Hearing is an essential sense, allowing us to connect with others and navigate the world around us. When you experience hearing difficulties, an accurate diagnosis is the first step towards effective treatment. There are several types of hearing tests and each has specific uses for assessing the type and severity of hearing loss. In this post we’ll explore bone conduction testing – what it is, how it works and when it should be used.
What Is a Bone Conduction Test?
A bone conduction test determines how well sound travels through the bones of your skull to the cochlea, a spiral shaped, fluid filled organ found in the inner ear. The test involves placing a bone oscillator on the mastoid bone behind your ear.
Unlike air conduction tests, which measure how sound travels through the air and into the ear canal, bone conduction bypasses the outer and middle ear to directly stimulate the inner ear.
Bone conduction testing is useful in identifying the type of hearing loss—whether it’s conductive, sensorineural, or mixed.
- Conductive Hearing Loss: This occurs when sound waves are unable to pass freely through the outer or middle ear. Common causes include ear infections, fluid in the ear, earwax build-up, or structural abnormalities. Bone conduction tests help identify conductive hearing loss by comparing results with air conduction tests.
- Sensorineural Hearing Loss: This type of hearing loss results from damage to the inner ear or auditory nerve. Causes can range from aging (presbycusis) to exposure to loud noises or genetic factors. The bone conduction test helps isolate whether the problem lies in the inner ear or the auditory nerve.
- Mixed Hearing Loss: When someone has both conductive and sensorineural hearing loss, a bone conduction test can help pinpoint the severity and nature of each component, guiding the most appropriate treatment.
The Science Behind Bone Conduction
Under normal circumstances, sound waves enter through the outer ear, travel down the ear canal causing the eardrum to vibrate. These vibrations are passed through the small bones in the middle ear to the inner ear, where they are converted into electrical signals that the brain recognises as sound.
With bone conduction, the process is different. Sound vibrations are transmitted directly through the bones of the skull to the inner ear. They reach the cochlea, which then converts them into electrical signals for the brain to process as sound.
Bone conduction is an essential part of how we hear in everyday life. For instance, when you speak, vibrations from your vocal chords are transmitted through your skull to your inner ears. This explains why your voice sounds different on a recording, as you’re hearing it via air conduction.
As bone conduction bypasses the outer and middle ear, it allows individuals with conductive hearing loss to still hear sounds through the vibrations that travel directly through the skull.
Comparing Bone Conduction and Air Conduction Tests
Although bone conduction and air conduction tests are both designed to assess hearing ability, they differ in their approach.
Air conduction testing evaluates the entire hearing pathway, from the outer ear to the inner ear. Sounds are delivered through headphones, and your ability to hear a range of frequencies and volumes is measured.
On the other hand, bone conduction testing focuses on the inner ear’s function by delivering vibrations through a bone oscillator placed on the mastoid bone behind the ear. This allows audiologists to determine if the hearing loss stems from issues in the outer or middle ear or the inner ear.
By comparing the results of air and bone conduction tests, audiologists can pinpoint the location and type of hearing loss.
When to Use Bone Conduction vs Air Conduction
Air and bone conduction tests are integral parts of a comprehensive hearing test. Here are some examples of when each testing method proves particularly beneficial:
- Air conduction testing is suitable for general hearing assessments, identifying the degree of hearing loss, and determining if further investigation is necessary.
- Bone conduction testing is particularly useful in cases of conductive hearing loss, helping distinguish it from sensorineural hearing loss.
- Both tests are often used in conjunction to provide a comprehensive understanding of the patient’s hearing health and guide treatment strategies.
What to Expect During a Bone Conduction Test
During the test, you will be seated comfortably in a sound booth so that external noise interference is minimised. The audiologist will then place a bone oscillator on the mastoid bone behind your ear. It’s a small device, often attached to a headband, that vibrates to deliver sound directly to the inner ear.
The bone oscillator produces sounds at varying frequencies and volumes and you will be asked to respond each time you hear a sound, either by raising your hand, pressing a button or simply indicating verbally.
The audiologist will then document these responses to create an audiogram, a visual representation of your hearing levels.
Interpreting Bone Conduction Test Results
The results of a bone conduction test are depicted on an audiogram displaying hearing thresholds, which represent the quietest sound a person can hear at different frequencies.
The results are typically plotted for both ears, with different symbols used to indicate air conduction and bone conduction thresholds.
By analysing the difference between air and bone conduction thresholds, audiologists can distinguish between conductive and sensorineural hearing loss.
This distinction is vital as it helps determine the underlying causes of hearing loss and provide insight regarding the correct treatment.
| Test Results | Potential Next Steps |
| Normal Hearing | No immediate action needed |
| Conductive Hearing Loss | Medical referral (ENT), hearing aids |
| Sensorineural Hearing Loss | Hearing aids, cochlear implants |
| Mixed Hearing Loss (Conductive & Sensorineural) | Medical referral (ENT), hearing aids |
Final Thoughts
Bone conduction testing is unique amongst hearing tests because it bypasses the outer ear and eardrum, directly stimulating the cochlea through skull vibrations. This allows assessment of inner ear function even if the outer or middle ear is compromised. This makes it an important technique for identifying conductive hearing loss.
If you or a loved one are experiencing hearing difficulties, please book a hearing appointment with us. Sound Hearing provides independent audiology services throughout London.