FIRST, MORE ABOUT SOUND

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Preston Robinson
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Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Sound Descriptors impression psi (pressure) db

1 FIRST, MORE ABOUT SOUND ways of describing sound in architectural acoustics Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Sound Descriptors impression psi (pressure) db (pressure level) example situations Architectural Acoustics: Cavanaugh and Wilkes Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2

Sound Magnitudes typo expressing magnitudes awkward numbers very awkward numbers integer, easy-to-use numbers Architectural Acoustics: Mehta, Johnson, Rocafort Ball State Architecture ENVIRONMENTAL

2 Sound Magnitudes typo expressing magnitudes awkward numbers very awkward numbers integer, easy-to-use numbers Architectural Acoustics: Mehta, Johnson, Rocafort Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Sound Power and Sound Power Level (PWL) Sound power is a characteristic of a source and is independent of the environment into which the source may be placed watts Sound power level (PWL) is a ratio PWL = 10 log 10 (W / W ref ) decibels W = actual sound power; W ref = reference sound power Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4

3 Sound Pressure and Sound Pressure Level (SPL) Sound pressure describes the density of acoustical energy at a specific point in an environment influenced by both source and space Pascals Sound pressure level (SPL) is a ratio SPL = 20 log 10 (P / P ref ) decibels P = actual sound pressure; P ref = reference sound pressure Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Sound Intensity and Sound Intensity Level (SIL) Sound intensity also descries the density of acoustical energy at a specific point in an environment influenced by both the source and the space W/sq cm Sound intensity level (SIL) is a ratio SIL = 10 log 10 (I / I ref ) decibels I = actual sound intensity; I ref = reference sound intensity Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6

4 Pressure versus Intensity Sound pressure and sound intensity both express the magnitude of audible acoustical energy at a defined point in an environment as influenced by both source and space; they are conceptually interchangeable concepts (but not numerically equal) Sound pressure (level) is typically used in architectural acoustics simply because it is easier to measure (using a moderately-priced sound pressure level meter) for architectural acoustics pressure (yes) intensity (no) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Sound Loudness Sound loudness is a description of the magnitude of sound energy at some point in an environment; it is influenced by source, space, and receiver; and is described qualitatively (using words) or pseudo-quantitatively (using phons; sones) Loudness: quiet, very quiet, irritatingly loud Loudness: xx phons, yy sones my opinion: phons and sones are not a great idea we WANT qualitative evaluations from human occupants in order to deal with noise Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8

Quantifying Loudness (if you feel you really must do so)

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Grondzik 9 Mapping Sound Magnitudes quantitative

5 Quantifying Loudness (if you feel you really must do so) db(a) versus sones versus phons Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Mapping Sound Magnitudes quantitative quantitative qualitative Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10

decibels cannot be added arithmetically 20 db + 20 db 40 db use the table above or

6 Mapping Sound Magnitudes (as levels db) design affects people interpret Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Weird Math: Adding Decibels decibels cannot be added arithmetically 20 db + 20 db 40 db use the table above or the adjacent nomograph to add db Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12

Working with Decibels (db) decibels representing sound power, sound pressure, or sound intensity cannot be added arithmetically 40 db of piano and 20 db of guitar do not equal 60 db

set quirky, yes but that s life Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Working with Decibels (db) don t be afraid of the decibel it beats other alternatives www.

7 Working with Decibels (db) decibels representing sound power, sound pressure, or sound intensity cannot be added arithmetically 40 db of piano and 20 db of guitar do not equal 60 db of jazz BUT decibels can be added/subtracted when dealing with acoustical indices, such as noise reduction (NR) and transmission loss (TL) as will be seen, coming up, in this slide set quirky, yes but that s life Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Working with Decibels (db) don t be afraid of the decibel it beats other alternatives important use the decibel, get to know it or forsake architectural acoustics Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14

NOW NOISE CONTROL studios atrium design studios to right, multi-purpose atrium (with no absorptive surfaces) to left, no sound barriers between studio and atrium interesting

8 NOW NOISE CONTROL studios atrium design studios to right, multi-purpose atrium (with no absorptive surfaces) to left, no sound barriers between studio and atrium interesting acoustics Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Noise Is unwanted sound And, not all noise is equally unwanted Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16

