IHS Acoustics and Sound 5 — Questions and Answers
Question 1: Which type of microphone converts sound pressure variations into electrical signals through the movement of a coil within a magnetic field?
- Dynamic (moving-coil) microphone (Correct answer)
- Condenser microphone
- Piezoelectric microphone
- Carbon microphone
Correct answer: Dynamic (moving-coil) microphone
A dynamic microphone uses electromagnetic induction: a diaphragm attached to a coil moves within a magnetic field, generating a voltage.
Question 2: The critical band concept in psychoacoustics refers to:
- A frequency range within which two tones interact and mask each other (Correct answer)
- The bandwidth of a hearing aid receiver
- The frequency range of normal speech
- The audiometric test frequency range
Correct answer: A frequency range within which two tones interact and mask each other
A critical band is a frequency region of the cochlear basilar membrane within which stimuli interact, causing masking and affecting loudness perception.
Question 3: Harmonic distortion in a hearing aid occurs when the device produces:
- Output frequencies that are integer multiples of the input frequency (Correct answer)
- A delayed echo of the input signal
- Random noise unrelated to the input
- Frequency-shifted versions of the input
Correct answer: Output frequencies that are integer multiples of the input frequency
Harmonic distortion adds overtones at whole-number multiples (harmonics) of the input frequency, degrading sound quality.
Question 4: Reverberation time (RT60) is defined as the time required for sound pressure level to decrease by:
- 60 dB after the source stops (Correct answer)
- 30 dB after the source stops
- 20 dB after the source stops
- 6 dB after the source stops
Correct answer: 60 dB after the source stops
RT60 is the time it takes for the sound energy in a room to decay by 60 dB once the sound source ceases.
Question 5: What term describes the frequency at which a structure naturally vibrates when excited, with minimal energy input?
- Resonant frequency (Correct answer)
- Cutoff frequency
- Nyquist frequency
- Corner frequency
Correct answer: Resonant frequency
The resonant frequency is the natural vibration frequency of a structure; at this frequency, even small driving forces produce large oscillations.
Question 6: Which measure represents the ratio of the sound power output of a device to the electrical power input, expressed as a percentage?
- Electroacoustic efficiency (Correct answer)
- Sensitivity
- Total harmonic distortion
- Signal-to-noise ratio
Correct answer: Electroacoustic efficiency
Electroacoustic efficiency expresses how effectively a transducer (e.g., hearing aid receiver) converts electrical energy into acoustic energy.
Question 7: In audiometric testing, 'insert earphones' reduce the chance of collapsed ear canals and also provide greater attenuation of contralateral sound. Their typical inter-aural attenuation is approximately:
- 70–80 dB (Correct answer)
- 40–50 dB
- 20–30 dB
- 10–15 dB
Correct answer: 70–80 dB
Insert earphones provide approximately 70–80 dB of inter-aural attenuation, substantially more than supra-aural earphones (~40 dB), reducing the need for masking.
IHS Acoustics and Sound 5
Which type of microphone converts sound pressure variations into electrical signals through the movement of a coil within a magnetic field?