A properly designed and specified loudspeaker sound system is essential for any integrated campus emergency mass notification system. Not everyone may have access to a telephone or an Internet-based communications device on the campus network or radio when the warning is given. Ultimately, everyone in the affected area must be able to get the same information — and instructions — loud and clear if campus public safety professionals hope to achieve the best possible outcome.
Unfortunately, myriad misconceptions abound about designing and specifying an emergency sound system. Further, many people are unfamiliar with ways to integrate available technologies to ensure the right message gets delivered at the right time. Here are five factors to consider when designing, specifying and installing an outdoor loudspeaker system.
1. Conduct an Onsite Acoustic Sound Survey
College and hospital campuses can be huge and subject to a variety of conditions that can affect how sound travels. In much the same way trees and buildings block light, they block sound. In addition, ambient sound from things like street traffic can create conditions that must be addressed. Wind conditions, as another example, can affect how much actual sound will reach its targeted ears.
A sound survey will help you determine the best locations for fixed speaker-system arrays and the sound levels you’ll need to reach at each location.
You should start by measuring sound levels — typically expressed as decibels (dB) — at the places where you want the sound to be heard. The sound levels should reflect the loudest-possible ambient conditions. For example, if the location on your campus is in an area subject to street traffic, make sure you record ambient sound levels when traffic noise is high. You should log the Equivalent Average Level (Leq) background sound levels and chart the noises heard during the survey. Each test session at each location should last at least five minutes using a tripod-mounted sound analyzer system set at 5’4” in height and conducted to American National Standards Institute (ANSI) standards.
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As a rule of thumb, you’ll want your loudspeaker to reach the targeted area 6dB to 10dB above the ambient level. Six dB is the minimum differential; 10 is double the ambient noise level. It will target the loudness or sound volume needed to get the attention of people in the area and overcome the din created by excited reactions to the warnings and instructions you are broadcasting.
Correlating your target sound levels with the physical characteristics of the campus will help you determine the placement of speaker arrays. Those locations could be on towers, poles or rooftops or a combination of the three. Locations also can be based on the characteristics of the loudspeakers selected. Manufacturers design speakers to meet specific needs — or in some cases, they give you the flexibility to focus sound in a more narrowly defined area or a wider area. While power output can be equal, the level of sound reaching the target can vary. Your survey will help you account for all of this.
2. Specify the Right Equipment
Not all loudspeakers are created equal, and not all sound pressures are equally loud. This is because the human ear does not respond equally to all frequencies. Humans are much more sensitive to sounds in the frequency range about 500Hz to 4kHz (500 to 4,000 vibrations per second) than to very low or high frequency sounds. Loudspeakers designed specifically for voice communication will be in a frequency range that accounts for the human ear and getting the right dB levels for each targeted location.
Harmonics are also a critical factor. Without going into all the technicalities of sound, good harmonics will produce full timbre for better clarity. Harmonics also should be relatively flat with a deviation of only 3dB from the base level. A loss of 20dB can result in a 75-percent reduction of the sound level.
This is not the time to “cheap out” with a system designed for sirens. Several manufacturers offer systems designed specifically for outdoor mass notification, and all meet minimum standards for range, clarity and integration with other mass-notification platforms, such as indoor speakers, E-mail and telephone dialers.
3. Integrate with Other Mass Notification Technologies
There is no single solution when it comes to notifying people in an emergency. Getting the same information to everyone affected at the same time is necessary to help you save lives.
