IHS Acoustics and Sound 4 — Questions and Answers
Question 1: Which phenomenon describes the bending of sound waves around obstacles or through openings?
- Diffraction (Correct answer)
- Refraction
- Reflection
- Absorption
Correct answer: Diffraction
Diffraction is the bending of sound waves around corners or through openings, allowing sound to be heard around barriers.
Question 2: A patient reports that a 1000 Hz tone sounds like it has a pitch of only 500 Hz. This distortion is an example of:
- Diplacusis (Correct answer)
- Recruitment
- Tinnitus
- Hyperacusis
Correct answer: Diplacusis
Diplacusis is a hearing distortion in which the same sound is perceived as having different pitches in each ear or at an incorrect pitch.
Question 3: What is the speed of sound in air at approximately 20°C (68°F)?
- 343 m/s (Correct answer)
- 760 m/s
- 1,125 m/s
- 1,500 m/s
Correct answer: 343 m/s
Sound travels at approximately 343 meters per second in air at 20°C under standard atmospheric conditions.
Question 4: The acoustic reflex threshold (ART) is typically how many dB above the pure-tone threshold in a normal ear?
- 70–100 dB SL (Correct answer)
- 10–20 dB SL
- 30–40 dB SL
- 5–10 dB SL
Correct answer: 70–100 dB SL
In normal-hearing ears, the acoustic reflex is elicited at approximately 70–100 dB above the pure-tone threshold (sensation level).
Question 5: Which measurement best describes the subjective loudness level of a complex sound compared to a reference 1000 Hz pure tone?
- Phon (Correct answer)
- Sone
- Decibel SPL
- Neper
Correct answer: Phon
The phon is a unit of loudness level that equates any sound to the dB SPL of a 1000 Hz pure tone judged equally loud.
Question 6: When two sounds of slightly different frequencies are presented simultaneously, listeners perceive a rhythmic pulsing called:
- Beats (Correct answer)
- Harmonics
- Resonance
- Interference pattern
Correct answer: Beats
Beats arise when two tones close in frequency combine, producing amplitude fluctuations at a rate equal to the difference between their frequencies.
Question 7: In a free-field environment, sound pressure level decreases by approximately 6 dB for every:
- Doubling of distance from the source (Correct answer)
- Halving of distance from the source
- 10-meter increase in distance
- Octave increase in frequency
Correct answer: Doubling of distance from the source
The inverse square law states that in a free field, SPL drops ~6 dB each time the distance from a point source doubles.
IHS Acoustics and Sound 4
Which phenomenon describes the bending of sound waves around obstacles or through openings?