Comprehensive Study Guide: Pure-Tone Audiometry, Transducers, and Audiogram Interpretation

Audiometric Evaluation and Symbol System

• Audiometric evaluation involves testing perceptual responses to acoustic stimuli first through air conduction ($\text{AC}$) and subsequently through bone conduction ($\text{BC}$).

• Results for each ear and presentation mode are plotted independently on a standardized grid known as an audiogram.

• Comparing air-conduction thresholds directly against bone-conduction thresholds enables precise clinical determination of the type of hearing loss present.

• Air-Conduction Symbol Conventions:

  • Right Ear (Unmasked): Circle symbol ($\text{O}$), rendered in red ink. (Mnemonic rule: Red, Right, Round).

  • Left Ear (Unmasked): Cross symbol ($\text{X}$), rendered in blue ink. (Mnemonic rule: Left, Blue, X).

  • Right Ear (Masked): Triangle symbol ($\triangle$), rendered in red ink.

  • Left Ear (Masked): Square symbol ($\square$), rendered in blue ink.

• Bone-Conduction Symbol Conventions:

  • Symbol orientation indicates the placement side of the bone vibrator transducer; symbols remain open relative to the test side.

  • Right Ear Unmasked Bone Conduction: Open bracket pointing right ($<$), rendered in red ink.

  • Left Ear Unmasked Bone Conduction: Open bracket pointing left ($>$), rendered in blue ink.

  • Right Ear Masked Bone Conduction: Left square bracket ($[$), rendered in red ink.

  • Left Ear Masked Bone Conduction: Right square bracket ($]$), rendered in blue ink.

Anatomical Pathways and Bone Conduction Principles

• Anatomical Subdivisions of the Auditory System:

  • Conductive Portion: Comprises the Outer Ear and Middle Ear.

  • Sensorineural Portion: Comprises the Inner Ear (cochlea), 8th Nerve (vestibulocochlear nerve), and Central Auditory System.

• Air Conduction ($\text{AC}$) Pathway: Acoustic waves travel through the outer ear canal, vibrate the tympanic membrane and middle ear ossicles, and enter the inner ear. AC testing assesses the complete auditory pathway ($\text{Conductive Portion} + \text{Sensorineural Portion}$).

• Bone Conduction ($\text{BC}$) Pathway: Acoustic energy is transmitted directly to the temporal bone via mechanical vibration, bypassing the outer and middle ear structures to directly stimulate the fluid and sensory hair cells of the cochlea ($\text{Sensorineural Portion}$).

• Physics and Physiology of Unmasked Bone Conduction:

  • Transducer used: Bone Oscillator / Vibrator (e.g., Radioear B71).

  • Placement site: The mastoid process of the temporal bone, positioned immediately behind the pinna.

• Crossover / Lateralization: Mechanical vibrations applied to one side of the skull propagate efficiently across the entire cranium, stimulating both the ipsilateral and contralateral cochleae simultaneously.

• Perceptual behavior: Bone-conducted sound naturally lateralizes to the better-hearing cochlea regardless of physical placement side.

• Diagnostic limitation: Unmasked bone-conduction thresholds reflect the response of the better-functioning inner ear, not necessarily the ear adjacent to the transducer placement.

• Clinical requirement: Clinical masking (introducing narrow-band noise via air conduction to the non-test ear) must be applied to isolate and assign thresholds to the target ear accurately.

Parameters of Hearing Loss and Classification

• Full diagnostic description of a patient's hearing profile on an audiogram requires systematically evaluating five key parameters:

  1. Laterality

  2. Type of Hearing Loss

  3. Degree of Hearing Loss

  4. Configuration / Pattern

  5. Symmetry Between Ears

• Laterality Classification:

  • Unilateral Hearing Loss: Hearing impairment identified in only one ear, while the contralateral ear exhibits thresholds within normal limits ($\le 25\,\text{dB HL}$).

