Sound
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| A fancy looking Time History. |
Sound is a physical phenomenon that stimulates the sense of hearing. It's formed of waves, of which there are two types; Transverse and Longitudinal. An example of Transverse waves would be a ripple in water, where the vibrations in the water are at a right angle to the disturbance. Longitudinal waves work much like Newton's Cradle, where the wave moves along before bouncing back in the other direction in a series of compression and rarefaction.
Some Facts
- For a transverse wave the Wavelength is the distance between two successive crests or troughs, this defines frequency.
- Amplitude is the height of the crests / troughs. This defines how much of the sound there is.
- The Velocity (v) of sound is 333 meters a second.
- The frequency (f) of sound is measured in Hertz.
- The Wavelength of sound is known as the lambda (λ).
- The formula for working out any missing variable in terms of sound is v=fλ.
Harmonics
A Harmonic is an integer multiple of the fundamental frequency. In English (or numeric form I guess) this means that if you're using components of 1000Hz (1kHz from here on out) that 3kHz would be the 3rd Harmonic of 1kHz. In much the same vein 3kHz would be the 6th Harmonic of 500Hz.
Sound Intensity, Level and Decibels
By far my favourite part of today's lecture this covers Decibels (dB) and how sound intensity is measured. It's measured in decibels which are a non linear logarithmic scale. - Sound Intensity Level = 10log10(Isound/Isound)dB
- log10(10)=1
- log10(2)=.3
- 10*0.3=3dB
- 40dB=.666 of 41dB
- 43dB=2*40dB
- This scales linearly.
- 3dB increase = 2*
- 6dB increase = 4*
- 9dB increase = 8*
- 12db increase = 16*
Logarithmic Proof:
- log1010=1
- log102=0.3
- log104=0.6
- log108=0.9
- 0.9 + 0.1 = 10 (if I cheat and work backwards because I know log1010=1) :D
Inverse Square Law
- I/R^2
- R = Distance. So the volume of a sound quarters as distance doubles, for example;
- 1m = 1R
- 2m = 0.25R etc
