Term
What are the 2 properties a source must have to vibrate? 

Definition
mass (m) and elasticity (E) 


Term

Definition
– The amount of matter present
– Applies to gases (**AIR**), liquids, & solids
– Air has both mass and weight



Term

Definition
Weight is a gravitational force
Weight is a force



Term

Definition
 Property that enables recovery from distortion of shape or volume (e.g. pinching skin)
– Air – the tendency of air volume to return to its former volume after compression (e.g., syringe) 


Term

Definition
All bodies remain at rest or in a state of uniform motion unless another force acts in opposition
• Magnitude of inertia is directly proportional to the mass 


Term

Definition
With every force there must be an equal and opposite reaction force
– Hammer & nail, bat & ball
– Force cannot exist by itself



Term

Definition
– elasticity is the reaction force to inertia
– Vibration sustained by opposing forces (i.e., inertia)
– For a period of time vibration continues without reapplication of external force 


Term

Definition
• When the density of air increases we call that compression
• When the density of air decreases we call that rarefaction
• So, when a sound travels through air there will be alternate regions of compression and rarefaction
• The medium of air is not displaced over a great distance
• The wave of disturbance moves through the medium 


Term

Definition
characterized by propagation of density changes through an elastic medium
• When we talk about sound we need to consider specific physical quantities such as:
– Mass
– Density
– Force
– Pressure
– Displacement 


Term

Definition
• There are three basic physical quantities
– Length
– Mass
– Time
• All other physical quantities are derived
– Displacement
– Velocity
– Acceleration
– Force
– Pressure
• Metric: MKS & cgs
– MKS
• Length (m)
• Mass (kg)
• Time (s)
– cgs
• Length (cm)
• Mass (g)
• Time (s)
• English: fps
– Length (ft)
– Mass (lb)
– Time (s) 


Term

Definition
• A measure of distance: the amount of spatial separation between two points
– How many times a unit (m, cm, ft) is contained in a given distance 


Term

Definition
• The quantity of matter present
• Defines the magnitude of inertia
• Inertia is proportional to mass
• MKS – kilogram (kg)
• cgs – gram (g)
• fps – pound (lb)
• The quantity of mass defines the amount of inertia 


Term

Definition
• A quantity expressed in seconds (s), minutes (min), hours (hrs), etc.
• Units of measure:
– MKS – second (s)
– cgs – gram (s)
– fps – pound (s) 


Term

Definition
• A change in position
• A vector quantity: incorporates both magnitude and direction 


Term

Definition
– The amount of displacement per unit time, OR
– The time‐rate of displacement
– Also a vector quantity
– Average velocity
• c = derived displacement (x)/time (t)
• Speed is a scalar quantity (i.e., only magnitude)
• s = d/t
Displacement per unit time
• MKS – m/s
• cgs – cm/s
• fps – ft/s, mph, etc. 


Term

Definition
• The time‐rate change in velocity
• A vector quantity
• Positive vs. negative acceleration (deceleration)
• a = Δc/t = (c2‐c1)/t 


Term

Definition
• A push or a pull
• The product of mass (m) and acceleration (a)
• F = ma
• Object has mass (inertia), which opposes change in motion: force is applied to overcome inertia
• Consequences of force
– Distortion of matter, and/or
– Acceleration of matter
Units of Measure:
• MKS – newton (N)
– Force required to accelerate a mass of 1 kg from c = 0 m/s to c = 1 m/s in 1 s
• cgs – dyne
– Force required to accelerate mass of 1 g from c = 0 cm/s to c = 1 cm/s in 1 s
• 1 N = 100,000 dynes 


Term

Definition
Pressure is a force exerted over an hour on the surface of an object
Pressure decreases as the area over which a force is applied increases.
• Force per unit area
• p = F/A
• p = 1 N/ 100 m2 = 0.01 N/m2 Units of Measure
• 1 N = 100,000 dynes
• 1m = 100 cm
• Thus, 1 N/m2 = 100,000 dynes/m2 (m X m) 1 N/m2 = 100,000 dynes/10,000 cm2 (100 cm X 100 cm)
• Thus, 1 N/m2 = 10 dynes/cm2
The Pascal (Pa)
• 1 Pascal (Pa) = 1 N/m2 or 10 dynes/cm2 


