| A | B |
|---|
| longitudinal | parallel vibrations |
| transverse | perpendicular vibrations |
| speed of sound with increasing T? | faster speed |
| pitch | perception of frequency |
| T | 1/f |
| v (speed) | frequency x wavelength |
| in a vacuum | sound cannot travel |
| compressions | particles jammed up together |
| rarefactions | particles spread apart |
| centre of a compression | particles at top speed; same direction as wave |
| centre of a rarefaction | particles at top speed; opposite direction as wave |
| amplitude | maximum displacement of particles |
| intensity | watts/m^2 |
| intensity level | dB |
| double the intensity | + 3dB |
| half the intensity | - 3 dB |
| ten times the intensity | + 10 dB |
| one hundred times the intensity | + 20 dB |
| one thousand times the intensity | + 30 dB |
| perception of loudness | measured in phons |
| 0 dB | I = 1 x 10^-12 W /m^2 |
| double the distance from 'all directions' source | divide I by 4 |
| triple the distance from 'all directions' source | divide I by 9 |
| superposition | overlapping waves add - pressure or displacement |
| standing wave | formed by two identical waves overlapping in opposite directions |
| nodes in a standing wave | half a wavelength apart |
| resonance | large A response from external source at a special f |
| pressure nodes | at open end of air column |
| pressure antinode | at closed end of air column |
| fundamental | first harmonic |
| diffraction | proportional to wavelength/width |
| width less than a wavelength | 'complete' diffraction |
| pipes closed at one end | only odd harmonics |
| electret-condenser microphone | relies on piezo-electric effect |
| dynamic microphone | moving-coil microphone |
| ribbon microphone | velocity microphone |
| baffle | stops waves from back of speaker interfering |
| speaker enclosures | standing waves formed inside these |
| tweeter | high frequency speaker (f > 2000 Hz |
| mid-range (squawker) | middle frequencies (400 - 4000 Hz) |
| woofer | low range frequencies (20 - 1000 Hz) |
| back waves from a loudspeaker | out of phase with front waves |
| loudspeakers | vibrate a (paper) cone at AC frequencies |
