| • What is a decibel? | • What does 'effective range' mean? |
| • What does the 'C' stand for in dBC? | • What does the "...@100 feet " mean? |
The decibel (abbreviated dB) is the unit used to measure the intensity of a sound (sound pressure). On the decibel scale, the smallest audible sound (near total silence) is 0dB. a sound that is ten times more powerful is 10dB. A sound 100 times more powerful (than 0dB) is 20dB. 1,000 times is 30dB and so on.
The decibel scale is logarithmic because the human ear is capable of hearing a very large range of sounds (the ratio of the difference in sound pressure from low level sounds to those that cause permanent hearing damage is more than a million). To deal with such a range, logarithmic units are useful. For instance, the log of a million is 6, so this ratio represents a difference of 120dB.
Here are some common sounds and their decibel ratings:
| near total silence - the quietest sound you can hear | 0dB |
| a whisper | 30dB |
| normal conversation, sewing machine, typewriter | 60dB |
| lawnmower, shop tools, truck traffic. 8 hours per day is the maximum exposure level. | 90dB |
| chainsaw, pneumatic drill, snowmobile. 2 hrs. per day is the maximum exposure without protection. | 100dB |
| loud rock concert, sandblasting, car horn. 15 minutes per day is the maximum exposure without protection. | 115dB |
| Gunshot, jet engine. Noise causes pain and even brief exposure injures unprotected ears. Maximum allowed noise with hearing protection. | 140dB |
It's important to remember that any sound above 85dB can cause hearing loss. The loss is related both to the intensity of the sound as well as the length of exposure. For instance, eight hours of exposure to 90dB can cause hearing damage, while any exposure to 140dB will cause immediate damage (and actual pain).
What is the definition of 'effective range'?
The effective range of any siren is the maximum distance at which it can be heard at a level of 70dB or louder. Environmental factors may alter this range in real-world applications.
What does the 'C' stand for in dBC on the siren sound ratings?
Not all sound pressures are equally loud. The human ear does not respond equally to all frequencies of sound. We are much more sensitive to sounds in the 1kHz to 4kHz range than to very low or high frequency sounds. Sounds measured in the 1-4 kHz range are usually referred to in units of dB(A). The C scale is more suitable for very high sound levels and is referred to as dB(C). There is also a rarely used B scale intermediate between A and C.
What does the "... @ 100 ft " mean after the siren's dB rating?
This signifies the distance from the siren at which the sound measurement was taken.
Will the siren perform to its rated specifications once installed?
Yes and no. Siren sound measurements are usually taken under controlled conditions, and many are tested outdoors to simulate real-world applications as best as possible. Some factors that tend to limit the effective range of any siren may include:
| • mounting height of less than 35 feet (between 35' and 45' is recommended) |
| • siren mounted near buildings or trees |
| • siren placement in a valley or ravine |
Conversely, some factors have shown to occasionally increase a siren's effective range, such as:
| • mounting height greater than 45 feet |
| • mounting the siren near a lake |
| • snow, fog, or rainy weather |
| • siren placement atop a hill or mountain (although this may limit the short range of the siren) |