Exam II Flashcards
Complex Vibration:
The sum of two or more simple vibrations. Simple vibrations that make up a complex vibration are called frequency components.
Fourier Theorem:
Any complex oscillatory (vibratory) motion is the sum of various sinusoidal motions of varying amplitude, frequency, and phase.
Complex vibration can be divided into two basic classes of back and forth motion:
1.
2.
- Aperiodic Vibration
2. Periodic Vibration
Aperiodic Vibration:
vibration without a repeating pattern in time
Frequencies do not have a common factor
Periodic Vibration:
vibration in which an object returns to the same point in space periodically (at equal periods of time) during the motion
Periodic vibration has:
1.
2.
- Fundamental frequency and a fundamental period
2. Harmonics
A Periodic frequency is composed of _________ that __________.
composed of frequencies that are integer multiples of a fundamental frequency, even if that fundamental frequency is not a part of the vibration (aka missing fundamental)
Fundamental Frequency:
The greatest common factor of all the harmonic frequencies (aka overtones) in the complex waveform.
Ex: waveform made up of 1500Hz, 1800Hz, 2400Hz, 2700Hz. Fund. frequency is 300Hz- GCF.
This is an example of a missing fundamental, because it does not start at 300. 5th, 6th, 8th, and 9th harmonics are given.
frequency = _______/________
Frequency = cycles/second = Hz F= 1/T
period = _________/_________
Period = seconds/cycle = seconds
Waveform Synthesis:
The process of combining several individual sinusoidal motions into a complex waveform.
Waveform Analysis:
The process of breaking down a complex waveform into individual sinusoidal waves.
Compression
bunching of particles causing increased density (in a wave)
Rarefaction
spreading of particles causing decreased density (in a wave)
Sound Intensity
the amount of sound power that travels through a specific area of the wave front surface
sound intensity = ____________/____________
sound intensity = power/area w/m^2
10 dB = ______x Louder
20dB = ______x Louder
30dB = ______x Louder
10 dB = 2x Louder
20dB = 4x Louder
30dB = 8x Louder
If sound source is moving toward listener, or listener moves toward sound source, frequency________.
Increases
If sound source is moving away from listener, frequency__________.
Decreases
The Doppler Effect
a shift in the frequency of a sound wave resulting from the movement of a sound source, the movement of a listener, changes in the medium, or a combination of these factors
Frequency depends only on __________, not _______.
Frequency depends only on speed, not distance.
Which property of a wave does not change due to the Doppler Effect?
Speed
The speed of a wave is determined by the properties of the medium, not the speed of the source or the observer.
Sound Pressure vs Sound Intensity
Sound Pressure: how compressed or rarefied particles are
Sound Intensity = How much sound power is transferred from the sound source to the surrounding area
A sound wave propagating through a medium will ultimately lose all of its energy because of _______.
Sound absorption by the medium and surrounding boundaries.
Sound absorption is the result of _________.
Internal friction within the medium which converts sound energy into heat as sound passes through a medium.
Internal absorption
absorption by the medium.
the dominant factor in sound energy dissipation in open spaces and large sports arenas
External absorption
absorption by space boundaries
the dominant factor in sound decrease in enclosed spaces such as auditoriums, living rooms, classrooms.
Absorption Coefficient
The ability of the medium and its boundaries to absorb the energy of sound waves.
Reflection
when a sound wave strikes the surface of a space boundary, part of its energy is absorbed by the boundary medium and the remaining energy is reflected back to space
Refraction
when a sound wave bends (changes direction) after entering a medium with a different density and stiffness.
Atmospheric Absorption:
The amount by which air absorbs sound depends on _______.
Frequency, relative humidity, and other factors.
Dispersion
If a sound wave hits a smooth, flat surface, all of the waves will reflect in the same direction.
If a sound wave hits a curved and rough surface, the sound energy may be reflected in different directions— this is called dispersion
Incident Wave
Original incoming sound wave
Angle of incidence
The angle at which the incident wave approaches the boundary compared to the normal line.
Attenuation
a decrease in the magnitude of a signal
When waves enter a medium of lesser speed (fast to slow) they bend _______ the normal line.
bend toward the normal line
When waves enter a medium of faster speed (slow to fast) they bend _______the normal line.
away from the normal line
Angle of reflection
angle at which the reflected ray bounces off the wall and into the original medium
Law of reflection:
Angle of reflection EQUALS Angle of incidence
Reverberation Time
The time required for the sound intensity to decrease to 1 millionth of its original magnitude.
Equivalent to sound intensity decreasing by 60 dB.
Total Internal Reflection
when 100% of the sound energy reaching a boundary is reflected back into the original medium;
When does total internal reflection occur?
Occurs when a sound wave enters a boundary with a denser medium and is traveling at a sufficiently large angle (greater than 90degrees past the normal line)
Critical Angle of Incidence
smallest angle at which total internal reflection can occur
Lower absorption coefficient (a) = __________ reflectivity (B)
Lower absorption coefficient (a) = HIGHER reflectivity (B)
Reverberation
The reflected sound energy within an enclosed space.
Sound Diffraction
the phenomenon of sound waves bending around objects and through openings in boundaries.
Diffraction increases as wavelength _____________.
increases.
Diffraction increases as frequency____________.
Decreases (waves spread out and bend more)
Shock Wave
When a moving object travels at or faster than the speed of sound, it compresses the medium in front of it and takes the compressed waveform with it.
Sonic Boom
Noise created by a shock wave. Not heard until it reaches the listener.
Minimum sound intensity heard by human ear:
20 uPa
1.0x10^-12 W/m^2
Threshold of pain
- 0x10^7 uPa
1. 0 W/m^2
Intensity Level Decibel (dB IL)
Standard means of measuring the amplitude of an acoustic signal
