FUNDAMENTALS OF SOUND

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Author:
CYNILISHUS
ID:
37658
Filename:
FUNDAMENTALS OF SOUND
Updated:
2010-09-27 16:42:45
Tags:
ABSORPTION REFLECTION REVERBERATION
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Description:
SOUND PROPAGATION
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  1. WAVE EFFECTS OR ACCOUSTIC EFFECTS ARE:
    FACTORS THAT AFFECT THE WAY SOUND TRAVELS IN SPACE
  2. EXAMPLES OF WAVE EFFECTS
    • ABSORPTION
    • REFLECTION
    • REFRACTION
    • INTERFERENCE
    • DIFFRACTION
  3. SOUND ABSORPTION
    REFERS TO A LOSS OF ENERGY AS A SOUND WAVE IS PROPAGATING THROUGH A MEDIUM
  4. MEDIUM
    SPACE FROM WHERE SOUND BEGINS AND ENDS
  5. BARRIERS
    WALLS, DOORS ETC.
  6. RESULTS FROM ABSORPTION BY THE (_______) AND ABSORPTION BY THE (_____)
    RESULTS FROM ABSORPTION BY THE (__MEDIUM__) AND ABSORPTION BY THE (__BARRIERS__)
  7. INTERNAL ABSORPTION
    ABSORPTION BY THE MEDIUM
  8. RESULT OF INTERNAL FRICTION WITHIN THE MEDIUM
    ***INTERNAL FRICTION CAUSES SOUND ENERGY TO BE CONVERTED TO:
    HEAT OR THERMAL ENERGY
  9. INTERNAL ABSORPTION
    IS THE PRIMARY FACTOR RESPONSIBLE FOR THE DISSIPATION OF SOUND ENERGY THAT OCCURS IN (_____)SPACES AND LARGE SPORTS ARENAS
    (OPEN SPACES)
  10. EXTERNAL ABSORPTION
    ABSORPTION BY SPACE IN BOUNDRIES
  11. EXTERNAL ABSORPTION
    RESULT OF THE TRANSFER OF ENERGY FROM ONE MEDIUM TO ANOTHER AS SOUND ARRIVES AT THE BOUNDARY BETWEEN TWO MEDIAS
  12. EXTERNAL ABSORPTION
    AFFECTED BY THE SIZE AND PHYSICAL PROPERTIES OF THE SURFACES SURROUNDING THE SPACE
  13. EXTERNAL ABSORPTION
    IS THE DOMINANT FACTOR RESPONSIBLE FOR SOUND REDUCTION IN (_____)
    CLOSED SPACES
  14. ABSORPTION COEFFECIENT
    A QUANTITY USED TO DESCRIBE THE ABILITY OF A MEDIUM AND ITS BOUNDARIES TO ABSORB THE ENERGY OF SOUND WAVES
  15. ABSORPTION COEFFECIENT
    • TOTAL AMOUNT OF SOUND ENERGY ABSORBED BY A MEDIUM IS A FUNCTION OF:
    • DISTANCE FROM THE SOUND SOURCE AND
    • PHYSICAL PROPERTIES OF THE MEDIUM
  16. ABSORPTION COEFFECIENT
    ABSORPTION BY A MEDIUM IS FREQUENCY DEPENDENT AND IS AFFECTED BY THE PRESENCE OF OBSTACLES OR IMPURITIES (HUMIDITY)
  17. ABSORPTION COEFFECIENT
    FOR A BOUNDARY VARIES FROM 0 TO 1 AND DEPENDS ON THE:
    • FREQUENCY OF THE PROPAGATING SOUND
    • THICKNESS AND STRUCTURE OF THE WALLS (BOUNDARIES)
    • AMOUNT OF WALL SURFACE
    • TYPE OF WALL MATERIAL (ie MOLECULAR STRUCTURE, DENSITY, UNIFORMITY AND TEMP)
  18. ABSORPTION COEFFECIENT OF 0 WOULD INDICATE THAT THE BOUNDARY (_____) ALL OF THE SOUND ENERGY, SO THAT NO ENERGY WAS (_____)
    • REFLECTED OR BOUNCED OFF
    • NO ENERGY WAS ABSORBED
  19. ABSORPTION COEFFECIENT OF 1 WOULD INDICATE THAT THE BOUNDARY (_____) ALL OF THE SOUND ENERGY SO THAT NO ENERGY WAS (_____) OR (_____) THROUGH THE BOUNDARY
    • ABSORBED-ALL OF THE SOUND
    • REFLECTED OR TRANSMITTED THROUGH THE BOUNDARY
  20. ABSORPTION COEFFECIENT
    SOFT POROUS MATERIALS ABSORB (_____) SOUND ENERGY THAN HARD, NON POROUS MATERIALS.
    (MORE)
  21. ABSORPTION COEFFECIENT
    SO SOFT, POROUS MATERIALS GENERALLY HAVE A (_____) ABSORPTION COEFFECIENT THAN HARD, NON-POROUS MATERIALS.
    EX: CARPET, FOAM, DRAPES, CELING TILES RUGS, CORK ETC.
    (HIGHER) WILL ABSORB MORE. COEFFECIENT CLOSER TO 1.

