Topic 8.2 sound Flashcards
Describe how sound sensation is recieved
- Compressions = close molecules
- Rarefactions = sparse molecules
- When either strike ear drum = sound
Describe the different types of frequencies
- Above 20 kHz = ultrasonic
- Below 20 kHz = infrasonic
How can speed of sound be predicted?
c = √ bulk modulus / density
Describe speed of sounds
- 0C = 331
- 20C = 343
- Increases by 0.61m/s each 1C rise
What factors is speed of sound independant of?
- Pressure
- Frequency
- Wavelength
Define pure tone
- Sound wave = amplitude varies sinusoidally
Define pitch
- High/low sounds = determined by wave frequency
- Higher frequency = higher pitch
Define loudness
- Measure of human perception of sound
- Higher intensity = louder
- Sensation of sound proportional to log of sound intensity
What is the value of 0 on the intensity scale?
1x10-2 W/m2
Define decibel
- Dimensionless unit = represents relative magnitude of intensities
What are different values of intensity on the dB scale?
- Normal conversation = 60-70 dB
- Speech = 70-80 dB
- Pain threshold = 120 dB
- Window break = 163 dB
Describe the vocal organs function in creating sound
- Cavities in mouth + nasal + pharynx = vocal tract
- Changes in shape = produce different sound
- To create sound = energy source needed = using air from lungs as exhaling
- Air vibrations = produced in larynx = vocal cords = band of muscular tissue
- Space between vocal cords = glottis
Describe the outer ear
- Function = catch sound waves
- Pinna has curves = catch sound + determine direction
- Guided to middle ear via ear canal until reaches eardrum
Describe middle ear
- Function = magnify sound pressure
- Ossicles = small bones suspended by ligaments
- Connected to oral cavity via eustachian tube
- Malleus attached to ear drum > incus > stapes
- Stapes attached to oval window = causes ossicle movent to move fluid in cochlea
Describe inner ear
- Cochlea = coiled up bone = filled with fluid
- It is divided = 2 halves via membrane = membrane turn waves > signals
- Cochlea does spectral analysis = stimulus split into frequency bands = critical bands
Describe 4 steps of hearing
1) Sound wave enter outer ear
2) Movement of tympanic membrane = transfer conduction via ossicles > oval window
3) Movement of oval window = compressional wave in cochlea fluid
4) Wave move membrane = primary auditory receptors = electrical signals generated = sent to brain
What is the normal auditory sensitivity?
- 20 Hz - 20kHz
- Ear most sensitive between 100-4000Hz
What levels of sound are harmful?
- Above 85 = harmful
- Pain threshold = 120
- Above 150 = physical damage
- 190-198 = eardrums rupture
- Around 200 can cause death in humans
Define doppler effect
- Apparent shift in frequency of sound when source + observer are in relative motion
