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Section A06 - Week 8 Filled

Section A06 - Week 8 Filled - WEEK 8 Dan's Section BIEB 166...

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WEEK 8 Dan’s Section – BIEB 166 – Dr. Nieh Wed. 5 – 5:50 PM @ CSB 004 OH: Wed 3 – 4 PM @ York 3010 A Lecture 17: Sound Propagation I. Distortion of frequency A) Spreading loss = global attenuation: Amplitude of frequency is inversely proportionate with distance from source. Ex) In air, a frequency loses 6 dB for every doubling of distance B) Pattern loss 1. Differential medium absorption – Certain frequencies attenuate less or more in different mediums. Ex) Lacewing vibrations on plant. 2. Scattering – Sound waves change paths with collision of medium molecules Ex) Wind scatter: 2-35 dB/100 m 3. Boundary effects – Sound waves propagate along the border of two different mediums a) Boundary waves: Occur when terrestrial sender and receiver are close to the ground. Only carries low frequencies. i. When sound reflects, it can undergo a phase shift. Direct wave and reflected wave cancel each other out from sender to receiver. ii. Male bird may modify sound if he sees female on the ground. b) In aquatic environments, higher frequencies propagate along the border i. Animals in shallow water must use high frequencies ii. ↓ water depth / ↓ surface density = ↑ cutoff frequencies 4. Refraction a) Terrestrial: Sound travels slower in cold temperatures and dense mediums i. Inertial properties of medium influence speed. Sound travels faster in less dense mediums because less dense materials have less inertia ii. Increased temperature = increased sound speed iii. Sound travels better/further in mediums with a lower speed of sound b) Aquatic environment: sound velocity is influenced by pressure & temperature i. Colder waters propagate sounds further ii. Increased pressure eventually overcomes cold temperature in deep
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  • Spring '09
  • Fortes
  • pressure difference detectors, sound intensity Ex, medium molecules Ex, low sound velocities, inherent directionality Ex

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