This is the Coaching materials in Acoustics Part 1 as one topic in ECE Board Exam taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies (EST), Communications Books, Journals and other Communications References. This particular Coaching Notes in Communications Engineering has random Questions and Answers in random topics. Make sure to familiarize this review notes to increase the chance of passing the ECE Board Exam.
Acoustics Coaching Materials Part 1
1. A vibration in an elastic medium to which the sense of hearing is responsive.
Sound
2. Pertaining to signals, equipment or devices that involve frequencies within the human hearing range.
Audio
3. Method of expressing amplitude of complex non-periodic signal such as speech.
Volume
4. In measuring intelligibility of sound, the number of recorded syllables as a percentage of number transmitted is termed as the
articulation efficiency
5. Generally used as the measure of the amplitude of the sound wave.
Sound pressure
6. A simple sound whose instantaneous waveform is that of a sine wave.
Pure tone
7. Sound reduction index is also called
transmission loss
8. Ability of sound to inhibit the perception of another sound
Masking
9. If the pressure component of the sound wave is in the form of a sine wave, its associated velocity component would take a
cosine wave
10. In acoustics, the amplitude of the pressure component is a function of the ______ of the medium.
young’s modulus
11. In acoustics, the volume velocity of the component is a function of the _____ of the material.
Density
12. Complex number equal to the ratio of complex pressure amplitude to the complex amplitude of the volume velocity
acoustic impedance
13. Acoustic energy flowing per unit area and per unit time
acoustic intensity
14. What is the approximate acoustic impedance for a wave in air at 20deg Celsius?
416kg/m2s
15. What is the speed of sound in water having a density of 1000 kg/m^3 and a Young’s modulus of 2.3x10^9N/m^2
1517m/s
16. Calculate the wavelength of sound wave in sea water whose frequency is 100 kHz at 25 degrees C?
1.52cm
17. If the wavelength of sound is 3.5cm in sea water, calculate its frequency. 43kHz
18. What is the speed of sound in air at 25deg C?
347m/s
19. The velocity of sound in dry air medium is 331.45 m/s. Calculate the new velocity if there is an increase of temperature equal to 10 degrees centigrade.
337.52 m/s
20. Speed of sound is 1000ft/s, what frequency has a wavelength of 24 inches?
500 Hz.
21. What do you call of the several sound sources which are related to each other?
Correlated sound sources
22. If several sounds come from several unrelated sources, the sources are called
uncorrelated sound sources
23. If sounds are produced from three loudspeakers which are driven from a single source (i.e. amplifier), the speakers are considered as
correlated sound source
24. Sound sources that are coming from different instruments are called
uncorrelated
25. If a sound receiver receives two sound waves, one directly from the source and the other from simple reflection (with short delay), the sound waves are considered as
correlated
26. If a sound receiver receives two sound waves, one directly from the source and the other from a long relay deflection, the sound waves are considered
uncorrelated
27. The sound at a particular point consist of a direct wave and a reflection with the same amplitude (P) but has been delayed by 1 ms. If the sound frequency is 1kHz, calculate the pressure amplitude in terms of P at this point.
2P
28. Calculate the total signal pressure level when two vocalists sing at the same pressure level of 1x10^-3 Pa each.
1.41x10^-3 Pa.
29. Frequency range of audible signal is
30. 20Hz-20kHz.
31. What is the normal audible range of the human ear?
20 Hz to 20kHz.
32. Audible sound that can be detected by human ear ranges from
16Hz to 16kHz.
33. Very low frequency or very low amplitude sounds.
Subaudible
34. Very high frequency sounds or very high amplitude sounds
Superaudible
35. Signals having frequencies below the range of human hearing
Infrasonic
36. Signals with frequencies above the range of human hearing
Ultrasonic
37. The wavelength of a 20 Hz sound propagating in air at 25 degC is
17.4m
38. The increase in level for uncorrelated sound sources of equal amplitudes is proportional to the
square root of the number of sound sources, 
39. The sound intensity is
inversely proportional to the square of the distance.
40. As sound propagates from the source, its intensity follows an
inverse square law.
41. Measure of sound intensity in comparison to another sound intensity.
Decibel*
42. A measure of the power density of a sound wave propagating in a particular direction
SIL
43. Is a measure of the total power radiated in all directions by a source of sound.
SWL
44. It is also known as sound power level.
PWL
45. Acoustic impedance is _____ the sound pressure.
directly proportional to the square of
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