Bone Conduction Test

What Is a Bone Conduction Test?

A bone conduction test is a diagnostic hearing assessment that measures the sensitivity of the inner ear (cochlea) by sending sound vibrations directly through the bones of the skull, completely bypassing the outer ear canal, eardrum, and middle ear structures. It is one of the most important tools in audiology because it allows the clinician to determine not just whether hearing loss is present, but what type of hearing loss it is — and that distinction is critical for choosing the right treatment.

In a standard hearing test (pure tone audiometry), sound is delivered through headphones or insert earphones. This is called air conduction testing, because the sound travels through the air in the ear canal, vibrates the eardrum, passes through the three tiny bones (ossicles) of the middle ear, and finally reaches the cochlea. Any problem anywhere along this pathway — from a plug of ear wax to a perforated eardrum to a stiffened ossicular chain in otosclerosis — will reduce the sound that reaches the cochlea and show up as a hearing loss on the audiogram.

Bone conduction testing takes a different route. A small vibrating device — the bone oscillator (also called a bone conductor or bone vibrator) — is placed on the mastoid bone behind the ear and held in place by a spring-loaded headband. When the device vibrates, the sound energy passes directly through the skull bone to the cochlea, stimulating the sensory hair cells without involving the outer or middle ear at all. By comparing the results from both pathways — air conduction and bone conduction — the audiologist can pinpoint exactly where in the auditory system the problem lies.

The Physics of Sound Transmission — Air vs Bone

Understanding why bone conduction testing works requires a brief look at the physics of how we hear. Sound can reach the cochlea by two routes:

Air conduction pathway

This is the normal route for everyday hearing. Sound waves enter the outer ear (pinna and ear canal), strike the eardrum (tympanic membrane), and cause it to vibrate. These vibrations are transmitted across the middle ear by the ossicular chain — three of the smallest bones in the human body: the malleus (hammer), incus (anvil), and stapes (stirrup). The stapes footplate pushes against the oval window of the cochlea, creating pressure waves in the cochlear fluid that stimulate the hair cells of the organ of Corti. These hair cells convert mechanical vibration into electrical nerve impulses, which travel along the auditory nerve to the brain. The middle ear acts as an impedance-matching transformer, amplifying the sound signal by a factor of approximately 25–30 dB to overcome the energy loss that occurs when sound passes from the air medium to the fluid medium of the cochlea.

Bone conduction pathway

When a vibrating object is placed against the skull, the vibration travels through the bone directly to the cochlea. This bypasses the outer ear canal, eardrum, and middle ear entirely. The cochlea responds to bone-conducted sound in essentially the same way as it responds to air-conducted sound — the hair cells are stimulated and nerve impulses are generated. Several mechanisms contribute to bone conduction hearing, including direct compression of the cochlear capsule, inertial movement of the ossicles relative to the skull, and vibration of the ear canal walls generating secondary air-conducted sound. The key clinical point is that bone conduction tests the cochlea and auditory nerve in isolation, free from the influence of any outer or middle ear pathology.

This is why the comparison between air conduction and bone conduction results is so diagnostically powerful. If the cochlea is healthy (normal bone conduction) but the sound is being blocked before it gets there (reduced air conduction), the problem must lie in the outer or middle ear — a conductive hearing loss. If the cochlea itself is damaged (reduced bone conduction), the hearing loss is sensorineural. If both pathways are affected, the hearing loss is mixed.

What Bone Conduction Results Reveal — Types of Hearing Loss

The comparison between air conduction and bone conduction thresholds produces one of three diagnostic patterns, each with different causes and different treatment pathways:

Conductive hearing loss

In conductive hearing loss, air conduction thresholds are reduced but bone conduction thresholds are normal. The difference between the two is called the air-bone gap. A significant air-bone gap (typically 10 dB or more) indicates that the inner ear is functioning well, but something in the outer or middle ear is preventing sound from reaching it efficiently. Common causes include:

• Ear wax build-up: Impacted cerumen blocking the ear canal — often resolved by professional ear wax removal
• Glue ear (otitis media with effusion): Fluid accumulation in the middle ear, extremely common in children. Tympanometry is particularly useful for confirming this diagnosis
• Middle ear infection (acute otitis media): Infection with fluid and inflammation in the middle ear space
• Eardrum perforation: A hole in the tympanic membrane, which may result from infection, trauma, or pressure injury
• Otosclerosis: Abnormal bone growth around the stapes footplate, restricting its movement and reducing sound transmission. Otosclerosis typically produces a characteristic air-bone gap that is greatest in the lower frequencies
• Ossicular chain discontinuity: Disruption of the chain of middle ear bones, which may occur after trauma or chronic infection

Conductive hearing loss is frequently treatable — whether through wax removal, antibiotics, grommets, or surgical procedures such as stapedectomy for otosclerosis. This is one of the most important reasons why bone conduction testing matters: it identifies cases where medical or surgical intervention may restore hearing, rather than simply managing the loss with hearing aids.

