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Physics Midterm 1 (Sound Waves (waveform = combo of repeated waves…

- - - - proportional to velocity (air molecules have to move faster with larger amplitudes)
        
        Energy is proportional to amplitude squared (i.e. multiply amplitude by 2 => multiply energy by 4) E = k^2A^2
    - - just temperament vs. equal temperament
        
        equal temperament
        
        middle C = 260 Hz
        
        A4 = 440 Hz
        
        just temperament: frequency of note changes based on what key it's being played in
      - octaves
        
        half-steps/semitones frequency ratio = 2^1/12
        
        1 musical cent = 1/100th of a half-step, frequency ratio = 2^(1/1200)
        
        almost everyone can hear change of 25 cents, few ppl can hear change of 5 cents
        
        1 octave up = double the frequency
        
        octave 2: C2-C3 (lower notes)
        
        octave 3: C3-C4 (to middle C)
        
        octave 4: C4-C5: (middle to high C)
        
        octave 5: C5-C6
        
        octave 6: >C6
        
        fifth frequency ratio = 3/2 (1.5)
      - inversely proportional to length (1/length, i.e. half the length => twice the frequency)
      - proportional to velocity
        
        Energy is proportional to frequency squared E = b^2f^2
      - basic range of hearing = 20 Hz-20,000 Hz or 20 kHz
- - - - Sound Intensity Level (SIL, aka sound lvl) - vol increases by certain amt every time you multiply intensity of certain amt
        
        intensity increases by factor of 10 => SIL increases by 1 bel (2 bels = factor of 100, 3 bels = factor of 1000)
        
        bel is a large unit, decibel more commonly used: 1 decibel = 1/10th of a bel THEREFORE 10 decibel increase in SIL = intensity increases by factor of 10
        
        fix scale: 0 dB = 10^-12 W/m^2 (inaudible lvl)
        
        perceived loudness: measured in sones, 1 sone = perceived loudness of 1 kHz sine wave at 40 dB
        
        loudness doubles when SIL increases by 10 dB
        
        also affected by pitch (thus frequency) --> lower frequency sounds carry less E, ear sensitivity to certain frequencies may make some sounds seem louder
    - - for reference: loud rock concert = 0.1, pin drop = 10^-12