9 Noise Annoyance In general, a person s annoyance (a subjective response) with a sound (noise) increases with increasing: loudness frequency narrowness of frequency range (less spectral breadth, perhaps moving toward pure tones) intermittency (just when you got used to it) unlocateability (where is that coming from?) undefinability (what is that?) intelligibility (the nosiness factor) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Noise Can Travel Via: Airborne sound transfer -- sound is transmitted through the air within (and surrounding) a building Structure-borne transfer -- sound is transmitted via building structural elements (steel, concrete, wood; floors, beams, walls) Duct-borne transfer -- sound is transmitted via ductwork (a very special case of airborne transfer) Impact sound -- sound is born at and borne (transmitted) via structure Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18

10 Noise Control Intervention Points At the source (by far the easiest option) select quieter sources; interpose distance between source and receiver; interpose spatial buffers; avoid conflicting adjacencies In transit (by far the most common option) through the use of sound barriers (be sure to reflect upon the inherent problems associated with structure-borne and duct-borne noise control using barriers) At a receiver (normally not a good design option) earplugs/muffs (OK in industrial environments) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 The Room Acoustics Context system boundary is this space OK? is this SPACE acoustically OK? room acoustics (next topic) looks at spaces incrementally; usually in isolation Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20

11 The Noise Control Context is this BUILDING OK? look at everything and more sources / paths / receivers room of interest system boundary Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Appropriate Background Sound/Noise There will always be some background sound in a space The design question is: what is an appropriate value for ambient sound in a space (to maximize performance; to reduce annoyance)? This is inherently a room acoustics issue, but setting criteria for acceptable room background noise is the starting point for Noise Control NC and RC curves provide a basis for benchmarking (design criteria) and are examples of single-number acoustical design indices (of which we will see many) References can provide guidance on what NC or RC value is historically considered most appropriate for a given building/client context Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22

loudness contours Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Sample NC

12 NC (Noise Criterion) Curves were developed using mechanical equipment noise (not music or crowd or traffic noise) the shape of the curves tracks the shape of the equal loudness contours Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Sample NC Recommendations less quiet more quiet Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24

13 RC (Room Criterion) Curves these are an update/revised version of NC curves NC and RC criteria currently coexist NC have not yet been retired Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 NC Compared to RC similar, but not Identical, criteria (see especially the high frequencies); the architect or the client will decide which approach is more appropriate for a given project is this a preferred target; or is this? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26

14 Noise Reduction (NR) Given 2 adjacent rooms, noise reduction (NR) is the difference in sound pressure level (SPL) from one room to the other such a difference is usually the result of a sound barrier NR = SPL 1 SPL 2 (in db) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Noise Reduction (NR) NR NRC NR is related to sound transmission NRC is related to sound absorption (and will be discussed under room acoustics) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28

15 Noise Reduction (NR) barrier blocks some sound; receiving room absorbs some sound source Δ SPL = NR NR is a function of barrier and receiving space characteristics Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Noise Reduction in Action ambient SPL (a result of PWL) = 55 desired SPL (from NC) = 35 sound barrier required? Δ SPL = NR = 20 db of NR Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30

Transmission Loss (TL) The ability of a barrier to prevent sound transmission (actually, its efficiency ) TL = -10 log (acoustic energy transmitted) (acoustic energy incident) (in db) reminder: log 1

16 Transmission Loss (TL) The ability of a barrier to prevent sound transmission (actually, its efficiency ) TL = -10 log (acoustic energy transmitted) (acoustic energy incident) (in db) reminder: log 1 = 0 log 0.5 = -0.3 log 0.1 = -1 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 31 Transmission Loss (TL) TL = x db at x Hz TL is a function only of barrier construction; it is an inherent characteristic of a wall/floor/ceiling assembly Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32

Grondzik 33 Approximate TL and NR Relationships (useful for early design decision making) NR = TL 1 if a live receiving space NR = TL +

17 Relating TL and NR NR is affected by the TL of a barrier and by the characteristics of the receiving space NR = TL -10 log (S) (A) (in db) where, S = surface area of the barrier A = total absorption in receiving room Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 33 Approximate TL and NR Relationships (useful for early design decision making) NR = TL 1 if a live receiving space NR = TL + 4 if an average receiving space NR = TL + 7 if a dead receiving space live average dead Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 34

ROOM ACOUSTICS. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1. Room Acoustics

ROOM ACOUSTICS. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1. Room Acoustics ROOM ACOUSTICS Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Room Acoustics Designing for room acoustics involves making architectural decisions that will support and enhance wanted sounds