Sound quality may not have been the top priority for the Spice Girls, says Robb Allan
"So even though we design speaker systems by computer - if we can't put our speakers in the right place because of video screens, or because of walkways, or the stage, it makes it harder."
Allan, who's also a live sound specialist for technology company AVID, points out that the Spice Girls have a particular problem because they spend a large proportion of the show on walkways in the middle of the crowd - putting them in front of the speakers.
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"They're not ideal on many levels, never mind sonically."
The problems with playing music in sports stadiums are well known, agrees Scott Willsallen, an Emmy Award-winning sound designer who has worked on multiple Olympic and Commonwealth Games ceremonies.
"In an auditorium that's built for amplified sound, most of the surfaces are pretty soft and fluffy, so any sound that's fired at them is absorbed; whereas a stadium is meant to reflect those sounds to make it more exciting for the crowd.
"The reverberation that helps make a sporting event really exciting makes a mess of the intelligibility of a concert."
There are ways around it, says Willsallen, who has even gone to the expense of hanging drapes around stadiums to absorb echoes and reverberations.
"It's an exercise that can be done - but in that touring world, where it's such a quick turnaround between venues, I imagine that's a tricky bit of economics."
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However, Allan says modern speaker systems - which are distributed across the stadium, rather than being placed at one end of the pitch - have largely eradicated that problem.
"Now we can point the audio into every little corner of the stadium, and predict it with great accuracy. We can change the way the speakers respond to humidity and the temperature. It's all computer-controlled and incredibly sophisticated. So issues are rare."
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"I'm certain that the next shows are only going to improve because people will be asking the right questions to figure out what the root of the problem is and solve that."