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Summary:

Using 100-year-old knowledge of an alternative audio technology, researchers were able to create a simpler speaker that might be possible to manufacture affordably.

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photo: Corbis / Jim Craigmyle

New speakers developed at China’s Tsinghua University create sound by warming and cooling air instead of producing vibrations, potentially leading to speakers that break less and can be incorporated into nearly any surface.

Traditional speakers, such as headphones, have moving parts that produce vibrations to create sound. More moving parts means more opportunities for something to break. The Tsinghua researchers instead turned to 100-year-old knowledge of the thermoacoustic effect, which uses a conductor material like carbon nanotubes to heat and cool the surrounding air to create sound waves.

Carbon nanotubes, which are made of rolled up sheets of carbon atoms, are excellent conductors. With other materials, it would be impossible to produce enough of the thermoacoustic effect to get quality sound.

Chemical & Engineering News reports that Tsinghua researchers first developed nanotube speakers in 2008, when they incorporated a film of carbon nanotubes into a flag, turning it into a flexible speaker. But the device quickly overheated, leaving it inoperable.

They have now overcome the heat problem by manufacturing a silicon chip that contains grooves. The nanotubes rest on top of the grooves, which allow heat to escape. A pair of carbon nanotube headphones they made has now lasted a year without overheating.

Screen Shot 2013-09-30 at 10.54.31 AMThe researchers say the chips could be manufactured in a facility similar to where computer chips are currently made, cutting down on cost. But further work needs to be done on manufacturing carbon nanotubes on a mass scale at an affordable price. Researchers are already experimenting with unusual techniques, such as building nanotubes with carbon atoms recycled from plastic bags.

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  1. Graphene is the new Gold!

    Here is an extract from the original 1925 Rice & Kellogg paper which summarized 10 loudspeaker technologies before settling on the stiff paper cone loudspeaker as we know it today.

    “1 ) A gold-leaf thermophone with an area of about one-half square foot, shown in Fig. 1 . The voice current superimposed on a direct current causes temperature fluctuations in the gold leaf. The adjacent air expands and contracts and produces sound waves.”

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