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PHYS 0872

Science of Sound: Science of Sound: Study guide for 2nd Test, Wednesday, Nov. 6, on Chapters 6-10. Bring a pencil and your student ID. The exam will be given in Walk Auditorium, Ritter Hall, not in our regular classroom. Chapter 6 There will be several questions on the anatomy and functioning of the human ear.  Pinna: collects sound  Auditory Canal: 2.5 cm to 3cm long, 1cm dimension, serves as resonance tube enhancing hearing by around 3,000 to 4,000 Hz  Ossicle Chain: hammer, ambel, and stirrup, transmit vibrations into inner ear  Eustechian Tube: equalizes pressure on both sides of eardrum  Eardrum: membrane, vibrates in response to pressure changes in a soundwave (can grow back if not burst too badly), lower mechanism amplifies vibrations in middle ear, hydraulic amplification (20 to 25 dB increase)  Cochlea: Coiled, tapered tube 3.5 cm long, filled with fluid called perilymph, divided into 2 parts by basilar membrane (vibrations of oval window lead to vibrations of basilar membrane which stimulate the hair cells)  Presbycusis: Lowering of upper limit as one ages (deterioration of hair cells)  Conduction deafness: Damage to ossicle chain or reduced mobility due to extra tissue from infections  Just Noticeable Difference (JND): - For changes in SIL is ½ to 1 dB, - For changes in frequency is almost 1 Hz for sounds with frequency <1000 Hz, much greater for sounds with frequency >5000 Hz  Binaural hearing and localization for low and high frequency sounds. - Wavelength << Distance (considerable blocking) - Wavelength >> Distance (little blocking) - For f > 4000 Hz main mechanism is the intensity difference at the ears - For f > 1000 Hz main mechanism is the phase difference (time difference) at the two ears  Relation between objective (physical) quantities SIL, frequency, waveform and the subjective (perceived) quantities loudness, pitch, timbre: - Tone color or timbre of a steady sound is determined by the waveform - SIL depends on amplitude - Pitch determined by frequency, multiplying frequency by 2 raises pitch an octave  Loudness level (LL, unit phon): always the same number as the intensity level of the 1000 Hz tone of that same loudness  All sounds that have the same SIL (dB) do not necessarily sound equally loud (PRACTICE THESE QUESTIONS)  On average people associate about a 10 dB increase in the SIL with a doubling of the loudness.  Human ear is most sensitive in the frequency range 3000 to 4000 Hz.  Loudness depends on the waveform especially at low frequencies where sine waves are barely audible  Equal loudness curves: Each contour represents a family of sine waves, with such combinations of intensity and frequency that they all sound equally loud Chapter 7  Chromatic scale: 12 semitone steps per octave. 1/12  Equal tempered tuning: Frequency is multiplied by N = 2 = 1.059,463 in going up a semitone.  Pythagorean (beatless) intervals f /f =2/1, 3/2, 4/3, 5/4, ...= 2.000, 1.500, 1.333, 1.250, … 12 7 5 4  Equal-tempered intervals f /f =2N 1 N , N , N , ... = 2.000, 1.498, 1.335, 1.260  Equal-tempered tuning: every semitone is tuned in the same way. Piece can be transposed in pitch without changing harmonic relationships.  In older tuning schemes the most important intervals are Pythagorean, other intervals are badly out of tune  Harmonic series f , 2f1, 31 , 1f , 1f ,1... (Pythagorean intervals)  Harmonics: a group of frequencies where they are all simple multiples of a single frequency, individual frequencies are called a harmonic  Overtones: any Fourier component of a sound except the one of lowest frequency Chapter 8  Fourier’s theorem: Mixing sine waves with frequencies from the harmonic series f , 2f , 1 1 3f1, 4f1, 51 , ... yields
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