Re: Echoes at Twickenham
Date: August 21, 2006 17:06
I was in A2 and the sound was very echoey. I'm an acoustic engineer and I've been thinking about what's going on. I think the echo may have been made worse by the columns of speakers at the back of the stadium bouncing off the rear walls and ceiling and then going back down to the front. Many people in the stands claim that the sound was crystal good though some thought it was poor.
I've tried to explain this below for those who are interested. If you hate science skip this bit now because it will be boring.
As an example, take my seat in A2. I must have been about 20 m from the front column of speakers. Since speed travels at 340 m/s then it takes about 60 ms for the sound to reach me. I reckon that the stadium is about 200m long so I get an echo about 1 second later from the main speaker column. In addition, I get an echo from the rear speaker column (although no direct sound). In addition to that, there are some speaker columns directed towards the east and west wings which will have a relatively short delay time to get to my seat (maybe 100 - 150 ms - i.e. a tenth of a second or so). Obviously the real situation is much more complicated with multiple reflections coming from all angles, but hopefully you can see why it is can be so bad. The roofs on the stands (which kept those in that area dry) probably make the sound worse because they prevent much of the reflected sound going up into the sky which, believe me, is the best place for it.
If you were halfway up the stadium you would see an echo some half a second after the original signal hit you. However, if you are lucky and in the direct signal path of the speakers, the direct sound will be muck louder than the echos and reverberation. In that case, you will perceive the sound to be crystal clear.
Hope this goes some way to explaining why it is like fighting a losing battle to get good sound in a stadium. Some stadiums are fitted with absorption to reduce reflections and reverberation. The new Wembley is due to have a variable absorption system fitted in the roof where you can make it more reverberant for football matches but reduce reflections and reverb for gigs.