The research at Brazil's Federal University of Santa Maria comes after the the vuvuzela, a plastic horn, created such a loud noise it disrupted play at the 2010 World Cup in South Africa and annoyed fans watching on TV.
Organizers of the Brazil games have introduced the caxirola, a maraca-like shaker, as the intended official instrument of the event. Invented by Brazilian musician Carlinhos Brown, it is designed to be more subdued than the vuvuzela.
The researchers asked 22 volunteers who had never seen the instrument to play it as they thought it should be played, while a recording device placed at the ear of each subject measured the sound level. They reported a single caxirola, at least, poses no threat to the user's ear.
The sound pressure levels were comparable to that of a normal conversation, and roughly 45 decibels lower than those of the vuvuzela, they said -- meaning it would take 30,000 caxirolas to produce the same sound pressure level as a single vuvuzela.
However, the caxirola may present an aerodynamics problem. After disgruntled fans hurled their caxirolas on the field during a match in April, officials banned the instrument for the Confederations Cup last summer.
The university researchers will present their findings at the Acoustical Society of America's annual meeting in San Francisco in December.