Lecture 2.0 - Decibel and Pure Tone Audiometry

Question 1

What is the range of pressure variations the human ear can detect?

Answer 1

0.00002 Pa - 200Pa

or

20 Micro Pascals - 200 Pa

Question 2

Why is using Pa as an amplitude measurement not ideal?

Answer 2

• This range is so vast that it becomes unmanageable
• It does not reflect the way we perceive sound. The ear responds logarithmically, not linearly

Question 3

What is the dB SPL?

Answer 3

• A way to describe the range of hearing more easily
• A logarithmic scale that compresses the range of sound intensities we can hear into more manageable numbers (0 dB SPL - 140 dB SPL).

Question 4

True/False: Our sensitivity to hearing the different frequencies the same (i.e., we are just as sensitive to 1000 Hz as 500 Hz).

Answer 4

False, we are not equally sensitive to all frequencies.

We are most sensitive to 1000Hz and get less sensitive as we deviate from this in either direction.

Question 5

Why is dB SPL not a great reference to use in hearing tests?

Answer 5

The normal range of hearing when using dB SPL is curved.

Therefore, a 40 dB loss across all frequencies gives a range of different values. This makes it difficult and confusing.

Question 6

What is dB HL?

Answer 6

When the dB SPL is normalised, it becomes the decibel hearing level (dB HL).

This means it is adjusted to a common value.

Question 7

Using dB HL, what is the range of normal hearing?

Answer 7

• 10 to +15 dB HL

Question 8

Using dB HL, what is the range of “slight hearing loss”?

Answer 8

16 to 25 dB HL

Question 9

Using dB HL, what is the range of “mild hearing loss”?

Answer 9

26 to 40 dB HL

Question 10

Using dB HL, what is the range of “moderate hearing loss”?

Answer 10

41 to 55 dB HL

Question 11

Using dB HL, what is the range of “moderate-to-severe hearing loss”?

Answer 11

56 to 70 dB HL

Question 12

Using dB HL, what is the range of “severe hearing loss?”

Answer 12

71 to 90 dB HL

Question 13

Using dB HL, what is the range of “profound hearing loss?”

Answer 13

> 91 dB HL

Question 14

True/false: a profound hearing loss means deafness

Answer 14

False, some people with a profound loss can still have sound awareness

Question 15

What are the categories used to describe hearing loss on audiograms?

Answer 15

Symmetry between ears: Symmetrical (same loss bilaterally, asymmetrical, unilateral)

Severity: summarised by the average of 4 frequencies (0.5, 1, 2 & 4 kHz).

Pattern: flat, gently sloping HF, steeply sloping, cookie bite

Configuration: conductive vs. sensorineural vs. mixed

Question 16

What are some positive and negative aspects to using supra aural headphones?

Answer 16

Positives
- Robust
- Some models can go to 12 kHz
- Poor ambient noise attenuation, but can be enclosed inside audio cups

Negatives
- Risk of a collapsed ear canal if positioned incorrectly
- Not ideal for child patients due to weight
- Low frequency sounds can leak out causing calibration differences

Question 17

What are audiocups?

Answer 17

Cups that can be added on to supra aural headphones to reduce ambient noise - useful for screening at work places

Question 18

What are some positive and negative aspects of using insert earphones?

Answer 18

Positives
- Most hygienic option
- No risk of ear canal collapse
- Lightweight so is well suited to children
- Good ambient noise attenuation
- Highest inter-aural attenuation of three classes

Negatives
- Insertion depth is a key variable
- Expense from consumables

Question 19

What are some positive and negative aspects to using Circum-aural transducers?

Answer 19

Positive
- Ability to test into the extended high frequencies
- Flattest frequency responses of the 3 main classes
- Good ambient noise attenuation
- No risk of ear canal collapse and reduced occlusion effect

Negative
- Not ideal for child patients due to the weight

Question 20

What are the three mechanisms of bone conduction?

Answer 20

1. Distortional (osseus) mechanism
   - Vibration of the skull leads to distortion of structures in inner ear
2. Intertial
   - The middle ear bones are suspended by ligaments in the middle ear. Vibrating the bones of the skull also causes the middle ear bones and structures to vibrate.
3. Osseotympanic mechanism
   - Vibrates column of air in the outer ear, causing the ear drum to vibrate as per normal air conduction
   - Some of the sound escapes the ear canal into the outside world
   - If the ears are occluded, this sound does not escape, leading to the occlusion effect.

Question 21

What is classified as a “significant ear difference”?

Answer 21

There is a 20 dB HL loss or more between the four frequency average