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2 physics of sound

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2 physics of sound

  1. 1. Physics of Sound Part 1 Sound waves How they are generated and travel
  2. 2. Sound Waves  Generation and Propagation  Sound wave = changes in pressure caused by vibrating object  Compression = High pressure  Rarefaction = Low pressure  Sound needs a medium to “vibrate”  Usually air, but could be anything  Speed of sound depends upon the medium Air = 1130 ft/sec Water = 5000 ft/sec Steel = 13000 ft/sec
  3. 3. Measuring sound waves  Sound waves are longitudinal waves  Vibrating object compresses the air around it.  Pushes air away leaving an area of low pressure  Vibrating object then compresses more air to create a “chain”
  4. 4. Measuring methods Cycle  A single push and pull of the vibrating object  One are of compression followed by one area of rarefaction  An initial increase in atmospheric pressure from the norm, followed by a drop below the norm and then a return to normal  Mathematically displayed by a sine curve  Pressure on Y axis  Time on X axis
  5. 5. Measuring methods Period (T) and Frequency (f)  Period - The time it takes to create one cycle  Frequency - The number of cycles in one second 1 f T =  Measured in Hertz (Hz) or cycles per second
  6. 6. Measuring methods Example It takes ¼ sec to create one cycle. What is the sound wave’s frequency? 1 4 cycles per second .25 f = =
  7. 7. Measuring methods  Frequency will determine pitch  High frequency = high pitch  Low frequency = low pitch  Octave – a doubling of halving of the frequency
  8. 8. Measuring methods  Human hearing range  Low range between 15 to 30 Hz  With enough power lower than 15 Hz can be felt, but not heard as “sound”  High range varies with age and gender  Women - up to 20 kHz  Men – between 15 to 18 kHz  High frequency range will lower with exposure to high levels of sound and age
  9. 9. Tuning  Traditional orchestra would tune First Chair Violin A first.  Remaining instruments would tune relative to that  A above middle C was tuned to about 420 Hz  As halls grew larger it was found to be desirable to tune sharper  1939 A was established to be 440 Hz  Corresponds to the 49th key on a full size piano  Tuning is not a science. The relative frequency difference is what is important
  10. 10. Measuring methods Wavelength  The distance from one area of compression to the next or one area of rarefaction to the next v f λ = l=wave length V = velocity of sound in medium usually 1130 ft/sec f = frequency
  11. 11. Measuring methods  Amplitude  How high the pressure goes above and below normal atmospheric pressure  Corresponds to how loud the sound is  “loudness” is relative to frequency and dependant on the listener.
  12. 12. Timber and Harmonics  Harmonics – multiples of a base frequency  Timber – the characteristics of a particular sound or instrument  Different harmonics combined in different levels
  13. 13. Physics of Sound Part 2 Basic Acoustics Inverse square law Reinforcement/cancellation
  14. 14. Interference  Phase  measurement of where the amplitude of a wave is relative to another wave  A cycle can start at any point in a waveform  Two waves with the same frequency can start at different times  Measured as an angle in degrees  Related to the sine wave representation of the wave
  15. 15. Interference  Constructive of destructive interference  Waveforms will add by summing their signed amplitude at each instant in time
  16. 16. Beats  Happens when two slightly different frequencies interfere  Often used in tuning
  17. 17. Standing waves  When sound waves bounce off of obstructions, they can interfere with themselves  Tends to reinforce some frequencies and attenuate others  Prevented by using  Non- Parallel walls, ceilings  Convex surfaces  Multi-level ceiling sections
  18. 18. Reverberance (Reverb)  Consisting of multiple, blended sound images caused by reflections from walls, ceilings and other structures which do not absorb sound  NOT echo  Echo consists of individual, non-blended sound images  Reverb time is related to  The time it takes for a sound to reduce to an inaudible level  Loudness of sound relative to background noise  Ratio of loudness of reverberant to direct sound  Short reverb time (less than 1.5 sec) is better for speech or drama  Long reverb time (more than 1.5 sec.) is better for music
  19. 19. Absorption  Controlling reflections can reduce or increase reverb time  Air tends to absorb frequencies above 2K Hz  Sight line obstructions  Frequencies above 10 kHz tend to not bend around corners well or other obstructions  l=1.3 inches for 10 kHz tone  Frequencies below 1kHz do very well  l=5.65 feet for 200 Hz tone  Specialists are often hired to “tune” a space acoustically
