Physics 1240 Thurs 5/4/06Today: Review for Final ExamFinal Exam Saturday May 6, 10:30am-1pm, Location: in-class50 multiple choice questions#2 pencil, eraser, calculator (no cell phones)Notes: 4 pages (one side per page) of 8.5”x11”paper, handwrittenIdentification required – student ID, driver’s license or state IDLook at concept tests and homework problems. Questions on the exam will not be identical to concept tests and homework, but will be similar in that they will test knowledge of the same material.New material (after Exam 3)Sabine’s formulaFormantsVocal foldsVocal tractExample of Sabine’s formulaWhat is the reverberation time at 1000 Hz for a 6m x 7m room with a 3m ceiling. The walls and ceiling are gypsum wallboard with α = 0.05 and the floor is heavy carpet on concrete with α = 0.4.Periodic motion -- repeats itself at regular intervalsf = frequency = 1 / periodP = period -- units of secondfrequency -- cycles/second -- 1/(second) - Hertz (Hz)A = Amplitude - how large the vibration isExam I materialSimple Harmonic Motion = Simple Periodic Motion = Sinusoidal MotionThis is a sine waveform:Only a vibration that repeats itself at regular intervals produces the sensation of a distinct pitchpitch – the sensation of how high or low a steady tone soundssteady tone – a sound that is held steady that produces the sensation of a musical noteFrequency (physical) determines pitch (sensation)very exact!Higher pitch = higher frequencyLower pitch = lower frequencyAn octave is a factor of two change in frequencyComplex Periodic WaveformsAudible Range: 20 Hz – 20,000 Hz(Frequencies the human ear can hear)Digital SamplingA “sample” of the sound is taken at very small time intervalsSampling rate is how many samples per secondCD Quality – this is a standardStereo – 2 channels, 16-bitSample rate is 44,100 Hz (or one sample every 0.0000227)Bit Depth (or dynamic range) is the range of possible valuesCD Quality0 to 216or from 0 to 65,536 or from -32,768 to +32,768CD quality is called “16-bit sound” or a “bit depth of 16”Other common bit depths8 bit 0 to 28(low quality digital sound) 24 bit 0 to 224(high quality digital recording) 32 bit 0 to 232CD Quality Sample Size Estimates44,100 samples/sec x 2 channels x 16 bits1 byte / 8 bit x 74 min x 60 sec/min = 783,000,000 bytesResonance – driving an oscillator at it natural frequencyThe speed of sound is 344 m/s(770 miles per hour)independent of frequency and amplitudegoes up with temperaturePressure = Force/Area - N/m21 pound = 4.5 NBackground air pressure is 1 atm = 100,000 N/m2Sound pressure fluctuations are very small, say 10-6atm100,001 N/m2down to 99,999 N/m2 (and back)This is only~ ±1 N/m2time 100,000Pressure, N/m2100,00199,999Transverse wave – motion of the medium is perpendicular to the direction of wave propagationLongitudinal waves – motion of the medium is in the direction of wave propagation The wave follows a path – the direction of propagationBut the “medium” – the material in which the wave propagatescan go “up and down” – perpendicular to the direction of propagationor “back and forth” – along the direction of propagationfrequency = speed / wavelengthf = v / λ(λ is the Greek symbol “lambda”)Beats00.20.4=0 0.05 0.1100 Hz105 Hzfbeats= f1–f2= 5 HzT = 0.2 sExam II materialdBs (SIL) and W/m2(intensity)Intensity proportional to the square of amplitudeHuman Earouter-middle-innerAuditory canalOssicles (hammer, anvil, stirrup)cochleabasilar membranehair cellsoval window, round windowExam II material cont...LoudnessLoudness versus SIL and frequencyPhonsMajor scale WWHWWWHChromatic scale H x 12H = 1.05946W = 1.05946 x 1.05945Perfect 5th7 half-steps – ratio of 1.5Major 3rd4 half-steps – ratio of 1.26 (why is Pythagoras wrong?)Octave - ratio of 2Exam II material cont...Harmonic series – f, 2f, 3f, ...periodic = distinct pitch = harmonic seriesFrequency spectra – intensity versus frequencyTimbre = frequency spectra + transientssame harmonic series does not mean the same frequency spectra. why?Given a note is the 9thharmonic, what is the fundamental?Exam II material cont...Synthesisadditivesubractivedigital samplingAM/FMADSRTopics covered on Exam IIIModular synthesisADSR envelopeTimbre and frequency spectrawhat is timbre? what is frequency spectraNatural modes, natural mode frequenciesnatural mode frequencies are not integer multiples of each otherTopics continued...Waves on a stringtension, mass, lengthf = n v/2Ln = 1,2,3, ...v = sqrt[ tension/ (mass/length) ]What happens if I increase the tension by 4? etc.Guitar plate natural modes of vibrationTopics continued...Waves in pipes (big topic)Pipe open at both ends – flute-typef = n 344/2Ln=1,2,3, ...Pipe closed at one end – clarinetf = n 344/4Ln=1,3,5, ...Waves in pipes continued...Conical pipes – oboe, saxophonef = n f1n=1,2,3, ...all harmonics present, no simple recipe for the fundamental, f1Bore holesregister keys/holes - go from f1 to 3f1octave keys/holes – go from f1 to 2f1Waves in pipes continued...Bore holes – measure length from closed end (mouthpiece end) to center of large bore holeregister keys/holes - go from f1 to 3f1octave keys/holes – go from f1 to 2f1no questions on brass instrumentsdo you know what a recorder (oboe, saxophone, clarinet, flute) is? - be able to categorize into a simple physical modelTopics continued... Architectural AcousticsQualities of good concert hall acoustics VolumeWell distributed soundClarityLow background noiseEnvelopment Performer satisfaction ReverberationSource widthAcoustical intimacyTopics continued... Architectural AcousticsReverberation time – what makes the reverb time go up or downTypical reverberation timesabsorption coefficientsless than 0.1 fairly reflective –smooth, hard surfacesgreater than 0.3-0.4 fairly absorbing rough, soft
View Full Document
Unlocking...