FRIDAY, Jan. 14 (HealthDay News) -- Riding in a convertible with the top down could damage your hearing, a new study warns.

U.S. researchers conducted sound level measurements using five different makes and models of convertibles. In 80 percent of the cars, noise levels were above 85 decibels (dB) when the top was down and the car was traveling at 55 miles per hour (mph) or faster.

Exposure to noise levels above 85 dB for prolonged periods is not recommended, according to the U.S. National Institute for Occupational Safety and Health.

At 75 mph, the mean level of noise in a convertible with the top down was 89.9 dB, the study authors found. (No excess noise exposure was found when driving a convertible with the top up, researchers noted.)

During the sound measurements when the convertible top was down, the car radio was off, there was no conversation between occupants, air conditioning was off, the car horn was not used, and there was no rain or rough weather.

In addition to the noise caused by having the top down, people in convertibles can also be exposed to extreme noise spikes while driving, such as when they're beside a motorcycle or truck, noted Dr. Anthony A. Mikulec, of the department of otolaryngology at Saint Louis University School of Medicine and colleagues.

And listening to music can be an issue too, because the volume levels required while driving a convertible with the top down significantly increased noise levels.

"In light of the results of this study, we are recommending that drivers be advised to drive with the top closed when traveling for extended periods of time at speeds exceeding [55 mph]," the researchers concluded in a news release.

The study was published in a recent online edition of the Journal of Laryngology and Otology.

More information

The American Academy of Otolaryngology -- Head and Neck Surgery has more about noise and hearing loss.