  20. 20. Acoustic attributes  Defined by Leo Beranek after a 6 year study of 54 concert halls  Used to define acoustic properties in terms that other trained professionals can understand
  21. 21. Acoustic attributes  Intimacy – Indicates the size of a room  How it sounds to the listener, not actual size  Determined by the initial-time-delay-gap (ITDG)  Interval between the sound that arrives directly at the ear and the first reflection  Usually considered to be the most important attribute
  22. 22. Acoustic attributes  Liveness  Related to Reverberance  Room size is related  More reflections is live. Less reflections is dry or dead  Warmth  More low frequency sound relative to mid frequency  Too much low frequency sound is said to be “Boomy”
  23. 23. Acoustic attributes  Loudness of direct sound  Inverse square law  Loudness of sound will decrease by one quarter every time the distance from the source is doubled  Definition or Clarity  Good definition when sound is clear.  Related to intimacy, liveness, loudness of direct and reverberant sound
  24. 24. Acoustic attributes  Brilliance  A hall that has liveness, clarity and intimacy  Diffusion  Relates to the orientation of reverberant sound  Where is the reflected sound coming from  It is preferable to have reverb sound coming from all directions
  25. 25. Intensity  Like pitch, loudness is a sensation in the consciousness of a listener  To produce a sound twice as loud requires 10 times the power  Inverse square law  Sound level is reduced by a factor of the square of the distance away from the source  If you move double the distance from the source, the sound intensity will by one quarter
  26. 26. Intensity  Intensity is a measurable quantity  SPL – Sound Pressure Level  dB – deciBel  A system of measuring a ratio between two powers  1dB change – Imperceptible change  3dB change – Barely perceptible  5dB change – Clearly noticeable  10dB change – About twice as loud  20dB change – About four times as loud
  27. 27. dB SPL Sound 150 dB Jet engine at 1m 140 dB Rock and Roll stack at 1m 130 dB Thunderclap, Air Raid Siren 1 Meter 120 dB Jet takeoff (200 ft) 110 dB Rock Concert 100 dB Train passing up close 90 dB Heavy traffic 80 dB Hair Dryer 70 dB City street 60 dB Noisy bar or restaurant 50 dB Open plan office environment 40 dB Normal conversation level 30 dB Library, Soft Whisper (5 Meter) 20 dB Quiet domestic environment 10 dB Broadcasting Studio, Rustling Leaves 0 dB Threshold of hearing in young adult
  28. 28. Sound Envelope  Listener does not hear individual cycles of sound waves  Attack – Time it takes for sound to rise from nothing to its greatest intensity. Usually short.  Decay – Time it takes for a sound to fall from its attack level to its sustaining level. Decay time is usually short  Sustain – The time during which the initial vibrating source continues to supply energy to the sound. Usually perceived as the duration and intensity of the sound  Release – Time it takes for the sound to drop from its sustain level to inaudibility after vibrating object stops supplying energy
  29. 29. Sound Design  How, what and why of a show
  30. 30. Interaction of Sound with other Show Elements  Script Identification of motivational cues - sounds listed in the script (cues that actors react to) Identification of environmental cue opportunities – locations, time of day, season, era, Identification of emotional cue opportunities – What do you want to say about actor, situation. . .
  31. 31. Interaction of Sound with other Show Elements  Acting Collaborate on what is “heard” on stage - Actors need to understand what sounds are part of the physical environment shared with the set and props. Some sounds are there for them to react to (Motivational) Some sounds need to be originated by a performer’s action (ring a bell, turn on a radio, etc...) Monitoring of stage action to off-stage locations Placement of wireless mics and stage monitoring / fold back
  32. 32. Interaction of Sound with other Show Elements  Costumes Musicals – wireless mics that need to be accommodated within costumes and hair  Scenic Location of on-stage devices (speakers, mics) Collaboration on scene shifts (needs/opportunities to cover transitions using sound cues – “Functional” sound cues) Identification of cues that support each other (sound used to reinforce scenic element that would normally make noise (car, train station, rain, etc. . .)
