The headphone industry is currently worth almost 20 billion dollars. Top brands such as Beats, Bose, JBL, Skullcandy, and Audio Technica are bandied about by diehard audiophiles and everyday commuters alike. Yet today's popular headphones, both in-ear and over-ear, are not the most user-friendly. Ironically, as desktop computers and smartphone paradigms have evolved, the design of the headphone has remained overwhelmingly stagnant -- the archetypal case features a dangling, twisted cable coupled with an ear tip that needs constant adjustment. Across generations of iPhones and Samsung Galaxys, headphones have featured only minor upgrades, most of which are for glamour rather than utility. A headphone overhaul has long been overdue.

When Apple introduced the iPhone 7 last week, our minds began to churn. The dethroning of the 3.5mm jack means that wireless audio and other technologies can finally take hold. But one thing has eluded the conversation -- the possibility of using bone conduction to fuel the next generation of smart devices.

The Product

We wanted to take what we knew about audio technology and push it in a different direction. We decided to build eyewear that allows you to listen to high-fidelity audio wirelessly via Bluetooth. Not just that, but audio only you can hear, not anyone else around you. Imagine walking on the beach with your Ray Bans wayfarers, except, instead of just looking like a boss and protecting your eyes, you're also jamming to Taylor Swift.

We did exactly that -- we outfitted eyewear with bone conduction technology. And in the process, we also wanted to solve a significant and dangerous issue that we see with typical headphones -- they often render you oblivious to your environment. We engineered our product in such a way that you can be completely aware of your context while still enjoying high-fidelity audio. Open-ear headphones don't even come close to providing the level of awareness that Sine provides. Also, they don't look as cool.

When we outfitted the eyewear, we worked to preserve the look and feel of regular top-tier eyewear. We spent hours making sure our prototype didn't look like most other hacky hardware projects. We soldered and manually wired our entire solution without any microcontrollers (Arduino or otherwise). We even worked to create a device-agnostic bluetooth solution. The solution does it's own digital signal processing and transmits stereo audio via bluetooth. Filters were generated to account for the attenuation of low frequencies and to ensure that frequency response curve was as close to horizontal as possible given the materials and time constraint.

An important, and often ignored point is the fact that 48 million Americans have significant hearing loss. Since bone conduction technology bypasses the ear drum, people with hearing loss would be able to hear audio from Sine with ease. This allows Sine to tap into a market that is much bigger than any pair of headphones.

In addition, the nature of this wearable device is such that it allows for many interesting features to be included. Siri/personal assistant integration is possible and completely achievable. Moreover, an autopause feature could be implemented so that the user will never lose his or her place while listening. When the eyewear is taken off, this state would be detectable, and music could be automatically paused and rewinded a few seconds.


The design features two 8 Ohm & 1 Watt transducers -- one per ear. These were designed in a special housing to ensure that sweat from did not cause the component to short through the skin. The transducers were connected to an amplifier that provides DSP and enables a gain of 16 dB. We also configured a bluetooth solution that supports IAP (Apple protocol) as well as most other devices. The product was designed to have competitive battery life, up to 500 mAh, and fairly low current draw so as to make it usable for day to day activity. In addition, we soldered and wired components to minimize the overall size of the device as much as possible -- something you typically don't see in the run-of-the-mill 36 hour hack.

By the end of the 36 hour period, we were able to supply audio from any bluetooth device and listen to it via bone conduction from the eyewear.



This project was extremely difficult to pull off, especially given the time constraint. We manually wired and created the prototype with materials that are easily available to us. Connections were finicky, and the overall low-quality condition of materials resulted in many components breaking, even despite the short time constraints:

  • Two bone conducting transducers broke, resulting from loose connection of wires in the stock model.
  • One amp shortcircuited itself and was quickly rendered unusable
  • Soldering rendered numerous sections of components and entire components unusable, and often required significant and meticulous attention to detail.

Hours were spent debugging various circuits using an ammeter and voltmeter.

Luckily, the group was prepared for such issues . However, the time used in attempts to resurrect these components caused many ideas to be cut.

The center of all electrical related problems lies in the RN52 bluetooth module. Loose connections caused the on-board LEDs to be unresponsive until later. Dropped bluetooth connections was also present, as well as a low-volume output. The former two were resolved with extensive testing. The latter was solved by increasing the gain of the amp connected.

Power draw also caused several issues. The original idea had power forked from one power source. However, inconsistent power draw from the bluetooth module and the amplifiers rendered the use of a voltage divider unreliable. The team scrambled to find separate batteries for the two modules in the current prototype.

** Physical model construction** On the second day, a request to 3D print a module for an enclosure was submitted at 1 pm. No response was given until 9 pm, and the statement told that we were to be unable to print our model. Within minutes, we quickly had to use laser cutting to provide a temporary housing.

Assembling Assembling was a brutal task, but we took it as a great learning experience.


How did we fare? We finished our prototype within the allotted time. At the very end, we had to make some concessions -- We were having issues soldering the components and placing them to a 55mm x 30mm x 28mm box due to unanticipated issues with the wires. As is the case with these sorts of projects, it took us a very long time to debug. In the end, we managed to successfully finish the prototype, but it wasn't as pretty as we wanted.

Preface: Team Background As a team whose expertise is mostly rooted in software and systems, we wanted to trudge into new territory with a hack that involved almost entirely hardware. We learned a ton in the process, and are very happy with that.

What we learned

We learned a significant amount from this project, especially in terms of designing and debugging complicated circuits, as well as assembling and designing a full-fledged accessory.

What's next for Sine

We believe that this product could be a really compelling vertical in the eyewear market, and think that more features could be built-in to make the experience even more compelling, such as autopause/autoplay.

In many ways, a lot of IoT wearables, especially eyewear, have tended to be unsuccessful and gimmicky. Take, for example, Google Glass, which was very much held in contempt by the general public. We believe that Google Glass failed for two significant reasons. The first is strictly social -- Google Glass featured a camera that would subtly record day-to-day interactions. Have no doubt, this easily comes across as constant leering, and many have described feeling bothered because someone was recording them with their Google Glass. The second reason, we venture, is the lack of painkiller features. Glass provided notifications, which act as great feedback loops for getting users engaged. Beyond that, however, new features were fairly limited and only replicated that which could be accomplished on an average smartphone.

Sine, by contrast, avoids being pidgeon-holed like Google Glass. Sine's core functionality can be introduced into popular eyewear frames from numerous companies. It will not be perceived as a social failure; in fact, we are inclined to think that it would achieve the opposite effect. The glasses do not double as video cameras; instead, they bring forth a single feature that is arguably a painkiller -- the ability to listen to music without hassle and without sacrificing comfort.

As mentioned previously, Sine-like technology also allows eyewear brands to effectively pitch themselves towards the 48 million American citizens who have significant hearing loss.

Built With

  • amplifiers
  • audio-engineering
  • bluetooth
  • bone-conduction-technology
  • digital-signal-processing
  • iap
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