Transmission Loss (TL) Basics

Transcription

1 NOISE CONTROL DESIGN not an architecturally-desirable approach to noise control Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Transmission Loss (TL) Basics Mass Law: in theory, TL will increase with increasing mass as shown in the graph Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Transmission Loss (TL) Basics Frequency Law: in theory, TL will increase with increasing frequency as shown in the graph Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Transmission Loss Realities Real World: TL increases about 4 db per octave (vs. 6 db in theory) because stuff happens (poor detailing, material defects, shoddy construction, etc.) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 Transmission Loss Realities Real World: actual assembly TL curves show performance realms compared to the smooth curves of the mass and frequency laws Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Transmission Loss Details performance follows the mass law resonance: bridge; drum performance deviates from mass law due to assembly resonance Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Sound Transmission Class (STC) a set of standard template curves is used to assign a single-number value (STC) to sound barrier performance in lieu of multiple TL values note the familiar (dba-like) shape of the curves Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Sound Transmission Class (STC) example: matching an actual TL curve and STC template curve to get STC value (there are established rules governing this procedure) graphically, an overlay of actual TL values is set on top of STC curves and moved around until the rules are met Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Designing with/for TL Mass law defines a basic reality (TL is not cheap or easy) Law of diminishing returns constrains mass law effects (getting high TL is not easy) The realities of actual construction chip away at the already dismal limits of the mass law Stiffness/resonance further decreases TL (yet these come automatically with increasing mass) except for lead curtains (which are massive yet flexible) multi-wythe barriers (series barriers that add mass without substantial stiffness increases) And then -- weak links such as holes viciously destroy barrier performance Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 A Starting Point for TL-STC acoustical situation tips for getting started with sound barrier selection (early design moves) design problem potential solution Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Building Codes and TL-STC code-minimum requirement; not necessarily optimum or even appropriate for a specific project or client a warning about flanking a big exemption (due to cost concerns) IIC more later excerpt from 2006 International Building Code Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Getting Data on TL-STC wall-mart performance details Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Envisioning Constructions for TL-STC an illustrated catalog of options Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Designing for TL General patterns to remember when dealing with TL: ideally, TL will increase 6 db for each doubling of barrier mass (as per the mass law) BUT practically, the TL increase in the real world is more like 4-5 db per octave do good details and supervise construction ideally, TL will increase 6 db for each doubling of frequency BUT practically, coincidence dip may cause a serious discontinuity in this frequency law pattern watch for this in critical applications a plot of TL versus frequency generally shows three performance zones one where mass rules and two where resonance and coincidence rule, with the details being specific to each assembly Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Designing for TL General patterns to remember when designing for TL: providing the same mass in two leaves/withes (separated panels) will provide better performance than in a monolithic panel (but will NOT double the performance) two dissimilar leaves perform better than two identical leaves filling the cavity between leaves (3/4 full) with acoustically absorbing material will increase TL (but it is the mass that drives TL, not the fluffy stuff) increasing the depth of cavity between leaves will reduce cavity resonance effect (and increase TL) separate leaves must be as separate as possible (the fewer and more flexible the connections/couplings the better) a weak link will dominate sound barrier performance; holes and gaps are the weakest link of all Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Parallel-Path Sound Barriers path 1 might be a masonry wall; path 2 might be a window Path 1 Path 2 the weak link rules! Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 Holes in Barriers holes are a really bad idea! Barrier Hole Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Flanking This term is used to describe the ability of sound (noise) to find the path of least resistance (to go around barriers) Design to avoid flanking Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Flanking high alpha = low rho but alpha includes tau unfortunately, the sound absorption coefficient for many materials is really the not reflected coefficient and includes transmitted sound Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 partition stops at ceiling; one grille serves two rooms Flanking gasket deteriorates; closure not quite 100% exam room in doctor s office Please keep this confidential, doc! movable partition, hotel meeting room anywhere or AB 101 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Masking Sound/Noise when all else fails, masking sound can be used to paint over problems: masking sound is intentionally-introduced background noise as an architect, think about intentionally adding unwanted sound! Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Impact Insulation Class criteria shopping mall impact insulation class: IIC Is a single-number index that expresses the ability of an assembly to block the transmission of impact sound (STC deals with airborne sound) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 Impact Insulation Class performance details Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Impact Insulation Class an illustrated catalog of options note the details in descriptions the details really matter Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 Never Forget to Design for Humans think also glare. or noise and the cubicle with the Muzak controls Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Never Forget Common Sense ice maker glare phones Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 don t forget why you design a building (it has something to do with people) design intent and design criteria (they are important) because it is too late for fixes after the building is built (these are passive systems) green buildings chasing LEED credits or designing good environments? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 no mas! no mass! a nice wind barrier and visual barrier NOT a sound barrier neither of these is a rational approach to noise control Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14