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PHYS 0872

Chapter 11  Anatomy of the violin: • Top plate = spruce (pliable wood) • Back plate = maple (harder wood) • High Bridge: sound post supports the tension of the strings, transfers vibrations to back plate, and is the pivot for vibrations of top plate  Motion of plucked string: two kinks traveling in opposite directions.  Motion of the bowed string: a single kink traveling along the string  As the "kink" or bend in the string travels from the bow to the bridge and back to the bow, the string slips on the bowhair  As the "kink" or bend in the string travels from the bow to the nut and back to the bow, the string sticks to the bowhair  If one bows the string upward near the right end of the string, the kink travels clockwise  In high quality instrument, main wood and air resonance are evenly distributed near the notes of open string  Sound radiation is uniform in all directions at low frequencies, perpendicular to top plate at high frequencies  Main wood resonance is vibration of top plate with sound post as pivot  Vibrations of strings and top plate and back plate, also air in the body combine to produce final sound Chapter 12  Air vibrates in a cylindrical tube with 2 open ends = pressure nodes (displacement antinode) at both ends  Air vibrates in a cylindrical tube with one open and one closed end = pressure antinode (displacement node) at closed end  Cylinder, two open ends: f =v/(1L); complete harmonic series f , 2f , 3f1, 4f1, .1.; 1 flute.  Cylinder, one open and one closed end: f =v/(4L1; f , 3f , 1f , 1f ,1...;1clarinet, auditory canal.  Cone, open at wide end: f =v/(1L); complete harmonic series f , 2f , 3f1, 4f1, .1.; 1 oboe, bassoon, saxophone.  Role of tone holes and register hole in changing pitch: holes change length of air column, change pitch nd  Bottom hole/register hole gives you 2 octave  Opening register hold produces a pressure node, eliminates F1, but leaves 2F1  The open hole, instead of the pipe end, becomes the pressure node (or displacement antinode)  The farther the hole is moved towards the top of the instrument (the blowing end), the shorter the allowed wavelengths, the higher the mode frequencies, and the higher the pitch of the note heard Chapter 13  Pressure antinode at mouthpiece of reed or brass instrument.  Nearly complete harmonic series [f mi1sing], 2f , 1f ,14f 1 ... in brass instrument.  The shorter the tubing is, the higher the pitch of the note played is. The slide on a trombone moves, changing the instrument's overall length.  Valves work by redirecting air into "loops" of extra tubing, note played without any valves pressed is the highest  Role of bell in increasing volume of the sound: - Bell and mouthpiece combinations modify standing wave patterns and frequencies in just the right ways to get a complete harmonic series of overblown notes - Bell quality increases fraction of sound that is emitted, especially at high frequencies - The lowest modes feel the flare of the bell sooner and so are shifted toward the higher frequencies appropriate to a shorter effective length Chapter 14 • Lungs- ◦ Maximum capacity- 6 liters ◦ Normal – 3 to 4 liters, about ½ a liter moving in and out with each breath ◦ Minimum – 1 liter • Vocal tract- throat, mouth, nasal cavity • Trachea- tube from lungs to vocal tract • Larynx- cylinder of cartilage at top of trachea containing vocal folds • Epiglottis- flap that closes larynx when swallowing • Vocal folds- folds of ligament with v-shape opening Bernoulli effect: The faster a fluid flows the less pressure it exerts. Vibration of the vocal folds: Air flowing between the vocal folds lowers pressure, pulls them together. Pressure builds up and the separate. The cycle repeats Elemental speech sounds: o Plosive Consonants: P,T,K vocal tract is blocked, then single puff of air is let through, vocal folds don’t vibrate o Voiced Plosives: B,D,G initiate vibration in vocal folds o Fricatives: f, th, s, sh voiceless (U, z, zh voiced) o Semivowels (glides): w,y o Liquids: l, r o Nasals: m, n, engma o Vowels: vocal folds vibrate periodically, harmonic series of frequencies Formants: broad bumps in the Fourier spectrum where there is amplification due to resonance of the vocal tract How do varying the tension of the vocal folds and the position of the vocal tract (mouth, throat, lips) affect the pitch and the vowel character of vowel sounds? Formant frequencies f1, f2 correspond to resonant frequencies of air vocal tract controlled by position of the throat mouth and tongue to determine vowel character Chest register: vocalis muscles that form part of the vocal folds are active, glottis closes during part of vibration cycle and the sound is rich in harmonics. Head and falsetto register: Vocalis muscles are inactive, glottis doesn’t close, sound is less rich in harmonics but voice is more agile. Soft sound: few harmonics, difficult to recognize vowel sound, because little input into the second formant Above high C: Difficult to recognize vowels because there is little input into the first formant Chapter 15 General criteria for acceptable auditorium or concert hall acoustics.  Precedence Effect: if the sound from the speakers is delayed electronically so direct sound arrives first, one has the impression that sound originates at front of the room o Shortly after the arrival of the direct sound, a series of semi-distinct reflections from various reflecting surfaces (walls and ceiling) will reach the listener. These early reflection
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