3Acoustics Sound is a longitudinal wave. Remember that longitudinal waves are made up of areas where the wave is compressed together, and other areas where it is expanded.Sound can be vibration which is pressure – felt but not heard.We will look in detail at three fundamental characteristics of sound: Speed, Frequency, and Loudness. *
4AcousticsSpeedThe speed of sound in air actually depends on the temperature of the air.The sound travels faster through media with higher elasticity and/or lower density.Speed of sound is 1130 feet per second or344 m/sLight is 186,000 miles per second
6AcousticsFrequencyMost often we will be looking at sound waves that humans can actually hear, which are frequencies from 20 – 20,000 Hz.Infrasonics -20 Hz - Ultrasound 20,000HzFrequency is sometimes referred to as pitch.
7AcousticsLoudnessThe loudness of a sound depends on the wave’s amplitude.This is why a stereo system has an “amplifier”, a device that increases the amplitude of sound waves.The louder a sound, the bigger the amplitude.This is also a way of measuring the amount of energy the wave has.
8AcousticsLoudnessThe system used to measure the loudness of sounds is the decibel system, given the unit dB.The decibel system is based on logarithms, which means for every step up by one, the sound is actually ten times louder. For example, a 15dB sound is ten times louder than a 14dB sound.* Lesson 49: Properties of Sound by Mr. Clintberg’s Study Physics
9Acoustics One of the loudest man-made sounds 215 dB That much sound energy creates heat.Water is used to absorb the energyThat’s steam you see. It’s not all smoke.If they did not use water to absorb the sound, the shuttle and tower would fail due to the energy generated from 215 dB.
10AcousticsNoise pollution is huge especially in our cities
23Acoustics Review Specification CSI Division – Acoustical Panel CeilingsQuality AssuranceClass “A”Coordination – Anything above the ceilingExtra Material
24Acoustics Review Specification CSI Division – Acoustical Panel CeilingsManufactures - PanelsMineral BaseType III (see slide 24)Pattern EI (see your handout for “E”+ “I”STC -35Tegular EdgeSize 24”x 24”Manufacture – Armstrong – Cirrus 584 (or equal) “by”Celotex or USG
25Acoustics Review Specification There are 20 types A Type III CSI Division – Acoustical Panel CeilingsTypes of MaterialThere are 20 typesA Type IIIMineral base with painted finish;Type includes:Form 1 Nodulated, cast, or moldedForm 2 Water feltedForm 3 Dry felted
33Sound Absorption Walls Plaster, gypsum or lime on brick = ά .02 Floor Wood = ά .10CeilingPlaster, gypsum or lime = ά .06(See handout)ά = Noise Reduction Coefficient (NRC) orSound Absorption CoefficientThis is similar to the example on page 791
34Sound Absorption What is the reverberation time with no finishes? Walls ά SabinsBack 10’x 32’= sfFront ’x 32’= sfSides (12’ave. x 98’) x 2 = ,352 sf3,120 sf x ά .02 =Floor31 x ,038 sf x ά =Ceiling31 x ,038 sf x ά =Total
35Father of Architectural Acoustics Sound AbsorptionT = .05 V/aWallace Clement SabineFather of Architectural Acoustics
36The Formula T = .05 V/a Sound Absorption T = Time of Reverberation T = Time of ReverberationV = Volumea = Sabins
37T= 3.32 seconds Sound Absorption The Formula T = .05 V/a V = Volume of room 31’x 98’x 12a = sabins of = 548.5T= .05(31’x 98’x 12’)/ 548.5T= .05(36,456)/548.5T= 3.32 seconds
38With acoustical tile & carpet, what would be the reverberation time? Sound AbsorptionWith acoustical tile & carpet, what would be the reverberation time?
39Sound Absorption Walls ά Sabins Floor with Carpet Ceiling Back 10’x 32’=Front 14’x 32’=Sides (12’ave. x 98’) x 2 = 2,3523,120 sf x ά =Floor with Carpet31 x 98 3,038 sf x ά =Ceiling- Acoustical tile(5x7) 8 each sf x ά .85 = 2383,038 sf – 280 sf 2,758 sf x ά = 165.5w/o carpet (769.7) Total
40T= 2.04 seconds Sound Absorption The Formula T = .05 V/a V = Volume of room 31’x 98’x 12a = sabins ofT= .05(31’x 98’x 12’)/T= .05(36,456)/T= 2.04 seconds
48Sound Absorption Change in Intensity Level, db 1 3 5 10 18 Change in Apparent Loudness Almost imperceptible Just perceptible Clearly noticeable Twice as loud Very much louder
49$8,296.00 for an imperceptible noise reduction! Sound AbsorptionFor a noise reduction of 2.11!Carpet3,136 sf of carpet or 348 sy at $22.00 sy = $7,666.00Acoustical Ceiling Tile280 sf x $2.25 = $630.00Total cost furnished and installed $8,296.00$8, for an imperceptible noise reduction!(For 1.48 db reduction just for the acoustical tile)
54Floor Sound Absorption Floor area (5 x 98)x 2 = 980 sf 3,038 sf x ά =Floor area(5 x 98)x 2 = 980 sf(32 -10) x 8 = 176 sf(32–10) x 5 = 11o sf1, 266 sf3,038 sf – 1,266 sf = 1,776 sf seating area
55Sound Absorption 1,776 sf x ά .80 =1,402.8 Walls ,120 sf x ά =Floor with Carpet1,266 sf x ά =With students1,776 sf x ά =1,402.8Ceiling- Acoustical tile(5x7) 8 each sf x ά .85 = 2383,038 sf – 280 sf sf x ά = 165.5Total 2,030.58
56Sound AbsorptionT= .05(36,456)/ 2,030.58T= .90 secondsThe seating alone with or without students has much more value than either the ACT or the Carpet.