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## Or How to make a client happy

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**Acoustics**Or How to make a client happy**Fundamentals of Architectural Acoustics**Acoustics**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. * Acoustics**Speed**• The 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 or 344 m/s • Light is 186,000 miles per second Acoustics**Frequency**• Most 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 20,000Hz • Frequency is sometimes referred to as pitch. Acoustics**Loudness**• The 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. Acoustics**Loudness**• The 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 Acoustics**Acoustics**• One of the loudest man-made sounds 215 dB • That much sound energy creates heat. • Water is used to absorb the energy • That’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.**Acoustics**Noise pollution is huge especially in our cities**Inverse Square Law**• Not in textbook Acoustics**Chapter 18**Sound in Enclosed Spaces Acoustics**Sound Absorption**• Noise Reduction Coefficient (NRC) Verses • Sound Transmission Coefficient (STC) (textbook class it Sound Transmission Class) Acoustics**Acoustics**STC**Acoustics**NRC**Review Specification**• CSI Division 09511 – Acoustical Panel Ceilings • See Handout in class • Also available on line at Arch 433 - Web Site Acoustics**Review Specification**• CSI Division 09511 – Acoustical Panel Ceilings • Submittals • Ceiling Samples – tile and grid • Tile 6 inch square samples Grid boxes – 3 samples each • Follow directions in section 01330 – Submittal Procedures • Ceiling layout – drawings – 3 sets • Attachment methods Acoustics**Review Specification**• CSI Division 09511 – Acoustical Panel Ceilings • Quality Assurance • Class “A” • Coordination – Anything above the ceiling • Extra Material Acoustics**Review Specification**• CSI Division 09511 – Acoustical Panel Ceilings • Manufactures - Panels • Mineral Base • Type III (see slide 24) • Pattern EI (see your handout for “E”+ “I” • STC -35 • Tegular Edge • Size 24”x 24” • Manufacture – Armstrong – Cirrus 584 (or equal) “by” • Celotex or USG Acoustics**Review Specification**• CSI Division 09511 – Acoustical Panel Ceilings • Types of Material • There are 20 types • A Type III • Mineral base with painted finish; • Type includes: • Form 1 Nodulated, cast, or molded • Form 2 Water felted • Form 3 Dry felted Acoustics**Review Specification**• CSI Division 09511 – Acoustical Panel Ceilings • Manufactures – Grid • Direct Hung • Powdered-Actuated Fasteners in Concrete - OK • Wire – 12 gauge • Hold Down Clips – Yes • Grid – 15/16” • Manufactures – Armstrong, Chicago, Interiors Inc. Acoustics**Review Specification**• CSI Division 09511 – Acoustical Panel Ceilings • Acoustical Sealant • At perimeter joints and openings • Flame spread & smoke development < 25 per ASTM E84 • Exposed • At perimeter joints and openings • Flame spread & smoke development < 25 per ASTM E84 • Concealed • BA-98 Pecora or Tremco Act. Sealant • AC-20 FTR or Sheetrock Act. Sealant, USG Acoustics**Review Specification**• CSI Division 09511 – Acoustical Panel Ceilings • Execution • Balance boarders • Splay hangers • Sealant @ wall angle • Screw attach wall angle • Cleaning Acoustics**Let’s do a sound absorption problem!!!!**Acoustics**Carpenter Hall Room 102**Foot print of Carpenter Room 102 32’ x 98’ Ceiling Ht. 14’ to 10’ average 12’ Sound Absorption @ 500Hz Sound Absorption**The Formula T = .05 V/a**and NR = 10log (a2/a1) We’ll get to the formulas later Sound Absorption**Walls**Plaster, gypsum or lime on brick = ά .02 Floor Wood = ά .10 Ceiling Plaster, gypsum or lime = ά .06 (See handout) ά = Noise Reduction Coefficient (NRC) or Sound Absorption Coefficient This is similar to the example on page 791 Sound Absorption**What is the reverberation time with no finishes?**Walls ά Sabins Back 10’x 32’= 320 sf Front 14’x 32’= 448 sf Sides (12’ave. x 98’) x 2 = 2,352 sf 3,120 sfx ά .02 = 62.4 Floor 31 x 98 3,038sf x ά .10 = 303.8 Ceiling 31 x 98 3,038 sf x ά .06 = 182.3 Total 548.5 Sound Absorption**Sound Absorption**T = .05 V/a Wallace Clement Sabine Father of Architectural Acoustics**The Formula T = .05 V/a**T = Time of Reverberation V = Volume a = Sabins Sound Absorption**The Formula T = .05 V/a**V = Volume of room 31’x 98’x 12 a = sabins of = 548.5 T= .05(31’x 98’x 12’)/ 548.5 T= .05(36,456)/548.5 T= 3.32 seconds Sound Absorption**With acoustical tile & carpet,**what would be the reverberation time? Sound Absorption**Walls άSabins**Back 10’x 32’= 320 Front 14’x 32’= 448 Sides (12’ave. x 98’) x 2 = 2,352 3,120 sf x ά .02 =62.4 Floor with Carpet 31 x 98 3,038 sf x ά .14 = 425.32 Ceiling - Acoustical tile (5x7) 8 each 280 sf x ά .85 =238 3,038 sf – 280 sf 2,758 sf x ά .06 =165.5 w/o carpet (769.7) Total891.22 Sound Absorption**The Formula T = .05 V/a**V = Volume of room 31’x 98’x 12 a = sabins of 891.22 T= .05(31’x 98’x 12’)/ 891.225 T= .05(36,456)/ 891.22 T= 2.04 seconds Sound Absorption**3.32 seconds vs. 2.04 seconds**Sound Absorption**NR = 10log (a2/a1)**NR = Noise reduction a2 = 2.04 seconds a1 = 3.32 seconds Sound Absorption**NR = 10log (a2/a1)**NR = 10 log (2.04 / 3.32) NR = 10 log (.614) NR = 2.11 Noise Reduction of = 2.11 db Acoustical tile alone = 1.48 db Sound Absorption**WHAT!**Sound Absorption Is this enough?**Sound 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**For a noise reduction of 2.11!**Carpet 3,136 sf of carpet or 348 sy at $22.00 sy = $7,666.00 Acoustical Ceiling Tile 280 sf x $2.25 = $630.00 Total cost furnished and installed $8,296.00 $8,296.00 for an imperceptible noise reduction! (For 1.48 db reduction just for the acoustical tile) Sound Absorption