Intruder Alarm Bell wiring
The main aspect of audible warning signalling systems is that the warning’s effective radius is limited to the immediate vicinity of the sound source. intruder alarm audio warnings are sometimes referred to as “local alarms.”
Many electrical devices can produce sounds, as is all too clear in today’s environment, and the majority of them can be used in security applications. However, because it is critical that the audible warning is recognised for what it is and is not confused with the surrounding noise, the alarm bell remains in many security alarm installations.
Of course, the main characteristic of an audible alarm is that it produces a loud sound. The sound energy can be transmitted in the form of travelling waves through any suitable medium by vibrations generated up in the medium’s particles in solids, liquids, and gases.
There are two types of sound waves: transverse waves, in which the particles of the transmitting medium move up and down along lines perpendicular to the wave’s motion, and longitudinal waves.The waves in which the medium’s particles vibrate back and forth along routes parallel to the direction of the waves sound energy is carried through liquids and gases by longitudinal waves. The sound energy can be propagated through a solid body by either longitudinal or transverse wave motions; or both forms.
A sound wave’s frequency is generally measured in Hertz (cycles per second) and the wavelength in feet or metric units. The speed of a sound wave is often expressed in feet per second or metres per second. The relationship between speed and wavelength, and frequency is as follows:
Speed = Wavelength x Frequency.
Let us now provide the sound wave properties with some actual values. In dry air at 20° C (68° F), the speed of sound is roughly 1,127 feet per second, or 750 miles per hour in round figures. Fortunately, the speed of sound in the air does not change with frequency.
The elasticity and density of the propagating medium also influence the speed of sound – for example, the speed of sound in fresh water at 25°C (77°F) is 4,897 feet per second, nearly five times that of air. The speed of sound in solids is generally faster than in gases or liquids, however, this relies on the sort of wave formed up in the solid’s body. A longitudinal wave in rolled aluminium, for example, travels at approximately 21,000 feet per second, whereas a transverse wave travels at around 9,971 feet per second.
The human ear cannot hear waves with frequencies that exceed or fall below specified thresholds. In terms of the ear, sound waves have three main properties: intensity, frequency, and duration. The ear can tolerate roughly 120db of noise. The ordinary conversational vocal tones are roughly 30-40db on this scale. According to British Standard 4737, the average sound level of an alarm bell measured at a distance of 3 metres, and 30° intervals around the bell shall be no less than 70dbA and no less than 65dbA in any one direction.
The external siren (bell box) is normally mounted in a high position where it may be seen and heard.
Learn more about intruder alarm installation and security news, sign up for our newsletters. At Cube, we provide hands-on training courses for those looking to start a new career in the fire and security industry. Our three-day Intruder Alarm course is suitable for those looking to begin a career in the Intruder Alarm Installation industry.