AMPLIFIER: Speaker Level

The Amplifier is the last stop before the signal reaches the loudspeakers. power amplifiers boorst, or amplify, electronic audio signals sufficiently to move the speakers, They do this by incresasing the gain (the volltage and power) of the signal from line level to speaker level.
Line level is around one volt. Speaker level depends on the type of system. It can range from:

4 to 20 volt or more for stereo sound system
up to 70 volts in a distributed sound system
up to hundreds of volts in large venues

Most amplifies have only a power switch and volume controls, Potentially, the more powerful the amplifier is, the greater the amplification of the signal, and the louder the sound from the speaker

SOUND SYSTEM SETUP

A very important question to consider when designing an audio system is, what is the purpose of the system? Will it reinforce sound or reproduce sound? Is the content live voice or program audio? How do you want the content to sound to the audience?

Voice reinforcement system include paging systems as well as five event support, such as panel discusions or presentations. Intelligibility is the most important factor in voice reinforcement systems: Therefore a single channel of audio is typically used. One channel playback is called monophonic, meaning "one sound". This result in each speaker playing identical sound. This is fine for a supermarket paging system, but for music and other performance sounds stereo is better.

Stereophonic playback has two channels. To the audience, sound from the left and right are distinctly separated, and sounds from the original source seem much more realistic. For example. if the drums were playing from the left side of the stage, their sound would come from the left speaker to an individual sitting in the audience.

Multi-channel or surround sound has a more complex stereo playback system. Surround sound can have five channels, and produces increasingly realistic sound. In movie theater, surround sound may be used to make the sound seem to the audience as if it were coming from a specific direction (right, center, rear, etc).

Power Amplifiers

The audio power amplifier is a component whose function is - as its name implies - to increase the power of an audio signal, so that the signal can drive one or more loudspeaker. In sound systems, the power amplifier is always the final active component in the signal chain, located just before the loudspeakers.
In small portable sound systems, the power amplifier may be build into the mixpower, as a convenience.
Full comprehension of the function and application of power amplifier requires an understanding of electrical power and its relationship to voltage, to resistance or impedance, and to current. The details of these relationships, stated by Ohm's Law and associated equations, are beyond the province of this book. But some basic understanding may be imparted by way of a classic analogy:
Thing of water being forced through a pipe. The greater the pressure being applied, the more water will move through the pipe. The smaller the diameter of the pipe, the less water will flow through it. In drawing a comparison with electricity, the water represents electrons (negatively-charged atomic particles), which constitute the electricity itself. To flow rate of the water represent the electrical current (abbreviated I), measured in amperes (amps for short). The pressure represent the voltage (sometimes called electromotive force, abbreviated E), measured in volts. The resistance to flow of the pipe, which decreases as its diameter increases, represents the resistance (R), measured in ohms (symbolized by Ω); the greater the resistance (i.e., the smaller the pipe diameter), the less current (water) will flow.
Consider the DC electrical circuit of this figure:

This is a direct-current (DC) circuit, which means that the current flows in one direction only. A DC voltage E from sourceS (a battery) is applied across a resistance R. This resistance is termed the load. The current flow I is represented by an arrow in the diagram. Notice that this is indeed a circuit. That is, the current flows   "around" from the point of highest voltage (or potential)-the negative (-) terminal of the battery - to the point of the lowest potential - the positive (+) terminal. Should the circuit be broken, the current would cease to flow.
In speaking of alternating current (AC), such as an audio signal, impedance is substituted for simple resistance. Impedance, also measured in ohms, is sometimesabbreviated Z, or Z, rather than R. The chief distintion between resistance and impedance is that the impedance of a loadd (such as a loudspeaker) is different frequencies. Nevertheless, loudspeakers are clasified by their nominal impedance - a single figure, which is used. 
Consider the AC electrical circuit of this figure:

This figure represent a power amplifier (the AC souce) driving a loudspeaker (the load - abbreviated RL on some amplifier spec sheets).

Electrical power (abbreviated P or Po), measured in watts (W), is the energy used to do the work when an electrical current is made to flow through a load resistance or impedance. Power is proportionate to the square of the voltage or current, which accounts for the different increases in dB of a signal when the power is doubled, as compared to when the voltage is doubled.

With this rudimentary background, the specifications of power amplifiers can be discussed meaningfully.

DISTORTION AND INTERFERENCE

Distortion and interference can result from several different causes. Check the essentials first: Make sure the mic has a fresh, fully charged battery. If you have a lavalier and a hand-held mic for the some receiver, be certain only one of them is turned on.
If you use more than one wireless system and they interfere with one another, relocating the receivers may help.
Some external RF interference may be beyond your control, especially in an urban area. If this is the case, try to determine which wireless system is being affected. You may have to send the system to the manufacture to have the frequency charged. Some manufacturers offer 'frequency-agile' systems, which allow  the user to switch to an alternate frequency, saving time, expense, and frustration, These systems usually cost a little more, but the extra expense is worth it when you need to change frequencies and get back on the air quickly. Be aware that some radio stations are part-time, and may create interference that wasn't there when you tested the system.