Prototype headphones detect which ear they are in

image captionA proximity sensor makes sure that the headphones always play the correct stereo channel

Prototype headphones which can tell which ear they are in have been developed by Japanese researchers.

The earphones use proximity sensors to detect if they are in the right or left ear in order to play the correct audio.

Researchers at the Igarashi Design Interface Project also found a way to tell if two people were sharing - and play a mono mix to each.

The team says it could help people enjoy games and movies which depend on users hearing the correct audio stream.

"We believe that checking the sides of the earphones before using them is annoying," said Daisuke Sakamoto, an assistant professor at the University of Tokyo, told the BBC.

"This may be a small problem, and earphones are intuitively used by everyone, but it's worth solving to give people better experiences," he said.


Mr Sakamoto and his colleague Kohei Matsumura, from the Japan Advanced Institute of Science and Technology, found that a mobile phone provided the inspiration for how to solve the problem.

"One day, I was calling with a smartphone which has a proximity sensor to turn on/off the display, and we were inspired to use a proximity sensor to detect the sides of the ears."

image captionResearchers have produced a video explaining how the headphones work

The prototype's sensor is embedded on the side of one of the earphones so that it points at a right-angle to the inside of the user's head.

When the bud is placed in the person's left ear the sensor points out into the air in front of them. When the bud is placed in their right ear it points towards the back side of their ear - registering an obstruction.

"When this distance is less than 30mm, the UEs [universal earphones] activate the right channel; otherwise, the channel is changed to the left," the researchers wrote.

Skin conductivity solved the problem of detecting whether the earbuds were being shared.

The equipment is designed to send a weak electrical charge out of the earphones, and then uses a sensor to see if the current can be detected flowing from one side to the other.

If they are plugged into a single person's ears, then the current flows along the user's skin and the equipment allows the sound to be played in stereo.

If they are plugged into separate people's ears then there is no connection and the equipment plays identical mono streams to both buds.

Automatic pause

The researchers said that in the future they might use a similar system to pause music automatically when the headphones were removed or to play different music to users sharing headphones.

In a promotional video, the researchers anticipate that if a manufacturer picks up the idea, their production costs could be less than a dollar per set.

But Mr Sakamoto told the BBC that while they had applied for patents, there were no current plans to mass produce the headphones.

"If someone or a company has an interest in our earphones and headphones, we would like to collaborate," he added.

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