds
At maximum RPM, with short acoustic-coupler (horn-extension) the Bell-Chrysler air-raid siren generates 138 dbC (approximately 134 dbA) at 100 ft. or 30 meters, 0 degrees on axis, in anechoic, full space environment, and an estimated 30,000 watts of overall acoustic power. The three Kockums steam horns mentioned above would generate around 132 dbC (approximately 126 dbA) at 100 ft., 0 degrees on axis, in anechoic, full-space and about 50,000 watts of overall acoustic power.
How loud is 138 dB? Very, Very, VERY LOUD!
138 dB C-weighted is approximately equal to 30,000 Watts of sound power.
The Chrysler Air Raid Siren is the loudest sound signaling device ever built. The threshold of pain is 130 dB, anything above that level causes immediate ear damage. The Chrysler Air Raid Siren produces that level of sound nearly 200 feet in front of the projectors. The Chrysler Air Raid Siren is approximately fourteen times louder than a jackhammer!
To give some perspective, the sound level on the deck of an aircraft carrier 50 feet from a military jet aircraft taking-off using an afterburner has been measured at 130 dB. The Chrysler Air Raid Siren measures 138 dB at 100 feet (nearly twice the sound level at twice the distance).
Most popular air raid and warning sirens today produce a sound level of 127 dB at 100 feet and provide a typical one-mile radius coverage area. At 138 dB the Chrysler Air Raid Siren is approximately two times as loud and will provide a two and one-half mile radius coverage area with the same sound level at the distant edge. The most powerful siren available for purchase today (American Signal's Tempest™ T-135-AC™) produces a sound level of 135 dB at 100 feet. The 3dB higher output of the Chrysler Air Raid Siren, at 138 dB, represents twice as much sound energy output.
Siren coverage is based on a 10 dB loss factor. That's to say, for every doubling of distance from the siren the sound level will be reduced 10 dB.
This is a recording of BigRed™ on May 25, 2003, the third time it was started and run in Texas. This time it we were testing the clutch and the engine was started and idled with the compressor clutch disengaged.
Sound Clip #6 - Start & Idle - No Siren .WAV file - 45 seconds (986KB)
This is a long recording of BigRed™ on May 25, 2003, during its entire fourth run in Texas. Again the engine is started with the clutch disengaged, idled, clutch engaged, and run up to about 3000 RPM, a hesitation while checking performance, then 4600 RPM - full throttle! (Note: The clutch works great, in the future the engine will be usually started and stopped with the clutch in either engaged or disengaged position.)
Sound Clip #8 - Full Run .WAV file - 59 seconds (1.25MB)
This is a recording of Harry Barry's Detroit siren as heard five miles away. Although the siren was pointed in Harry's direction, it was not visible over a ridge between the two distant points. The siren was mounted on a trailer and not at optimum height for sound coverage. At this distance it takes the siren sound about twenty-four seconds (same length of time as this clip) to travel from the siren to the listener. The siren volume was estimated to be 55 to 58 dB at this distance!
Sound Clip #10 - Warning Signal .WAV file - 24 sec.(256KB)