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SOUND 
Michael Drolet -- 2012
Home BEHRINGER MX802




 
INTRODUCTION:

There are many terms used to refer to the complicated-looking piece of electronic gear sitting on the table in front of the Sound Booth window:
console, mixer, mixing board, sound board, mixing desk, sound desk.
 [I will try to be consistent and to always refer to the mixer.  If  I slip up, you now know the other possible terms.]
In a production studio, the mixer is used to route sound signals from various sources, (microphones, CD players, FX units) to various destinations (usually tape machines, hard disk recorders or FX units). It can also be used to modify the tonal quality (EQ) or relative balance of the sound signals passing through it.
In a performance space, the mixer serves to route the various sound sources (microphones, CD players or FX units) to various loudspeakers on the stage or throughout the house. It allows you to control where the sounds will be heard and how loud they will be.
The same mixer will generally serve for either the production studio or performance space.  One of the mixers we have at  John Abbott is a Behringer MX802. It is representative of mixers you will find in small production studios or theatre spaces today.

Although the MX802 is smaller than the Mackie Onyx 1640i, which we use on most productions, it functions in much the same way and will be a stepping stone to understanding more complicated mixers.

BEHRINGER MX802 FRONT PANEL

(click on image for larger view)

BEHRINGER MX802 MIXER:

In a sound system,  a source of sound is referred to as an output.  A destination is referred to as an input. Building a sound system involves connecting sources to destinations  --   an output to an input to an output to an input.....and so on.

The sources could be the outputs of mics. on stage, CD players,  effects units or tracks from a computer.The destinations could be the inputs of the House speaker system, onstage monitors, headphone amps or effects units.

The Behringer mixer allows you to simultaneously control and route, any (one or more) of eight sound sources  to either of two main destinations; the MAIN MIX outputs and/or to two AUX SEND  outputs.

In a sort of technical short-hand, this mixer may referred to as a 8:2 mixer (with 2 AUX sends) to indicate it offers 8 inputs, and 2 main outputs (with 2 AUX sends).
Although the mixer may appear to be complicated, it is in fact, composed of only a few different building blocks, called modules or strips. Each type of module groups together all the controls and internal circuitry to perform similar functions.
In our mixer, there are 4 MONO input modules, grouped together on the left side of the mixer, 2 STEREO input modules in the centre and a single MAIN MIX module  on the right.
You will only need to learn the operation of these few modules, in order to "master" operation of the entire mixer. We'll have a look at the front panel controls and the signal flow through each of the modules in turn.


There are two types of signal sources in common use today:
    • mic level -- typically a few millvolts -- very small signals from microphones, guitar pickups
    • line level -- one tenth to several volts -- relatively large signals from FX processors, CD players, iPods, MP3 players

Different circuitry is often required to handle these two differing signal levels without adding distortion or noise. Because of this,  it's important to always connect a source to the correct mic or line-level socket.



MONO INPUT MODULES:
The 3-pin XLR,  "MIC" (rophone) connector is provided for use with professional microphones.
The TRS (Tip-Ring-Sleeve) or 1/4 inch, "LINE IN" connector is provided for use with line-level sources, like CD players, or FX units.
 Only one connector can be used at a time on each input channel.

MONO input
low cut LOW CUT (High Pass Filter):
  • cut 18dB/octave from  75Hz
  • can be used to cut traffic or air conditioning rumble
  • don't use on bass guitars or tubas.
The "GAIN" control allows you to adjust the input strip so that you can operate with the channel "LEVEL" control in its normal range, around "-0-" on the scale. This assures that the signal will have the maximum headroom and minimum noise.
Headroom is the level difference available between normal level and the point of distortion.
Noise is the background hiss you hear when you turn the gain or volume up too much.

At the "-0-" position, there is still 15 dB of gain available, should the input signal drop in level. We say that there is 15 dB of gain-in-hand.

This gives you room to maneuver should the input signal change.


Working with the channel "LEVEL" control at "-0-" also allows for smooth fades in or out.
EQUALISER (EQ):

The equaliser (EQ) on a mixer is the sound equivalent of a colour gel in lighting.
Just as you can make a lighting effect "warmer" or "colder" by inserting one or more gels in front of the light source; an EQ inserted in the signal path can be used to make a sound effect "warmer", "colder" or more or less "present".
The EQ on the Behringer MX802 is rather rudimentary, but functional.  It consists of one control, "HIGH",  to boost or cut the high frequencies ("sizzle"), and another, "LOW" to boost or cut the low frequencies ("boominess".  A third control, "MID",  can boost or cut the mid frequencies ("presence").


eq hi
HIGH:  (Shelving)
  • boost or cut 15dB @ 12kHz
mono eq aux level pan
eq mid
MID:
  • boost or cut 15dB
  • centre frequency 2.5kHz
  • vocal presence
   eq low
LOW:  (Shelving)
  • boost or cut 15dB @ 80Hz

Some of the signal from each input channel can be sent to a stage monitor, so the performers can hear themselves. The "AUX 1" control adjusts how much of each channel is sent to the AUX2 SEND output, PRE FADER -- before passing through the input channel "LEVEL" control. The level sent to AUX1 is unaffected by the house mix.

