-
WAVE EFFECTS OR ACCOUSTIC EFFECTS ARE:
FACTORS THAT AFFECT THE WAY SOUND TRAVELS IN SPACE
-
EXAMPLES OF WAVE EFFECTS
- ABSORPTION
- REFLECTION
- REFRACTION
- INTERFERENCE
- DIFFRACTION
-
SOUND ABSORPTION
REFERS TO A LOSS OF ENERGY AS A SOUND WAVE IS PROPAGATING THROUGH A MEDIUM
-
MEDIUM
SPACE FROM WHERE SOUND BEGINS AND ENDS
-
BARRIERS
WALLS, DOORS ETC.
-
RESULTS FROM ABSORPTION BY THE (_______) AND ABSORPTION BY THE (_____)
RESULTS FROM ABSORPTION BY THE (__MEDIUM__) AND ABSORPTION BY THE (__BARRIERS__)
-
INTERNAL ABSORPTION
ABSORPTION BY THE MEDIUM
-
RESULT OF INTERNAL FRICTION WITHIN THE MEDIUM
***INTERNAL FRICTION CAUSES SOUND ENERGY TO BE CONVERTED TO:
HEAT OR THERMAL ENERGY
-
INTERNAL ABSORPTION
IS THE PRIMARY FACTOR RESPONSIBLE FOR THE DISSIPATION OF SOUND ENERGY THAT OCCURS IN (_____)SPACES AND LARGE SPORTS ARENAS
(OPEN SPACES)
-
EXTERNAL ABSORPTION
ABSORPTION BY SPACE IN BOUNDRIES
-
EXTERNAL ABSORPTION
RESULT OF THE TRANSFER OF ENERGY FROM ONE MEDIUM TO ANOTHER AS SOUND ARRIVES AT THE BOUNDARY BETWEEN TWO MEDIAS
-
EXTERNAL ABSORPTION
AFFECTED BY THE SIZE AND PHYSICAL PROPERTIES OF THE SURFACES SURROUNDING THE SPACE
-
EXTERNAL ABSORPTION
IS THE DOMINANT FACTOR RESPONSIBLE FOR SOUND REDUCTION IN (_____)
CLOSED SPACES
-
ABSORPTION COEFFECIENT
A QUANTITY USED TO DESCRIBE THE ABILITY OF A MEDIUM AND ITS BOUNDARIES TO ABSORB THE ENERGY OF SOUND WAVES
-
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
-
ABSORPTION COEFFECIENT
ABSORPTION BY A MEDIUM IS FREQUENCY DEPENDENT AND IS AFFECTED BY THE PRESENCE OF OBSTACLES OR IMPURITIES (HUMIDITY)
-
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)
-
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
-
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
-
ABSORPTION COEFFECIENT
SOFT POROUS MATERIALS ABSORB (_____) SOUND ENERGY THAN HARD, NON POROUS MATERIALS.
(MORE)
-
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.
-
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.
-
SOUND REFLECTION
REFERS TO THE BOUNCING OF SOUND WAVES OFF A BOUNDARY
SOUNDS BOUNCING OFF A BOUNDARY
-
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.
-
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)
-
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
-
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.
-
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
-
SOUND REFLECTION
- THE SUM OF THE ABSORPTION COEFFICIENT AND THE REFLECTION COEFFIECIENT MUST EQUAL 1.
- ***see equation on handout
-
SOUND REFLECTION
SOUND ABSORPTION AND REFLECTION ARE IMPORTANT IN CONSIDEATIONS FOR THE CONSTRUCTION OF:
- CONCERT HALLS
- CLASSROOMS
- HOSPITALS
- LIBRARIES
-
SOUND REFLECTION
ORIGINAL INCOMING SOUND WAVE IS CALLED THE (_____)
INCIDENT WAVE
-
SOUND REFLECTION
(_____) IS THE ANGLE AT WHICH A SOUND WAVE APPROACHES A BOUNDARY.
ANGLE OF INCIDENCE
-
SOUND REFLECTION
WAVE THAT BOUNCES BACK OFF THE BOUNDARY IS CALLED THE (_____)
REFLECTED WAVE (BOUNCES BACK OFF BOUNDARY)
-
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)
-
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.
-
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.
-
SOUND REFLECTION
THIS SPREADING OF REFLECTION IS CALLED (_____) OR (_____)
DISPERTION OR DIFFUSION
-
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.
-
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.
-
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)
-
SOUND REFRACTION
(_____) ANGLE AT WHICH ORIGINAL SOUND WAVE APPROACHES A BOUNDARY
ANGLE OF INCIDENCE
-
SOUND REFRACTION
(_____) ANGLE AT WHICH THE REFRACTIVE WAVE TRAVELS THROUGH THE SECOND MEDIUM
ANGLE OF REFRACTION
-
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
-
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!!!
-
REVERBERATION TIME AND ECHO
WHEN SOUNDS ARE REFLECTED FROM A BOUNDARY, A LISTENER RECIEVES DIRECT AND REFLECTED SOUNDS.
-
REVERBERATION TIME AND ECHO
DIRECT SOUND OF THE TALKER'S SPEECH REACHES THE LISTENERS EAR (_____) THE REFLECTED SOUND.
BEFORE
-
REVERBERATION TIME AND ECHO
REFLECTED SOUND ENERGY IN AN ENCLOSED SPACE IS CALLED (_____).
REVERBERATION
-
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
-
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
-
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
-
REVERBERATION TIME AND ECHO
THE EQUATION FOR ABSORPTION
SEE EXAMPLES HANDOUT PAGE 10 - 13
-
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
-
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.
-
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.
-
LIVE ROOM = REFLECTIVE OR HIGHLY REVERBERANT
CLASSROOMS: LOW REVERBERATION TIME IS BETTER.
-
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
-
DEAD ROOMS HAVE:
VERY ABSORBING SURFACES...
|
|