Term

Definition
• Sound energy is transferred through a medium at some rate
• POWER: the rate at which energy is transferred; Energy transferred per unit time
• ENERGY: the capacity to do work, whereas POWER is the rate at which energy is expressed The WATT – 1 WATT = 1 joule/s (MKS): 


Term

Definition
• Intensity: Energy per second per square meter
• Units of Measure
– Intensity: watt/m2
• Absolute: The intensity is 3.15 X10‐2 watt/m2
• Relative: Level = Ix/Ir
• For each value of Ix, the ratio Ix/Ir (the level) depends on the value of Ir 


Term

Definition


Term
10fold change in Ix?
10^{10} to 10^{9} 

Definition


Term
2fold change in Ix?
2x10^{6} to 4x10^{6} 

Definition


Term

Definition
the reference intensity must always be specified
Ir = 10^{12} watts/m^{2} 


Term
Four Scales of Measurement 

Definition
• Nominal
• Ordinal
• Interval
• Ratio 


Term

Definition
• Objects are the same or different
• The letter A is different from the letter B
• The numeral (or a symbol that labels something) 1 is different from the numeral 0 


Term

Definition
• Two things are the same or different and,
• One object has more or less of some quantity than another
• Letters are not numbers: cannot be added
• Numerals are not numbers either: can’t be added
• E.g., doctor using a scale of 0‐10 to indicate degree of improvement in some condition(0 no improvement) and (10 disappearance of the condition) 


Term

Definition
• Size of the interval between adjacent numbers is known and is constant
• The size of the interval is called the BASE
• Successive units are formed by adding (or subtracting) base to each number
• Because the base is known we can say that one object is a certain number of intervals more or less than another 


Term

Definition
• One unit on the scale is so many times greater or less than another
• Successive units are formed by multiplying (or dividing) each number by the BASE
• Successive units differ by a constant ratio, which is the BASE
• The numbers on the scale differ by a constant ratio, and
• They can be expressed as the base, 2 in the previous example, raised to progressively higher powers 


Term

Definition
• 1. Law 1: (X^{a})(X^{b}) = X^{a+b}
• 2. Law 2: X^{a}/X^{b}= X^{ab}
• 3. Law 3: (X^{a})^{b}= X^{ab}



Term

Definition
• 1. Law 1: Log ab = Log a + Log b
• 2. Law 2: Log a/b = Log a – Log b
• 3. Law 3: Log a^{b} = b Log a
• 4. Law 4: Log 1/a = ‐ Log a 


Term

Definition
• Pressure is force/unit area
• Unit of measure (MKS):
N/m2
Pa, where 1 Pa = 1 N/m2
μPa, where 1 μPa = 1 μN/m2
To derive an appropriate equation, we consider intensity and pressure in relation to impedance of the medium.
• I is proportional p^{2}
• OR, p √I (the square root of I)
• dB IL: Ir = 10^{12} watt/m^{2}
• An intensity of 10^{12} watt/m^{2} creates a pressure in air of 20 (2 X 10^{1})µPa
• Therefore, for dB SPL, the reference pressure, pr, is 20 µPa
• pr is 2 X 10^{1}µPa
dB SPL = 20 log (px/pr) 


Term
2fold change in px?
2x10^{5} to 4x10^{5} 

Definition


Term

Definition


Term
Combining Sound Intensities from Independent Sources
Equal Source Intensities 

Definition
• dB_{N} = dB_{i} + 10 log_{10}N_{, }
i = dB SPL (or dB IL) from one source
N = # of sources combined 


Term
Combining Sound Intensities from Independent Sources
Unequal Source Intensities 

Definition
• Three steps in solution
1. Calculate intensity from each source
2. Add intensities (carefully)
3. Calculate decibels
• One source = 80 dB SPL, and a second source = 83 dB SPL
• dB = 80 Ix = 1 X 10^{4}
• dB = 83 Ix = 2 X 10^{4}
• Sum of Ix = 3 X 10^{4}
• dB = 10 log (3 X 10^{4} /10^{12})
= 10 log (3 X 10^{8})
= 84.8 dB IL (dB SPL) 


