According to the American National Standard Institute (ANSI), the definitions are as follows:
The frequency of a warning tone used in rating a siren's Sound Pressure Level is critical in evaluating the performance of an outdoor warning siren, where the siren's warning tones are expected to carry over great distances.
Whelen siren systems are designed to optimize the production and projection of low frequency warning tones. It is documented that higher frequency tones attenuate (lose power) more over distance than low frequency tones.
A warning siren capable of producing 124 dB at 100 feet with a 500hz warning tone will be more effective than a siren producing 124 dB at 100 feet using a 1,000hz warning tone. This factor should be considered in planning a warning system.
Consider this example of the attenuation of higher frequency tones that is apparent in our everyday life...
As you are standing out in your yard, your neighbor's teenage son has the stereo in his car blasting as he is coming down the road towards your house. The earth seems to shake as the "boom, boom, boom" of the low frequency bass notes are felt beneath your feet and on your ears. It is not until the car is very near to you that you can hear the high frequency acoustic guitar and voices. As the car passes you, these high frequency tones seem to disappear, but the pounding and thumping of the "boom, boom, boom" bass can still be heard and felt.
This scenario clearly demonstrates that ability of the lower frequency tones to be heard at a farther distance than the higher frequency tones.
In short, remember that not all 124 dB (at 100 feet) sirens are alike.
The most important thing is that the combination of solar panel output and battery capacity must handle the siren standby power requirement, while also maintaining enough charge on the batteries to meet the run-time requirements of the siren. These requirements vary with location, seasons, and weather.
A solar powered siren depends on a properly sized battery bank for power during bad weather such as rain, snow, or fog. A Whelen siren has a battery capacity of 230 amp-hours. Typical standby current is about 50mA, therefore, after two weeks of total darkness, only 16.8 amp-hours of capacity have been drained from the batteries. There is still plenty of capacity for a number of siren tone activities.
All Whelen sirens are equipped with a large battery bank. The batteries actually power the siren during any warning tone or message. Therefore, any Whelen siren will meet its specified run-time, regardless of whether it is powered by AC or solar.
Realistically, this is only critical if batteries have been drained significantly, from considerable use. For example, ten activations at 3 minutes each.
A more likely scenario might be: Four activations at 3 minutes each, with a WPS2810. This means that 44 amp-hours of capacity has been used, therefore 44 amp-hours need to be replaced. An SBC260 solar option will supply approximately 3.37 amps in good sunlight, therefore after 13 hours, the batteries will be fully recharged. Remember that even without recharging, the siren has battery capacity left for six more 3 minutes activations, in this example.
No. Any siren sitting on a pole in the middle of an open area is susceptible to lightning. The key is how well the siren is protected from the inevitable strike.
There are two basic ways that lightning can damage a siren. One way is from energy that is picked up through the atmosphere by a nearby strike. This energy is often coupled through the radio antenna or radio coax cable. The other way is from energy that is coupled onto the AC power lines, in the form of a voltage transient. In either case, the siren must be protected from the inevitable.
Whelen does a number of things to protect against lightning damage.
No. Whelen's Omni speakers are made of fiberglass reinforced Lexan, and Whelen's directional speakers are fiberglass. In either case this is a non-conductive material. Lightning will seek the path of least resistance, which is the steel pole mounting bracket and its associated ground wire. The pole top mounting bracket is a nice lightning rod.