Foundations of Acoustics Flashcards
(24 cards)
What is AIR PRESSURE?
The force that air exerts on the object it touches, normalised by its contact area
What is the average air pressure?
101,000Nm^2 or 1.01x10^5Nm^2
What type of wave is a soundwave?
Longitudinal wave
What is the physical construction of a sound?
Vibrations caused by variations in air pressure over a short period of time
Define a PURE TONE
The simplest form of sound, represented (temporally) by a sinusoidal wave
What are the properties of a pure tone (in its temporal/sinusoidal representation)?
- Pressure as a function of time
- Periodic/regular
- 1 sine component
What is the speed of sound?
343m/s
Define COMPRESSION
Band of high pressure where there is a high density of air particles, corresponding to the sine peak
Define RAREFRACTION
Band of low pressure where there is a low density of air particles, corresponding to the sine trough
Define AMPLITUDE; how is it measured and does it effect sound?
- The degree of pressure fluctuation
- Measured from bassline to extrema
- Effects LOUDNESS - the higher the amplitude, the louder the sound
Define FREQUENCY; how is it measured? What is its units? How does it effect sound?
- The amount of sinusoidal wave cycles per second
- Measured in Hz
- The physical correlate to pitch: x2 = ^8ve; (x2)(x1.5) = ^compound p5th
Define PHASE: what range of values can it take?
The position along the wave cycle a sound starts, between 0 and 2π
What is the formal definition (equation) for a SINE WAVE?
x(t) = A sin(2πft + ø)
Relative pressure = Amplitude x Sin(2π (frequency (Hz) x time (s)) + phase)
Define WAVELENGTH
The distance between two peaks of a sinusoidal sound wave
the length of a full cycle
What is the equation for WAVELENGTH?
λ = v/f
Wavelength (m) = Speed of the wave* (m/s) / Frequency (Hz)
- 343m/s in std atmospheric conditions)
What is FOURIER THEOREM?
The theory that every periodic wave can be expressed by the addition of sine waves of differing amplitudes/frequencies/phases
Define HARMONIC COMPLEX TONES
A wave built by adding multiple sine waves with increasing frequencies that are integer multiples of a common fundamental frequency
Define a SAWTOOTH wave
adding infinite pure tones in an arithmetic sequence
y = sin(x) + 1/2sin(2x) + 1/3sin(3x)…etc
y = 1/n sin(nx) + 1/(n+1) sin((n+1)x)…etc
Define a SQUARE wave
adding infinite pure tones in an arithmetic sequence, omitting even harmonics
y = sin(x) + 1/3sin(3x) + 1/5sin(5x)…etc
y = 1/(2n+1) sin((2n+1)x) + 1/(2n+3) sin((2n+3)x)…etc
Define TEMPORAL REPRESENTATION
Visualising sound via fluctuations in pressure over time (vibrations)
Define SPECTRAL REPRESENTATION
A visualisation of the sine components of a complex tone separated out into its constituent pure tones
What is a Spectrogram?
A visual representation of a sound’s spectral properties over time as they change over time
Define HARMONICS; what do they look like in spectral representation?
When the upper tones of a complex wave are integer multiples of a common fundamental frequency, shown via equally spaced lines on the harmonic spectrum
Define PARTIALS; what do they look like in spectral representation?
When the upper tones of a complex wave are NOT integer multiples of a common fundamental frequency, shown via unequally spaced lines on the harmonic spectrum
