Despite the drawback, Canadian start-up ORA Sound has developed a range of speakers using the material to give district improvement to users. Its GrapheneQ, a graphene oxide-based composite is stiff and lightweight, but is also easy to shape and inexpensive to manufacture. ORA claims that GrapheneQ shows sound quality comparable to high-end audio materials while being only slightly more expensive than the most basic. The name was chosen because of its low density and high stiffness which, it is claimed, allows for louder drivers with a lower Q resonance in acoustic transducers.
Rather than use chemical vapour deposition (CVD) to create graphene films, which is cost and labour intensive, potentially harmful to the environment and requires reaction chambers and whiterooms, ORA decided upon graphene oxide. It also allows ORA to produce speakers at scale.
“Graphene oxide can be handled and slurried and just left to dry,” explained co-founder of ORA Sound, Xavier Cauchy. “It’s much easier to have a macroscopic device made out of graphene oxide material than it is with crystalline CVD graphene. And, it’s more environmentally sound.”
The Graphene used by ORA is bought in and has proprietary additives mixed in to make it even stronger. The stronger the membrane, the better the frequency response and lower distortion. GrapheneQ has a Young’s modulus of 130GPa, allowing sound waves to travel very quickly through the material producing better overall sound quality. The material has very high thermal conductivity too, which makes it less likely to be damaged from overheating – a common cause of speaker damage. The ‘Holy Grail’ in terms of a material for speaker design, according to Cauchy, is one that is as stiff as possible while being as light as possible.
“This is difficult to do with materials like Kevlar or carbon fibre, if you want to want to make these very thin, you will have problems with isotropy of the forces,” Cauchy continued. “Graphene solves that problem with one single step. Graphene has strength on one axis – the planar direction – and speaker membranes are two-dimensional by design, so we have strength in just the direction we want.”
Compared to other materials traditionally used to make speaker membranes, graphene is difficult to shape. Mylar, for instance, can be stamped and shaped straight out of a sheet of boPET (Biaxially-oriented polyethylene terephthalate). However, GrapheneQ is easier to shape than CVD graphene because of its method of production as well as the additives ORA uses. It is also claimed to display performance that matches, and even exceeds, that of materials that are used in high-end audio speakers such as beryllium and CVD diamond.
What’s more, Cauchy says that because of the GrapheneQ speakers’ low Q resonance they require less damping by the driver, meaning they are more energy efficient and could help to increase the battery life of mobile devices.
“A loudspeaker typically has an efficiency of around 2%, which means that 98% of energy is lost through heat in the coil and damping,” he said. “By making it twice as light, we calculated that we could get an efficiency of around 70% with a driver designed specifically for GrapheneQ. This is also considering that the speaker would break-up at the same frequency.”
The alternative, for real audiophiles, is that the GrapheneQ speakers can be made at the same weight as traditional speakers, reducing efficiency but increasing strength further, which drastically increases the fidelity of the speakers to ultrasonic levels.
The ORA team used a theoretical model that calculates the bending mode frequencies of materials. From this, the team calculated the figure of merits to compare GrapheneQ to other materials. It was then tested with a frequency response measurement device to see at what frequency the sound would begin to break-up and distort.
“Break-up is where the frequency causes the membrane to vibrate in resonance and it starts to vibrate in the opposite direction than you want it to,” explained Cauchy. “Effectively what you’ll have is a soundwave cancellation at certain frequencies which, to the human ear, just sounds distorted and nasty.”
This was where the team found that GrapheneQ showed equal-to-better performance than diamond and beryllium. From here prototypes have been made and tested; a small, stiff version for use in tweeters; a thicker, lighter version for larger loudspeakers; and another which, as yet, is under wraps.
GrapheneQ speakers have been incorporated into headphones, which were displayed at the Consumer Electronics Show (CES) in Las Vegas last month. This was seen as the perfect way to compare the performance of GrapheneQ against materials like Mylar.
Future applications include frequency drivers in Bluetooth speakers, tweeters for high-end audio equipment where high frequencies will be explored, and micro-speakers for smartphones where improvements to sound quality and battery efficiency will be demonstrated.
“We are continuously making it better,” Cauchy exclaimed. “The beautiful thing about this material is that it’s highly tuneable, you can do virtually anything with it. If we were to dream, we might also find an application for GrapheneQ anywhere where carbon fibre is used at the moment, because of its strength.”
Cauchy said that ORA have been approached by major players in the audio and consumer electronics industries and after CES thoughts are turning to collaborations. To get all the advantages from GrapheneQ – and to make it the standard material for loudspeaker membranes going forward - the speaker would need to be placed in a bespoke driver. As ORA don’t have the manpower to do this and phone manufacturers redesign their drivers with every model, it would seem that partnering with a manufacturer would be a sound idea.
A brief history of the graphene speaker
- In 2011, researchers from Seoul’s National University were the first to develop a transparent, lightweight speaker made from Graphene for possible use in windows and displays as well as in noise-cancelling devices.
- In 2013, University of California, Berkley scientists created the first earphone sized thin-film graphene-based speakers, measuring 5mm in diameter and 30nm thick, that were claimed to outperform the best traditional earphones on the market.
- Most recently, in September 2016, researchers from Korea Advanced Institute of Science and Technology (KAIST) produced a thermoacoustic speaker based on graphene oxide said to be specifically aimed at the mobile audio market.
- Sound in a thermoacoustic speaker is produced by rapid heating and cooling of the material, rather than by vibrations, so they do not need to be encased in an acoustic box.
- Using 3D graphene aerogels, the KAIST team fabricated an array of loudspeakers that were said to withstand over 40W input power and showed a sound pressure level comparable to those of previously reported 2D and 3D graphene loudspeakers. Pull quote: “It’s much easier to have a macroscopic device made out of graphene oxide material than it is with crystalline CVD graphene.”Xavier Cauchy“The beautiful thing about Graphene is it’s highly tuneable. We might find applications where carbon fibre is used at the moment.”Xavier Cauchy