Sensorineural hearing loss

In sensorineural hearing loss, both air conduction and bone conduction thresholds are equally reduced, with no significant air-bone gap. This pattern indicates that the problem lies within the cochlea, the auditory nerve, or the central auditory pathways. The outer and middle ear are working normally — sound is reaching the cochlea efficiently — but the cochlea or nerve is not processing it properly. Common causes include:

• Age-related hearing loss (presbycusis): The most common cause of sensorineural hearing loss in the UK, affecting an estimated 12 million adults according to the RNID. It typically affects the higher frequencies first and progresses gradually
• Noise-induced hearing loss: Damage to the cochlear hair cells from prolonged or sudden loud noise exposure. See our guide to protecting your hearing
• Genetic and congenital causes: Including inherited hearing loss and hearing loss caused by prenatal infections such as cytomegalovirus (CMV)
• Sudden sensorineural hearing loss: A medical emergency requiring urgent treatment, typically with corticosteroids
• Ototoxic medications: Certain drugs, including some antibiotics and chemotherapy agents, can damage the cochlea

Sensorineural hearing loss is usually permanent and is most commonly managed with hearing aids or, in severe to profound cases, cochlear implants. The bone conduction test confirms the sensorineural nature of the loss and helps determine the degree, guiding the audiologist`s recommendation.

Mixed hearing loss

Mixed hearing loss combines elements of both conductive and sensorineural loss. Both air and bone conduction thresholds are reduced, but air conduction is worse than bone conduction, producing an air-bone gap on top of a raised bone conduction baseline. This pattern is seen when a patient has an underlying sensorineural loss (for example, age-related hearing loss) complicated by a superimposed conductive component (for example, ear wax or glue ear). Management may involve treating the conductive element first — which can produce a noticeable improvement — and then addressing the residual sensorineural loss with hearing aids if needed.

The Bone Conduction Test Procedure

Bone conduction testing is performed as a standard part of any full diagnostic hearing assessment at both NHS and private audiology clinics. It is not a separate appointment — it is integrated into the audiometry session alongside air conduction testing. Here is what to expect:

Placement of the bone oscillator

The audiologist places a small, flat vibrating device (the bone oscillator) on the mastoid bone — the bony prominence you can feel directly behind your ear. It is held firmly in place by a spring-loaded metal or plastic headband that sits across the top of your head. Some audiologists may choose to place the oscillator on the forehead instead, particularly if mastoid placement is difficult or if cross-hearing between the ears needs to be carefully controlled.

Masking

Because bone-conducted sound vibrates the entire skull, there is a risk that the non-test ear may pick up the signal — a phenomenon called cross-hearing. When this is suspected, the audiologist introduces a masking noise (usually narrowband noise) into the non-test ear through a headphone or insert earphone, ensuring that only the intended ear is being tested. Masking is a technically demanding aspect of audiometry and is one of the reasons why bone conduction testing should always be performed by a qualified audiologist who can make the correct masking decisions. The British Society of Audiology (BSA) publishes detailed recommended procedures for masking during bone conduction audiometry.

Testing procedure

The procedure follows the same principles as air conduction audiometry. Tones are presented at different frequencies — typically 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz — and the audiologist finds the quietest level at which you can hear each tone (the threshold). You respond by pressing a button or raising your hand each time you hear a tone, no matter how faint. The bone conduction thresholds are then plotted on the audiogram using standardised symbols: typically square brackets [ ] or angle brackets < > for bone conduction, alongside the circles (right ear) and crosses (left ear) used for air conduction.

