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Transverse Waves
Molecular motion moves perpendicular to the direction of wave motion (waves in water)
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Longitudinal Wave
Molecular motion moves along the same axis as the wave motion.
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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)
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Vibrations
Free-
Forced-
- Free- vibration void of an outside force to perpetuate it's movement (pendulum)
- light dampening
- heavy dampening
- Forced- vibration set into motion by an outside force will remain unaltered until the outside force is removed (swing)
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Frequency
- 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)
- Effects of:
- Lenght- as length increases, frequency decreases
- Mass- as mass increases, frequency decreases
- Stiffness- as stiffness increases, frequency decreases
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Resonance
- 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.
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Sound Velocity
- Speed with which sound travels from the source to another point.
- Velocity of sound in air (20°C at Sea Level) is 344
- meters/second.
- Increased velocity=acceleration
- Decrease velocity=deceleration
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Wavelength
Wavelength is measured from any point on a wave to the same point on the next wave
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Phase
- 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.
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Complex Sounds
- 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
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Intensity
- 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
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The Decibel
- 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
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Decibel
- 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.
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Logarithms
- 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.
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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
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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.
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Hearing Level
- 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.
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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.
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