    • ***HOWEVER, A POROUS MATERIAL CAN BECOME LESS ABSORPITIVE WHEN COVERED WITH A LESS POROUS MATERIAL (ie CONCRETE COVERED WITH PAINT)
    • EX: IF YOU TAKE CORKBOARD AND PAINT IT, WILL CHANGE ABSORPTION ABILITIES.
  22. ABSORPTION COEFFECIENT
    USUALLY, SOUND ABSORPRION INCREASES WITH SOUND FREQUENCY. HOWEVER, FOR SOME STIFF MATERIALS THIS IS NOT THE CASE, AND THE ABSORPTION COEFFECIENT IS HIGHER FOR LOW FREQUENCY SOUNDS. ie GLASS ETC
    IN GENERAL, BARRIERS TEND TO ABSORB HIGH FREQUENCY SOUNDS MORE THAN LOW.
  23. SOUND REFLECTION
    REFERS TO THE BOUNCING OF SOUND WAVES OFF A BOUNDARY
    SOUNDS BOUNCING OFF A BOUNDARY
  24. REFLECTION COEFFICIENT

    REFLECTION COEFFICIENT = ENERGY REFLECTED BACK FROM BOUNDARY TO THE SPACE DIVIDED BY THE SOUND INTENSITY AT THE BOUNDARY.
    IS A QUANITY THAT DESCRIBES THE EFFECTIVENESS OF A BOUNDARY IN REFLECTING SOUND WAVES.
  25. SOUND REFLECTION

    VARIES FROM 0 TO 1 AND DEPENDS ON:
    • FREQUENCY OF THE ARRIVING SOUND
    • PROPERTIES OF THE BOUNDARIES (MOLECULAR STRUCTURE) DENSITY, UNIFORMITY, AND TEMPERATURE)
  26. SOUND REFLECTION

    A REFLECTION COEFFICIENT OF 0 INDICATES THAT THE BOUNDARY (__1__) NONE OF THE SOUND ENERGY; THEREFORE ALL OF THE ENERGY IS EITHER (_2___) OR (_3___) THRU THE MEDIUM.
    • 1. REFLECTED
    • 2. ABSORBED
    • 3. TRANSMITTED
  27. SOUND REFLECTION

    A REFLECTION COEFFICIENT OF 1 INDICATES THE BOUNDARY (__1___) ALL OF THE SOUND ENERGY; THEREFORE, NO ENERGY IS (__2___) OR (_3____).
    • 1. REFLECTED
    • 2. ABSORBED OR
    • 3. TRANSMITTED.
  28. SOUND REFLECTION
    ALL THE ENERGY ARRIVING AT A BOUNDARY IS EITHER ABSORBED OR REFLECTED, SO THE TOTAL SOUND INTENSITY MUST EQUAL THE SUM OF TWO:

    I=Iabs + Iref
  29. SOUND REFLECTION
    • THE SUM OF THE ABSORPTION COEFFICIENT AND THE REFLECTION COEFFIECIENT MUST EQUAL 1.
    • ***see equation on handout
  30. SOUND REFLECTION

