Sound System : Intermediate stage-equalizers,Mixer Amplifiers and Pre-Amplifier

We talked in the previous topic about the Audio Mixers and actually Many mixers designed these days call the tone controls on each channel “equalizers”.

2- Equalizers: 
Equalization: is the process of adjusting the strength of certain frequencies within a signal. The circuit or equipment used to achieve equalization is called an equalizer.
Equalization is used to compensate for the discrepancies of a room's acoustics (which may be loud) while recording or broadcasting.


Equalizers are dividing into three types:

1-    Graphic:see fig.1
Graphic equalizers consists of a bank of sliders for boosting and cutting different bands (or frequency ranges) of sound. The number and width of filters depends on application.

A typical equalizer for professional live sound reinforcement has some 25 to 31 bands, necessary for quick control of feedback tones and room modes. Such an equalizer is called a 1/3-octave equalizer because the center frequency of each filter is spaced one third of an octave away from its neighbors, three filters to an octave. Equalizers with half per octave are common where less precise general tone-shaping is desired—this design is called a 2/3-octave equalizer.


2-    Parametric:see fig.2
 Parametric equalizers allow audio engineers to control the three primary parameters of an internal band-pass filter which are amplitude, center frequency and bandwidth. Bandwidth is typically labeled "Q" on the unit, which stands for Q factor. The amplitude of each band can be controlled, and the center frequency can be shifted, and widened or narrowed.

3-    semi-parametric or a sweepable graphic equalizer:
It allows users to control the amplitude and frequency, but uses a pre-set bandwidth of the center frequency. In some cases, semi-parametric equalizers allow the user to select between a wide and a narrow preset bandwidth.


3- Mixer Amplifier:See fig.3
It is a mixer with a power amp built into it (these are often referred to as powered mixers.
The two main factors in choosing a mixer amp are the number of mixer channels and the wattage of the power amp(s).

1- The number of channels on the mixer:
It determines how many different audio signals you can mix together. Some Channels include a microphone input (with a suitable pre-amp) and some channels are mono while some are stereo (although two mono channels can be used as one stereo)

2- The power of the Mixer power amplifier:
This power must be matched with the PA speakers you are going to be using. Power amps rated significantly higher than the speakers can damage both speakers and amps if not used very carefully. To determine the wattage of amps and speakers you need to know what spaces they need to fill, whether indoors or outdoors (outdoor amplification needs to be about twice as many watts to sound about the same volume) and how loud the sound needs to be. Also the types of sounds need to be considered


4-Pre-Amplifier:see fig.4
A preamplifier is an electronic amplifier designed to prepare an electrical signal for further amplification.
Preamplifiers may be located in a separate housing, incorporated into the housing or chassis of the amplifier they feed or mounted in other items of equipment, such as microphones.

in the next Topic, I will explain all about the Power Amplifiers, please keep following.

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