IHS Acoustics and Sound 2 — Questions and Answers
Question 1: What does RT60 (reverberation time) measure in room acoustics?
- The round-trip travel time of sound between two parallel walls
- The time required for sound to decay by 60 dB after the source stops (Correct answer)
- The room's frequency response at 60 Hz
- The echo delay measured in milliseconds
Correct answer: The time required for sound to decay by 60 dB after the source stops
RT60 is the time required for sound energy to decay by 60 dB after the source stops, serving as the standard metric for room reverberation and its impact on speech clarity.
Question 2: How does a higher signal-to-noise ratio (SNR) affect speech intelligibility for hearing aid users?
- It reduces speech clarity by masking critical frequencies
- It improves speech intelligibility by making the signal stronger relative to background noise (Correct answer)
- It has no measurable effect on speech understanding
- It increases reverberation in the listening environment
Correct answer: It improves speech intelligibility by making the signal stronger relative to background noise
A higher SNR means the desired speech signal is substantially louder than background noise, directly improving the listener's ability to understand speech, especially for those with hearing loss.
Question 3: What is the primary cause of acoustic feedback in hearing instruments?
- A depleted battery causing voltage fluctuations
- Amplified sound from the receiver leaking back into the microphone and being re-amplified (Correct answer)
- A loose or corroded battery contact
- Excessive cerumen blocking the microphone port
Correct answer: Amplified sound from the receiver leaking back into the microphone and being re-amplified
Acoustic feedback is a closed loop where amplified sound from the receiver (speaker) escapes and re-enters the microphone, is amplified again, and creates the characteristic whistle or squeal.
Question 4: What is the key distinction between sound pressure level (SPL) and hearing level (HL)?
- SPL is measured in Hz; HL is measured in dB
- SPL uses a fixed physical reference (20 µPa); HL is referenced to average normal hearing thresholds that vary by frequency (Correct answer)
- SPL is used for hearing aids only; HL is used exclusively for audiometers
- There is no practical difference between the two scales
Correct answer: SPL uses a fixed physical reference (20 µPa); HL is referenced to average normal hearing thresholds that vary by frequency
SPL is referenced to a fixed pressure of 20 µPa across all frequencies, while HL adjusts for the ear's varying sensitivity so that 0 dB HL represents the average normal hearing threshold at each test frequency.
Question 5: In acoustics, what does one octave represent?
- An increase of exactly 1,000 Hz between two tones
- A doubling of frequency (Correct answer)
- A tenfold increase in sound intensity
- A fixed interval of 8 semitones used only in audiometric testing
Correct answer: A doubling of frequency
One octave equals a doubling of frequency; for example, 500 Hz to 1,000 Hz is one octave, and 1,000 Hz to 2,000 Hz is the next octave.
Question 6: What is the primary purpose of a directional microphone system in a hearing aid?
- To amplify all surrounding sounds equally in every direction
- To improve speech understanding in noise by emphasizing sounds arriving from in front (Correct answer)
- To eliminate the need for a volume control
- To reduce battery drain compared to omnidirectional microphones
Correct answer: To improve speech understanding in noise by emphasizing sounds arriving from in front
Directional microphones enhance sounds arriving from in front while attenuating sounds from behind and the sides, effectively improving the signal-to-noise ratio during face-to-face communication.
Question 7: What does total harmonic distortion (THD) measure in hearing instrument performance?
- The maximum output level of the hearing aid in dB SPL
- The ratio of unwanted harmonic energy to the fundamental frequency energy, expressed as a percentage (Correct answer)
- The full frequency range of the amplification channels
- The overall gain of the hearing instrument in dB
Correct answer: The ratio of unwanted harmonic energy to the fundamental frequency energy, expressed as a percentage
THD quantifies the distortion introduced by a hearing aid by measuring energy in harmonic frequencies relative to the intended fundamental, with lower percentages indicating cleaner, higher-quality amplification.
IHS Acoustics and Sound 2
What does RT60 (reverberation time) measure in room acoustics?