• Bilateral Hearing Loss: Hearing impairment identified in both ears.

• Differential Diagnosis by Hearing Loss Type:

  • Sensorineural Hearing Loss ($\text{SNHL}$):

  • Air-conduction and bone-conduction thresholds are both elevated beyond normal limits ($> 25\,\text{dB HL}$).

  • Air-conduction and bone-conduction thresholds are superimposed or overlapping within $10\,\text{dB}$ of each other (absence of a significant air-bone gap, i.e., $\text{ABG} < 15\,\text{dB}$).

  • Pathology location: Inner ear (cochlear hair cells), 8th cranial nerve, or central auditory pathways.

• Conductive Hearing Loss ($\text{CHL}$):

  • Bone-conduction thresholds remain strictly within normal limits ($\le 25\,\text{dB HL}$).

  • Air-conduction thresholds are elevated ($> 25\,\text{dB HL}$).

  • Presence of a clinically significant Air-Bone Gap ($\text{ABG} \ge 15\,\text{dB}$), where AC thresholds are worse than BC thresholds by $10\,\text{dB}$ or more.

  • Pathology location: Outer ear canal or middle ear cavity.

• Mixed Hearing Loss ($\text{MHL}$):

  • Both air-conduction and bone-conduction thresholds are elevated outside normal limits ($> 25\,\text{dB HL}$).

  • Bone-conduction thresholds are significantly better than air-conduction thresholds, exhibiting an Air-Bone Gap ($\text{ABG} \ge 15\,\text{dB}$).

  • Pathology location: Coexisting outer/middle ear conductive dysfunction and inner ear/nerve sensorineural impairment.

• Air-Bone Gap ($\text{ABG}$) Quantitative Definition:

  • The frequency-specific intensity difference, calculated in decibels, between the air-conduction threshold and bone-conduction threshold:   $\text{ABG} = \text{Threshold}_{\text{AC}} - \text{Threshold}_{\text{BC}}$

  • An $\text{ABG} \ge 15\,\text{dB}$ signifies a conductive component requiring medical or surgical evaluation.

• Pure-Tone Average ($\text{PTA}$):

  • Definition: The arithmetic mean of an ear's air-conduction thresholds at $500\,\text{Hz}$, $1000\,\text{Hz}$, and $2000\,\text{Hz}$:   $\text{PTA} = \frac{\text{Threshold}_{500\,\text{Hz}} + \text{Threshold}_{1000\,\text{Hz}} + \text{Threshold}_{2000\,\text{Hz}}}{3}$

  • Clinical purpose: Synthesizes multi-frequency threshold data into a single representative number to summarize overall hearing sensitivity across speech-frequency channels.

• Severity Categories and Functional Speech Perception Impacts:

• Normal Range ($\le 25\,\text{dB HL}$): No noticeable obstacle to understanding faint or soft speech.

• Mild Hearing Loss ($26\text{--}40\,\text{dB HL}$): Frequent difficulty detecting faint or distant speech; subtle acoustic cues missed.

• Moderate Hearing Loss ($41\text{--}70\,\text{dB HL}$): Consistent difficulty perceiving conversational-level speech without amplification.

• Severe Hearing Loss ($71\text{--}90\,\text{dB HL}$): Inability to understand normal conversation; can hear only shouted or heavily amplified acoustic signals.

• Profound Hearing Loss ($\ge 91\,\text{dB HL}$): Unable to understand even high-intensity amplified speech; relies primarily on tactile or visual communication.

  • Terminology: "deaf" vs. "Deaf":

• Lowercase "deaf": Refers to the audiological condition of profound hearing loss or complete lack of response at maximum audiometer outputs.

• Capitalized "Deaf": Refers to cultural, linguistic, and social identity associated with members of the Deaf community who communicate via sign language.

Audiometric Configurations and Slopes

• Configuration describes the overall shape and contour of hearing thresholds mapped across the frequency spectrum (Hall, p. 138):

  • Flat: Air-conduction thresholds across all tested frequencies remain within a $20\,\text{dB}$ margin of one another.

