Case Study of Emergency Notification System for University
How we Designed the PA over IP System
RUniversity is a small private liberal arts university in the Midwest with approximately 2,500 undergraduate students and 500 graduate students. The university has four colleges/schools: the college of arts & sciences, the school of management, the school of graduate and professional studies, and the research college of nursing.
The university upgraded their network over the past three years. They improved the reliability of networks and upgraded their Internet speed. They have also added additional services for redundancy and increased efficiency for all users by replacing old Internet routers and traffic management equipment. This is but a short list of some of the network upgrades that the Computer Services department at R University has been engaged in.
Recently R University approached Kintronics requesting assistance in a new project. The goal of the project was to provide a complete paging system to notify students of emergency situations. A special committee of faculty and staff were tasked with finding a solution that would not only notify students of emergency situations, but also exploit the existing network infrastructure. By using the existing infrastructure they were able to deploy the systems quickly and reduce the labor costs. Since the PA over IP system is treated like any other network with a set of peripheral devices, the in-house IT staff could install and operate the system. This eliminated the need to hire independent installers to install cables and other devices throughout the buildings. Kintronics provided a solution that met their criteria. In what follows is a description of the methodology that we used to develop a system unique to their needs.
Clarifying the Objectives:
Our first task was to clarify exactly what the school wanted to accomplish. Did they want the faculty and students to hear the announcement in the halls, in the classrooms, dorm rooms, outdoor areas, etc? This allowed us to determine where the people (the “ears”) would be. They clarified the need for hearing the announcements mostly in the hallways and common areas and in some outdoor areas as well.
The university has approximately 24 buildings situated on approximately 52 acres. Each building varies in size and shape, and total square footage. Given this information we devised a means to determine exactly where the speakers should be placed, so as to ensure that everyone in the target areas would be able to hear the emergency announcements clearly.
Determining where the Speakers would be Located
We started at the location of the “ears”, and determined what the minimum Sound Pressure Level (SPL) was required to be heard over the background noise in each area. Working back from the “ears" we can then determine how far away speakers are from the people based on the sound level output from various types of speakers.
Sound Pressure Level (SPL)
Also, probably more important than either of the aforementioned, is the relationship between the actual Sound Pressure Level and what we perceive as sound. For instance a Sound Pressure Level of 85 decibels would be equivalent to an average amount of traffic on a busy street. Theoretically the sound pressure level associated with a particular sound is based on the geometry of the object producing the sound, and the objects surrounding, or nearby the sound-producing source. As an example consider the objects surrounding the sound-producing source. Let’s say for instance that the point source is a speaker.
Figure 1 depicts a single speaker that radiates sound in all directions. There are no objects in its path to impede the sound from traveling in all directions. The Sound Pressure Level (SPL) is measured with a sound level meter (Figure 2).
In practice a sound level meter is used to determine the precise sound pressure level at a certain distance. To make things easier, all speaker manufacturers provide the SPL at 1 M away from the source, and at 1 Watt power. They sometimes will also provide the sound output at full power input. As an example consider the specifications for the PH10T speaker. It has a SPL of 112 dB at a 1-meter distance, with a full input power rating of 10 WATTS.
We can use a complex formula or use an easier simplified method to determine how much sound is available as we are further away from the speaker. In the article “How Loud is Loud?” an outline of the basic equations for measuring sound pressure levels and determining the relationship between the decrease in sound as a function of distance that the individual is away from the speaker were reviewed. The simplified method says that we lose 6dB of sound each time we double the distance away from the speaker. So at 2 M the sound goes down to 106dB, at 4 M it is at 100 dB, and at 8 M it’s about 94dB. At 10 M we estimate that the sound level is approximately 92 dB. Ten meters is equivalent to approximately 30 feet.
92 dB corresponds to the sound that a diesel truck or motor cycle (loud one) makes. In the results section, we provide a real world example using a set of requirements from a recent client of ours.
The information above can be used to determine approximately where the speakers should be placed for a specific SPL. The objective was to make sure that everyone heard the message. Here’s how we used the information in the previous section to determine near optimal placement of the speakers on one floor of R University’s all-purpose building. Consider Figures 3.
This is the basement floor of the all-purpose building. This floor has an approximate area of 25,000 square feet. Using the floor plan we developed a simple relationship between the drawing measurements and the actual building measurements (i.e. scale). Once the scale was determined, we were able to mark off on the drawing where each speaker should be placed based on the speaker specifications. The details have been omitted for brevity.
Our client determined that each floor should be covered with a SPL of 90-95 dB or greater. For Figure 3 the speakers were placed based on the aforementioned SPL requirement. The speaker that most closely matched our client’s requirements was a PH20T. Each speaker covers an area of approximately 75 feet with an SPL of 90 dB or greater. The orientation of each speaker is largely dependent on the radiation pattern as shown below in Figure 4.
Figure 4, is similar in nature to Figure 1. It demonstrates how far the sound produced by a speaker will reach in all directions. Just like in Figure 1 the speaker is located in the middle of the circle, but it is not shown in this figure, and the dashed line indicates the radiation pattern for the PH20T. It is clear that the radiation pattern resembles a ripple in a pond when a solid object is thrown into the center of it (i.e. omnidirectional). Looking at the radiation patterns we can see that the entire floor is covered with a SPL of at least 90 dB, which coincides with the requirements of our clients. The areas that are not covered have little or no traffic.
We selected the IP7-SS20 amplifier to drive each of the speakers. This amplifier provides an output of up to 20 watts, which is more than enough to achieve the sound level required. Since they connect directly to the network, it was very easy to install. Special software called Talkmaster-EE was installed on two computers (with microphones) that can be used to make announcements. This provided a complete emergency announcement system that used the existing network infrastructure for connecting the amplifiers (with speakers) to the central office. For more details about this system take a look at our article Paging over IP.
R University is one of many clients that we have helped in determining speaker requirements and speaker locations within each building. At Kintronics we use an analytical approach to problem solving. Each solution that we develop for our clients is based on the information that they provide us with. We do not add components superfluously to a client’s system. We pride ourselves on the ability to translate client requirements into system requirements, and make the necessary recommendations. It is our job and responsibility to ensure that the: lives, property, valuables, etc. that our client’s have entrusted us to protect, are safe at all times. We provide the correct solution the first time and provide a very thorough explanation to our clients about the system design.
If you require assistance with translating: ideas or security requirements into system requirements, please contact us at 1-800-431-1658 or 914-944-3425 or use our contact form.
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