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Article from Technology Notes from Kintronics (http://www.imakenews.com/kin2/e_article001072907.cfm?x=b11,0,w)

April 17, 2008

Planning and Installing Your PA over IP System

It's easy to install this emergency alert systemhttp://www.kintronics.com/IPpa/IP%20PA%20Systems.h...

by Ed Gaynor

The disaster at Virginia Tech and problems at other college campuses have brought to sharp focus the need for campus wide alertsystems. A recent USA Today article describes a number of ways college campuses have addressed this problem. They include e-mail

messages, cell phones and sirens. The best warning system allows you to alert not only the whole campus but also specific sections of

the campus, buildings and even individual classrooms. Network attached PA systems provide this excellent flexibility and are also easy to

install. After all you can use the existing network infrastructure for much of the wiring. Many people have asked, Is this something I

can do myself? And our answer in the overwhelming majority of cases is: Yes you can! This article reviews how you can specify and

install PA over IP systems.

If you have some knowledge of connecting computers to networks, you will f ind it easy to connect IP amplifiers to this same network.

The only issue may be what speakers to select and where to place them. Although it may seem somewhat complex at face value, it

really is relatively easy and can be done by most anyone. Lets explore each segment

Speaker Placement and Installation

Well start with an area that concerns some of our customers, although it really shouldnt! Proper speaker placement and installation is

the key to a robust PA system. The challenge is to install a PA over IP system so that you can communicate a message to people in a

particular area. Whether it is installed in a school, office, park, etc, the message needs to be clear and understandable.

When considering where and how to install PA speakers, there are several variables to examine:

How loud should each speaker be?

Does the coverage area need to be seamless? In other words, each speaker has a coverage area where the sound is

understandable. Do you need to ensure that there are no dead spots, where sound cant be heard clearly?

How do I mount my speakers?

How do I wire my speakers?

Determining the Speaker Volume

The loudness of a speaker is based on the type of speaker and the amount of power used to drive the speaker. Just like your home

stereo, the bigger the amplifier the louder and clearer the sound from the speakers. To give you some idea of how loud various sounds

are, take a look at chart A. You will notice that the measure of loudness is the decibel or dB. The decibel is a relative term used to

compare Sound Pressure Levels (SPL).

When determining the loudness of the speaker, one must first consider the amount of ambient noise in the immediate listening area.

The listening area is informally defined as the area where most people will be most of the time. Based on this, we can specify the

Sound Pressure Level (SPL) needed to cut through the ambient noise, without being overpowering.

CHART A

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Value Description

0dB SPL The threshold of hearing This is the quietest sound that a child or

young adult with good hearing can detect at 1kHz. It is not silence

(although in terms of how loud it is in a P.A. system it might as well

be): it is the level from which all other values using the decibel (SPL)

scale is calculated.

10 - 20dB SPL A gentle breeze through the trees.

20 - 30dB SPL A soft whisper (at 1 meter).

30 - 40dB SPL A quiet auditorium.

40 - 60db SPL Background music in a cafe, bar or restaurant.

60 - 70dB SPL Typical conversation levels (from the listener's position).

70 - 80dB SPL The cabin of an aircraft during normal cruise conditions.

80 - 90dB SPL Typical wedding or dinner-dance band (typical audience position).

90 - 100dB SPL Loud orchestra (playing as it would sound in the front row of the

audience).

100 - 110dB SPL Typical disco.110 - 115dB SPL A loud rock band (front rows of audience).

115 - 130dB SPL Threshold of pain. Often given as 120 dB SPL, this varies with

frequency, and from person to person.

140dB SPL Jet engine from 3 meters.

If you are truly interested in a detailed explanation of sound pressure levels, please see Issue 40 of our newsletter, How Loud is Loud.

For our purposes, it is only important to be able to determine the optimal volume level needed for each of your speakers and the

amplifierpower needed to get that speaker output.

The optimal volume (SPL) for our speakers is calculated in two steps. The first step is to add 10db to our ambient noise level from

Chart A (the rule of thumb for PA installation is that the SPL for each speaker should be approximately 10db greater than the ambient

noise level in the listening area). For example, in a quiet classroom where the background level is 60db, we need approximately 70db of

sound from our speakers to be heard above the background noise.

The further away the speaker is, the less sound we hear. Of course, this is obvious, but if we want to get more scientific about it,

the sound level goes down by 6dB each time you double the distance. So the second step is to add 6db to the result of our first

calculation every time the distance from the speaker to the listening area doubles to compensate for the distance.

Take a look at the picture below.


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To make sure you have the right sound levels at a certain distance from the speaker just add 6 dB every time the distance doubles. If

we wanted the person who is 4 M away from the speaker to hear the same 120 dB of sound as the person standing only 1 M away, we

need to increase the power output of the speaker to 132 dB. Of course, if we raised the sound level, we better warn the person next to

the speaker to hold their ears (132 dB is way above the threshold of pain). Take a look at the table 1 for some examples of how much

sound needs to be added at different distances:

Table 1.

Distance away from the speaker Amount of sound level to add

1 M or 3.28 ft 0 dB

2 M or 6.56 ft 6 dB

4 M or 13.12 ft 12 dB

8 M or 26.24 ft 18 dB

16 M or 52.48 ft 24 dB

Adjusting the Speaker Volume

The loudness of the speaker can be adjusted by changing the power (wattage) reaching the speaker. The more power, the louder it is.


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In order to adjust the power on our speaker, we simply connect to one of the different terminals or taps on our speaker transformer.