• Sloping: Thresholds demonstrate a gradual increase in hearing loss severity toward higher frequencies at a rate of approximately $10\,\text{dB}$ per octave.

• Rising: Thresholds demonstrate a gradual improvement in hearing sensitivity toward higher frequencies (poorer low-frequency sensitivity).

• Sharply Sloping: Hearing loss severity worsens rapidly toward high frequencies at a rate exceeding $20\,\text{dB}$ per octave.

• Precipitous / Ski Slope: Near-normal or mild hearing loss thresholds in low frequencies followed by an abrupt, vertical drop in sensitivity above a specific threshold frequency (e.g., steep decline above $2000\,\text{Hz}$).

• Corner: Measurable responses are confined exclusively to low frequencies at high stimulus intensities in the lower-left corner of the grid; no responses at mid-to-high frequencies.

• Notch: A distinct, circumscribed drop in hearing threshold over a narrow frequency range (commonly centered at $4000\,\text{Hz}$ due to noise exposure), returning to better thresholds at higher frequencies.

• Cookie-Bite: Poorer hearing sensitivity concentrated in the mid-frequency region ($1000\text{--}3000\,\text{Hz}$), with relatively better thresholds in both low and high frequencies.

• Reverse Cookie-Bite: Better hearing sensitivity in the mid-frequency range, accompanied by poorer thresholds at low and high frequency extremes.

Symmetry Between Ears

• Symmetrical Hearing Loss: Both ears demonstrate matching degree, configuration, and threshold values across frequencies within acceptable clinical tolerances.

• Asymmetrical Hearing Loss: Thresholds between the right and left ears differ significantly in degree, configuration, or overall level at one or more frequencies.

Clinical Audiometry Protocol and Patient Setup

• Comprehensive Test Sequence Steps:

  1. Detailed Case History Collection

  2. Outer Ear Examination via Otoscopy

  3. Patient Seating and Spatial Orientation

  4. Delivering Patient Instructions

  5. Selecting Transducers

  6. Stimulus Presentation and Threshold Determination

  7. Plotting Results on the Audiogram

• Seating and Booth Setup Requirements:

  • Testing takes place inside a double-walled or single-walled sound-attenuated booth ($2 \times 2\,\text{m}$ standard dimension).

  • The patient chair is positioned at an angle so the patient cannot view the clinician's hands or the audiometer control panel, preventing visual cueing during signal delivery.

• Patient Instruction Guidelines:

  • Instructions must be clear and direct: "You're going to hear some beeping sounds; I want you to press the button any time you hear the beep. Sometimes the sounds will be soft, even if they're very soft, if you hear it, push the button."

  • Use the Talk Forward microphone function on the audiometer to communicate clearly into the patient's headphones at an adjustable intensity level.

• Response Paradigms:

  • Button Press (standard for adult patients).

  • Hand or Finger Raising.

  • Verbal Acknowledgement ("I hear it").

  • Conditioned Play Audiometry (e.g., dropping pegs into a pegboard game, used for pediatric populations aged $2\text{--}5\,\text{years}$).

• Control Dynamics: Clinicians control signal intensity, presentation frequency, signal mode, and presentation timing; patients control the behavioral response output.

Acoustic Transducers in Audiometry

• Transducer Options and Selection Criteria:

1. Supra-Aural Earphones:

   • Representative Model: Telephonics TDH-39.

   • Description: Foam-cushioned cups supported by a metal headband resting directly against the outer ear pinna.

• Disadvantages:

  • Minimal attenuation of low-frequency environmental ambient noise.

  • Risk of mechanical canal collapse in elderly or pediatric ears with compliant cartilage, generating an artificial/false conductive hearing loss.

1. Insert Earphones:

   • Representative Models: Etymotic Research ER-3A / ER-3C.