Some of the signal from each input channel can be sent to an external effects processor to add an effect -- artificial reverberation, for instance.  The "AUX 2" control adjusts how much of each channel is sent to the AUX2 SEND output, POST FADER -- after passing through the input channel
"LEVEL" control.  The level sent to AUX2 follows the house mix.
The "PAN" control allows us to place individual sounds so that the are heard to come from somewhere between the two MAIN MIX outputs.
If the "CLIP" LED flashes briefly every couple of minutes, the signal level is not too high. But if it flashes continually, you will have to reduce the input signal to avoid distortion.
    • adjust the "GAIN" control down (counter-clockwise)
    • insert an external attenuator (pad) at the input connector
    • move the microphone farther from the source. 
The MONO input channel "LEVEL" control is your operational control over the signal level during a recording or performance. It allows you to smoothly fade an individual sound in or out.


STEREO INPUT MODULES:
A pair of TRS (Tip-Ring-Sleeve) or 1/4 inch, "LINE IN" connectors is provided for use with line-level sources, like CD players, or FX units.

Often, such devices are stereo so Left and  Right signal sockets are provided.

A mono source connected to the Left socket will feed both left and right channels equally.
stereo inputs


The "EQ" and "AUX" sections of the STEREO input channel module are identical to the MONO input channel module.

















The "BAL(ance)" control allows us to place individual sounds so that the are heard to come from somewhere between the two MAIN MIX outputs.

The STEREO input channel "LEVEL" control is your operational control over the signal level during a recording or performance. It allows you to smoothly fade an individual sound in or out.

stereo level bal fx

MAIN MIX MODULE:

Stage monitors can be connected to the PRE-FADER AUX SEND 1 socket.

An external effects processor can be connected to the POST-FADER AUX SEND 2 socket.

The output of fx processors must be brought back (returned) to the mixer in order to be heard,  The STEREO AUX RETURN sockets are used for this function. 

The AUX RETURN sockets are wired so that if you only connect to one pair of sockets, both AUX RETURN 1 and 2 are sent the same signal.

aux returns
The "AUX  RETURN 1" control adjusts the volume of the effects return signal connected to the  AUX RETURN 1 sockets.  AUX RETURN 1 can only be sent to the MAIN MIX OUT to feed the house speakers.

The "AUX  RETURN 2" control adjusts the volume of the effects return signal connected to the  AUX RETURN 2 sockets.   The "FX TO AUX 1" switch selects whether the AUX RETURN 2 signal is sent to the MAIN MIX OUT (to feed the house speakers.) or to AUX 1 (to feed the stage monitors).


The "POWER" led indicates that AC  power is available.

The "48V" LED  indicates that phantom power is being applied to  all 4 MONO Inputs..

The "L and R" LED meters indicate the signal level being sent to the MAIN MIX output.  To avoid distortion, ride the gain so as to no hit the red "CLIP" LED.


The "2-TK TO CTRL ROOM" switch sends the 2-TRACK IN  (MP3 player) signal to the booth monitors (instead of the MAIN MIX signal).  This would be used to check the 2-TRACK IN in the booth, without the audience hearing it.

The "2-TK TO MIX" switch sends the 2-TRACK IN  (MP3 player) signal to the MAIN MIX output (instead of the MAIN MIX signal). The would be used to send the 2-TRACK IN signal to the house speakers for the audience to hear.


The "MAIN MIX" fader controls the volume sent to the MAIN MIX output. In theatre use, this would most often be a pair of powered speakers in the house.

The "PHONES/CONTROL ROOM" control adjusts the volume heard on headphones connected to the PHONES socket, or a pair of speakers in the booth connected to the CTRL ROOM OUT sockets.

main mix

The 2-TRACK RCA sockets are intended for connection of an external cassette or MP3 recorder/player.

External equipment such as a stereo power amp or powered speakers can be connected to a  pair of  TRS (Tip-Ring-Sleeve) sockets labelled MAIN OUT.

A pair of headphones can be connected to the PHONES socket.

A pair of control room (sound booth) speakers can be connected to the CTRL ROOM OUT sockets.

main out

REAR PANEL:
On the rear of the mixer is the connector for the external power supply.

The POWER SWITCH turns the mixer on. 

Some condenser or electret type microphones can be powered externally, eliminating the need for batteries. The power required can be supplied by the mixer via the same cable used to carry the microphone signal to the mixer.

This system is called phantom powering. The "PHANTOM" switch  activates this function for the 4 MONO inputs.
power phantom switches

BLOCK DIAGRAM:
This block diagram of the console shows the path a signal follows from input to output.(click on image for larger view)
BEHRINGER MX802 BLOCK