This set of Audio Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Microphone Types – Crystal, Capacitor, Electret and Carbon”.
1. On which principle is the working of crystal microphone based?
a) High impedance
b) Medium impedance
c) Piezoelectric effect
d) Electromagnetic Induction
View Answer
Explanation: Crystal microphone works on the principle of piezoelectric effect. The crystals used are quartz, tourmaline, rochelle salt and ceramic. Crystal microphone is used in home recording systems and mobile communication.
2. On which microphone ceramic can work on high temperature upto 100 degree Celsius?
a) Ribbon
b) Crystal
c) Moving coil / dynamic
d) Carbon
View Answer
Explanation: Ceramic is most suitable for crystal microphone because it has ability to work on high temperature upto 100 degree Celsius and is not susceptible to moisture. When pressure is applied on the crystal, it deforms and momentary displacement of charge takes place within the crystal structure which creates a potential difference between two surfaces of the crystal.
3. In which form the mechanical force on the crystal is developed in both directions when there is pressure of sound waves?
a) Compressions and rarefactions
b) Compressions
c) Rarefactions
d) Neither compressions nor rarefactions
View Answer
Explanation: When there is pressure of sound waves, compressions and rarefactions develops mechanical force on the crystal in both directions. Due to this compression and rarefaction, a potential difference is generated. This is proportional to the mechanical pressure applied to the crystal by the sound waves.
4. Which type of microphone is used for mobile communications?
a) Crystal
b) Capacitor
c) Carbon
d) Electret
View Answer
Explanation: Unlike moving coil and ribbon microphone, crystal microphone has no frequency inequality with direction. The cost of crystal microphones is very low. The main application of crystal microphone is that it is used in mobile communication and home recording systems.
5. What is the capacitor equation for the capacitance microphone?
a) C = kA / d
b) C = kA + d
c) C = kA – d
d) C = kA * d
View Answer
Explanation: Capacitance is inversely proportional to the distance between two plates. The capacitor equation is, c = kA/d
Where, k = dielectric constant of medium between the plates.
A = cross-sectional area of plates
d = distance between two plates.
6. What is the output impedance of capacitor microphone?
a) 25 Ω
b) 0.25 Ω
c) 1 Ω
d) 100 MΩ
View Answer
Explanation: The effect of temperature is negligible for capacitor microphone. It provides high SNR (Sound to Noise Ratio) and frequency response is excellent. So, the output impedance is highest in capacitor microphone compared to all other microphone which is 100 MΩ.
7. Which type of microphone is used in sound level meter?
a) Electret
b) Capacitor
c) Crystal
d) Carbon
View Answer
Explanation: Capacitor microphone requires external bias supply. As the frequency response of capacitor microphone is excellent it is used in sound level meter and in professional high-fidelity recording. Capacitor microphone is also used as a standard microphone for calibrating other microphones.
8. Which of the following microphone is coated with thin layer of Teflon at the back plate?
a) Electret
b) Capacitor
c) Carbon
d) Crystal
View Answer
Explanation: The back plate of the Electret microphone is coated with a thin layer of Teflon. This layer is negatively charged at the time of manufacturing. The negative charge induces positive charge on the diaphragm. This establishes an electric field across the gap of the capacitor plates. This results in a terminal voltage.
9. Which of the following is used as tie-clip microphone?
a) Cardioid
b) Carbon
c) Capacitor
d) Electret
View Answer
Explanation: The electret microphone is cheap and it does not require external supply. As the electret microphone is small in size and light in weight it is used in tie-clip microphone. It is also used as wireless microphone in sports meets.
10. Identify the microphone from the below figure.
a) Carbon
b) Electret
c) Cardioid
d) Capacitor
View Answer
Explanation: Carbon microphone is shown in the figure. Carbon granules are enclosed between two metal plates. Its upper plate is attached to a movable diaphragm. The lower metal plate is fixed and it is isolated from the diaphragm. A protective cover is used to protect the unit.
11. What happens to the resistance of carbon microphone when carbon granules are pressed and the current through the circuit increases?
a) Increases
b) Decreases
c) Constant
d) Increases and decreases
View Answer
Explanation: When carbon granules are pressed (length decreases), the resistance decreases, hence the current through the circuit increase is according to the equation, R = ρl/A. When carbon granules loosen, the resistance increases, hence decreasing the current through circuit.
12. What is the equation for the instantaneous current through load resistor in carbon microphone?
a) I = E / R + δr
b) J = E / r + δr
c) J = E / R + δr
d) I = D / R + δr
View Answer
Explanation: The resistance of circuit will be varying according to pressure (r = R0 + δr) thus, the instantaneous current through the load resistor will be denoted by equation.
I = E / R + δr
13. Which of the following microphone has the lowest cost in compare to other microphones?
a) Cardioid
b) Capacitor
c) Electret
d) Carbon
View Answer
Explanation: A carbon microphone has the transducer which converts sound to electrical audio signal. As carbon microphone has the limited frequency range and small dimensions it has the lowest cost among all the microphones. Thus, carbon microphone is the cheapest among all the microphones.
14. Which of the following microphones is used only in telephones?
a) Moving coil
b) Ribbon
c) Carbon
d) Electret
View Answer
Explanation: The carbon microphone is mechanically very strong and rigid. It also has small dimensions. As the cost of microphone is lowest and due to limited frequency range, it is useful only in telephones. It is also sometimes used in portable radio communication sets.
15. What is the distortion in carbon microphone?
a) 5%
b) 1%
c) 500%
d) 10%
View Answer
Explanation: A carbon microphone has the transducer which converts sound to electrical audio signal. The distortion in the carbon microphone is highest among all the other microphones which is 10% because its dimensions are small and is mechanically very strong and rigid.
16. What is the sensitivity for capacitor microphone?
a) 3 × 103μV
b) 100 × 103μV
c) 5 × 103μV
d) 20 × 103μV
View Answer
Explanation: When the capacitance of the capacitor changes, the charge on the capacitor tends to remain the same and force voltage change in according to the equation. V = Q / C. It is sensitive to temperature and moisture which cause leakage of charge. Thus, the sensitivity of capacitor microphone is given as 3 × 103μV.
Sanfoundry Global Education & Learning Series – Audio Engineering.
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