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60 Cards in this Set
- Front
- Back
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What is sound?
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Sound=wave disturbance that travels through any medium
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3 properties necessary to produce sound waves:
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Force, vibrating mass, and elastic medium. To have sound, there must not only be a VIBRATING “SOURCE” but also a VIBRATING “MEDIUM”. A SOUND SOURCE must have ELASTICITY AND INERTIA in order to vibrate and produce sound. Almost every object has inertia and elasticity and therefore almost every object can be set into vibration. • The FORCE on the object to make it move defines inertia.
• The ability of the object to return to a starting state after it is deformed or moved defines elasticity. If there is no elastic material - or elastic medium - there is no production or propagation of sound. |
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Explain vibrations
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VIBRATION is the movement of an object from one point in space to another point and usually back again to the original point. VIBRATING OBJECTS: have a sequence of COMPRESSIONS (sound particles squeeze together) and RAREFACTIONS (sound particles spread apart).
As the vibrator swings to the left and right, you get compressions with rarefactions between them. |
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Explain Forced/Free Vibration/Damping
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FREE VIBRATION: even though no specific frequency of vibration is imparted to the system during the initiation of the motion, the system vibrates at one specific frequency...its NATURAL FREQUENCY. It’s the frequency at which they vibrate BEST.
It is also a characteristic of a free vibrator to absorb sound energy best when the energy source has a frequency which is the same as the vibrator. FORCED VIBRATION: if just enough energy is supplied continuously to the vibrator to make up for the loss of energy through mechanical resistance (damping), then it is possible to maintain a constant amplitude of vibration over time. This is a forced vibration. DAMPING: the resistive forces that come upon a freely vibrating object; some degree of damping is inevitable. |
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Explain compression/rarefaction
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COMPRESSION (C) OR CONDENSATION: waves of greater than atmospheric pressure.
RAREFACTION (R): waves of less than atmospheric pressure. |
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Longitudinal versus Transverse Waves
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Transverse waves-molecular motion is perpendicular to the direction of wave motion. (Float bogging up and down)
Longitudinal waves-more important to understanding of sound--air molecules move along the same axis as the wave itself when a force is applied (motion of wheat blowing in a field) |
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Sine Wave
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Waves behaving in simple periodic oscillation are often called sine waves.
A body moving back and forth is said to oscillate. Once cycle of vibration, or oscillation, begins at any point on the wave and ends at the identical point on the next wave...this is a sine wave. SINE WAVES (simple waves) have amplitude, frequency, and starting phase |
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Explain Frequency
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FREQUENCY (f): how often, within a given amount of time, we complete one vibration or one cycle. Frequency is the number of complete cycles per second.
A high frequency (high pitch or cps...cycles per second) has a larger number. Frequencies are now measured in HZ, rather than cps. The Hz unit was named after Heinrich Hertz: a German physicist. The RANGE OF HUMAN HEARING is 20 Hz to 20,000 Hz LOW FREQUENCIES have relatively long periods & long wavelengths HIGH FREQUENCY SOUNDS have relatively short periods & short wavelengths. |
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Period
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The PERIOD of a sign wave is the time required to generate one cycle.
Period=1/frequency |
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Wavelength
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The WAVELENGTH is the distance in feet between identical points on two adjacent waves. As length decreases, frequency increases. Conversely, as length increases, the number of hertz decreases. (shorter string-faster/longer string-slower).
Wavelength=a characteristic of sound proportionately related to frequency is wavelength. The length of a wave is measured from any point on a sinusoid to the same point on the next cycle of the wave. Formula for determining wavelength is w=v/f. |
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Resonance
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Resonance-natural rate of vibration of a mass is called its resonant frequency. Although mass may be set into vibration by a frequency other than its resonant frequency, when the exernal force is removed the oscillation will revert to the resonant frequency until it is damped. (Ex. glass shattering/musical notes)
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Explain Sound Velocity
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Velocity of a sound wave is the speed with which it travels from the source to another point.
The SPEED at which the energy travels from the source to the ear is the VELOCITY OF SOUND; it is predictable. Velocity of Sound through Air is 344 meters (1130 feet ) per second at standard pressure-temp (20 degrees Celsius at sea level). When temperature and humidity increased speed of sound increases. At higher altitudes speed of sound is reduced. The SPEED OF SOUND (C): is dependent on the medium’s density and temperature. At sea level at 20 degrees C or 68 degrees F, the SPEED OF SOUND is 344 meters/second or 1130 FEET/SECOND. (through air). It is determined by a number of factors-density of the medium. Closer together the molecules, the shorter journey each particle makes before striking its neighbor and the more quickly the adjacent molecules can be set into motion.===Sound travels faster through a solid than a liquid and faster through a liquid than a gas Formula for determining velocity is v=fw |
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Phase
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relationship in time between two or more waves.
