Skip to Content

Department of Linguistics

SPEECH ACOUSTICS

Basic Acoustics

Robert Mannell

Some Practice Questions

Don't forget to convert to standard units before calculating your answer

1) If the frequency (f) of a sine wave is 300 Hz, what is the period (T) of that wave?

2) If the period (T) of a wave is 100 msecs, what is its frequency?

3) If the period (T) of a wave is 50 msecs, what is its frequency?

4) If the frequency (f) of a sine wave is 1000 Hz, what is the period (T) of that wave?

5) If the frequency (f) of a sine wave is 63 Hz, what is the period (T) of that wave?

6) If the frequency (f) of a sine wave is 99 Hz, what is the period (T) of that wave?

7) If the frequency (f) of a sine wave is 1023 Hz, what is the period (T) of that wave?

8) If the period (T) of a wave is 3.1 msecs, what is its frequency?

9) If the period (T) of a wave is 0.01 msecs, what is its frequency?

10) If the period (T) of a wave is 10,000 msecs, what is its frequency?

11) If the period (T) of a wave is 10 secs, what is its frequency?

12) If the period (T) of a wave is 3 minutes, what is its frequency?

13) The frequency (f) of a wave is 120 Hz and the speed of sound is 330 ms-1. What is the period (T) and the wavelength ()?

14) The frequency (f) of a wave is 0.12 kHz and the speed of sound is 330 ms-1. What is the period (T) and the wavelength ()?

15) The wavelength () of a wave is 12 mm and the speed of sound is 330 ms-1. What is the period (T) and the frequency (f)?

16) The period (T) of a wave is 20 msec and the speed of sound is 330 ms-1. What is the frequency (f) and the wavelength ()?

17) On a piece of graph paper

  a. Draw a sine wave
    Amax = 25 µPa
    T = 100 msecs
  b. Draw a second sine wave on the same sheet
    Amax = 50 µPa
    T = 200 msecs
    In phase (0 phase) with the first sine wave
  c. Add the two waves together on the graph.

18) Do exactly as in 1) above, but the second sine wave must be 90° (/2 radians) out of phase with the first.

19) On a piece of graph paper

  a. Draw a sine wave
    Amax = 50 µPa
    T = 100 msecs
  b. Draw a second sine wave on the same sheet
    Amax = 50 µPa
    T = 100 msecs
    90° (/2 radians) out of phase with the first sine wave
 

c. Add the two waves together.

20) On a piece of graph paper

  a. Draw a sine wave
    Amax = 60 µPa
    T = 50 msecs
  b. Draw a second sine wave on the same sheet
    Amax = 60 µPa
    T = 50 msecs
    180° ( radians) out of phase with the first sine wave
  c. Add the two waves together.

21) If intensity (I) is 32 Wm-2 at 10 metres from the sound source what is the intensity at:-

  1. 20 m
  2. 30 m
  3. 100 m
  4. 5 m
  5. 7.3 m
  6. 11.6 m
  7. 22 km
  8. 10 mm

22) If pressure (P) is 60 µPa at 10 metres from the sound source what is the pressure at:-

  1. 20 m
  2. 30 m
  3. 100 m
  4. 5 m
  5. 7.3 m
  6. 11.6 m
  7. 22 km
  8. 10 mm

23) Determine the R.M.S. average of the following pressures (µPa).

4, -3, -2, 0, 1, 3, 5, 2, -2

24) What is the value in dB of the ratio of pressure P1=500 µPa relative to pressure P2=50µPa?

25) Determine the dB (IL) value of the following intensities relative to the standard intensity (I0 = 10-12 Wm-2)

  1. 10-8 Wm-2
  2. 10-11 Wm-2
  3. 2 x 10-12 Wm-2
  4. 1 Wm-2
  5. 3 x 10-6 Wm-2

26) Determine the dB (spl) value of the following pressures relative to the standard pressure (P0 = 20µPa)

  1. 50 µPa
  2. 0.00005 µPa
  3. 0.00005 Newton.m-2
  4. 50 Pa
  5. 33 µPa

27) Determine the dB (SPL) value of the resultant sound when the following pairs of sounds are added together.

  1. 20 dB (SPL) + 20 dB (SPL)
  2. 20 dB (SPL) + 25 dB (SPL)
  3. 5 dB (SPL) + 100 dB (SPL)

28) A sound has an amplitude of 50 dB

What would be the resultant dB of the sound if:-

  1. the intensity is halved
  2. the pressure is doubled
  3. the intensity is multiplied by 5
  4. the pressure is divided by 3

Answers to the Practice Questions

Attempt each question before you refer to these answers!

1. 0.00333 s (3.33 msecs)

2. 10 Hz

3. 20 Hz

4. 0.001 s (1 msec)

5. 0.0159 s (15.9 msec)

6. 0.0101 s (10.1 msec)

7. 0.000978 s (0.978 msec)

8. 322.6 Hz

9. 100,000 Hz (100 kHz)

10. 0.1 Hz

11. 0.1 Hz

12. 0.00556 Hz

13. 0.0083 s; 2.75 m

14. 0.0083 s; 2.75 m

15. 3.64 x 10-5 s; 27,500 Hz

16. 50 Hz; 6.6 m

17. -

18. -

19. -

20. -

21. 8, 3.56, 0.32, 128, 60.05, 23.78, 6.61 x 10-6, 3.2 x 107 Wm-2

22. 30, 20, 6, 120, 82.2, 51.7, 0.027, 6 x 104 µPa

23. 2.828 µPa

24. 20 dB

25. 40, 10, 3, 120, 65 dB

26. 7.96, -112, 7.96, 128, 4.35 dB

27. 23, 26.2, 100 dB

28. 47, 56, 57, 40.5 dB