We may still be years away from Facebook's augmented reality glasses becoming an actual product, but we now know a little more about how they might work.

A new patent filing reveals additional details about Facebook's AR glasses, including how they might handle audio. The patent, originally filed in January but published Thursday, describes a "cartilage conduction audio system for eyewear devices."

The glasses' overall design is similar to what we saw in a previous patent published in 2017, though it now appears plans for the glasses are much further along.

Using sensors, as well as those that sit inside the ear, the glasses would be able to project sound into your ear while also allowing you to hear ambient noise around you. The idea is similar to headphones that use bone conduction technology, though the patent notes that its cartilage conduction method is more comfortable and reliable than bone conduction.

"The audio system includes a transducer coupled to a back of the ear of the user," the patent explains. "The transducer generates sound by vibrating the back of the ear [...] of the user, which vibrates the cartilage in the ear of the user to generate acoustic waves corresponding to received audio content."

For Facebook, the ability to deliver sound while not interfering with the ability to hear ambient noise is a key feature for an AR headset, as the wearer needs to be able to interact with the world around them. It also suggests that Facebook intends for the glasses to be worn for an extended period of time. The company did not immediately respond to a request for comment.

"A user wearing a head-mounted display in a VR, AR, and MR system can benefit from keeping the ear canal open and not covered by an audio devices," the patent states."The user can have a more immersive and safer experience and receive spatial cues from ambient sound when the ear is unobstructed."

Though Facebook has spoken publicly about its plans to build AR glasses a handful of times, relatively little is known about the project. The company said in 2017 that such a product is at least five years away.

Business Insider reported in January that Facebook's Reality Labs, its division for AR and VR research, has a group working on the glasses. One of the employees listed on this latest patent, Ravish Mehra, is a researcher at Facebook's Reality Labs, according to a LinkedIn profile.