London, Jul 31 (IANS): Motorcycle helmets may be protecting bikers' brains but they could also be leaving them vulnerable to hearing loss.

Kennedy O. Adetifa, M. Carley, N. Holt and I. Walker, researchers in mechanical engineering, management and psychology from the universities of Bath and Bath Spa, Britain, mapped the airflow and noise patterns to find out why.

The distinctive roar of a Harley's engine is loud, but studies have revealed the biggest source of noise for motorcyclists is actually generated by air whooshing over the riders' helmets.

Even at legal speeds, the sound can exceed safe levels. Now, they have identified a key source of the rushing din, the Journal of the Acoustical Society of America reports.

Researchers placed motorcycle helmets atop mannequin heads, mounted them in a wind tunnel, and turned on the fans, according to a Bath statement.

By placing microphones at different locations around the helmet and at the mannequin's ear, they found that an area underneath the helmet and near the chin bar is a significant source of the noise that reaches riders' sensitive eardrums.

The team also investigated how helmet angle and wind speed affected the loudness. Future tests will move beyond the wind tunnel to real-life riders on the open road.

The findings may one day be used to design quieter helmets, saving riders' ears for the enjoyment of hard biker rock, the researchers said.