A PA system consists of microphones, mixers, amplifiers, loudspeakers, and cables. Microphones capture sound and convert it to electrical signals which are sent to a mixer. The mixer allows combining of multiple audio sources and controls their levels before sending the signal to an amplifier. The amplifier strengthens the signal which is then sent to loudspeakers that convert it back to sound waves audible to the public. Crossovers and separate drivers are often used to optimize different frequency reproduction. Cables properly connect all the components.

1. Kazim Pardhan

2. What is a PA system?
 An electronic amplification system used
as a communication system in public
areas
 http://wordnetweb.princeton.edu/perl/webwn?s=pa%20system

4. How do PA systems work?
 Microphones
 The goal of a PA system is to provide "public address", or
a way to transmit audio communication to a group. This
transmission can begin with a microphone, which is a
device that can assist in magnifying an audio source's
volume. A microphone is classified as a device that
transforms sound into an electrical signal. Microphones
used in PA systems are usually dynamic or condensers.
Dynamic microphones are more rugged than condensers
and are able to withstand the elements a little better.
Condenser microphones utilize their own power source
and produce better-quality audio signals, but can
sometimes be so sensitive that they also receive
background noises.
Paul Bright. How Do PA Systems Work?. Available:
http://www.ehow.com/how-does_4964034_pa-systems-work.html. Last
accessed 04/03/2013.

5.  Mixers
 If a microphone or another audio source is
used in a PA system, it is plugged into a mixer.
The mixer allows for multiple channels of
sound to be broadcast at different levels. This
can help prevent feedback if a PA system will
involve multiple microphones, instruments, or
other audio sources. For example, someone
may use a PA system to sing along with a pre-
recorded CD. The CD track could be plugged
into one channel, while the singer's voice
would be broadcast through another.
Paul Bright. How Do PA Systems Work?. Available:
http://www.ehow.com/how-does_4964034_pa-systems-work.html. Last
accessed 04/03/2013.

6. Mixer
 1. Channel Input 2. Trim 3. Channel Volume 4. EQ 5. Channel Effects 6. Master Volume 7. Master Effects
8. Master Outputs
Robert Wishart. How to set up a P.A Sound System. Available:
http://www.thesingingtutor.com/pasetup.htm. Last accessed 04/03/2013.

7.  Amplifier
 The amplifier is usually side by side or
incorporated with the mixer. The amplifier's job
is to magnify the audio signal by manipulating
its varying frequency qualities. Gain in an
amplifier refers to the decibel level of the
sound coming out of the speakers. Another
quality, Output Dynamic Range, refers to the
loud and soft levels of a specific channel's
sound. Too low of an output could result in
just broadcasting noise; too high of an output
can lead to distortion.
Paul Bright. How Do PA Systems Work?. Available:
http://www.ehow.com/how-does_4964034_pa-systems-work.html. Last
accessed 04/03/2013.

8. Amplifier

9.  Loudspeakers
 The loudspeaker is the output end of the PA
system, transforming the electrical signal back into
sound that a group can hear. A good loudspeaker
system will separate the differing sound frequencies
and broadcast them through different sound
channels for better quality output. Parts of a
loudspeaker system include a
woofer, which broadcasts low frequency sounds; and
tweeters, the drivers of high frequency output. Some
speakers also contain crossover systems that are
responsible for separating these
frequencies, reducing the electrical noise that can
sometimes accompany a PA system broadcast.
Paul Bright. How Do PA Systems Work?. Available:
http://www.ehow.com/how-does_4964034_pa-systems-work.html. Last
accessed 04/03/2013.

10.  The Drivers
 Drivers are the components that produce the sounds. They are
generally comprised of a coil of wire sitting within a magnetic field. As
electric current flows through the coil of wire it moves within the
magnetic field. By attaching a diaphram to the coil, we can make a
volume of air move at the same time and produce sound waves.
 A single driver can be capable of producing the full range of audible
sounds. In practice, however, multiple drivers are more common in a
loudspeaker for efficiency reasons. A two-way system would have a
low-to-mid range frequency driver and a high-frequency driver too. One
of the reasons for separating these out is that high frequencies are
more directional. High frequency drivers are normally mounted along
with a horn in order to control the direction. If you take a look at the
specification for a loudspeaker, you should find a Dispersion property.
This indicates the angle at which the high frequencies leave the
loudspeaker. Narrower dispersion angles (30° - 60°) are more suited to
long-throw speaker applications whereas wider angles (90° - 100°) are
better for short-throw.
Public Address (PA) Basics. Available: http://www.livesystems.co.uk/pa-
basics.html. Last accessed 04/03/2013.

11.  Crossovers
 When a loudspeaker has more than one driver we need a way to split
the frequencies so that the low frequencies go to the low frequency
driver and the high frequencies to the high frequency driver, etc. This is
done using a Crossover.
 A crossover splits an incoming audio signal into its component
frequency bands. Most two-way or three-way loudspeakers have an
inbuilt crossover network that does this job. This is known as a Passive
Crossover. More advanced systems use an external crossover known
as an Active Crossover. This works slightly differently as it is inserted
before the amplifier. In this case, you will require additional amplifier
channels to run each individual driver. This technique is referred to
as Bi-Amping. Such systems tend to sound cleaner, more detailed and
controlled with each driver being run by its own dedicated amplifier
channel. The down side is the expense as more amplifiers are required
as well as the active-crossover itself.
Public Address (PA) Basics. Available: http://www.livesystems.co.uk/pa-
basics.html. Last accessed 04/03/2013.

12.  Impedance
 We mentioned Impedance when we talked about amplifiers. This is a measure of the
Load that the speaker represents to the amplifier. It is measured in Ohms (W). Most
speakers have an Impedance of either 4W, 8W or 16W. This figure must be taken into
account when choosing the correct amplifier to use.
 But what happens when you want to connect two or more loudspeakers to the same
amplifier channel? Does the impedance change? Well, yes it does, but not as you may
expect. When speakers are connected together they are connected in parallel. When
this happens the following maths applies:
 To deal with more than two loads you just keep on adding terms to the right. So two
8W speakers would give a total of 4W and three 8W loads would give you a total load
of 2.67W. Be careful not to make the load too small. Most amplifiers have a minimum
load that they can drive, 2Wbeing the common minimum. Always check the
specifications of the equipment.
Public Address (PA) Basics. Available: http://www.livesystems.co.uk/pa-
basics.html. Last accessed 04/03/2013.

13.  Cables & Connections
 Cables, although among the cheapest
items in a PA, are very important. These
carry the audio signals between
components and should therefore be
chosen carefully in order to minimise
losses and interference which could
degrade the resulting sound.
Public Address (PA) Basics. Available: http://www.livesystems.co.uk/pa-
basics.html. Last accessed 04/03/2013.