ALLEN & HEATH GL4800 User Manual page 49

Using the GL4800 for Front-of-House (FOH)
The console is positioned within the listening area so that the sound fed to the audience
can be accurately balanced and controlled. In larger systems the performers monitors may
be controlled from a separate console positioned at the side of the stage (on-stage
monitor). Where this is not possible the monitors are controlled from the FOH console.
You may also be required to provide separate recording, broadcast and zone feeds, and
even record the show for the performers.
This application demonstrates the versatility of the GL4800. Here, the console controls a
LCR + delay fill speaker system, stage monitors, stereo broadcast feed, with 2-track and
multitrack recording. Signal processing devices such as effects and graphic EQ are shown
inserted.
The Importance of Inserts on the Outputs
A graphic equaliser is inserted into each of the main L,R and M outputs to adjust for the
natural acoustic resonances which can colour the sound and result in troublesome acoustic
feedback. Inserting these rather than plugging them between the console outputs and
amplifier inputs gives two advantages:
1. The long cable runs can be driven from the console balanced XLR outputs
without signal loss and interference pickup. Many lower cost graphics do not have
this drive capability.
2. You can monitor the effect of the graphic using AFL.
The Main Left, Centre, Right (LCR) Outputs
Most sound systems use speaker stacks positioned left and right of the stage. Larger
systems and many fixed theatre systems include a mono stack hung centrally above stage
front. Here, the main sound source such as vocals is sent to the mono stack while music
and effects may be sent to LR. The stereo image is usually kept narrow for the benefit of
the audience positioned closer to one of the speaker stacks.
Use group PAN to control the stereo image to LR.
Use LR to MONO to mix some LR to the mono output to get the best balance
between the speakers.
The LR Delay Fills
In larger venues additional 'fill' speakers are positioned nearer to the audience seated
furthest from the stage. In a theatre these may feed the raised balcony. The intention is to
improve clarity without distracting the audience from the source of the sound itself.
Because of the distances involved the acoustic delay between the originating sound source
and the fill speakers becomes obvious to the listener as a distracting delay (around
1millisecond per foot). It is also important to EQ the sound to prevent distraction, usually
by removing some LF and HF. In some cases you may wish to send a different mix from LR
to the fill speakers. The GL4800 offers two ways of controlling fills :
1. Use the MATRIX outputs if you want the fill mix to be different to the LR mix.
Select
2. Use the LR2 outputs with POST selected so that the fills follow the LR faders.
Here, the balance between the main speakers and fills is set using the LR2 output
level trims. Select
graphic EQ into the inserts. Adjust these to remove the audible delay at the listening
position, and to EQ for least distracting effect. Use AFL to check the effect of the
inserted equipment.
GL4800
User Guide
OUT REV for balanced XLR output and inserts,
OUT REV for XLR and inserts. Patch a stereo delay unit and
or
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