Term

Definition
Sound Source >Medium>Receiver



Term

Definition


Term

Definition
Building blocks of all sound 


Term
Characteristics of a Sine Wave 

Definition
• Frequency/Period
• Phase
• Amplitude
• (wavelength)



Term

Definition
– How quickly a sine wave
repeats itself
– Number of cycles
completed in 1 sec
– Unit: Hertz
f = 1 / T
(f = 1 / Pr)



Term

Definition
– How long it takes to complete 1 cycle. – Unit: sec, ms
T = 1 / f
(Pr = 1 / f)



Term

Definition
• sec vs. ms
milli = 1/1000
1 ms = 0.001 sec
1 sec = 1000 ms
• milli vs. micro
milli = 1/1000
micro = 1/1,000,000
• Hz vs kHz
kilo = 1000 times
1000 Hz = 1 kHz
2 kHz = 2000 Hz



Term

Definition
• Distance traveled during one period
• Equation:
λ = s / f
s = speed of sound
f = frequency
• Examples in air (s = 340 m/s)
f = 1100 Hz
• λ = 340/1100 = 0.3m
f = 550 Hz
• λ = 340/550 = 0.6m 


Term

Definition
• How big is the displacement, how far did the
vibrating object move?
• Types of amplitude:
Peak
Peak‐to‐Peak (2 x Peak)
RMS amplitude



Term

Definition
• How big is the displacement, how far did the vibrating object move? • Types of amplitude: Peak Peak‐to‐Peak (2 x Peak) RMS amplitude 


Term

Definition
• RMS = root‐mean‐square
1. square amplitudes
2. compute mean (average)
3. compute square root
• RMS = 0.707A
• Peak Amplitude = 1.414RMS 


Term

Definition
• Composed of more than one sine wave
• Harmonic complex
– All sine waves are integer multiples of the lowest frequency
– Terminology:
• f_{0}, f_{1}, f_{2}, f_{3}, f_{4}, etc. = harmonics
f_{0} and f_{1 }are the same
sound composed of sine waves at the following frequencies:
125, 250, 375, 500, 625, 750, 875, 1000 Hz
• Speech sounds may be harmonic complexes
Example: Vowel sound might consist of f0 = 200 Hz and 40 harmonics. 


Term
Complex Stimuli: Transients 

Definition
– Sounds with very short duration
– AKA click, tone burst, impulse
– Examples: hand clap, gun shot 


Term

Definition
– Amplitude varies randomly over time
– Example: White noise 


Term

Definition
– Amplitude variations as a function of time
– Temporal waveform
 time waveform
 xaxis is time 


Term
Frequency Domain of Stimuli 

Definition
– Amplitude variations as a function of frequency
– Spectral representation/amplitude spectra/power spectra
 xaxis is frequency



Term

Definition
takes a complex waveform and figures out all the individual sine waves that make it up 


Term

Definition
• Broadband or white noise
– All frequencies present
– Amplitudes distributed according to a Gaussian (standard bell curve) distribution
– Phase relationship of the components is random
– White noise = Gaussian noise
 white noise is aperiodic 


Term

Definition
• Noise that has more limited frequency content than white noise
• How do you create narrowband noise?
– Pass white noise through a filter
Characterizing Frequencies:
 what frequencies "pass
 cutoff frequency
 rejecction rate 


Term

Definition
Top: Low Pass, let low frequencies through
Top/Middle: High Pass, let high frequencies through
Bottom/Middle: Band Pass
Bottom: Band Reject 


Term
Overall Level/Total Power Measure for Noise 

Definition
• The sum of all the sinusoids present in the
noise



Term
Spectrum Level (N_{0}) Measure for Noise 

Definition
• Energy in any single component of noise must be less than the total power
• Spectrum level is the average power in 1‐Hz band of the noise
• N_{0} = spectrum level
• OAL = overall level of noise (total power) in dB
• BW = bandwidth of noise in Hz
• N_{0} = OAL – 10 log BW 

