2 Basic Acoustic

Question 1

Why is the basics of the physics of Biomedical Acoustics important?

Answer 1

It is the backbone for an engineer in biomedical acoustics providing essential theoretical aspects needed for understanding clinical rehabilitation or diagnostics.

Question 2

What are the basic properties of moving bodies in the context of Basic Acoustics Physics?

Answer 2

Displacement (s), velocity (v), and acceleration (a) with equations v = v0 + at, v2 = v0^2 + 2as, and s = v0t + 1/2at^2.

Question 3

What is the unit of measurement for weight (m*g) and force?

Answer 3

Weight is measured in Newtons (N) and force is also measured in Newtons (N).

Question 4

What is the formula for force?

Answer 4

F = ma where F is force, m is mass, and a is acceleration.

Question 5

What is the formula for kinetic energy (Ekin)?

Answer 5

Ekin = 1/2 mv^2 where m is mass and v is velocity.

Question 6

What is the formula for potential energy (Epot)?

Answer 6

Epot = mgh where m is mass, g is the acceleration due to gravity, and h is height.

Question 7

What are the three elements of an electrical circuit?

Answer 7

The Voltage (U), the current (I), and the resistance (R).

Question 8

What is Ohm’s Law?

Answer 8

R = V/I where R is resistance, V is voltage, and I is current.

Question 9

What is Young’s Modulus?

Answer 9

Young’s Modulus is a mechanical property that measures the tensile stiffness of a solid material quantifying the relationship between tensile stress and axial strain.

Question 10

What does young’s modulus change to in 3D (since sound is used in 3D)?

Answer 10

Bulk modulus.

Compression force per unit area / decrease volume per unit area

Question 11

What is the unit of pressure in acoustics?

Answer 11

Pressure is measured in Pascals (Pa).

Question 12

What is the formula for pressure (P)?

Answer 12

P = F/A where F is force and A is surface area.

Question 13

What is the equation for the adiabatic process in acoustics?

Answer 13

An adiabatic process occurs without transferring heat or mass between the system and its surroundings.

Question 14

Define vibration in the context of motion.

Answer 14

A vibration is when a point of motion always returns to the starting point with the motion being random in any direction.

Question 15

What is oscillation?

Answer 15

Oscillation is when a point goes in one direction, returns to the starting point, and then goes in the opposite direction, repeating the process.

Question 16

What is a sine wave?

Answer 16

A sine wave is a mathematical curve that describes a smooth periodic oscillation and is the graph of the function sine.

Question 17

What variables are associated with sinusoidal motion?

Answer 17

Amplitude (A), frequency (f), angular frequency (2πf), and phase.

Question 18

How are different sine waves perceived by humans?

Answer 18

The sine wave of less frequency is perceived as softer than the sine wave of high frequency.

Question 19

What is the solution for the differential equation for sine waves?

Answer 19

The solution for the differential equation for sine waves is of the form: y(t) = A sin(ωt + φ) where A is the amplitude, ω is the angular frequency, and φ is the phase constant.

Question 20

What is underdamping?

Answer 20

Underdamping refers to a condition in an oscillatory system when the damping equals 0. The system will oscillate forever without any change in amplitude.

Question 21

What is normal damping?

Answer 21

Normal damping refers to the condition in a vibrating system where the damping force is proportional to the velocity of the vibrating object resulting in a gradual reduction of the amplitude of oscillation over time without causing a significant delay or overshoot in the response.

Question 22

What is overdamping?

Answer 22

Overdamping is a phenomenon in mechanical and electrical systems where the damping force is so strong that it prevents the system from oscillating, allowing it to return to equilibrium slowly without overshooting.

Question 23

What does the quality factor (Q factor) represent?

Answer 23

The Q factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is, defined as the ratio of a resonator’s center (peak) frequency to its bandwidth (the frequency at 1/sqrt(2) of the peak value).

Question 24

What is a longitudinal wave?

Answer 24

Longitudinal waves are waves in which the particle displacement is in the same direction as or the opposite direction to the direction of wave propagation (parallel).

Sound in air is a typical example of a longitudinal wave

Question 25

What is a transverse wave?

Answer 25

A transverse wave is a type of wave in which the oscillations occur perpendicular to the direction of the wave’s travel.

Question 26

What is sound pressure?

Answer 26

Sound pressure is the local pressure deviation from the ambient atmospheric pressure caused by a sound wave.

Question 27

What is the formula for sound intensity (I)?

Answer 27

I = W/A where W is power and A is the area.

Question 28

What is the formula for the speed of sound in air?

Answer 28

c = √(RT) where R is the specific gas constant and T is the temperature.

Question 29

What is the difference between atmospheric pressure and sound pressure?

Answer 29

Atmospheric pressure is caused by the gravitational attraction of the planet on the atmospheric gases and changes slowly, while sound pressure is a local deviation caused by sound waves with low amplitude and fast oscillations.

Question 30

What is the characteristic amplitude of sound pressure?

Answer 30

Often 1 Pascal (1 Pa) and fast oscillations.
1 Pa = 94 dB

1 Pa = 94 dB.

Question 31

What is the significance of diffraction in sound?

Answer 31

Diffraction allows sound waves to bend around obstacles, enabling sound to be heard even when the source is not directly facing the listener.

Question 32

What is the relationship between temperature and the speed of sound?

Answer 32

The speed of sound increases with temperature; it is typically faster at lower altitudes and slower at high altitudes.

Speed of sound only depends on the temperature NOT the pressure

Question 33

Define reverberation time.

Answer 33

Reverberation time is the time required for reverberant sound to decrease by 60 dB.

Question 34

What is the equation for standing waves in relation to length (L)?

Answer 34

f0 = 1/2L where f0 is the fundamental frequency and L is the length.

Question 35

What is the formula for sound intensity in relation to pressure?

Answer 35

I = P^2/(ρc) where P is sound pressure, ρ is the density, and c is the speed of sound.

Question 36

How is the sound intensity of a source described at short distances?

Answer 36

As a sphere wave which is attenuated with distance.

Question 37

How is the sound intensity of a source described at longer distances?

Answer 37

At farther distances, the curvature of the sphere gets flatter such that sound can locally be described as a plane.

Question 38

Why does a person on top of a hill/mountain hear sound better than someone at the bottom if sound was coming from the bottom level?

Answer 38

At larger distance, sound is a plane wave. Therefore the top of the wave would move slower than the bottom (due to temp. difference). This diffraction makes the sound ‘bend’ upwards.

Question 39

How would the direction of the wind (in relation to the sound source) affect hearing?

Answer 39

When the wind increases (above the source) in the same direction the sound travels in, the top part speed up therefore bending the sound down

(opposite is true when the sound and wind are in different directions)

Question 40

What is sound called when it is received directly from the source?

Answer 40

Direct sound. The direct energy is the straight line energy from the sound source to the ear or a microphone.

Question 41

In room acoustics, if the receiver of a sound is further away, what has a major impact on the received sound?

Answer 41

The absorbance and reflection of the walls have a major impact on the received sound.

Question 42

At what frequency does diffraction in sound take place?

Answer 42

Around 1000Hz.

Question 43

What is head shadow in sound?

Answer 43

Head shadow refers to the phenomenon where the human head blocks sound waves, creating a difference in intensity and timing when sounds reach each ear. This effect helps in localizing the direction of sound.

This occurs at higher frequencies because the head/torso is larger than the wavelength of the sound