A future iteration of AirPods could take advantage of bone conduction technology to deliver sound in a variety of situations where normal headphones are not effective, with a proposed system combining bone conduction with normal sound transmission.
Over the years, bone conduction has been a way for people to listen to music or take phone calls using headphones, not to mention earbuds. Instead of transmitting sound through the air, bone conduction devices instead touch specific points on a user’s head, sending sound into the skull and through the ear, where the vibrations are translated into sound.
Such systems have their advantages, for example by allowing the ear canals to be free and allowing users to hear their surroundings at the same time as the audio of the device. It is also useful in some cases where there is damage to the ear that prevents normal use of headphones or earphones. It also helps in situations where air-based methods like loudspeakers fail, such as if a user is underwater.
Bone conduction has certain drawbacks that limit its usefulness, the first being its ability to operate at high frequencies. While human hearing typically ranges from 20 Hertz to 20,000 Hz, bone conduction is only truly effective at levels below 4000 Hz, with audio quality deteriorating at higher Hertz ranges.
The fact that it needs head contact is also an issue, as it can tickle the user at high intensities, making them uncomfortable to wear.
In a patent granted to Apple on Tuesday by the US Patent and Trademark Office titled “Multipath audio stimulation using audio compressors,” Apple suggests that bone conduction problems may be alleviated, in part by supporting standard air conduction methods. .
An example of a headset that integrates bone conduction with normal use of headphones.
The plan involves two general zones of attack, covering audible ranges and compression.
Audio signals are filtered into three categories, consisting of high frequency components, medium frequency components and low frequency components. The medium and low frequency components are then processed using compressors to reduce the dynamic range, and then put together into a combined component.
This combined signal is then sent through the user’s skull using bone conduction, due to the fact that it consists of low frequency and medium frequency signals within its range of use. The high-frequency component, which would not be effective when sent via bone conduction, is instead sent through the air to the ear as usual.
Bone conduction and a speaker combined could cover a full audio range for the user.
Apple suggests that the air conduction system is constructed in such a way that it does not block the ear canal from other audio sources, namely that it still allows the user to hear the surroundings.
The result is a system in which the user enjoys the advantages of bone conduction over environmental audio, while also enjoying the advantages of the full audio range by receiving high frequency sounds via an alternative method. In cases where environmental audio can drown out high frequency sound, users would still get the mid and low frequency signals through bone conduction.
The filing lists its inventor as Tomlinson Holman and was originally filed on May 25, 2018.
This is not the first time Apple has considered using bone conduction technology. The 2014 and 2015 patent filings indicate that he was looking for wireless headphones that use bone conduction. Despite years of work, Apple has yet to introduce a bone conductive product, but the existence of its AirPods line appears to be a suitable candidate for the use of the technology.