bone conduction headphones
Bone conduction headphones -- sometimes called 'bonephones'-- are headphones that transmit sound waves through the bones in a user's skull instead of their ear canal. When in use, the bones in a user's skull will vibrate to amplify the sound waves, allowing users to listen to device audio, while keeping their ears free. This benefits people with a hearing disability, or who need to use their ears for staying aware of their surroundings.
How bone conduction headphones work
Bonephones use a method called bone conduction audio technology. In this method, a transducer converts audio data to vibrations, which travel along the user's bone structure to the cochlea, an inner ear structure that transmits the information along the auditory nerve as a signal to the brain. In effect, the user's skull is the device's speaker. This is contrasted against normal headphones, which emit vibrations through speakers placed in or on top of the outer ear.
Sound is technically just a vibration of particles. Most people generally think of vibrations in the air when they think of sound, but sound can also travel through solids and liquids. Therefore, flesh and bone can function as a speaker, because particles in a solid can vibrate too. In fact, solids transmit sound faster than air and water, because the particles in a solid are the most tightly packed together. This makes solids the best conductors of sound, followed by water, then air, which have looser particle configurations.
This may seem counterintuitive, as listeners generally experience distortions in sound when trying to hear something through a liquid or solid. If a listener is underwater, someone speaking above the surface would sound garbled. If loud music is playing next door, the listener generally perceives it as muffled. These distortions occur not because liquid and solid are worse sound conductors, but because in both examples, the sound is first passing through air, then into the other medium.
Bonephones are designed to account for this fact. Most models have a strap that wraps around the back of the user's head, securing vibration-generating pads against the skin just above each ear. The pads curl over the top of the ear slightly to help hold the device in place on the user's head. Securing these pads against the user's skin minimizes sound distortions because the sound travels directly from the pads through the skull in one straight shot, without air in between.
In general, bonephones are used to allow individuals to listen to audio privately and while on the move, just like regular headphones. However, bonephones are different because they bypass the outer and middle ear entirely. They also have a unique design that lends itself to physical activity, unlike most basic headphones. For these reasons, they may be preferred over regular headphones by:
- gym-goers and other physically active people who need headphones designed to stay on their head while exercising;
- joggers or bikers who want to keep their ears open for approaching traffic or people trying to say something to them;
- users who listen to audio in a social environment and need to be at least partially attuned to what peers or announcements are saying;
- users with impaired hearing, whose use of standard headphones may be physically obstructed by assistive technology; and
- users with impaired hearing who would likely experience better sound quality through bone conduction than through damaged ears.
The central advantage of bonephones is that they don't use the ears. For many users, this is beneficial because they can use their headphones while remaining attuned to the outside world.
Bypassing the ears makes bonephones especially beneficial for hearing-impaired users as well because it enables them to listen to audio with more clarity than they were previously able to through standard earbuds. For example, a listener who is deaf in one ear would be able to hear audio in stereo through bonephones. Additionally, if the listener has a hearing aid, they can leave it in while still listening to music through bone conducting headphones.
Bonephones also eliminate the risk of hearing damage that comes with listening to audio too loud through standard headphones. The eardrum is much more fragile than the flesh and bone that bonephones act on.
Their thin and secure design also makes them appealing to physically active users. One bonephones manufacturer -- AfterShokz -- originally designed bonephones for use in the military. Some bone conduction headphones also have memory, and users can upload songs directly to them. This may be another selling point for especially active users.
Despite the novelty and select usefulness of bonephones, they have been met by consumers with mixed responses.
Many users agree that the sound quality in bonephones is worse than regular headphones. Specifically, users report that they are generally quieter and have weaker bass frequencies.
There are also downsides to the physical design. Some users note that playing music at higher volumes causes an unpleasant or strange vibrating sensation in their face. This design also causes a certain amount of sound leakage, which may be a problem for those who want to listen to something privately or listen to something in a quiet setting without disturbing anyone. Other users complain about the fit of the headphones, which, depending on the user and model, can be uncomfortable.
Bone conduction headphones are also significantly more expensive than run-of-the-mill earbuds. In 2020, basic Apple earbuds cost approximately $30, whereas some popular bone conduction models are priced at $130. For this price, users could buy normal headphones with far better sound quality than several bone conducting models. There are some very cheap bonephones available, but the majority are much pricier than the alternative.
Top bone conduction headphones
Bonephones are commonly marketed to athletes because of their sleek design. Some of the top bone conduction headphones on the market include:
- AfterShokz's Trekz Titanium -- Six hours of playback, Bluetooth-enabled, reasonably priced.
- AfterShokz's Trekz Air -- Similar features to the Titanium model, but more expensive. This is because the Air model is 20% lighter. Also, Air models have Bluetooth v4.2 instead of Titanium's v4.1.
- WinnerGear's Exobone -- Sweatproof, lightweight, foldable design appeals to athletes. It has good sound quality and charges quickly.
- Vidonn's F1 -- Fits well, has noise-canceling features for voice calls.
- Bose's Frames -- Sunglasses with bone conduction technology in them. They are enabled for Bose AR (augmented reality), which is an audio-only augmented reality
- Siusumfo's Bone Conduction Headphones -- Lightweight, long battery life of over 4 hours continuous use, waterproof design, Bluetooth v5.0.
- Shangri-La's Bone Conduction Headphones -- Bluetooth, 8 GB of memory, one of the cheapest models without unanimously poor user reviews.
Although the concept of using bones as an amplifier seems futuristic, the idea has been around for centuries. The classical music composer Beethoven used bone conduction to help him continue writing music after going deaf. He would put one end of a rod in his mouth and the other end against the piano, sending the vibrations through the rod into his skull, allowing him to "hear" the music he was playing. Some animals are also able to communicate through bone vibrations.