This evening I returned to the site of Friday On The Green to hear what the show sounded like. The event producer states that this event typically draws between 1500 and 3000 people. Based on the people I saw, I would guess there was at least 3000 people. More people means more territory to cover.
Near the stage the PA sounded relatively good. As I moved further away from the PA the intelligibility dropped off along with the SPL level until what I could mostly hear was low end. This is to be expected because low frequencies can travel much greater distances than high frequencies. Consequently, as you move away from the sound source the high frequencies are reduce due to air but the low frequencies keep right on going. Depending on the expected coverage area, you might add delay speakers to compensate for the SPL and high frequency losses due to distance. You can only push a certain PA so much before you run out of headroom. In the case of the PA system in discussion, the PA is simply not capable of producing enough SPL for the outdoor audience which this time was huge in comparison to previous Friday On The Green events.
Here is a good website that explains how distance affects sound intensity & the inverse square law.
HyperPhysics – Inverse Square Law Sound webpage
Simplified, the sound level (intensity) coming from any PA (with a few exceptions) is going to diminish by 1/2 with each doubling of distance. For example, if you measure 100db at 1 foot, you will measure 94db @ 2 feet, 88db @ 4 feet, 82 @ 8 feet, etc…
This means a few important things.
1. In order for a PA to be loud enough far away, it has to be much much louder up close.
2. If the PA is stacked on the ground or the stage and the audience is able to get any where near the PA, they will be subjected to excessive SPL IF the PA is loud enough further away.
2. Raising up the PA reduces the level discrepancy between being close and being far away.
3. The PA you choose for a given event MUST be capable of a certain SPL output without distortion or else you’ll either be forced into distortion to meet the expected SPL requirements at a distance OR you’ll have to accept a lower SPL level and those farther away will have bad sound.
This event is a perfect example of an undersized PA system. There is no way this PA (in it’s current configuration) can provide even coverage to the audience. Obviously there is different levels of “unqualified” when it comes to PA systems. While this PA might seem “unqualified”, This is probably the best PA the event has had to date. The first time I went to an Friday On The Green event, the entire PA was a few small Mackie SR450 mains and (1) Mackie 1×18″ sub per side. The current QSC PA is like a Rolls Royce in comparison.
Given the size and shape of the audience, Friday On The Green warrants a much larger rig with side fills, front fills and if the PA can’t be raise high enough, delay speakers. Budget limitations are what limit the PA configuration.
Friday On The Green happens all Spring and Summer long so I’m sure there will more chances to measure and discuss this event…