    SOUND ABSORPTION AND REFLECTION ARE IMPORTANT IN CONSIDEATIONS FOR THE CONSTRUCTION OF:
    • CONCERT HALLS
    • CLASSROOMS
    • HOSPITALS
    • LIBRARIES
  31. SOUND REFLECTION

    ORIGINAL INCOMING SOUND WAVE IS CALLED THE (_____)
    INCIDENT WAVE
  32. SOUND REFLECTION

    (_____) IS THE ANGLE AT WHICH A SOUND WAVE APPROACHES A BOUNDARY.
    ANGLE OF INCIDENCE
  33. SOUND REFLECTION

    WAVE THAT BOUNCES BACK OFF THE BOUNDARY IS CALLED THE (_____)
    REFLECTED WAVE (BOUNCES BACK OFF BOUNDARY)
  34. SOUND REFLECTION

    REFLECTED WAVE SIDE NOTE:
    ANGLE OF THE REFLECTED WAVE IS EQUAL TO THE ANGLE OF THE INCIDENT WAVE, BUT IN OPPOSITE DIRECTION (ie THE TWO ARE MIRROR IMAGES)
  35. SOUND REFLECTION

    IF A WALL IS FLAT OR SMOOTH:
    ALL SOUND ENERGY IS REFLECTED IN THE SAME DIRECTION, WHICH MAY CREATE AREAS THAT ARE UNUSUALLY LOUD IN A ROOM.
  36. SOUND REFLECTION

    IF A WALL IS CURVED OR ROUGH:
    THE SOUND ENERGY REFLECTED FROM DIFFERENT PLACES ON THE WALL MAY BE REFLECTED IN DIFFERENT DIRECTIONS.
  37. SOUND REFLECTION

    THIS SPREADING OF REFLECTION IS CALLED (_____) OR (_____)
    DISPERTION OR DIFFUSION
  38. DISPERSION OR DIFFUSION
    IS GENERALLY BETTER TO DISPERSE SOUNDS THROUGHOUT THE ROOM (via curved walls and rough surfaces) TO AVOID LOUD SPOTS.

    SOMETIMES FOCUSED REFLECTION IN A ROOM IS PURPOSELY ENHANCED.

    **in whispering galleries, whispered speech from one side of the room can be heard clearly on the other side of the room.
  39. SOUND REFRACTION

    AS A SOUND ENTERS A NEW MEDIUM, THE:
    FREQUENCY REMAINS THE SAME BUT THE SPEED OF SOUND CHANGES

    THIS CAUSES WAVELENGTH AND DIRECTION OF SOUND TO ALSO CHANGE.
  40. SOUND REFRACTION

    THE CHANGE IN DIRECTION (ie bending) OF SOUND WAVE PROPAGATION AS THE SOUND PASSES BETWEEN:
    TWO DIFFERENT MEDIA AT AN OBLIQUE ANGLE OR

    THROUGH A SINGLE MEDIUM OF VARYING DENSITY (temperature)
  41. SOUND REFRACTION

    (_____) ANGLE AT WHICH ORIGINAL SOUND WAVE APPROACHES A BOUNDARY
    ANGLE OF INCIDENCE
  42. SOUND REFRACTION

    (_____) ANGLE AT WHICH THE REFRACTIVE WAVE TRAVELS THROUGH THE SECOND MEDIUM
    ANGLE OF REFRACTION
  43. SOUND REFRACTION

    DIFFERENCE BETWEEN THE ANGLE OF INCIDENCE AND THE ANGLE OF REFRACTION THROUGH THE SECOND MEDIUM DEPENDS ON THE (_____) AND (_____) OF THE TWO MEDIA.
    DENSITY AND STIFFNESS
  44. SOUND REFRACTION

    ANGLE OF REFRACTION DEPENDS ON THE (_____) THROUGH THE FIRST MEDIUM AND THE (_____) THROUGH THE SECOND MEDIUM
    • SPEED OF SOUND
    • SPEED OF SOUND

    ****see graphs in notes!!!
  45. REVERBERATION TIME AND ECHO
    WHEN SOUNDS ARE REFLECTED FROM A BOUNDARY, A LISTENER RECIEVES DIRECT AND REFLECTED SOUNDS.
  46. REVERBERATION TIME AND ECHO

    DIRECT SOUND OF THE TALKER'S SPEECH REACHES THE LISTENERS EAR (_____) THE REFLECTED SOUND.
    BEFORE
  47. REVERBERATION TIME AND ECHO

    REFLECTED SOUND ENERGY IN AN ENCLOSED SPACE IS CALLED (_____).
    REVERBERATION
  48. REVERBERATION TIME AND ECHO

    LARGE SPACES AND SPACES WITH HIGHLY REFLECTIVE WALLS PRODUCE (_____) OF REVERBERATION.

