Can you control noisemaking chaos? Brazilian planners hope so.
They'd rather not have the ear-splitting vuvuzela which took over the 2010 World Cup in South Africa. Tens of thousands of those instruments blaring in packed stadiums became a major annoyance, disrupting players and even fans watching on TV.
So organizers for the 2014 World Cup in Brazil have introduced the maraca-like caxirola as the official instrument of the event. The caxirola, based on the African caxixi, was invented by Brazilian musician Carlinhos Brown to be more subdued than the vuvuzela. Will it take off? The vuvuzela was already part of the culture in Africa, it was not created for the event. Manufacturing enthusiasm is often difficult. But if it takes off, you're a lot less likely to get ear damage if you are on the business end of it, they say.
Will it catch on? Credit: FOX Sports
Is it? Talita Pozzer and Stephan Paul of the Federal University of Santa Maria in Brazil studied the acoustics of the instrument, finding that a single caxirola, at least, poses no threat to the user's ear. In their analysis, the researchers asked 22 volunteers who had never seen the instrument to play it as they thought it should be played, finding that people tend to either shake it along its longer axis or its shorter axis. A recording device placed at the ear of each subject measured the sound of the caxirola.
The researchers found that if shaken along the longer axis, the instrument produces twice the sound energy as when shaken along the shorter axis. But because volume depends logarithmically on the sound energy, the difference is only just noticeable to the ear. In both playing styles, the sound pressure levels were comparable to that of a normal conversation – and roughly 45 decibels lower than that of the vuvuzela, corresponding to 1/30,000th times the sound energy. In other words, you would need 30,000 caxirolas to produce the same sound pressure level as a single vuvuzela.
The researchers also captured the acoustic signature of the caxirola played in both styles, measuring how the frequency and intensity of the sound varies over time. The signature was similar in both cases.
The next step, Paul said, is to measure the caxirola's sound power levels, which, unlike sound pressure levels, are independent of distance and the instrument's surroundings. The researchers can then input those measurements into a computer model of soccer stadiums, simulating exactly what kind of noise thousands of caxirolas would make, showing whether or not it would be harmful.
Since its introduction last year, the caxirola has already been mired in controversy. After disgruntled fans hurled the instrument on the field during a match in April, officials banned the instrument for the Confederations Cup last summer. Whether the caxirola will be distributed during the 2014 World Cup has yet to be determined, Paul said.
Perhaps it's not the caxirola's acoustics that's a cause for concern – but its aerodynamics.
To be presented at the 166th meeting of the Acoustic Society of America, Dec. 2-6, 2013, in San Francisco. Source: American Institute of Physics