Acoustical Engineering Solutions

Transcription

1 Acoustical Engineering Solutions

2 Scott Harvey, PE Thank you for attending!

3 Copyright Materials This presentation is protected by US and International Copyright laws. Reproduction, distribution, display and use of the presentation without written permission of the speaker is prohibited. Phoenix Noise & Vibration, LLC 2006

4 At the end of this program, participants will be able to: 1. Understand basic acoustic principals and terms 2. Define acoustics and its place in building design 3. Understand how acoustics can affect building performance 4. Design buildings with acoustics in mind

5 One definition: the qualities or characteristics of a room, auditorium, stadium, etc., that determine the audibility or fidelity of sounds in it.

6

7 the branch of physics that deals with sound and sound waves.

8 What is sound? Any pressure variation (in air, water or other medium) that the human ear can detect. B&K

9 What is Noise? Noise is Unwanted Sound (aka my neighbor s stereo)

10 How is sound quantified Amplitude or loudness Variation in the air pressure around us The bigger the variation, the louder the sound Frequency or pitch/tone How quickly we vary the pressure The quicker the variation, the higher the tone

11 Loudness measured in decibels (db) db = 10 x log(pressure 2 /refpressure 2 ) From this we observe: logarithmic simply a comparison between two numbers Human Range: 0 to 130 db

12 decibel named after Alexander Graham Shown here with Helen Keller and Ann Sullivan

13 We measure noise in decibels or db for a lot of reasons, two being... Broad range of numbers to a manageable scale Comparisons are easier

14 Reduces the broad range of numbers to a manageable range of numbers. Humans hear from 20 to 20,000,000 micro-pascals In decibels, this is reduced to a range of 0 to 120 db.

15

16 Eases Comparisons Example of the logarithmic nature: Change in db Subjective Response 3 db Barely Perceptible 5 db Clearly Perceptible 10 db Twice as Loud

17 Frequency (tones) measured in Hertz (Hz) 1 Hz = 1 cycle/second Human range 20 Hz to 20,000 Hz

18 Named for Heinrich Rudolf Hertz Famous German Physicist First person to transmit and receive radio waves

19

20 80 70 Sound Pressure Level, db Frequency, Hertz

21

22 Room Acoustics (Concert Halls plus) Room to Room Noise Control Acoustics Background Noise Control Outdoor to Indoor Noise Control

23

24 Traditional Acoustics Concert Halls Drama Theaters Performance Venues Houses of Worship But wait

25

26

27

28

29

30

31

32

33 Achieve proper acoustics by defining desired character of the space Maximize the acoustical efficiency within the room by controlling the wanted sound within the space Minimize unwanted sound (background noise)

34 Reverberation time (RT) the time it takes for sound pressure level to decay by 60 db from its steady state value after the sound source has been terminated. Measured in seconds

35 Reverberation Time 90 Sound Pressure Level, db RT = 3.6 seconds Time, seconds

36 What controls reverberation time? Room Size (Volume) Room Finishes Room Shape Therefore, we can control RT by changing either the size, shape or finishes of the room.

37 Range of Recommended Reverberation Times 3 Reverberation Time, sec Room Use Acoustical Solutions, Inc.

38 Reverberation Time Change with Room Volume Equal Finishes RT, seconds ,000 10, ,000 Room Volume, cubic ft

39 Reverberation time varies with frequency Reverberation Time, Seconds Measured Design Goal Frequency, Hz

40 RT's of Famous Concert Halls RT, seconds Royal Albert Hall, London Kennedy Center, Washington, D.C. Symphony Hall, Boston Frequency, Hz Beranek, Music, Acoustics, and Architecture, Wiley, 1962

41 NOT JUST FOR PERFORMANCE HALLS. LEED for Schools specifies 0.6 seconds for core learning space < 10,000 ft seconds for core learning space >10,000 ft 3 but < 20,000 ft 3

42 Room Finishes Absorbers Reflectors Diffusers

43 Sound Absorbers surfaces which absorb sound and prevent reflections Generally Soft Materials Sound Absorption Coefficient NRC The perfect absorber is an open window

44 Absorption Coefficient a measure of the sound absorbing property of a surface. More specifically, absorption coefficient is defined as the fraction of the incident sound energy absorbed (otherwise not reflected) by a surface. Noise Reduction Coefficient (NRC) a single number rating derived from measured values of sound absorption coefficients of a material at 250, 500, 1000, and 2000 Hz. NRC is an estimate of the sound absorptive property of an acoustical material.

45 Open Window NRC = 1.0

46 Marble Floor NRC = 0.01

47 Change in RT with Treatment 1000 cu ft, gyp bd walls 3.5 RT, seconds Concrete Floor, NRC = 0.02 Carpeted Floor, NRC = Frequency, Hz Carpeted Flr/Acoustical Tile Ceiling, NRC = 0.57

48 Reflectors are opposite absorbers Also ranked using NRC scale Used to direct sound Caution: Avoid large, parallel reflective surfaces Kinetics Noise Control

49 Diffusers scatter the sound energy Used to enhance acoustical quality of a listening room Studios, practice rooms, recital halls, concert halls

50 Carpet Absorber

51 Painted Gypsum Board Reflector

52 Painted CMU Reflector

53 Acoustical Tile Ceiling Absorber

54 Metal Decking Reflector? Or Diffusor?

55 Plywood Reflector

56 Glass Reflector

57 People Absorber

58 Acoustical Metal Decking Absorber

59 Unpainted CMU Resorber?????

60 8,100 ft 2 277,000 ft 3 Wood Floor Gyp Walls Metal Ceiling

61 Measured Design Goal

62 Range of Recommended Reverberation Times 3 Reverberation Time, sec Room Use Acoustical Solutions, Inc.

63 Ceiling/Wall Absorption Measured

64

65 Wall Absorption Measured

66 Measured Design Goal Tectum Roof Deck

67

68

69 Sound Transmission Class (STC) Ceiling Attenuation Class (CAC) Impact Insulation Class (IIC)

70 Sound Barrier device used to block sound transmission from one point to another. Transmission Loss per frequency Sound Transmission Class (STC) a single number rating of the partition s ability to block speech frequencies from one side to another.

