Basic Acoustics

Question 1

air pressure is

Answer 1

1000 Pa

Question 2

air pressure

Answer 2

1000 hPa

Question 3

is the speed of spreading sound the same as the speed of molecules themselves?

Answer 3

no

Question 4

speed of sound

Answer 4

340 m/c

Question 5

longitudinal wave

Answer 5

direction in which molecules oscillate is the same as the direction of the wave itself

Question 6

is sound a longitudinal or transverse wave

Answer 6

longitudinal

Question 7

transverse wave

Answer 7

direction in which molecules oscillate is perpendicular to the direction the wave is travelling

Question 8

microphone measures sound waves how?

Answer 8

transforms air pressure changes into electrical signals, which are then available for future processing

Question 9

how is a microphone made/set up

Answer 9

• a membrane stretched over a closed compartment
• back plate stable
• front plate mobile (diaphragm)
• sound wave forces membrane inward or outward dues to stable air pressure in the compartment
• the small movements of membrane generate small electrical signals
• thin light coil to make membrane move

Question 10

sounds journey though microphone

Answer 10

1) front plate
2) back plate
3) battery
4) output audio signal

Question 11

oscillogram

Answer 11

sound pressure (amplitude) is plotted vertically against a horizontal time axis

Question 12

frequency equation.

Answer 12

F(Hz)=1/T[s]

Question 13

speech frequencies typically between

Answer 13

80Hz - 10,000Hz

Question 14

wavelength calculation of a sound wave when given period

Answer 14

Distance d[m]= c[m/s] * time [s]

Question 15

Perceptually or acoustically does it make a difference what the phase difference is

Answer 15

it doesn’t make a difference what the phase difference is

Question 16

is amplitude relative in a digital enviroment

Answer 16

yes

Question 17

cosine wave is

Answer 17

sine +/- 90 degrees

Question 18

analog signal

Answer 18

continuous signal

Question 19

digital (time axis) signal

Answer 19

sampling

Question 20

digital (amplitude axis) signal

Answer 20

quantization

Question 21

nyquist theory

Answer 21

If you want to record speech (acoustic signals), then for technical reasons your sampling frequency has to be double the highest frequency you want to record

Question 22

Sound pressure level equation

Answer 22

SPL= 20* log10 p/p0

Question 23

2 main types of microphones

Answer 23

• electro(dynamic) microphone

- condensor micropone

Question 24

microphone capsule size

Answer 24

• big capsule (larger than half inch)

- small capsule (smaller than half inch)

Question 25

directivity of the recording fild

Answer 25

omnidirectional (collect all sound)

directional (only take sound from certain direction)

Question 26

types of directional microphones

Answer 26

cardioid

supercardioid