PHASE is discussed in terms of degrees of angle (e.g. 45 degrees, 90 degrees, 180 degrees). The starting phase: of a sinusoid (sine) wave is the point in the cycle at which the object begins to vibrate. The wave starts at 0 degrees. At the high point of the compression it is at 90 degrees. It goes back down to the baseline and that is 180 degrees. It goes down to the low point of the rarefaction and that is 270 degrees. When the wave goes back up again to the zero it is at 360 degrees. One complete cycle consists of 360 degrees (a sine wave makes a circle). Wave A and B are 45 degrees out of phase. Wave C and D are 90 degrees out of phase. Wave E and F are 180 degrees out of phase. The sine wave does not have to start at 0 degrees, The starting point can be anywhere. It’s the point in the cycle at which the object begins to vibrate. When an oscillation has a beginning at 0 or 360 degrees it is said to be in phase with the standard... |
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Aperiodic sounds
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Aperiodic sounds vary randomly over time, do not have fundamental frequencies and are usually perceived as noise.
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Complex wave
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When two or more sine waves or pure tones are combined a complex wave occurs.When two or more pure tones of different frequencies are generated simultaneously, their combined amplitudes must be summed at each instant in time. Although the fundamental frequency determines all the harmonic frequencies, the harmonics do not all have equal amplitude. During speech, alternating the size and shape of the vocal tract, mostly by moving the tongue results in frequency and intensity changes that emphasize some harmonics and suppress others. The resulting wave form has a series of peaks and valleys. Each of the peaks is called a formant, and it is manipulation of formant frequencies that facilitates the recognition of different vowel sounds....
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Intensity
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Intensity--it is important that we know not only how fast but also how far a body vibrates--its intensity. The distance mass moves from the point of rest is called its amplitude. Because our concern is with particle motion in air, it is assumed that if a greater force is applied to air molecules, they will move further from their points of rest, causing greater compressions and greater rarefactions, increasing the particle displacement and therefore the amplitude.
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Three properties are necessary to produce sound waves:
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1. A Force = intensity of the wave 2. A Vibrating Mass = air molecules are the mass undergoing vibration. Air molecules and their vibratory motion seem to be connected by springs. 3. An Elastic Medium = air itself has an elastic nature.
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Intensity and pressure are two different ways of looking at
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the same sound wave.
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Why do we need acoustic reference or sound reference points?
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Will help to define the different thresholds (in terms of SPL, HL, SL, IL) Important to develop or define:
How cold is a cold temperature? How soft is a soft sound? Beginning Point Zero Point Threshold |
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THE DECIBEL (dB)--who, what, etc...
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*Developed by Alexander Graham Bell
*dB = 1/10 (tenth) of a Bel *No fixed absolute value. Means nothing by itself *Usually measured in a range of 0 to 140 dB *Dimensionless number t = log of a ratio of 2 powers or pressures * It is exponential * It is a logarithmic unit of measurement that expresses the magnitude of physical quantity relative to a specific reference level *Measurement unit for intensity (loudness), sound pressure level *Measurement of intensity used in acoustics and audiometry, electronics |
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What is the Reference of Zero in dB
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Beginning Point in Sound = 0 dB
* 0 dB does NOT mean the absence of sound. *In terms of sound, the physical reference point for 0 dB is 20 μ Pa *It means the amount of sound pressure you are comparing is equal to the reference level and no pressure increase occurs |
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What is a Threshold?
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Lowest point in intensity that a person can perceive the stimulus
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How is Threshold Measured?
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Measured in various ways:
Intensity Level (IL) ,Sound Pressure Level (SPL) , Hearing Level (HL), Sensation Level (SL) |
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What does a decibel always have?
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A decibel is a ratio that does not have an absolute or fixed value, it always has a reference level.
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Reference level for 0 dB IL
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10-12 watt/m2 OR 10-16 watt/cm2
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Reference level for 0 dB SPL
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20 micropascals (μ Pa) OR 0.0002 dyne/cm2
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Reference level for 0 dB HL
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Audiometric Zero-ANSI standards
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Reference level for 0 dB SL
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Patient's threshold
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What is intensity?
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Intensity (aka magnitude, strength, amplitude) = the amount of energy transmitted per second
over an area of 1 square meter |
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treten
(tritt, trat, [hat] ist getreten) |
to step, walk
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What is there an absolute and relative measure of...?