71

72 There are noise barriers and there are noise absorbers. Barriers are not absorbers. Absorbers are not barriers. Many times the absorber is somewhat transparent. Barriers are generally composed of dense, heavy material layers. (Quiz Later)

73 Barrier or Absorber? Barrier

74 Barrier or Absorber? Absorber

75 Barrier or Absorber? Barrier

76 Barrier or Absorber? Absorber

77 Barrier or Absorber?????

78 STC ASTC Subjective Description Most sentences clearly understood Speech can be heard with some effort Loud speech can be heard with some effort Loud speech essentially inaudible Loud music heard faintly 75+ Most noises effectively blocked Credit: Architectural Acoustics: Principles and Design 1999

79

80 STC developed for speech, applied to many other noise sources such as: Mechanical Transportation Music

81 One cost effective way to add STC points to a wall system is through the use of Resilient Channel Cost effective but NOT SO SIMPLE (This really needs much more time )

82 Single Legged, RC-1 (Dietrich RC Deluxe) Double Legged, RX-2

83

84

85

86

87

88 Ceiling Attenuation Class (CAC) the measure for rating the performance of a ceiling system as a barrier to airborne sound transmission through a common plenum between adjacent close spaces. (Architectionary) Diracdelta.co.uk

89 CAC is similar to STC Applied primarily to lay in ceiling tiles CAC < 25 considered poor CAC > 35 considered good

90 Impact Insulation Class (IIC) - A single number rating used to compare the effectiveness of floor-ceiling assemblies in providing reduction of impact-generated sound such as footsteps.

91

92 The popularity of hard surfaced floors and condominiums has brought a lot of attention on IIC ratings. Most Any Carpet and pad > 60 IIC Hard floors < 40 IIC IBC /IRC standards are 50 IIC

93

94 Hard surfaces Low partition heights Small-ish cubicles

95

96

97 Background noise in non-residential buildings is influenced by a variety of sources Interior Sources Other employees Phones, printers, copiers, keyboards, etc. Cubicle partition heights Open plan office design HVAC

98 Exterior Sources Transportation Schools/Daycare centers Mechanical Equipment Construction/Landscaping Have the most design capability on HVAC components and mechanical equipment (emergency generator, cooling towers, elevators, etc.)

99 Single number ratings describing the relative loudness and speech interference properties of a given noise spectrum Used to specify background noise levels for various space uses, mainly HVAC and mechanical noise Noise Criteria (NC) Simple No assessment of sound quality Room Criteria (RC) Mark II Evaluates sound quality Diagnostics

100

101 Airborne Equipment location Duct break out Air flow Diffusers Structure Borne Proper Isolation Springs Pads Roof Curbs

102 Courtesy of ASHRAE

103 Courtesy of ASHRAE

104

105

106

107

108

109

110

111

112

113

114

115 Courtesy of ASHRAE

116

117

118

119

120

121

122 Transportation Noise Computer Modeling Building Shell Analysis Common Building Elements Windows and Doors: The Weak Link OITC

123 Planes, Trains, & Automobiles On-site measurements Computer Modeling HUD Noise Guidebook Ldn in dba

124 Typically measured using the A-weighted db scale or dba The A-weighting simulates human hearing and is generally used for overall, environmental noise measurements. A-Weighting 10 Adjustment Factor, db Frequency, Hz

125

126

127 Calculates a room s interior noise level based upon: Exterior Noise Level Composite STC Rating Windows, Doors Walls, Roof Miscellaneous Room Size & Volume Room Absorption Can be either very general or very detailed

128 Building Element STC Rating Construction Exterior Walls Brick Vinyl Siding Vinyl Siding w/rc x 4 wood studs, an exterior layer of ½ OSB or plywood, 3 of fiberglass batt insulation, 5/8 interior layer of drywall ½ Insulated Window 28 1/8 glass, ¼ air space, 1/8 glass 1 Insulated Window 35 ¼ glass, ½ air space, ¼ glass 5/8 Laminated, Insulated Window 35 Two 1/8 panes laminated together, ¼ air space, 1/8 glass Standard Patio Door 29 ½ thick glass lite mounted in polystyrene frame Upgraded Patio Door 36 1 dual glazed unit composed of 3/8 laminated glass, ½ air space, and 1/8 double strength glass

129

130 Outdoor-Indoor Transmission Class: an A- weighted single number rating of the transportation sound reduction effectiveness of a partition that separates an indoor space from the outside. STC Speech Frequencies OITC Transportation Frequencies Window STC Rating OITC Rating ½ Insulated /8 Laminated, Insulated 35 31

131 Restrictions on Exterior Façade Finishes Lots of Glass High STC Rated Windows and Doors = $$$ Green Building Design Bigger Windows Fresh Air Openings

132 Room Acoustics (Concert Halls plus) Room to Room Noise Control Acoustics Background Noise Control Outdoor to Indoor Noise Control

133 Questions? Lunch? Discussion?

134 Acoustical Engineering Solutions