Jan 6, 2011 10:40 PM
Jan. 6, 2011 -- Driving a convertible with the top down may seem like fun, but people who go 55 miles per hour or faster may be increasing the risk of hearing loss over time, new research indicates.
That's due in part to the noise of the wind, but also to extreme noise "spikes" heard when passing loud vehicles, such as a bus or motorcycle.
The study used noise level standards of the National Institute of Occupational Safety and Health, which says decibel levels greater than 85 are considered excessive.
The researchers used a sound meter, operated by a passenger in test cars. These passengers took eight to 10 sound measurements at various points in their rides in the area of driver's left ear, and at various speeds.
Driving at 55 mph with the top down produced sound level measures above 85 decibels in 80% of convertibles tested.
Driving at 75 miles per hour produced average sound levels of about 89.9 decibels, about equivalent to the sounds made by vacuum cleaners, big trucks, a garbage disposal, or loud music.
When driving with the top closed, no excessive decibel levels were recorded.
In all tests, radios were off, car horns weren't used, and the weather was good, with no rain or other inclement weather.
"When the convertible automobiles were driven with the top open (down), high levels of noise were consistently recorded," says A.A. Mikulec, MD, FACS, of Saint Louis University School of Medicine. "Although driving for short distances under such levels of noise exposure is unlikely to cause a significant degree of noise-induced hearing loss, our study demonstrates that long-duration driving at high speeds with the convertible top open (down) will increase the driver's risk of hearing loss."
The scientists conducted tests on five convertibles, including a Ford, a Nissan, a Saab, a Saturn, and a Porsche, recording noise levels at 55 miles per hour (mph), 65 mph, and 75 mph.
Saturns had more noise both at the lower and higher speeds, when tops were down. When tops were up, that is, closed, the Porsche model was the noisiest car.
The quietest car was the Saab, a 2005 Aero model.
Therefore, the researchers recommend that people who drive convertibles drive with the top closed when traveling for extended periods.
The study is published in the Journal of Laryngology and Otology.