Apple sold more than 14m iPods in the last three months of 2005

Apple has introduced volume controls for iPods following fears about links between personal music players and potentially irreversible hearing loss.

The company has made available a free download update allowing users to set a personal maximum volume limit.

Parents will also be able to set a locked limit on their child's players.

Health experts want more studies into the effect on hearing of earphones and Apple is facing a US legal action claiming the iPod can damage hearing.

Greg Joswiak, Apple's IPod marketing vice president, said it was responding to "increased attention in this area".

He said: "We want to offer customers an easy to use option to set their own personal volume limit."

Legal claim

The update is available for the iPod Nano and models with video playback capabilities.

It lets parents set a maximum volume limit on a child's iPod and lock it with a combination code.

Earlier this month, the US National Institutes of Health said new studies were needed into the effects of in-ear headphones.

It was responding to calls by a US congressman into the possible long-term effects of loud music on hearing.

John Kiel Patterson, of Louisiana, is suing Apple in the US District Court in San Jose, California.

He says his iPod is capable of generating more than 115 decibels, a dangerous noise level, and is not safe for prolonged use.