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Last Saturday L* and I went to WaveAid, a benefit concert for victims of the 2004 Indian Ocean Earthquake (commonly referred to as “the tsunami”). 11 (predominantly) Australian artists donating their time to help raise money, including the return of silverchair and Midnight Oil.
I was mainly there to see the Oils, having not seen them on their final tour before they broke up a few years back. But before they came on later that night, I was amazed to hear the Finn Brothers do acoustic versions of a bunch of Split Enz (finishing with I got you) and Crowded House songs, and have most of the SCG singing along. That’s roughly 47000 people. I didn’t realise Crowded House were so popular, and that so many of their songs had become part of Australian rock history. Anyway…
Now when I say 47000 people, it is actually impossible to hear that many people sing at the same time of course, but not for the reasons you’re probably thinking.
Sound travels at roughly 340 metres per second on such a hot day although it is boosted by body heat. The SCG is at least 200 metres from the main stage to the top of the far stands, meaning it takes about 600 milliseconds (over half a second) for the sound to travel the full distance. Because light travels almost instantaneously at 200 metres, a person at the back won’t hear what they see until over half a second after the fact. Half a second doesn’t sound like much, but our senses think it is, especially when trying to sing along to visual guitar strumming.
To get the main stage sound to the very back, you’re either going to permanently deafen the people down the front, or you’ll have to place extra speakers at the back. Of course the latter is the case, and at the SCG you’ll find about half a dozen speakers around the ground, staggered at various distances from the stage. If you pumped electrical signals into those, you’ll find the sound comes out in almost perfect time with what people are seeing, at all distances, which is what we want to happen. However the problem is the people at the back will now here the immediate sound, plus six other signals slightly delayed by about 100 milliseconds apiece, as each speaker’s audio arrives from different distances, causing an almost deafening echo or reverb. You’ve probably experienced a smaller version of this at a school sports carnival, where they use multiple speakers around an oval.
The solution is to use digital delays to delay the sound coming out of each speaker, by the time it takes sound to get from the main speakers to the target speaker. So if you have a speaker 100 metres back, the PA will be configured to delay the signal being sent to it by about 300 milliseconds. Likewise the back speakers, 200 metres out, will be delayed by 600 milliseconds. This way the sound from every speaker, will arrive at the same location all at the same time that the sound from the actual performance arrives.
Of course sound is omnidirectional, so sound out of the back speakers will also travel forward, meaning the distance between each speaker needs to be carefully calculated.
So if you’re at the back, what you see on stage is still going to be out of sync with the audio, but at least the sound will be clear and have no noisy echo. Unless of course you have a PA which is able to send audio 600 milliseconds forward in time.
What this means is that when the audience sings along, not only will the front and back of the audience actually be out of sync, due to the delayed audio, but they’ll be gradually staggered from front to back, like a mexican wave. Due to this staggering, we find that only small sections of audience are ever in sync, and thus are not actually vocally loud enough to make an audible impact on other sections of the audience. So, 47000 people at once? More like 1000 people at once. Although if the people down the front had super hearing, they’d be able to hear the singing at the back, and wonder why it was delayed by 1.2 seconds.
Getting back to WaveAid, when the Oils finally came on, we were about 10 metres from the stage, right in front. They kicked off with Read about it, not one of their better known songs, but the entire audience (mileage may vary) for as far as we could hear, were singing along. A couple standing next to us who weren’t Oils fans, even had huge grins on their faces, marvelling to the chorus of 47000 voices (slightly staggered) who knew most of the lyrics. Peter’s opening words “I’m probably the only member of parliament currently singing in a band [..] some of us may have moved on, but what we stand for still hasn’t changed” then set the tone for the rest of their set.
The highlight of the night was when drummer Rob Hirst started a simple snare beat, which the audience immediately recognised as Dead heart, and started humming Doo do, doo do, doo do do for about a minute before any other instruments kicked in. The couple next to us kept looking around, unable to stop grinning. To then hear 47000 people singing about giving Australia back to the Aborigines, was probably the most significant and positive political statement I’ve heard made in this country for many years. And the music was great as well. 🙂
A bunch of lefties? I doubt it. Aussies enveloped in the emotional rhetoric of Australia’s greatest ever live band? Perhaps. 47000 people who care about human life, tolerance and a world population living together in peace? Most likely. John Howard take note. You have three years.
Update: I’m pretty sure the songs were Read About It, Say Your Prayers, Best of Both Worlds, King of the Mountain, Forgotten Years, Power and the Passion, and Dead Heart. I can’t remember the exact order.