Lecture 2: Noise and Sound

Question 1

Difference between sound and noise

Answer 1

Sound = something that can be heard.
Noise= sound when it’s unwanted, unpleasant or loud

Question 2

What is sound/noise? how does it emerge?

Answer 2

By increased and decreased air pressure differences like an oscillation. Air molecules move from constantly sand thus travel. Sound is produced by vibrating object that puts pressure of the molecule of the air. Vibrating object is moving the air molecules: compressing and uncompressing it. –> wave.

Question 3

What is oscillation?

Answer 3

Repetitive movement around some equilibrium
* Equilibrium position = when you don’t put any force to the thing. It doesn’t move.
* When you hit it, it gets further from the equilibrium position
Amplitude = how far the pendulum gets from the equilibrium. Max displacement from the equilibrium position in an oscillation.

Question 4

What is amplitude and what do large and small amplitudes lead to?

Answer 4

Amplitude = maximum displacement from the equilibirum position in an oscillation. Basically: strength of sound that leads to loudness
Large amplitude: loud sound
Small amplitude = quiet sound

Question 5

What is a period?

Answer 5

Time for a complete oscillation

Question 6

What is a wavelength?

Answer 6

The peak-to-peak distance on a wave measured at a single time - like in a snapshot

Question 7

What is frequency?

Answer 7

Number of completed cycles in one second = F (in hertz/Hz)

Question 8

Low frequency leads to high pitched sounds. High frequencies lead to low pitched sounds

Are these statements true?

Answer 8

Both are false. Low frequency equals low pitch. High frequency equals high pitch.

Question 9

What does the wavelength depend on?

Answer 9

SPeed of sound and frequency.

Question 10

How is intensity measured?

Answer 10

power (w in watt) / area (m2). Intensity of radiant energy is power transferred per unit area.

Question 11

What is the difference between a line source and a point source?

Answer 11

Noise level decreases stronger with a distance for a point source than for a line source

Question 12

What is sound propagation?

Answer 12

Process by which sound waves travel through a medium, typically air. Perfect propagation = when sounds are perfectly received. Never happens cause its always reflected by something

Question 13

Absorption with sound?

Answer 13

Sound waves disappear in the material.

Question 14

How does reflection of noise emerge?

Answer 14

If a room is completely empty. We only have reflection. There are no objects that hinder the sound waves.

Question 15

How do Intensity and pressure relate to each other?

Answer 15

Power is produced at the source. Not about energy, but it’s purely about the source. Energy does not change when we move further. Balloon/honey: expansion is similar to expansion of sound source: Honey is reducing because it’s getting thinner. This is also the case with sound intensity. It changes as we get further from the sound source.

Question 16

Explain how sound and our perception of loudness does not increase linearly with the actual increase in sound intensity.

Answer 16

In many everyday situations, our perception of change is linear.
o 500 m, double is 1000 m
* When we hear something this is not the case. It’s logarithmic.

o If we double the level of noise, we don’t experience it as double. Ears are more sensitive to low intensity noises and less sensitive to louder ones.

 Because we want to cover a wider range of sounds. If we were sensitive to louder noises we would lose our ears basically.

Practical reasons with log 2 causes 50 + 50 dB to be 53 dB.

Question 17

What does deflection lead to?

Answer 17

With hot air you have faster sound speed. With cool air you have slower sound speed.