   • Description: Compact transducers connected via thin sound tubes to expandable, single-use disposable foam eartips inserted into the ear canal.

• Clinical Advantages:

  • Superior ambient noise reduction (mid and high frequencies).

  • Prevents test-induced ear canal collapse.

  • Highly hygienic and comfortable.

  • High Inter-Aural Attenuation (IAA), markedly reducing crossover and masking requirements.

• Insertion Technique & Shallow Insertion Warning:

  • Proper technique: Compress foam tip tightly, pull pinna upward and backward, and seat deeply into the canal.

  • Shallow insertion penalty: An improper seal creates acoustic leakage, allowing long-wavelength low-frequency acoustic energy to escape. This causes a false low-frequency conductive hearing loss!

 * Deep insertion benefits: Establishes a sealed acoustic volume, stabilizes physical fit, and ensures reliable calibration.

• Limitations: Unsuited for ear canals with structural malformations (e.g., complete aural atresia), higher unit expense, vulnerability to cerumen clogging, and tendency for young children to pull out the foam tips.

1. Circum-Aural Headphones:

   • Representative Model: Sennheiser HDA 200.

   • Description: Large dome earcups completely surrounding the pinna without applying direct pressure to it.

• Clinical Applications: High-frequency extended audiometry ($> 8000\,\text{Hz}$, up to $16000\,\text{Hz}$) required for ototoxicity monitoring.

• Features: High passive ambient noise attenuation; bulky and heavy for small children.

1. Sound-Field Loudspeakers:

   • Description: Calibrated speakers presenting sound into the testing room rather than into ear-specific transducers.

• Applications: Evaluating un-aided binaural hearing in uncooperative infants and assessing aided performance with hearing aids or cochlear implants.

• Room Acoustic Considerations: Susceptible to standing waves (nodes and antinodes) and phase cancellation. Continuous pure tones must never be used in sound field testing; warbled tones or narrow-band noise ($\text{NBN}$) are required.

1. Bone Oscillator / Vibrator:

   • Representative Model: Radioear B71 / B-71.

   • Description: Electromagnetic oscillator housed in a plastic casing held against the mastoid process by a spring steel headband.

• Placement Precautions: Position firmly on the mastoid process behind the ear pinna; the oscillator casing must not touch the pinna (contact introduces tactile or localized acoustic perception artifacts). Eyeglasses, headbands, and hair must be cleared.

Transducer Intensity Output Limits

• Maximum Transducer Output Limits across Audiometric Frequencies ($\text{dB HL}$):

  • $125\,\text{Hz}$: TDH-39 = $85\,\text{dB HL}$, ER-3A = $90\,\text{dB HL}$, Radioear B-71 = NA.

  • $250\,\text{Hz}$: TDH-39 = $105\,\text{dB HL}$, ER-3A = $100\,\text{dB HL}$, Radioear B-71 = $45\,\text{dB HL}$.

  • $500\,\text{Hz}$: TDH-39 = $120\,\text{dB HL}$, ER-3A = $110\,\text{dB HL}$, Radioear B-71 = $65\,\text{dB HL}$.

  • $1000\,\text{Hz}$: TDH-39 = $120\,\text{dB HL}$, ER-3A = $115\,\text{dB HL}$, Radioear B-71 = $75\,\text{dB HL}$.

  • $2000\,\text{Hz}$: TDH-39 = $120\,\text{dB HL}$, ER-3A = $115\,\text{dB HL}$, Radioear B-71 = $80\,\text{dB HL}$.

  • $3000\,\text{Hz}$: TDH-39 = $120\,\text{dB HL}$, ER-3A = $115\,\text{dB HL}$, Radioear B-71 = $80\,\text{dB HL}$.

  • $4000\,\text{Hz}$: TDH-39 = $120\,\text{dB HL}$, ER-3A = $115\,\text{dB HL}$, Radioear B-71 = $75\,\text{dB HL}$.

