PA Systems and Setups

PA Systems and Setups

When it comes to live music performance, the sound systems have always been something I've noted - but not particularly considered in terms of set-up, positioning and behind-the-scenes operation. At The Forum, we have a stereo pair of suspended Funktion 1 line arrays, with 6 D&B J-Subs. Smaller 'fill' speakers are between the subs to provide sound projection where the suspended line array sound trajectories cannot adequately reach (see diagram below). Further back in the room there are delay speakers in the bars which project the sound at a delayed time, to merge with the sound from the main PA after the time it takes to travel across the room.

I spent some time around the venue and in the amp room, looking at the amps and determining the signal path from the DJ/band to the mix console to the speakers.

The signal route of The Forum's Main Auditorium is as follows:

1. Signals generated through DJ equipment/band onstage -->
2. XLR's fed into an onstage 48 channel patch bay -->
3. 48 channel snake runs under dance floor to Front of House (FOH) patch bay -->
4. Channels fed in via looms into mixing console and mixed -->
5. Mixed audio sent via main L+R output into FOH patch bay -->
6. Audio goes to amp room where it is distributed to various D&B D12 amplifiers -->
7. Amplifier speakon outputs return to stage and connect to corresponding multicores and speakers.

Personally, I'd like to know more about the industry standards in PA set-ups and standards, so that I am aware of and have attained knowledge of their application potentials should I encounter them in my career. Entertainment companies such as Vortex Events offer sound and lighting for events, often offering packages which may consist of visual, sound, stage sound. At a recent event at The Forum, I assisted Vortex Events in setting up a DJ PA in the main foyer. This consisted of a stereo pair of L'Acoustic Subs and stacked line arrays, which were positioned in two corners of the room due to convenience, ie. out of the way of customers and displays.

For higher end applications and permanent fixtures, careful positioning may be required to deliver the best sound based on the complex physical principles of multiple sound sources and frequency distributions. Upon research, I've discovered that projection visualisation softwares such as MAPP help plan PA positioning on these grounds. Some compromises have to be made in the name of practicality and budget.

In the image above, we can see the comparison of two speaker stacks (3 on the top, 20 on the bottom), and their predicted loudness trajectory in dB SPL denoted by colour, with red as loudest and dark blue as quietest. The X and Y axes provide room dimensions in meters. These visualisations are made at a frequency of 1KHz. Information such as this can be used to predict to a level the interactions between multiple speaker sources to give an idea of how effective placements will be on the listening quality from the audience's perspective. 

Bibliography

Sound On Sound (2006) Line Arrays Explained: The Science and the Magic [Online] Available at 

http://www.soundonsound.com/sos/mar06/articles/live_linearrays.htm [Accessed on 2/12/2015]