In a patent granted today by the U.S. Patent and Trademark Office titled “Multipath audio stimulation using audio compressors,” Apple lays out its conception of an audio device that seeks to overcome the issues usually associated with bone conduction. Bone conduction technology allows users to listen to sound without earpieces by transmitting vibrations through specific points on specific points on a users’ skull to reach the ear. While some bone conduction audio devices already exist on the market, they have remained fairly unusual.
Bone conduction works best at lower frequencies, with audio quality deteriorating at higher frequencies, and some users may find the necessary head-contacts uncomfortable. Apple’s patented bone conduction system is unique because it combines it with normal air-based sound transmission to overcome the drawbacks of other bone conduction systems.
Apple explains that audio signals could be filtered and compressed into three categories, high-frequency components, mid-frequency components, and low-frequency components. A combined signal of the low and mid-frequency components would be transmitted through the user’s skull with bone conduction, but the high-frequency component, that would otherwise be ineffective via bone conduction, would be sent through the air as normal. The patent suggests that the necessary air conduction system in this setup would be constructed in such a way as to not block the ear canal. Apple’s hybrid system therefore combines the advantages of both bone and air-based audio conduction.
Apple has previously explored bone conduction technology to bring advanced noise cancellation to earbuds. Unlike this system, the previous patent works in reverse, using accelerometers to detect vibrations in the skull for noise cancellation. While Apple has brought noise cancellation to AirPods Pro, it has yet to institute any bone conduction technologies in its products. The technology would seemingly fit most comfortably into the successful AirPods line, but patents are not always indicative of Apple’s immediate plans.