  • $6000\,\text{Hz}$: TDH-39 = $110\,\text{dB HL}$, ER-3A = $105\,\text{dB HL}$, Radioear B-71 = $(50)\,\text{dB HL}$.

  • $8000\,\text{Hz}$: TDH-39 = $100\,\text{dB HL}$, ER-3A = $90\,\text{dB HL}$, Radioear B-71 = $(45)\,\text{dB HL}$.

• Note: Output capabilities for bone transducers ($\text{B-71}$) are significantly lower than air-conduction transducers due to physical output power constraints and harmonic distortion limits at high force levels.

Signal Types and Research Findings

• Stimulus Signal Types:

  • Pure Tone: Single-frequency continuous sine wave. Can become monotonous during extended testing, leading to patient fatigue or sleepiness.

  • Pulsed Tone: Pure tone pulsing rapidly on and off ($225\,\text{ms}$ on/off duty cycle); improves detection against background tinnitus.

  • Warbled Tone: Frequency-modulated pure tone; eliminates standing waves in sound field testing.

  • Narrow-Band Noise ($\text{NBN}$): Noise band filtered around a specific center frequency.

  • FRESH Noise (FREquency Specific Hearing assessment): Specially filtered noise featuring steep out-of-band energy rejection rates.

• Comparative Stimulus Research (Norrix & Anderson, 2015):

  • Investigated threshold sensitivity across four stimulus types (Pure tone, Warbled tone, FRESH noise, Narrow-band noise) in 12 adults with hearing loss using supra-aural headphones.

  • Findings: Narrow-band noise ($\text{NBN}$) yielded significantly easier signal detection and lower (better) thresholds at high frequencies ($> 2000\,\text{Hz}$) compared to pure tones, warbled tones, and FRESH noise.

  • Thresholds for pure tones, warbled tones, and FRESH noise were equivalent across all frequencies.

Psychophysical Threshold Measurement Techniques

• Evaluation of Threshold Presentation Strategies:

  • Ascending Technique: Begins well below threshold ($0\,\text{dB HL}$) and increases in $5\,\text{dB}$ increments until response. Risk: Patient may delay responding until well above threshold (yields false elevated thresholds).

  • Descending Technique: Begins at suprathreshold levels ($50\,\text{dB HL}$) and decreases in $5\,\text{dB}$ steps. Risk: Patient may continue responding below true threshold (yields false optimistic thresholds).

  • Bracketing Technique (Hughson-Westlake Method): Combines descending search for initial response with ascending runs to establish threshold.

• Hughson-Westlake Standardized Procedure (Hughson & Westlake 1944; modified by Carhart & Jerger 1959):

  • Up 5, Down 10 Rule:

  • After a positive response (+): Decrease intensity by $10\,\text{dB}$.

  • After a negative response (-): Increase intensity by $5\,\text{dB}$.

  • Initial Starting Intensity:

  • Begin at $30\,\text{dB HL}$ for listeners with suspected normal hearing.

  • Begin at $50\,\text{dB HL}$ if hearing loss is suspected.

  • If no response occurs at initial level, increase in $20\,\text{dB}$ steps until the first response is elicited.

  • Criteria for Threshold: The lowest dB HL level at which a response is obtained on at least 50% of ascending trials (minimum of 2 responses at the same level out of 3 presentations).

  • Presentation Duration: Tones are presented for $2\text{--}4\,\text{seconds}$ per trial.

Test Sequence, Protocols, and Reliability

• Initial Ear Test Selection:

  • Always begin testing in the better-hearing ear first to facilitate task comprehension and establish baseline levels required for masking decisions.

  • If hearing appears equal in both ears, start with the right ear.

  • Complete air-conduction testing for both ears before commencing bone-conduction testing.

• Frequency Testing Sequence:

  • Human hearing range: $20\text{--}20000\,\text{Hz}$.

  • Primary speech spectrum: $300\text{--}8000\,\text{Hz}$.

