---

TECHNICAL INFORMATION

Comparison of Yelp and Wail Sirens with Directional Quadrasonic Sirens

1.  Fire Engine fitted with Yelp and Wail sirens - incorrectly located by both motorists.

2.  Fire Engine with Quadrasonic Sirens - correctly located by both motorists.
They will hear the direction of the approaching fire engine and take appropriate action
without freezing or panicking.

Most motorists have the experience of hearing emergency vehicle sirens, but are unable to locate the direction the vehicles are approaching from. This is because;

•  Electronic sirens often use rising frequency sounds which change continuously.
​The human psychoacoustic system has insufficient time to lock on to the sound because the frequency is constantly changing, often over a very short time

•  The high frequencies of electronic sirens bounce off walls and buildings with little perceptible change in volume or pitch.
This makes it difficult for motorists to differentiate between the original siren sound and the reflected sound

•  Current sirens have a narrow sound beam projecting mainly forward but not to the sides.
This makes them hard to detect, especially at crossroads

---

DETECTION LEVELS

COMPARISON OF EFFECTIVENESS OF ELECTRONIC SIRENS (signals 1-4) WITH PULSED SINUSOIDAL SIGNALS (6)
US GOVT RESEARCH -1977
The Quadrasonic Siren System uses pulsed sinusoidal signals (6)

 U.S. Department of Transport - report on effectiveness of sirens -1977.  Most detectable signal (6) Pulsed sinusoidal then (5) Sinusoidal; (1) Wail; (3) Electronic Hi-Lo; (4)Electromechanical. Least detectable signal  Yelp (2) - one of the main sirens still in use today World wide.

Note how signal (6) pulsed sinusoidal - is 3 to 4  times more detectable than signal (2) - yelp.

Subjects aged over 64 scored significantly higher with most signals. Older people lose the ability to hear higher frequencies, the high frequency components of some sirens are a distraction and add confusion to the listeners' perception of the direction of the source signal.

---

These tests were commissioned by the United States Department of Transport in August 1977. 
These sirens continue to be used today with detrimental effects on the health and safety 
of the public and emergency services personnel.

---

​Electronic sirens are proven to have poor effectiveness.  
​Fit Quadrasonic Directional Siren Systems for improved efficiency and safety.