Rude Awakening: Low-Frequency Sounders
Back then, it was common to use bells to signal an alarm. As technology changed, it was found that the bells emitted too much electrical noise back into the system and it caused problems with transistors and integrated circuits.
For years, there has been concern about the waking ability of fire alarm audible notification appliances. In general, they have gone through numerous changes since the 1980s. Back then, it was common to use bells to signal an alarm. As technology changed, it was found that the bells emitted too much electrical noise back into the system and it caused problems with transistors and integrated circuits.
Next came mechanical horns. They were better than bells, but as operating voltages in panels lowered, they also created problems due to electrical noise in the system. Next came electronic horns. These worked much better, but to reduce current draw, the frequencies of the horns were higher. They did not penetrate walls and doors as well as the older bells and mechanical horns, so more appliances had to be installed.
One problem with the higher frequency is that is the range many aging individuals first start losing the ability to hear. Studies have been done on alerting the elderly with hearing loss as well as young children. Results of some studies have shown that voice messages (especially a parent’s voice for small children) can be more effective than horns for waking individuals. Also, lower frequencies seemed to be better heard by those with hearing loss.
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