Physical acoustic I & II
What is a derived quantity, and name the 5 derived physical quantities we learned about.
A derived quantity is a quotient or product of two fundamentals, or of fundamental and derived, physical quantities.
displacement, velocity, acceleration, force, pressure
What is the definition of a waveform and what is on the y-axis and x-axis?
A waveform is a plot of change in amplitude of displacement (x) over time.
y-axis: displacement
x-axis: time
what is the formula for sound intensity and sound pressure level?
sound intensity: dB= 10 log (Ix/Ir) Ir= 10^-12 watt/m^2
sound pressure: dB= 20 log (Px/Pr) Pr= 2 x 10^1 uPa
What is a complex wave?
What are 2 synonyms used for displacement when referring to a waveform.
A complex wave is any sound wave that is not sinusoidal.
Decibel and amplitude
List the 5 parameters of a filter and the 4 types of filters.
parameters= center frequency, upper cutoff frequency, lower cutoff frequency, bandwidth, attenuation rate.
types= low-pass, high-pass, band-pass, band-reject
In order to vibrate, a source must have what two properties? Please explain them.
1. mass- the amount of matter present. 2. elasticity- property that enables recovery from distortion of shape or volume.
Explain the damping system.
No damping system- does not decrease over time, nothing is working in opposition
Low-damped system- over time motion decreases
Highly-damped system- much earlier amount of time for the object to stop moving
Ix =?
60 dB IL
What is the first harmonic and second harmonic? Please give an example of this.
First harmonic= fundamental frequency
second harmonic= first overtone
100, 150, 200, 250, 300
100= fundamental frequency and first harmonic.
150= first overtone
What is attenuation rate?
It is the rate at which energy for frequencies is rejected, and it is expressed in dB/octave.
What is Newton's third law of motion? Also, what is compression and rarefaction.
3rd law: with every force there must be an equal and opposite reaction force.
compression- density increases
rarefaction- density decreases
What is acoustic impedance? What are the two components? Please explain the components.
Acoustic impedance is a force that exist that oppose or impede motion. The two components are resistance and reactance. Resistance is friction that occurs, and it is independent of frequency. Reactance is forces that oppose motion in frequency selective way and is dependent of frequency.
98 dB SPL
amplitude spectrum- amplitude of acoustic energy as a function of frequency
phase spectrum- the starting phase as a function
Whats the difference between a narrow and broad tuning system.
A narrow tuning system is a good sound generator. It has lower resistance, less damping, and longer free vibrations at Fnat. A broad tuning system is a good receiver of sound. It has a higher resistance , more damping, and brief free vibrations.
What are the 2 types of wave motion, and please explain them.
Transverse- motion of the particles are perpendicular to the wave motions.
Longitudinal- particles are moving parallel to the wave form.
What is frequency and period? Please explain the conversions for each and provide examples.
frequency- the rate at which a sinusoid repeats itself. Hz to kHz divide by 1000. Example: 3000Hz = 3kHz. kHz to Hz multiply by 1000. Example: 4kHz = 4000Hz.
period- the time required to complete one cycle. s to ms multiple by 1000. Example: 7s = 7000ms. ms to s divide by 1000. Example: 2000ms = 2s.
77 dB SPL corresponds to what absolute pressure?
1.4 x 10^5
What are the differences between sawtooth waves and square waves.
Sawtooth waves have odd and even integer multiples, while square waves have odd integer multiples only.
Center frequency= frequency corresponding to maximum amplitude of vibration
upper cutoff frequency= the frequency above Fc for which amplitude of response is 3 dB less than response at Fc.
lower cutoff frequency= frequency below Fc is 3 dB less than at Fc.
bandwidth= the change in frequency defines the range of frequencies passed by the filters.
Please explain what a spring-mass system and pendular motion is.
Spring-mass system: at equilibrium, nothing has acted upon the spring mass system. Then when you apply a force to the object and release it, the object passes through equilibrium and goes through a point of maximum displacement.
pendular motion: at the points of maximum displacement, it stops moving, therefore the inertia force is 0. The restoring force is at maximum because it is as far away from the initial position.
What is RMS amplitude, starting phase, instantaneous phase, and the five dimensions of a sine wave.
RMS amplitude: RMS is standard deviation of all instantaneous amplitude. RMS = A (.707)
starting phase- the angle, in degree, at the moment rotation begin.
instantaneous phase- angle of rotation at a specified moment in time.
5 dimensions: frequency, period, amplitude, phase, and wavelength.
Calculate the intensity from two sources where one source is 65 dB SPL and the second source is 85 dB SPL
85.04 dB SPL
What is a period wave and an aperiodic wave? Please explain the differences and provide examples.
periodic wave- a wave that repeats itself over time. An example would be a sine wave.
aperiodic wave- a wave that lacks periodicity. An example would be a white noise or fricatives.
Explain what a low-pass, high-pass, band-pass, and band-reject filter
low-pass= passes energy below some Fu and attenuation energy above Fu. The parameters: Fu and attenuation rate.
high-pass= passes energy above some FL and attenuates energy below FL. The parameters: FL and attenuation rate.
band-pass= passes energy between some FL and Fu and attenuates energy below FL and Fu.
band-reject= reject energy between some FL and Fu