  • Standard Air Conduction Frequencies: $250\,\text{Hz}$, $500\,\text{Hz}$, $1000\,\text{Hz}$, $2000\,\text{Hz}$, $3000\,\text{Hz}$, $4000\,\text{Hz}$, $6000\,\text{Hz}$, and $8000\,\text{Hz}$.

  • Standard Bone Conduction Frequencies: $250\,\text{Hz}$, $500\,\text{Hz}$, $1000\,\text{Hz}$, $2000\,\text{Hz}$, $3000\,\text{Hz}$, and $4000\,\text{Hz}$.

  • Extended High-Frequency AC: $10000\,\text{Hz}$, $12000\,\text{Hz}$, $14000\,\text{Hz}$, and $16000\,\text{Hz}$.

• Order of Frequency Presentation:

  • Start at $1000\,\text{Hz}$, proceed upward to $2000\,\text{Hz}$, $3000\,\text{Hz}$, $4000\,\text{Hz}$, $6000\,\text{Hz}$, and $8000\,\text{Hz}$.

  • Retest $1000\,\text{Hz}$ as an internal reliability check.

  • Finish with low frequencies: $500\,\text{Hz}$ and $250\,\text{Hz}$.

• Test-Retest Reliability Standards:

  • Permissible test-retest threshold variation: $\pm 5\,\text{dB}$.

  • Example: Trial 1 threshold at $1000\,\text{Hz} = 10\,\text{dB HL}$, Retest threshold at $1000\,\text{Hz} = 15\,\text{dB HL}$ (a $5\,\text{dB}$ variance is within acceptable limits).

  • Clinical significance: Ensures diagnostic confidence, differentiates true progressive clinical change from measurement noise, and helps detect malingering.

• OSHA Standard Threshold Shift ($\text{STS}$):

  • Regulated under the Occupational Safety and Health Administration (OSHA) for industrial noise exposure monitoring.

  • Definition: An average shift/worsening of $10\,\text{dB}$ or more at $2000\,\text{Hz}$, $3000\,\text{Hz}$, and $4000\,\text{Hz}$ in either ear relative to baseline testing.

Psychophysical Measurement Pitfalls

• Psychophysical Factors Affecting Audiometric Validity:

  • Habituation:

  • Definition: Decreased patient response to repeatedly presented stimuli.

  • Effect on Testing: Patient underreports thresholds, producing false negatives (hearing appears worse than actual sensitivity).

  • Expectation:

  • Definition: Patient anticipation of a stimulus based on perceived rhythm/pattern.

  • Effect on Testing: Patient overreports thresholds, producing false positives (responding when no tone was delivered).

  • Malingering:

  • Definition: Intentional misrepresentation or feigning of hearing loss (pseudohypacusis).

  • Effect on Testing: Invalidates behavioral test results; requires objective verification (e.g., OAEs, ABR, acoustic reflexes).

ChimeIn Practice Questions and Case Interpretations

• Case 1: Audiogram showing elevated AC thresholds, normal BC thresholds, and an Air-Bone Gap ($\text{ABG} \ge 15\,\text{dB}$).

  • Question: What type of hearing loss is this?

  • Answer: Conductive Hearing Loss ($\text{CHL}$).

• Case 2: Identification of Mixed Hearing Loss from audiogram options.

  • Question: Which audiogram represents a mixed hearing loss?

  • Option Analysis:

  • Audiogram A: AC elevated ($50\text{--}80\,\text{dB HL}$), BC elevated ($20\text{--}40\,\text{dB HL}$), with an $\text{ABG} \ge 15\,\text{dB}$. Correct Answer: Mixed Hearing Loss.

  • Audiogram B: BC normal ($0\text{--}10\,\text{dB HL}$), AC elevated ($50\text{--}60\,\text{dB HL}$) with an $\text{ABG} \ge 15\,\text{dB}$. (Conductive Hearing Loss).

