lecture17_th3_11

lecture17_th3_11 - are? i swarm 4’ Prolonged exposure to...

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Unformatted text preview: are? i swarm 4’ Prolonged exposure to roughly what “threshold” level of decibels will cause gradual hearing loss? A) Any level, given long enough exposure B) 70 dB or higher C) 90 dB or higher D) 110 dB or higher E) 130 dB or higher - 90 Decibels Prolonged exposure to any noise above 90 decibels can cause gradual heanngloss. - 100 Decibels No more than 15 minutes unprotected exposure recommended. - 110 Decibels Regular exposure of more than 1minute risks permanent hearing loss. 3/20 Phys 1240: Sound and Music LAST TIME: Decibels. TODAY: Intensity versus distance from source, ears, hearing. NEXT TIME: Hearing, exam review. READ: 6.3, 6.4 - Homework 7 and Reading Question 8 due today. - Exam 2 is next Thursday — Practice exam posted on course website. — No homework next week. — Reading question will still be due Thursday. Adding dB corresponds to multiplying intensity +10 dB means *10 in intensity +20 dB means *100 in intensity Check it out! +20 dB is the same as +10 dB +10 dB Each ADDITION of +10 dB means MULTIPLICATION of *10 in the intensity. (*10*1O is the same as *100) 5/20 Chorus effect Adding instruments => add the intensities (AND, nice, richer sound from the subtle beating...) lf sound from different sources is perfectly IN phase (or OUT of phase) (constructive or destructive interference) then it’s not so simple... (But this is not going to happen with natural instruments!) 6/20 Imagine sources with AMPLITUDE=1 => INTENSITY ~ (Amp)2 = 12 = 1 If have TWO such sources, EXPECT total intensity = 1+1 If DESTRUCTIVE interference: AMP = 1-1 =0 => INTENSITY ~ 0 2 = O. Silence! If CONSTRUCTIVE interference: AMP = 1+1 =2 => INTENSITY ~ (2)2 = 4. LoudII Average of O and 4 is (I!) There is a source in the center emitting sound outward. How does loudness of the sound at r compare to that at R? a) loudnessmtr) > loudnessR - ou-nessmm ou~nessR o) loudnesstatr) = loudnessR d) Not enough information STrtRT 4! mama-r 44 There is a source in the center emitting sound outward. How does intensity of the sound at roompare to that at R? d) Not enough information Slicker question (Asiming no friction/losses, etc) How does the total power (Energy/second) passing through the whole spherical surface at r compare to that at R? f/flxx A) Pr> PR R B) P,.<PR D) ?? 10/20 The area of a sphere grows like Radius squared Intensity = Power/ area So, intensity of sound decreases like 1/(Radius squared). 12/20 DOUBLE distance to a sound source (outside) => sound intensity is 0.25 times as big (you could say it decreases 4 times) Table 5.1 says 6dB <=> 4x (look it up!) Doubling distance lowers the SIL by 6 dB. (Or even MORE, if some sound energy is lost to heatl...) (Or LESS, if lots of sound reflects...) START 4! DI$§L£Y + [bodfi «are ... 34 d1?) 1° 910—2» soego toodB !3licker question”§% r Standing 10 meters from the speakers at an outdoor concert, the SIL is 100 dB. Assuming “no losses”, how loud is it at 20 meters? 80 meters? A)50 dB 33 dB B)50 dB 38 dB C 94 dB 88 dB ) D) 94 dB .....82 dB E) Something totally different ".3 Effi‘firflh 1435'.“ 14/20 Alec H. 3.1: mm Wily OUTER MIDDLE INNER 15/20 Middle ear Ossicular chain ."I"- E, /"' .' Malleus “1005 S t ' tapes /’ C ochlea External ear canal 'l‘ympanic membrane Tympamc cam)” Eustachian tube Discussion What is the physics and function of the “hammer, anvil and stirrup” (ossicles) in the middle ear? - Why have a middle ear at all? Slicker question \luhy have a middle ear? A) To provide an amplifier of pressure waves B) To better couple pressure waves from “air” medium to “liquid” medium C) To protect the inner ear from extremely loud sounds D) To maintain the tympanic membrane (eardrum) in proper equilibrium E) More than one of the above Innerear Cochlea The body's microphone 18/20 19/20 hair cells Hair cells current mechanically —l.>~ senste channels membrane potential 20l20 Basilar membrane 0” Fabio Mammano (/ http :l/wwwneurophys.wisc.edul~ychen/audito ry/animation/animationma in .html Fabio Mammano ...
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This note was uploaded on 08/24/2010 for the course PHYS 1240 taught by Professor Holland,murray during the Spring '08 term at Colorado.

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lecture17_th3_11 - are? i swarm 4’ Prolonged exposure to...

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