 Two separate studies have found that the quality of headphones used with portable music players can have a significant impact on potential damage to hearing from prolonged listening.
In one study, Cory Portnuff at the University of Colorado and Brian Fligor at Harvard Medical School discovered that supra-aural headphones - the kind that sit over the ear - produce slightly lower loudness than in-ear and canal headphones at the same volume setting.
Their research led them to produce a table of maximum listening times, based on US National Institute of Occupational Safety and Health (NIOSH) damage-risk criteria. At 70 per cent volume, supra-aural headphones are safe for up to 20 hours use in a day, while ear buds allow just six hours and canal-style headphones, or isolators, which sit deeper in the ear to block out background noise, allow just 3.4 hours of safe listening.
In separate a test, Fligor and Terri Ives from the National Balance Institute found that the type of headphone's will affect the volume that a listener sets to block out background noise.
They asked 100 students to listen to music on an iPod using three headphone types and recorded the volume settings that the students selected. In a quiet environment they found that the average volume setting was similar and at a safe level for each headphone type. But when background noise was introduced, the volume was raised to unsafe levels for the earbud and supra-aural 'phones; only the canal type blocked enough noise to allow users to listen at a safe volume.
'Damage to hearing occurs when a person is exposed to loud sounds over time,' said Portnuff. 'The risk of hearing loss increases as sound is played louder and louder for longer durations.'
He said that although not everyone shares the same risk, there is no way of telling who will be affected or by how much.
'Today, however, we have no way of predicting who has "tough" ears and who has "tender" ears,' he said. 'Hearing loss occurs slowly and is often not noticed until it is quite extensive, so early prevention is the key.'
Simon Aughton |