  • Audiogram C: AC elevated ($10\text{--}70\,\text{dB HL}$), BC elevated ($10\text{--}70\,\text{dB HL}$), superimposed with no ABG ($< 10\,\text{dB}$). (Sensorineural Hearing Loss).

• Case 3: Audiogram configuration with threshold at $15\,\text{dB HL}$ at $250\,\text{Hz}$ dropping to $60\,\text{dB HL}$ at $8000\,\text{Hz}$.

  • Question: Which configuration best describes this pattern?

  • Answer: Sloping configuration.

• Case 4: Transducer selection for ototoxicity monitoring.

  • Question: A 50-year-old adult is being tested for early signs of ototoxicity up to $16\,\text{kHz}$ in a quiet booth. Which transducer is most appropriate?

  • Answer: Circum-aural headphones (e.g., Sennheiser HDA 200, calibrated for high frequencies up to $16\,\text{kHz}$).

• Case 5: Transducer selection for an uncooperative infant.

  • Question: Which transducer is most appropriate for testing an infant who will not tolerate earphone placement?

  • Answer: Sound-field speakers.

• Case 6: Transducer selection for unilateral complete aural atresia.

  • Question: A 6-year-old has complete aural atresia in the right ear but normal anatomy on the left. You want to estimate cochlear function in the atretic ear. Which transducer arrangement should be used?

  • Answer: Bone vibrator placed on the mastoid process with clinical masking delivered via an insert earphone in the normal left ear.

• Case 7: OSHA Standard Threshold Shift Calculation:

  • Baseline thresholds: $2000\,\text{Hz} = 5\,\text{dB HL}$, $3000\,\text{Hz} = 5\,\text{dB HL}$, $4000\,\text{Hz} = 10\,\text{dB HL}$.

  • Baseline Average = $\frac{5 + 5 + 10}{3} = 6.67\,\text{dB HL}$.

  • Current thresholds: $2000\,\text{Hz} = 20\,\text{dB HL}$, $3000\,\text{Hz} = 25\,\text{dB HL}$, $4000\,\text{Hz} = 25\,\text{dB HL}$.

  • Current Average = $\frac{20 + 25 + 25}{3} = 23.33\,\text{dB HL}$.

  • Shift magnitude: $23.33 - 6.67 = 16.67\,\text{dB}$.

  • Question: Is this considered a meaningful Standard Threshold Shift?

  • Answer: Yes (the shift exceeds the $10\,\text{dB}$ OSHA threshold criterion).

• Case 8: Audiogram Interpretation - "Which ear is worse?" Exercises:

  • Exercise 1 (Unilateral vs Bilateral severe comparison): Left ear shows profound SNHL ($40\text{--}115\,\text{dB HL}$) with unmasked AC/BC; right ear shows elevated AC ($40\text{--}110\,\text{dB HL}$) but masked BC ($[$) is better ($30\text{--}70\,\text{dB HL}$) yielding a large ABG. Left ear is worse (has greater sensorineural cochlear deficit).

  • Exercise 2 (Asymmetrical SNHL): Right ear AC ($O$) is within normal limits ($0\text{--}25\,\text{dB HL}$) at low/mid frequencies; Left ear AC masked ($\square$) is elevated across all frequencies ($30\text{--}70\,\text{dB HL}$). Left ear is worse.

  • Exercise 3 (Asymmetrical Conductive/Mixed): Left ear AC ($X$) is within normal limits ($0\text{--}10\,\text{dB HL}$); Right ear AC masked ($\triangle$) is elevated ($50\text{--}65\,\text{dB HL}$). Right ear is worse.

  • Exercise 4 (Symmetrical Sloping SNHL): Both ears show identical sloping curves from $20\,\text{dB HL}$ at $250\,\text{Hz}$ down to $85\,\text{dB HL}$ at $8000\,\text{Hz}$ with superimposed BC thresholds. Neither ear is worse (symmetrical hearing loss).