# Department of Linguistics

## SPEECH ACOUSTICS

## Basic Acoustics

## 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 | ||

A_{max} = 25 µPa |
||

T = 100 msecs | ||

b. Draw a second sine wave on the same sheet | ||

A_{max} = 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 | ||

A_{max} = 50 µPa |
||

T = 100 msecs | ||

b. Draw a second sine wave on the same sheet | ||

A_{max} = 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 | ||

A_{max} = 60 µPa |
||

T = 50 msecs | ||

b. Draw a second sine wave on the same sheet | ||

A_{max} = 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:-

- 20 m
- 30 m
- 100 m
- 5 m
- 7.3 m
- 11.6 m
- 22 km
- 10 mm

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

- 20 m
- 30 m
- 100 m
- 5 m
- 7.3 m
- 11.6 m
- 22 km
- 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 P_{1}=500 µPa
relative to pressure P_{2}=50µPa?

25) Determine the dB (IL) value of the following intensities relative to
the standard intensity (I_{0} = 10^{-12} Wm^{-2})

- 10
^{-8}Wm^{-2} - 10
^{-11}Wm^{-2} - 2 x 10
^{-12}Wm^{-2} - 1 Wm
^{-2} - 3 x 10
^{-6}Wm^{-2}

26) Determine the dB (spl) value of the following pressures relative to the
standard pressure (P_{0} = 20µPa)

- 50 µPa
- 0.00005 µPa
- 0.00005 Newton.m
^{-2} - 50 Pa
- 33 µPa

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

- 20 dB (SPL) + 20 dB (SPL)
- 20 dB (SPL) + 25 dB (SPL)
- 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:-

- the intensity is halved
- the pressure is doubled
- the intensity is multiplied by 5
- 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 10^{7}
Wm^{-2}

22. 30, 20, 6, 120, 82.2, 51.7, 0.027, 6 x 10^{4} 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