1CT 3.1.1The following sound could be classified as…i. Originalii. Naturaliii. Transienta) i. onlyb) ii. onlyc) i. and ii.d) i.,ii., and iii.e) i., ii., and iv.Bird chirpOboeAnswer: For the sound of the bird chirping, it can bedebated what the sound really is, so I will not asksomething so ambiguous on an exam, but here’swhat I think; the sound is a recording, and notfrom the “live” bird, so it is not original. Eventhough it is a recording, it is a sound that isfound in nature and not artificially made by man,so it is natural, though one could argue that aspeaker is making it and therefore it is areproduced sound. The sound seems transientsince the bird produces a lot of short chirps.CT 3.1.2The following instrument could be classified as?a) Percussionsb) Stringsc) Windsd) It deserves its own classificationbellsAnswer: The primary instruments in this recordingare bells, which are percussion instruments.CT 3.2.1Which of the following is generally acharacteristic of percussion instruments?a) The sound does produce a clear sensationof pitchb) The larger the amplitude of the vibrationsthe louder the soundc) The larger the surface area of the objectthe softer the soundd) The sound produced is transiente) More than one of theseAnswer: A clear sensation of pitch is not generally produced by a percussioninstrument, it’s quite variable. Depending on the type of instrument (i.e. Bellsor a drum) this pitch may be slightly variable by striking the instrument indifferent places.(Some bells do make a pretty clear pitch, many drums donot) Larger amplitudes of vibration move more air and therefore producelouder sounds. Increasing surface area also moves more air, so (c) isincorrect. The sound of a percussion of a percussion instrument is transientsince it is not taking energy from an outside source to sustain itself.CT 3.2.2What happens to the energy that was originallypresent in the vibration on a percussioninstrument?a) It all turns to heatb) It turns to a combination of heat and soundc) It is transferred into pure potential energyand is then able to dissipated) The force of gravity cancels out all theenergye) There is no energy present when an objectvibrates steadilyAnswer: The instrument produces a sound which wehear, so it is clear that some of the energybecomes sound energy. There is additionallysome energy that goes into heating. Thevibration of the instrument causes the instrumentto warm a little and the sound wave that pushesout heats the air ever so slightly.2CT 3.2.3This is a picture of the Marimba:What is the importance of the symmetry of thepipes?a) To get a full range of notesb) To complete the resonancec) To improve and clarify the soundd) Aestheticse) Some other reasonAnswer: It turns out that the pipes on the marimba aredeceiving - see your textbook (fig 3.3) for theexplanation.CT 3.2.4If I double the surface area of a percussioninstrument, what happens to the pitch?a) It gets higherb) It gets lowerc) It remains the samed) Not enough informationWhat happens to the loudness?a) It increasesb) It decreasesc) It remains the samed) Not enough informationAnswer: The larger the area of the drum, the more airthat it can move, so increasing the area wouldincrease the loudness.Answer: Doubling the surface area will mean that the soundwaves have farther to travel to go “out and back”, takingmore time - that is, the natural resonant frequencies will belower. This means the frequency of vibrations is lower,thus the pitch will go down.CT 3.2.5Will the sound produced by a tuning fork diefaster if I hold it close to the microphone?a) Yesb) Noc) Not enough informationWhat if I touch it to this desk?Answer: Holding the tuning fork closer to themicrophone will make very little difference. Theenergy leaving the tuning fork (making soundwaves) is leaving *anyway*, whether or not themicrophone is nearby makes little difference.(Unless you actually TOUCH them) Placing the tuning fork on the table will cause thesurface of the table to vibrate. Since the tablehas such a large area, the fork will loose itsenergy very fast and stop producing sound veryquickly.CT 3.3.1aWhich lasts longer, the vibration of astring on an electric guitar, or on anacoustic guitar?(Assume the same string, plucked thesame)A) Electric guitar strings vibratelongerB) Acoustic guitar strings vibratelongerC) Both should vibrate the sameD) ???Answer: The electric guitar will vibrate longerbecause on the acoustic guitar the vibratingstrings cause the resonating chamber to vibrate.Energy is taken from the strings to make theback of the guitar vibrate, so the strings will stopsooner. The electric guitar has an electronicpickup which is not mechanical, so it extractsmuch less energy3CT 3.3.2If I shorten the string of this instrument whathappens?a) The pitch goes upb) The pitch goes downc) The sound gets louderd) The sound gets quietere) More than one of theseWhat if I increase the tension?Answer: Shortening the string will increase the pitch.When the string is shortened you can think of thewaves echoing back and forth along the string ina shorter time: shorter period for “reinforcement”means higher frequency (and pitch.) Increasing the tension will also make the stringvibrate faster because the string vibrates like asimple harmonic oscillator and the tension issimilar to the spring constant K.CT 3.4.2What is the function of finger holes in a flute?a) To create an edgetoneb) To shorten or lengthen the pipec) Emphasizes the affects of the reedd) Mostly aesthetice) More than one of theseAnswer: Since λ.freq = v is always true and since fora wind instrument v = speed of sound in air =344 m/s then by changing λ we also changefreq. The finger holes are how λ is changed in aflute.CT 3.4.3aHow do you raise the pitch of a stringinstrument by exactly one octave?a) Put your finger down exactly halfwayalong the stringb) Put your finger down somewhere elsec) Increase the tension by a factor of 2d) More than one of theseDoes this same idea work for percussion instruments (like a drum head?)Freq (SHM) = const * √ (K/mass) λ * freq = speed of wave = const* (√ Tension/mass)Answer: Putting your finger down half way along the string will increasethe pitch by 1 octave. An octave means that the frequency isdoubled. Doubling freq means the λ must be halved in order tohave the same wave speed. If we wanted to increase the tension,then we would need to quadruple the tension and
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