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

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1 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 within a given space. Design methods consist of good (informed) decision-making regarding room materials and spatial geometries. Design tools provide procedures to sort the good from the bad. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Reminder Frequency the mix of frequencies is to sound what the mix of wavelengths is to light color note: SPL values (y-axis) are taken in the environment and must therefore specify location (in this case distance relative to the sound source) same weighted single-number dba values, but different frequency patterns Architectural Acoustics: Egan Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Reminder Octave Bands octave band octave band Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 Reminder Acoustic Elements Source The origin of a wanted (or unwanted) sound; architectural design decisions can exert influence on some sound sources Path How the source energy gets to the receiver; this is where architectural design for room acoustics can exert the most influence Receiver Where sounds end up; receiver reactions are the basis of design intent and criteria (OPR); little architectural influence is possible at the receiver Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Source/Path/Receiver equipment, people, instruments, appliances design decisions affect paths << rarely used in architectural acoustics << measured << perceived Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Acoustical Fields OPEN distance sound distribution in the built environment may involve three reception zones: (1) near field (2) free far field (3) reverberant far field OPEN ENCLOSED: typical room acoustics scenario Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Acoustical Fields OPEN versus ENCLOSED in a small space, the action is here and enclosure details have little effect in a large space, most action is here and enclosure details are of concern SMALL VERSUS LARGE Architectural Acoustics: Mehta, Johnson, Rocafort Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Acoustical Design Criteria There is NO unified theory of acoustical success, comfort, or acceptability, No acoustical comfort zone has been defined For the designer, each of the owner s acoustical project requirements must fend for itself Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Acoustical Design Intents To To To To To To Establishing intents and criteria appropriate to a specific project and space is the architect s responsibility (as the expert) with help from the client (as the user). Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Acoustical Design Criteria w db(a) x AI y NC z db at 500 Hz 80% occupant satisfaction 2 local design awards no complaint calls at midnight positive responses that equal those for lighting Criteria (as discussed earlier this semester) are benchmark values that define success for the owner and/or design team; once established nothing less should be acceptable hit the defined targets Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Typical Room Acoustics Design Intents Avoidance of anomalies (design errors) Echo Creep Focusing Flutter Distortion Adequate loudness Often linked to appropriate background SPL (NC) Acceptable reverberation Appropriate articulation Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Room Acoustics Anomalies Echo see the next slide Creep and Focusing Flutter Distortion room materials change the distribution of sound frequencies by differential absorption Architectural Acoustics: Egan Wikipedia: An anomaly is any occurrence or object that is strange, unusual, or unique. It can also mean a discrepancy or deviation from an established rule, trend, or pattern. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Avoiding Echo Echo is a reflection of a sound event (a footstep, a syllable, a word, a hand clap) that is sensed as being temporally separate from the original sound signal (hey, hey, hey, hey) Echo is rare in most building spaces (or it occurs in a space, such as a stairwell, where it is generally inconsequential) The potential for echo is a function of reverberance (room hardness ) and of room size Avoid hard rooms (and really avoid large, hard rooms) Design criterion is usually no echoes Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Avoiding Creep See sketch for definition (creep involves multiple relaying reflections) Creep in modern buildings is rare (but not impossible) Caused by curvilinear (or faceted planar) focusing geometry and hard surfaces Avoid the above combination Design criterion is usually no creep Who is that clown? Who is that clown? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Avoiding (unwanted) Focusing See sketch (the red lines) for definition focusing involves directional reflections that concentrate sound Very possible with curved space geometries A function of curvilinear geometry and hard surfaces Avoid the above combination Design criterion is usually no focusing base diagram from Architectural Acoustics: Egan Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 Avoiding Flutter Flutter is a standing wave (see sketch) Not a common phenomenon, but it is interesting (and often disturbing) when it occurs resulting in closely adjacent areas of high and low sound pressure Caused by a parallel surface geometry and hard surfaces Avoid the above combination Design criterion is usually no flutter Architectural Acoustics: Egan Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Avoiding Distortion Distortion is a rebalancing of sound frequencies in the reverberant field (following a reflection) Not a big deal for most speech, but a serious issue for live music in larger spaces Caused by the inherent acoustical absorption characteristics of typical building materials Avoid by carefully selecting room finish materials to provide a balanced absorption spectrum A realistic design criterion is usually limited distortion (seeking no distortion would prove very expensive) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Distortion for most materials, sound absorption is not the same for all frequencies assembly #51 generally reflects low frequencies, but very seriously absorbs higher frequencies Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Adequate Loudness Intents (a few of several possibilities) Provide adequate loudness for unamplified voice Provide adequate loudness for amplified voice Provide adequate loudness for small-group music Criteria (again, just some possibilities) A minimum SPL (sound pressure level) of xx dba at point x A minimum SPL at 500 Hz of xx db at point x Design Validation Involves a crunching of numbers (see the next few slides) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Adequate Loudness Loudness (sound pressure level) at a point of interest results from the interaction between sound source energy and the environment (materials and geometry) SPL = PWL + effects of the space reverberant component free field component SPL = PWL + 10 log [(Q/4πr 2 ) + (4/R)] distribution distance room PWL = sound power level; SPL = sound pressure level Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Adequate Loudness: Design Variables Q is a source configuration or distribution factor (representing degrees of sound source constraint/concentration): Q = 1 for free distribution (source suspended in room) Q = 2 for planar distribution (source against a wall) Q = 4 for bi-planar distribution (source at a cove) Q = 8 for tri-planar distribution (source in a corner) the higher the Q value, the greater the SPL for the same power Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 Adequate Loudness: Design Variables r is the distance between the source and an identified point of interest/analysis (a point where a receiver may be located) 1/r 2 represents the effect of the inverse square law (energy spreads out over an increasing area, thus reducing its density) the lower the r value, the greater the SPL for the same power Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Adequate Loudness: Design Variables R is the room constant where, R = Sά / 1-ά where (further) S = surface area of the room enclosure planes ά = average sound absorption coefficient of room surfaces Sά is the total absorption of the room (in Sabins) this is also sometimes represented as A (more info later) examples: R for absorptive room (0.9/0.1) = 9 R for average room (0.5/0.5) = 1 R for reflective room (0.1/0.9) = 0.1 the lower the R value, the greater the SPL for the same power Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 Room Acoustics Example Key Elements: absorption reflection diffusion noise control Philharmonie Essen Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Room Acoustics Example Royal Festival Hall Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 Crystal Cathedral Orange County, CA smileosmile.com/ jeremysarber.com/ Room Acoustics Example Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Serpentine Gallery London, UK temporary pavilion Frank Gehry (beyond titanium) Room Acoustics Example Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14