  33. 33. Interaction of Sound with other Show Elements  Props “Active” on-stage devices that may be props  Lights Identification of cues that support each other Thunder and lightning, Day time or night time, Lights used to represent outdoors and other items/times that would normally have a recognizable sound associated with it. Identification of transitions where cues should go together
  34. 34. Interaction of Sound with other Show Elements  Music direction Vocal reinforcement (micing) Music reinforcement (micing, direct feeds and mixing) Vocal/music monitoring for performers and/or band  Choreography Music cues Reinforcement of foot fall (Mic cues for tap dancing) Music monitoring for dancers
  35. 35. Interaction of Sound with Other Show Elements  Stage Management Cueing Monitoring of stage action to booth Intercom systems
  36. 36. Use of Sound in the Theatre What Audience Hears – Company Hears  Elements that are part of the show  What an audience hears. Cues, Aural Reinforcement  Support for the Overall Production  What the company hears Monitoring, Communications Recording
  37. 37. Use of Sound in the Theatre What Audience Hears – Company Hears  Sound Cues - “created” sounds that advance the story Sound effects, music transitions and underscoring. Produced / reproduced through mechanical or electronic means Mechanical – real sounds (sheet metal for thunder, crash box for breaking glass, ½ coconuts for horse galloping, actors making bird calls) Also called practical Electronic reproduction Sounds stored as signals on CDs, Minidisks, computer files
  38. 38. Use of Sound in the Theatre What Audience Hears – Company Hears  Reinforcement of aural elements of production  Mic cues for vocal and musical performance  Orchestra Mics  Instrument direct feeds
  39. 39. Use of Sound in the Theatre What Audience Hears – Company Hears  Monitoring – Providing performers and members of the company a portion of the sound from the performance to assist with their performance.  Stage monitors for singers to hear the band – and themselves – Fold back  Pit monitors for band to hear vocals – and themselves  House monitoring for crew positions, back stage and dressing rooms so company can hear “what’s going on”
  40. 40. Use of Sound in the Theatre What Audience Hears – Company Hears  Communications Intercoms for cueing and communications among the company  Recording Live feeds of performance for film, video and audio recording
  41. 41. Paper work, paper work, paper work…. CUE DEVICE INPUT CH LEVEL DEVICE OUTPUT CH LEVEL FADE TIME NOTES SUFFOLK COUNTY COMMUNITY COLLEGE SOUND CUE SHEET Show:_________________________________________ Sem / Year _____/_____ Page _____ of _____
  42. 42. Paper work, paper work, paper work…. CUE # Sound Cue Placement PG. Type Location A Preshow music At house opening 7 Called Cluster / BOH B Preshow announcement with house to half 7 Called Cluster C Preshow fade with blackout 7 Called Cluster / BOH D Narrator with lights up 7 Called Cluster E "Loser" with lights up 9 Called USC F music cut Chuck: "…the fuck!" 9 Called USC G Awesome sound Agnes: "Go." 13 Called cluster H Mission Impossible theme Agnes: "…the intro music!" 14 Called cluster I music cut ??? 14 Called cluster J Narrator TOS 18 Called cluster K T.V. with lights up 18 Called USC L T.V. fade Tilly: "…not good at all." 19 Called USC M magic Agnes: "What are you doing?" 23 Called cluster N fight music Chuck: "…what happens next - " 24 Called cluster O music cut end of fight 24 Called cluster P Narrator into LL Cool J Lilith: "…kicketh some ass." 26 Called cluster R "Waterfalls" with lights up 28 Called cluster S Voice Over Tilly: "…Let's do this!" 29 Called cluster T magic missle with spell 29 Called cluster U Farrah explodes Farrah: "Oh no." 29 Called cluster V Cheerleader enterance Agnes: "…would be a bad thing, right?" 34 Called Cluster W music cut 34 Called Cluster X cube eats Steve: "…oh neat, a jello mold!" 47 Called USC Y cube transforms Tilly: "…call it Miles." 49 Called Cluster Z "Gonna Make you Sweat" Chuck: "…Cheerleaders!!!" 59 Called Cluster AA Footsteps with blackout 69 Called SL BB Tiamat Roar 69 Called SL CC Tiamat fight 69 Called SL DD Curtain call with lights up 71 Called Cluster
  43. 43. Paper work, paper work, paper work….
  44. 44. For Next Class  Read  The Spaghetti Factor!, Coleman  Patches and Facility Panels, Coleman  Soldering and Soldering 2 PDF Study for Quiz 1