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Audiology Tuning Fork Tests

Underlying Mechanisms: Air vs. Bone Conduction

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The Standard Tuning Fork: 512 Hz

• Low enough to produce a tone perceptible by bone conduction
• High enough to avoid tactile vibration confounding the result (lower frequencies like 128 Hz can be felt)
• Falls within the critical speech frequency range

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The Tests

1. Rinne Test

1. Strike the tuning fork and place the vibrating tines near the external auditory canal opening (AC position)
2. Then place the stem on the mastoid process (BC position)
3. Ask: "Which is louder?" or use the sequential method: hold at mastoid until no longer heard, then move to EAC — ask if sound returns

According to Harrison's (p. 1037): "with conductive hearing loss of ≥30 dB, the bone-conduction stimulus is perceived as louder than the air-conduction stimulus."

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2. Weber Test

1. Strike the tuning fork and place the stem on the midline — vertex of the skull, forehead, or upper central incisor teeth
2. Ask: "Where do you hear the sound — left, right, or center?"

• The occluded/damaged middle ear creates an environment where ambient noise is excluded, reducing "masking" in that ear
• Bone-conducted energy is not dissipated via the normal ossicular pathway, so more energy reaches the cochlea on the conductive-loss side
• This is also why plugging a normal ear with a finger causes the Weber to lateralize to that side (the occlusion effect)

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3. Schwabach Test

1. Place the vibrating fork stem on the patient's mastoid
2. When the patient signals they no longer hear it, immediately transfer to the examiner's mastoid

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4. Bing Test (Occlusion Test)

1. Place the fork stem on the mastoid
2. Alternately occlude and release the external auditory canal with a fingertip
3. Ask if the sound gets louder when the ear is blocked

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5. Gelle Test

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Combined Interpretation Summary

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Clinical Pearls

• Always use a 512 Hz fork — 256 Hz causes too much tactile sensation, 1024 Hz is too quiet for BC
• Strike the fork against the knee or palm, not a hard surface (avoids overtones)
• The Rinne only detects conductive loss when the air-bone gap is ≥30 dB — smaller gaps may not be picked up
• Tuning fork tests are screening tools, not replacements for formal pure-tone audiometry
• In a noisy clinical environment, results may be unreliable; audiometry in a sound-treated booth is the gold standard

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Audiologic Evaluation & Audiogram Interpretation

The Minimum Audiologic Test Battery

1. Pure tone air-conduction thresholds
2. Pure tone bone-conduction thresholds
3. Speech reception threshold (SRT)
4. Word recognition score (WRS)
5. Tympanometry
6. Acoustic reflexes
7. Acoustic reflex decay

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1. Pure Tone Audiometry

How It Works

The Audiogram Grid

Standard Audiogram Symbols

Air-Bone Gap (ABG)

• ABG = 0 → No conductive component
• ABG ≥ 10–15 dB → Significant conductive component
• Maximum possible ABG is ~60 dB (the limit of the conductive mechanism)

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2. Severity Classification of Hearing Loss

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3. Audiogram Patterns by Type of Loss

A. Normal Audiogram

• All thresholds ≤25 dB HL
• AC and BC overlap (no ABG)
• Flat across all frequencies

B. Conductive Hearing Loss

• BC normal (≤25 dB HL across frequencies) — cochlea and nerve intact
• AC elevated — outer/middle ear pathway blocked
• ABG present at affected frequencies
• Pattern depends on pathology:
  • Mass-dominant (middle ear effusion): thresholds elevated predominantly at high frequencies
  • Stiffness-dominant (early otosclerosis): elevations at low frequencies
  • Mixed stiffness + mass: flat elevation across all frequencies

C. Sensorineural Hearing Loss (SNHL)

• BC and AC both elevated in parallel — no ABG
• Cochlea or auditory nerve is damaged
• Common patterns:

D. Presbycusis Audiogram

E. Mixed Hearing Loss

• Both AC and BC are elevated (SNHL component)
• ABG is still present (conductive component on top)
• Example: Chronic otitis media with superimposed presbycusis

F. Conductive Loss with Air-Bone Gap (Clinical Example)

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4. Speech Audiometry

A. Speech Reception Threshold (SRT)

• The lowest intensity at which the patient correctly repeats 50% of spondee words (two-syllable words with equal stress, e.g., "baseball," "hotdog")
• Should agree with the pure tone average (PTA) of 500, 1000, and 2000 Hz within ±10 dB
• Discrepancy between SRT and PTA suggests non-organic hearing loss (functional/malingering)

B. Word Recognition Score (WRS) / Speech Discrimination Score

• Monosyllabic words presented at a suprathreshold level (usually SRT + 30–40 dB)
• Expressed as percentage correct (0–100%)
• Distinguishes cochlear from retrocochlear pathology:

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5. Tympanometry (Immittance Audiometry)

Tympanogram Types (Jerger Classification)

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6. Acoustic Reflexes

Reflex Testing

Interpretation

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7. Distinguishing Cochlear vs. Retrocochlear on Audiometry

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8. Integration: Tuning Fork Tests + Audiogram

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Key Clinical Pearls

• Pure tone audiometry defines the presence, type, and severity of loss; tuning fork tests are screening tools that must be confirmed by formal audiometry
• The SRT–PTA agreement rule (within ±10 dB) is an important validity check; larger discrepancies raise suspicion for functional hearing loss
• Rollover on WRS and acoustic reflex decay are the two most important screening signs of retrocochlear pathology — prompt MRI internal auditory canals with gadolinium if either is present
• The 4 kHz notch on audiogram is pathognomonic for noise-induced hearing loss; unlike presbycusis, it recovers slightly at 8 kHz
• Ménière's disease is the classic exception among SNHLs — it affects low frequencies first, opposite to most other SNHL causes

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