Sound System : Intermediate stage

Stage Purpose: 

receiving the electrical output signals from input stage devices/transducers for carrying out some process like  amplification, controlling, equalizing, compressing or panning on this signals.

Stage structure:

The Intermediate Devices included in this stage Differ from Sound System to another according To the Used Input and Output Devices in this System but generally the Intermediate Devices types included in this stage will be as follows:

•  Audio mixer
• Equalizers
• Mixer amplifier
• Mixer pre-amplifier
• Power amplifier (boosters)
• Pre-amplifier
• Monitor unit
• Speaker selector
• Power supply
• Remote control unit
• Crossover

1-audio Mixer:see fig.1

 Audio Mixers are used for connecting the different input devices and for selecting any of them for broadcasting.

Un-powered mixers usually have only input impedance and these tend to be referred to as either high impedance or low impedance according  to the type of signal that the mixer will accept. Many mixers will accept both types of impedance and have two different types of jacks for this purpose.

fig.1:Audio Mixer

As a general rule of thumb, if the input jack is an XLR type (three pin-see fig.2) it is low impedance, and if it is a phone type (1/4”) it is high impedance. Phono type input plugs (RCA- see fig.3) are always high impedance.

fig.2:XLR Jack

fig.3: Phono Jack

If you plug a high impedance signal into a low impedance input (or visa versa) it will not damage anything, but it will not sound very good. Depending how far off the impedances are, the signal will be weak and lacking in frequency response (tone).

Microphones can be either high or low impedance; however, instruments such as guitars and keyboards are generally high impedance. Consumer electronics such as tape decks, CD players and tuners are always high impedance and should not be plugged into microphone inputs.

Mixers Types:

Mixers are divided into two parts:

• The master section
• The channels Section

A- Master Section: see fig.4

Most manufacturers locate the master section on the right side of the mixer, although some large consoles might have it in the middle. The master section controls the output of the mixer to all of the various other components that are hooked up to it. These might include crossovers, equalizers, effects processing devices (delays, reverbs, compressors, etcetera) and monitors.

fig.4:Master Section

Most of these controls are simply volume controls to determine how much signal you want going to any devices hooked up to your mixer. You will often find some tone controls (equalizers) to modify the tone of the sound and switches to dictate what each control affects.

B-Channel Section: see fig.5

The channels tend to be duplications of each other so, once you have one figured out, you will have them all figured out. All channels tend to have the same types of things on them, just more or less of each one, depending on the market that the manufacturer is targeting.

fig.5:Channels Section

Many mixers designed these days actually call the tone controls on each channel “equalizers”. 

and these equalizers will be our next topic's target.