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Intensity
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Absolute Measure Intensity
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Absolute Measure of acoustic power in watts = rate at which energy is consumed
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Intensity level only exists when there is a reference given. Therefore......
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Therefore, the term Intensity Level in dB IL should only be used when the reference is 10-12 watt/m2 under standard conditions
-- Standard conditions = 200 degrees Celsius/Centigrade, 760 mm mercury for Barometric Pressure |
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Intensity Reference=
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Intensity Reference measured in watts
...Usually measured as: IR = 10-12 watt/m2 = (.000000000001 watt/m2) = 10-16 watt/cm2 |
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Intensity Output=
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(ie: loud speaker)
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Sound Intensity is a specifically...
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defined quantity and cannot be sensed by a simple microphone, nor would it be valuable in those recordings if it could
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Sound Intensity = most commonly measured using the
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dB scale
dB = 10 x log (I0/IR) |
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Sound Pressure (dB SPL) is NOT the same physical quantity as
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Sound Intensity (db IL).
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Intensity Difference =
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level difference between Sound Pressure and Sound Intensity
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Sound Intensity (db IL) characteristics
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Hearing is sensitive to sound pressure, which is RELATED to sound intensity. Sound Intensity can also be described in terms of Pressure or Power.
Audiologists prefer to measure sound intensity in terms of Pressure |
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Most common usage of dB in reference to sound loudness
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dB SPL
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What is the "Sound reference point"?
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the quietest sound that can just be perceived by the best ear OR the nominal threshold of human hearing
0 dB SPL |
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Pressure =
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Force per unit Area
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Unit of Force =
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= Newton (N)
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1 Newton (N) =
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Force that will accelerate 1 kilogram (kg) of mass (Mass) a distance of 1 meter (Distance) per second (Time).
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Sound Pressure unit =
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Pascal (Pa)
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1 Pascal =
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1 Newton per square meter (1 Newton applied to a meter squared) OR
1 Pa = 1 N/m2 |
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The smallest, softest sound pressure variation required to produce a just audible sound to healthy young ears is approximately:
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0.00002 Pa = 20 μ Pa = sound of a mosquito flying 3 meters away
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0 dB SPL =
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μ = 1 millionth part of
20 μ Pa |
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AUDIOGRAM
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Defines amount of hearing loss a person has based on their threshold at a given frequency
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The human ear is NOT equally...
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Human ear is NOT equally sensitive to all frequencies
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In the normal ear, the hearing is ____sensitive than the standard of 0 dB SPL
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Less
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instrument designed to test hearing sensitivity at different frequencies which are recorded
on an audiogram |
Audiometer
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1938....Beasley...???
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tested a variety of
persons hearing at the frequencies or octaves on the audiogram. He averaged all of their thresholds onto an audiogram and determined that the human ear is NOT equally sensitive to all frequencies |
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American National Standards
Institute (ANSI) published standards in 2004 for Audiometric Testing (aka Audiometric Zero). 0 dB HL at 1000 Hz...? |
0 dB HL at 1000 Hz = 7.5 dB SPL
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Humans = hear from
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20 Hz – 20,000 Hz
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HEARING LEVEL (HL)
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dB measured in Hearing Level (HL)--Converted from dB SPL to db HL
Audiogram determines each patient’s individual threshold 7.5 db SPL at 1,000 Hz = 0 db HL Each frequency at 0 db HL represents a different value SPL |
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SENSATION LEVEL (SL)
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Auditory threshold of an individual; Term used to designate an intensity level above threshold;
Must know patient's threshold (softest sound they can hear) at a given frequency before you can identify the SL level |
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If audiologist wants to present a stimulus to a patient at 20 dB SL at 1000 Hz" and patient's threshold at 1000 Hz was 25 dB HL. The stimulus would be presented to the patient at
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45 dB HL
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Patient 1 has threshold at 20 dB at 1000 Hz Patient 2 has threshold at 30 dB at 1000 Hz Patient 3 has threshold at 40 dB at 1000 Hz
However, all patients hear this at 40 dB Sensation Level. Audiologist presents a 20 dB SL to all these patients |
Patient 1 has threshold at 20 dB at 1000 Hz + 20 dB = 40 dB. Aud presents the tone at 40 db HL Patient 2 has threshold at 30 dB at 1000 Hz + 20 dB = 50 dB. Aud presents the tone at 50 db HL Patient 3 has threshold at 40 dB at 1000 Hz + 20 dB = 60 dB. Aud presents the tone at 60 db HL
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