Molecular motion moves perpendicular to the direction of wave motion (waves in water)
Molecular motion moves along the same axis as the wave motion.
Sine and Sinusoidal Wave
Sine waves: a wave that begins it's cylce of oscillaion at one point and ends it's cycle at the same exact point on the next wave
Sinusoidal Waves: puretone (showing only one frequency with no tones superimposed)
Free- vibration void of an outside force to perpetuate it's movement (pendulum)
Forced- vibration set into motion by an outside force will remain unaltered until the outside force is removed (swing)
Frequency refers to the amount of time it takes to complete one cylce per second (CPS) in acoustics this measurement is known as Hertz (Hz)
Lenght- as length increases, frequency decreases
Mass- as mass increases, frequency decreases
Stiffness- as stiffness increases, frequency decreases
The vibration of an object at certain frequencies
A resonant frequency is a natural frequency of vibration determined by the physical parameters of the vibrating object.
Speed with which sound travels from the source to another point.
Velocity of sound in air (20°C at Sea Level) is 344
Wavelength is measured from any point on a wave to the same point on the next wave
If a tone has an oscillation that begins at 0 (or 360) it is said to be in phase with the standard.
Interference-whenever more than one tone is introduced there is an interaction among sound waves.
Two tones with the same frequency and phase will amplify each other.
Two tones with identical frequency but 180 out of phase will cancel each other out.
Complete reinforcement and cancelation rarely happen outside of the laboratory
Beats-when two tones of almost identical frequency are presented there will be an increase and decrease in the resulting sound intensity, this change in amplitude is perceived in beats.
Complex sounds are the product of two or more sinusoidal waves combined.
Complex waves can be analyzed in terms of its sinusoidal components.
Periodic sounds-sounds that repeat over time (speech & music), fundamental frequency: the lowest rate of a sounds vibration.
Aperiodic sounds-random sounds, no fundamental frequency, percieved as noise
The intensity of a vibration, or how far the vibration moves depends on:
Force- the greater the force, the greater the displacement, therefore the greater the amplitude.
Very small amounts of force are required to stimulate hearing
Pressure- is generated whenever force is distributed over a surface area
Five Important Aspects to Know:
1.It involves a ratio
2.It utilizes a logarithm
3.It is nonlinear
4.It is expressed in terms of reference levels (must be specified)
5.Is a relative unit of measurement
The decibel (dB) is the unit used to measure sound.
The decibel scale expresses a ratio between two sound pressures, you can't add and subtract them making the decibel nonlinear.
Your ears can hear everything from a feather brushing lightly on paper to a jet place engine.
In terms of power, the sound of the jet engine is about 1,000,000,000,000 times more powerful than the smalles audible sound.
Therfore, the decibel scale is a logarithmic scale because the human ear is increadibly sensitive.
A logarithm is a number expressed as an exponent that tells how often a number is multiplied by itself.
On the decibel scale, the smalles audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB.
Intensity Level (IL)
Intensity Level is occasionally used to express the decibel with an intensity reference
IL is not a common unit of reference in audiology
Sound Pressure Level
Sound pressure level (SPL) used to express the decibel with a pressure reference.
Audiologists and acousticians more commonly measure sound in terms of pressure rather than intensity.
Sound Pressure Level is part of a standard system of how we express the pressure of a sound.
Hearing Level (HL) was developed out of studies that carefully measured the hearing of young adults.
These studies were conducted to determine threshold levels that would equal 0dBHL.
The lowest sound intensity that stimulated normal hearing is called 0dBHL.
HL became a conversion of SPL at certain frequencies.
Sensation Level (SL)
Sensation Level (SL) is the number of decibels of a sound above an individuals threshold.
If, at 1000 Hz you have a 5 dB threshold, and you are presented with that tone at 50dBHL, you can label this 45dBSL.