Duration and comfort

Bone conduction testing adds approximately 5 to 10 minutes to a standard hearing assessment. The test is completely painless and non-invasive — you will feel a slight vibration against the bone behind your ear, similar to the buzzing of a mobile phone, and you will hear tones at various pitches. Some people find the headband mildly uncomfortable due to the spring pressure, but it is worn for only a few minutes and is well tolerated by virtually all patients, including older adults and children.

Reading the Audiogram — Understanding the Air-Bone Gap

The audiogram produced by a combined air and bone conduction assessment is the audiologist`s primary diagnostic tool. It displays hearing thresholds in decibels (dB HL) on the vertical axis and frequency in Hertz (Hz) on the horizontal axis. The key diagnostic feature revealed by bone conduction testing is the air-bone gap:

• No air-bone gap (air and bone conduction thresholds are equal or within 10 dB): The hearing loss is sensorineural. The cochlea or auditory nerve is the site of the problem.
• Significant air-bone gap (air conduction thresholds are worse than bone conduction by 15 dB or more): There is a conductive component. Something in the outer or middle ear is attenuating the sound before it reaches the cochlea.
• Air-bone gap with raised bone conduction thresholds: A mixed hearing loss is present — both the conductive pathway and the cochlea are contributing to the loss.

Your audiologist will explain your audiogram in full, showing you where your thresholds fall relative to normal hearing and what the pattern means for your specific situation. Understanding the type of hearing loss is essential because it directly determines the management pathway: conductive losses may be medically or surgically treatable, sensorineural losses are typically managed with hearing aids, and mixed losses may benefit from a combination of approaches.

When Is Bone Conduction Testing Needed?

Bone conduction testing is included as a standard component of any full diagnostic hearing assessment. However, it is particularly important in the following clinical scenarios:

• Whenever air conduction audiometry shows a hearing loss: The audiologist needs to determine the type before making any recommendations. Without bone conduction data, the distinction between conductive and sensorineural loss cannot be made
• Suspected middle ear pathology: Patients with symptoms suggestive of glue ear, otosclerosis, chronic ear infection, or eardrum perforation will always require bone conduction testing to quantify the conductive component
• Pre-surgical assessment: Before ear surgery — such as tympanoplasty, stapedectomy, or grommet insertion — the surgeon needs bone conduction thresholds to understand the cochlear reserve and predict the likely outcome of the procedure
• Asymmetric hearing loss: When hearing is significantly worse in one ear than the other, bone conduction testing helps determine whether the asymmetry is conductive, sensorineural, or mixed, and whether further investigation (such as MRI to rule out acoustic neuroma) is warranted
• Monitoring known conditions: Patients with otosclerosis, chronic middle ear disease, or Meniere`s disease often require serial bone conduction testing to monitor progression and guide treatment decisions
• Hearing aid candidacy: For patients considering hearing aids, bone conduction results help the audiologist determine the most appropriate type and fitting strategy

Bone Conduction Testing and Related Assessments

Bone conduction testing rarely occurs in isolation. It is part of a comprehensive audiological assessment that may also include:

• Tympanometry: An objective test that measures eardrum compliance and middle ear pressure, providing complementary information about middle ear function. A Type B tympanogram (flat trace) combined with a significant air-bone gap on the audiogram is a classic pattern for glue ear
• Otoacoustic emissions (OAE): A test of outer hair cell function in the cochlea. OAEs are typically present when bone conduction thresholds are normal and absent when cochlear hearing loss exceeds approximately 30–40 dB
• Speech-in-noise testing: Assesses how well you hear and understand speech in background noise, which can be affected differently in conductive versus sensorineural hearing loss
• Auditory brainstem response (ABR): An objective, frequency-specific test of the auditory nerve and brainstem pathways, used when behavioural audiometry is not possible or when retrocochlear pathology is suspected

Together, these tests give the audiologist a comprehensive picture of your hearing, enabling accurate diagnosis and evidence-based treatment recommendations.

Where to Get a Bone Conduction Test

Bone conduction testing is available at both NHS audiology departments (via GP or consultant referral) and private audiology clinics. It is included as a standard part of a full diagnostic hearing assessment at no additional cost — you do not need to request it separately. Providers such as Boots Hearingcare, Specsavers Audiology, and Hidden Hearing include bone conduction testing in their comprehensive hearing assessments. Use our search tool to find audiologists near you, compare availability, and book an appointment online. Whether your hearing loss turns out to be conductive, sensorineural, or mixed, the bone conduction test is the assessment that provides the answer — and the answer determines your best path forward.