    SMALL SPACES AND SPACES WITH WALLS COVERED WITH ABSORBING MATERIAL PRODUCE (_____) REVERBERATION.
    LARGE SPACES=ALOT OF REVERBERATION

    SMALL SPACES = VERY LITTLE REVERBERATION
  49. REVERBERATION TIME AND ECHO

    THE AMOUNT OF REVERBERATION IS MEASURED USING THE REVERBERATION TIME (RT)

    IS THE TIME IT TAKES FOR A BRIEF SOUND TO DECREASE IN SOUND PRESSURE 1000 TIMES (ie 60 dB) AFTER SOUND SOURCE STOPS.

    DEPENDS ON THE (_____) OF THE ROOM AND THE (_____) PROVIDED BY THE BOUNDARIES OF A ROOM.
    • VOLUME (SIZE OF A ROOM) AND
    • ABSORPTION
  50. REVERBERATION TIME AND ECHO

    REVERBERATION TIME IS CALCULATED USING THE SABINE EQUATION:
    RT = 0.161 V/A

    • 0.161 IS A CONSTANT USED FOR AIR
    • RT IS REVERBERATION TIME IN SECONDS
    • V IS VOLUME OF THE ROOM IN m^3
    • A IS THE TOTAL ABSORPTION OF THE BOUNDARIES
  51. REVERBERATION TIME AND ECHO

    THE EQUATION FOR ABSORPTION
    SEE EXAMPLES HANDOUT PAGE 10 - 13
  52. REVERBERATION TIME

    IMPORTANT NOTES:
    REVERBERATION TIME CHANGES WITH THE FREQUENCY OF THE SOUND SINCE THE
    ABSORPTION COEFFICIENTS OF THE BOUNDARIES ARE FREQUENCY DEPENDENT.

    REVERBERATION TIME CAN VARY FROM PRACTICALLY 0 (no reverberation) TO SEVERAL SECONDS IN LARGE AND REFLECTIVE SPACES.
    SHORTER REVERBERATION TIME = LESS REVERBERATION

    LONGER REVERBERATION TIME = MORE REVERBERATION
  53. REVERBERATION TIME

    LIVE ROOMS HAVE LOTS OF HIGHLY REFLECTIVE SURFACES AND HIGHER REVERBERATION TIMES.
    EXAMPLES: MEDIEVEL CHURCHES, DOMES, AND LARGE WAREHOUSES MAY HAVE MORE RT'S OF AROUND 3.0 TO 5.0 SECONDS OR MORE.
  54. REVERBERATION TIME

    THEATRES AN CONCERT HALLS NEED STRONG BUT DIFFUSE REFLECTIONS FROM WALLS AND CEILING IN ORDER TO DIRECT SOUNDS FROM THE STAGE TO THE AUDIENCE.
    • FLOORS, SEATS AND AUDIENCE MEMBERS ARE ABSORPTIVE
    • CONCERT HALLS WITH AN RT OF ABOUT 2.0 TO 2.5 SECONDS ARE GOOD FOR CLASSICAL AND ROMANTIC MUSIC.
  55. LIVE ROOM = REFLECTIVE OR HIGHLY REVERBERANT
    CLASSROOMS: LOW REVERBERATION TIME IS BETTER.
  56. REVERBERATION TIME

    DEAD ROOMS
    • HAVE HAD A LOT OF HIGHLY ABSORBING SURFACES AND LOWER AVERAGE REVERBERATION TIMES
    • (as low as .3 to .5 seconds)

    EXAMPLES: CONTROL ROOMS, AUDIO SOUND BOOTHS, LIBRARIES ETC
  57. DEAD ROOMS HAVE:
    VERY ABSORBING SURFACES...

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