Sustainable materials sound good


Audio Files

The speaker membrane is only 50 μm thick

Cellulose fibres covered with magnetic nanoparticles have been used to make ultrathin loudspeakers by researchers in Sweden. The material could provide a cheaper and more sustainable alternative to the polymers traditionally used in speakers.

Conventional loudspeakers contain a bulky magnet that is becoming harder to incorporate into our ever-shrinking gadgets. A coil attached to the speaker membrane is essential for moving the membrane and creating sound waves but the force of this coil can also reduce sound quality. The biocomposite membrane developed by Richard Olsson, Lars Berglund and their teams at the Royal Institute of Technology in Stockholm removes the need for a bulky magnet and enhances sound quality because there is no coil in contact with the membrane.

To make the biocomposite membrane, magnetic nanoparticles are securely fastened along cellulose nanofibrils to make a magnetic gel. This gel can be sprayed from a spray gun nozzle to give a membrane with a uniform spread of particles.

It is important to have an even spread of particles as an uneven spread would cause the already stiff material to become brittle. ‘The stiffness of cellulose means it is well-suited to a quick reacting acoustic membrane,’ says Olsson. Cellulose nanofibrils have mechanical properties comparable to high performance synthetic fibres and come from a renewable source – wood pulp.

The properties of the membrane can be finely tuned by attaching different magnetic nanoparticles to the cellulose nanofibrils. Incorporating magnetic particles into the membrane itself, which is only 50 μm thick, means there is no bulky external magnet. A coil still drives the membrane but does not need to be directly attached.

With only an even layer of air pressing against the membrane surface the sound quality delivered by the loudspeaker is impressive and Canadian musician Romi Mayes allowed the team to use her music to demonstrate this quality.

Wendelin Stark, an expert in functional materials at ETH Zurich in Switzerland, is excited by the new material. ‘It allows very soft, well-defined movements, as each magnetic particle draws on a fibre. Such uniform application of force allows the kind of movement required for high quality sound generation.’

The team are now working to increase the volume of their loudspeaker without compromising the sound quality.


Related Content

Chemistry World podcast - December 2013

3 December 2013 Podcast | Monthly

news image

We discover how spin chemistry guides migrating birds and explore the science of cheese

Cellulose catalyst rewrites rules of attraction

21 December 2010 News Archive

news image

A magnetic catalyst for the conversion of biomass into sugar that can be pulled out for reuse

Most Commented

How to print a crystal in 3D

17 April 2014 Research

news image

Rather than looking at a crystal on a screen, print it out and hold it in your hand

Dinosaur mass extinction may have been triggered by acid rain

11 March 2014 Research

news image

Asteroid impact could have produced enough sulfur trioxide to dramatically lower ocean pH