Each tap will provide a certain wattage that can be varied to either increase or decrease the volume level (SPL) of the speaker. If we

double the power to a speaker, we will gain 3db of sound. So if we start with a speaker that provides 98dB when powered by 1 watt, it

will provide 101db when 2 watts are used (a 3db increase). Consequently, we can reduce the Sound Pressure Level (SPL) by reducing

the power to the speaker from 1 watt to 0.5 watts and the result will be a reduction in SPL to 95db (a 3 dB reduction).

The sound level (SPL) can be different at each speaker location. By keeping track of the wattage assigned to each of our speakers, we

can later calculate the number of speakers that can be driven by one amplifier. Table 2 provides the power levels (in watts) for sometypical situations. In this case we assumed that the ceilings are 10 ft high and that the listening level is 6ft away from the speakers.

We also assumed that the speaker provides 98 dB at 1 watt, at 1 M (3.28 ft) away from the speaker.

Table 2.

Power required to

speaker (W)*

Typical classroom (25 x25 ft) 0.5

Hallway with students 1Cafeteria 2

Manufacturing area 4

*The power taps are set at the transformer connected to each speaker.

Speaker Coverage and Location

Now that weve determined the proper volume for our speakers, we must define our coverage area. This is the area in which an

individual speaker can be heard clearly. For example, a speaker can have a nominal coverage angle of approximately 100 degrees. The

picture below indicates the area that can typically be covered by this type of PA speaker.


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In this example, the speakers are 6 ft away from the heads of the chi ldren and we have estimated that the speakers can be 15 to 20 ft

apart. If the ceiling is higher, the distance between the speakers increases.

Selecting the Type of Speaker

Depending on the requirements of your PA over IP installation, you can select from a variety of different speakers and they can be

mounted in various ways. You can select ceiling speakers, wall mounted speakers and even directional speakers that broadcast the

sound down a hallway. In a typical office environment with a suspended ceiling, you can buy speakers that can simply replace an entire

ceiling panel or you can easily cut a hole in an existing panel and position your speaker in it. If you are installing your system in an

area with an inaccessible ceiling, it may be simpler to use one of the many wall mounted speakers options available. For outside

installations, a surface mounted weatherproof horn or speaker might be what is required.

Speaker Wiring

Wiring speakers in most PA type applications (as well as a PA over IP system) involves the use of transformers to allow for several

speakers to be attached to a single amplifier and to ensure that the audio signal can be routed great distances to the speakers with littleor no signal degradation. However, these transformers are inherently inefficient and thus we are not able to utilize the full output from

our amplifier. The rule of thumb when calculating the speaker to amplifier ratio is to allow for 20% overhead for wiring loss at the

amplifier. Thus, a 20 watt amplifier should be considered to have 16 available watts for speaker wiring.

The speakers are wired in parallel just like some Christmas lights (see the diagram below). As you can see, the network attached

amplifier transformer output leads are attached to each speaker as if that speaker were directly connected to the amplifier by itself. The

taps on the speaker transformer are then used to vary the wattage to the speaker and subsequently change the volume level of that

speaker.


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The number of speakers that can be used with a single amplifier can be determined by adding up the wattage requirements for each

speaker and ensuring that the total does not exceed 80% of the total available amplifier wattage. For example, an outdoor horn may

require its own amplifier because of its hefty power requirements. Conversely, you may be able to wire up to 10 conventional ceiling

speakers to a single amplifier. It is very important to avoid overloading each amplifier with too many speakers.

Selecting the Amplifier

Once you know how much power each speaker needs, you can determine what amplifier to use and how many speakers you can attach

to each of the amplifiers. When connecting our IP Amplifiers, here are the most important considerations:

How do I want to power the amplifier? What type of speakers will I use?

Are there network drops available near where I want to install the speakers?

Each amplifier that you use is in your PA over IP system is really just another network attached device similar to a computer or network

printer. You just simply attach an Ethernet cable to the amplifier. The software (Talkmaster) runs in a computer on the network and is

used to configure each amplifier and establish a unique IP address. Using a microphone attached to this computer you can talk to any

one of the amplifiers or just to one amplifier (and attached speakers). Take a look at the diagram below for more clarification.


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There are basically 4 types of amplifiers available that are separated into 2 categories: 110VAC (or 220VAC) powered and Power

over Internet (PoE). Both have advantages and disadvantages. The 110VAC powered amplifier comes with the AC adapter and is

plugged into a standard 110VAC wall socket and thus you must account for this when determining where to physically place it. The

110VAC amplifier has the advantage of providing 20 watt output which will allow you to attach many speakers. The PoE amplifier on the

other hand can be incredibly convenient because it draws its power from the network cable to which it is attached. But, there is a cost

for this convenience a PoE amplifier is less powerful (only 8 watts) than its 110VAC counterpart and can only power a few speakers.

All of these amplifiers attach to your existing network using a standard or powered Ethernet network switch. To make this easier in

terms of connections, there are also versions of each amplifier that have 2 network ports: 1 for connection to the Control Center and anextra port that can be used for non-POE connections such as computers. This can allow the installer to reduce the number of network

switch connections.

In summary, walk around your facility to get some idea of the background noise, determine the type of speakers you want and how

much sound output is required, calculate the number of speakers you can attach to one amplifier, install the speakers, connect the

amplifiers to the network and install the software. Its easy!

Of course, if you have any questions about any of this just contact us at 914-944-3425 or send us a message. We will be happy to help.

Published by Bob Mesnik


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Copyright 2013 Kintronics, Inc.. All rights reserved.For more information, please contact us 1-800-431-1658 o r 914-944-3425 (outside the USA) or by email infohome at kintronics.com

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