Acoustics Review Flashcards
What is acoustics?
Science of sound
What’s the key to being a sound source?
Having the ability to vibrate
What must an object have to vibrate?
Mass & elasticity
What is pressure dependent on?
The amount of force and the area its being applied to
What’s the formula for pressure?
P= F/A
What are the 2 types of wave motion?
Transverse & Longitudinal
What is a transverse wave?
Vibration of particles is 90degress from direction of wave movement
What is a longitudinal wave?
Vibration of particles is parallel to direction of wave movement
Which wave is a sound wave?
Longitudinal
What does longitudinal waves consist of?
Condensation & Refraction
What is condensation?
Molecules are packed closely
There’s high pressure (+1)
What is rarefaction?
Molecules pull away and due to elasticity and inertia it moves it past the molecule’s original point
-1
What is a sine wave?
A pure tone sound wave that moves through a medium
How is a wavelength measured?
It’s measured from any point on a sinusoid to same point on the next cycle of wave
What is the formula of a wavelength?
W = v/f
What happens as frequency increases?
Wavelength decreases
A short wavelength has what type of frequency?
High
A long wavelength has what type of frequency?
Low
Frequency is perceived as…
Pitch
Another way to identify frequency is…
By how many cycles occur over time
What is the formula for frequency?
F = 1/t
What is a period?
It’s the time to complete one cycle
Period is the..
Inverse of frequency
What is the formula for period?
T = 1/f
How does frequency effect mass?
Greater mass = lower frequency
How does frequency effect length?
Short length = higher frequency
How does frequency effect stiffness?
More compliant = lower frequency
More stiff = higher frequency
What is amplitude?
The distance the mass moves from the point of rest
Amplitude is perceived as…
Loudness
What is a complex sound?
It has a # of different frequencies and amplitudes
What is fundamental frequency?
The lowest rate of a sound’s vibration
What are periodic sounds?
A complex sound that repeats over time
What is an aperiodic sound?
Complex sound that does not repeat over time.
Complex sounds consist of…
Periodic & Aperiodic sounds
What is a decibel?
It measures amplitude (pressure) or intensity(energy) of sound
What do we use decibels for?
The logarithmic scale. It compares an observed value to a standard or reference value
What is the standard reference?
Intensity = 10^-12 w/m^2
What is the effective standard reference?
0 dB
Is sound present @ 0dB?
Yes, because there’s measured intensity or pressure
What is Observed Level?
Level of intensity or pressure that is measure or observed when a sound is present
For the observed level, what is being compared?
The value is compared to the reference level to get the decibel
What does a positive decibel mean?
There was MORE intense/higher pressure (Louder) than reference
What does a negative decibel mean?
There was LESS intense/lower pressure (Softer) than reference
What does a 0-value mean?
Means observed level is equal to reference
What is the pressure @ the reference level?
Pressure = 20 micro Pascals
What is the Intensity Level formula?
db(IL) = 10 x log (Io/Ir)
What is the Sound-Pressure Level (SPL) formula?
db(SPL) = 20 x log (Po/Pr)
Is Hearing Level the same as SPL?
No
What is Hearing Level?
It’s a normative reference and is used for audiological purposes
For Hearing Level, since the human ear has different sensitivity at different frequencies, what occurs?
The different amounts of pressure (SPL) equate to 0HL @ each frequency
Define Threshold
It’s the softest level at which a tone can be perceived 50% of the time
Define Sensation Level
of decibels a sound is above individual threshold
What’s the formula for dB SL for finding threshold?
db SL = dbHL of presented sound - dB HL threshold
Define psychoacoustics
It’s the study of relationship between physical stimuli (wavelength, amplitude) and the psychological response to the stimuli
When it comes to pitch, what does it deal with?
Highness vs Lowness
What is the human range of hearing?
20-20,000Hz
When it comes to loudness, what does it deal with?
Soft vs Loud
What does loudness relate to?
Intensity/Pressure
What is the relationship between our ears and frequency?
It is not equally sensitive to all frequencies
Define localization
It’s the ability to tell which direction a sound is coming from
For localization to occur, what must it interact with?
Our ears, time, & intensity
Define reverberation
It’s a reflected sound wave and incident sound waves interacting
What does reverberation cause?
It causes sound to be perceived as coming from a direction other than its source
What type of setting does not cause reverberation to occur?
Free field & Anechoic Chamber
What is another name for a sound wave?
Incident wave
What occurs once an incident wave is generated?
- Transmission wave
- Absorption wave
- Reflection wave
What is a transmission wave?
A sound wave traveling through air w/o obstruction
What is an absorption wave?
Energy of sound wave is decreased (damped) due to friction from obstructing materials
What is a reflection wave?
An energy of a sound wave hits an obstruction and bounces back
What type of surface does a reflection wave bounce of?
A harder surface
What does the reflected sound wave do to our ears?
The reflected sound waves reach our ear slightly after the incident wave and this prolongs the sound
How can reverberation affect communication?
It can cause speech sounds to overlap and blend together
What is an echo?
A verrrrrrrrrrrrrrrrrrrrrrrrrrrrrry long delay when one hears two separate distinct sounds
Define impedance
It’s a resistance to the transmission of acoustic energy
What type of material causes more impedance?
Denser material
Define masking
Two sounds being heard at the same time because of a change in threshold of sound A due to the introduction of sound B
Which sound is the masker?
Sound B
How does sound A become inaudible?
By sound B
What two types of sound measurements are audiologist interested in?
- Hearing ability in patients (dB HL)
2. Sound pressure levels in the environment (dB SPL)
What is an audiometer?
Determines hearing sensitivity and to complete supra threshold testing
What does supra mean?
Testing above the threshold (aka Sensation Threshold)
What does an audiometer generate?
Pure tones of different frequencies from 125-12000 Hz
What does the audiometer typically test?
From 250-8000 Hz
On the audiometer, what else can be presented besides a pure tone?
- Mic/live voice
- CD/tape
- Noise
- Warble/Pulsed tone
What are transducers?
It’s how sound from the audiometer gets into our ears
What are the transducers for Air Conduction?
- Supra-aural
- Circumaural
- Inserts
- Speakers
What is the transducer for Bone Conduction?
Bone Conduction oscillator (vibrator)
What is a sound level meter?
A device measuring what is perceived to the human ear
What is the sound-level meter important for?
Industrial settings & for background noise in testing situations
What is calibration?
Establishing the relationship between a measuring device and the units of measure
How can a calibration occur?
- Daily biologic/listening check
2. Yearly calibration
