# Coaching Materials in Acoustics Part 1 for ECE Board Exam

Compiled coaching materials in Acoustics Part 1 as one topic in ECE Board Exam taken from different sources including but not limited to Communications books, past Board Exams Questions, Journals and the Internet.

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

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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