No Headphones Required - Hearing Through Bone Conduction

By Scott Bressler, Ph.D.

Have you ever gone to bed with your headphones on?? If you have, you know that after a while they can get uncomfortable, especially if you’re a side-sleeper.? Wireless earbuds aren’t really any better, and what’s worse is if they fall out in the middle of the night your morning starts off with a mini search-and-recovery mission.? Maybe you’re the kind of person that plays music over speakers in your bedroom.? That’s fine if you sleep by yourself, but what if you have a bed partner that prefers to sleep in silence?? It would be so much easier if you could just pipe sound directly into your brain.? Sorry to say neurotech isn’t there (yet), but there is another option – bone conduction.

What is bone conduction and how does it work?

Sound is just vibrations traveling through some sort of medium.? If that medium is air, those vibrations are alternating patterns of high and low air pressure that move your eardrum in and out in response to those pressure changes.? The backside of your eardrum delineates the start of the middle ear and is connected to a system of three of the tiniest bones in your body, the incus, malleus, and stapes.? These bones are arranged in a way to concentrate the vibrational force from the eardrum to the oval window, a membrane separating the air-filled space of your middle ear from the fluid-filled space of your cochlea.? Hair cells inside the cochlea respond to these vibrations and convert them into neural impulses.? The hair cells connect to your auditory nerve which then sends the neural representation of what you heard to your brain. [1, 2]??

With bone conduction, a modified speaker or driver is placed over a bony part of your head and vibrates your skull directly.? Your cochlea, in turn, is subject to these vibrations because it is completely encased in the temporal bone of your skull.? And as with air-conducted sound, the hair cells convert these vibrations into a neural signal. [3]? So, not exactly a direct path to your brain, but two steps closer by skipping over your outer and middle ear.

Elemind’s bone conduction speaker

You may be familiar with the company AfterShokz? and their bone conduction headphones.? Their bone conduction drivers sit just behind your ears on the bony part of your head called the mastoid process.? What users love about their product is that your ear canals are open and unblocked allowing you to hear sounds from your surrounding environment.? Elemind’s bone conduction driver sits over the middle of your forehead.? We decided on this positioning for comfort, especially for side sleepers, but the bone conduction principle still applies.? Because it’s directly vibrating your skull, most of the sound energy is conducted to your ears with very little sound being transmitted through the air.? Of course this means you’ll be able to clearly hear the sounds produced by the Elemind headband, but anyone near you will not.? Additionally, like the After Shokz? headphones, your ears remain unobstructed allowing you to still be able to hear sounds coming from your bedroom or other areas of your house, apartment, hotel room, etc.

How good is the sound?

Because of the physics of transmitting sound through biological tissue, bone conduction speakers aren’t able to reproduce the full range of frequencies audible to the human ear (20 Hz to 20 kHz).? Low frequencies are not well represented, which is why they’re better suited for listening to speech, whose frequency content occupies the middle of the hearing spectrum.

The sounds the Elemind headband plays are a combination of pink noise pulses synchronized to a specific phase of your brain’s alpha waves over a background audio scene of gently falling rain.? Both of these sounds are well-suited to be reproduced through Elemind’s bone conduction speaker because of their rich content in the mid and upper frequency ranges.

One question we often get is whether our headband can be used on a plane or in a room with a loud air conditioner.? Is it loud enough?? The answer is yes, but you’ll need to wear earplugs to block out the external acoustic noise.? Before you learned about bone conduction, plugging your ears to hear better would have sounded (no pun intended) quite strange, right?? Now, not so much.

What do you mean by “pink noise pulses?”

Different from white noise, whose frequency content is equally loud across the entire 20 Hz to 20 kHz range, the power in the pink noise spectrum decreases as the frequencies increase.? The result is noise that is less harsh and more pleasing to listen to.? The pulsing of the pink noise is timed to a specific phase in your brain’s alpha wave cycle, which the headband measures in real time.? Alpha waves are an 8-12 Hz oscillation that is very prominent when your eyes are closed while you’re awake and goes away once you’ve fallen asleep.? The power and frequency of these oscillations wax and wane as you transition from wakefulness to sleep and as a result the pink noise pulses take on a semi-random timing pattern.? To the uninitiated, it can sound like the headband is malfunctioning.? We assure you, as weird as this may seem, this is completely normal.? Many of our clinical study subjects and early testers have described the experience as “distracting, but in a good way.”? As it turns out, this gentle, distracting acoustic stimulation timed to the brain’s primary wake-sleep distinguishing oscillation helped three quarters of our sleep study participants consistently fall asleep faster night after night. [4].

Want to hear this for yourself?? Pre-order our Elemind sleep headband from our website, https://elemindtech.com .

1) Schnupp, J., Nelken, I., and King, A. Auditory Neuroscience: Making Sense of Sound, MIT Press (2012).

2) Moore, B.J., An Introduction to the Psychology of Hearing, Fifth Edition, Elsevier Academic Press (2004).

3) Tonndorf, J. A New Concept of Bone Conduction. Arch. Otolaryngol. 87, 595–600 (1968).

4) Bressler, S., Neely, R., Yost, R. M. & Wang, D. A randomized controlled trial of alpha phase-locked auditory stimulation to treat symptoms of sleep onset insomnia. Scientific Reports. 14, 13039 (2024)

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