ARCHITECTURAL ACOUSTICS. Sound. bandshell; Honolulu, HI a passive, architectural system. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1

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1 ARCHITECTURAL ACOUSTICS SOUND & HEARING Sound bandshell; Honolulu, HI a passive, architectural system Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Sound Can architecture be heard? Most people would probably say that as architecture does not produce sound, it can not be heard. But neither does it radiate light and yet it can be seen. We see the light it reflects and thereby gain an impression of form and material. In the same way we hear the sounds it reflects and they, too, give us an impression of form and material. Differently shaped rooms and different materials reverberate differently. Experiencing Architecture: Steen Eiler Rasmussen Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Architectural Acoustics Preview Fundamentals The basic stuff you must understand to be able to design acoustically-acceptable spaces Noise Control Designing with a focus on reducing unwanted sounds (within and between spaces) Room Acoustics Designing with a focus on enhancing wanted sounds within individual spaces Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Light* versus Sound Light Acts as a wave Electromagnetic Wavelength Very fast High energy Some quirky units Travels through vacuum Sound Is a wave Mechanical Frequency Fairly slow Low energy The decibel No * since we ve already covered light, this is perhaps a useful comparison Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 Sound conceptually An audibly evaluated pressure variation Sound is energy that is heard Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Sound physically A pressure variation (energy) in an elastic medium (usually air), that can be detected by the human ear (with frequency generally falling between 20 and 20,000 Hertz for the typical college-age person) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Vibration conceptually A tactilely evaluated pressure variation Vibration is energy that is felt Vibration generally becomes an architectural design issue at frequencies below the audible range (< 20 Hz) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Noise conceptually Unwanted sound Noise is unwanted sound. Noise is a qualitative concept. Noise is analogous to glare; it is a negative phenomenon perceived by an individual. Saying unwanted noise is totally redundant. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Basic Architectural Acoustics Terms Sound is heard Vibration is felt Noise is unwanted sound (or possibly unwanted vibration although almost any vibration in a building is going to be unwanted) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Properties of Sound SPEED used as a scientific reference value as in the speed of sound (Mach) 340 meters per second in air (versus 299,792,458 m/s for light) in most building situations this means sound transfer is NOT instantaneous the transit time for sound in large spaces is often discernable plane breaking the sound barrier: Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Properties of Sound FREQUENCY 20 to 20,000 Hz (statistically) Hz = Hertz Hertz = cycles per second these frequencies correspond to 17 to meters wavelength vs nm for light Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Frequency the frequency distribution of a sound defines its tonal character; similar to the way wavelength distribution defines the color of light Frequency Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Frequency There are 19,980 discrete integer frequencies within the range of human hearing (20,000 Hz minus 20 Hz); it is difficult to consider/discuss all these frequencies individually unless it is done graphically Averaging across frequencies is a bad idea (valuable information will be lost through the averaging process) The octave band concept comes to the rescue Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Averaging as a Bad Idea averaging intensity across all frequencies would suggest these three sounds are the same they are not 1 Intensity 2 3 average Frequency Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Octave Bands An octave is a doubling (in this case, a doubling of frequency) An octave band is a range or span of frequencies identified and named by a center frequency (these include 31.5, 63, 125, 250, 500, 1000, 2000, 4000, 8000, 16,000 Hz) Information about sound characteristics (such as intensity) at several (perhaps 4, or 6, or 8) octave bands is generally used to describe architectural sounds Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Octave Bands as a Good Idea these three sounds look different at most octave bands Intensity average octave band center frequencies Frequency Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 Properties of Sound ENERGY sound is a lower quality form of energy than light it is mechanical versus electromagnetic raw energy and acoustical effect are not equivalent you wouldn t want to heat a building with sound, but the ear is very sensitive the ear is not, however, equally responsive to all frequencies (some sound energy has a greater impact on people than other sound energy) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Sound and Materials Sound that encounters a building material may be: reflected (reflectance, rho) absorbed (absorbtance, alpha) transmitted (transmittance, tau) Due to the law of conservation of energy: rho + alpha + tau = 100% these properties/concepts parallel those that apply to light Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Sound Measurement and Units A Preview Sound power (W, watts) source property Sound pressure (Pa, pascals) space property Sound intensity (W / sq cm) space property Sound power level (db, decibels) source property Sound pressure level (db) space property Sound intensity level (db) space property Loudness receiver perception quantitative basic quantitative derived Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Hearing outer ear middle ear inner ear receiver transmitter transformer the ear reacts to sound pressure through a linked series of mechanical motions triggered by sound pressure, these motions result in the generation of nerve signals Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Hearing Sensitivity hearing is most sensitive here equal loudness contours all points on any given curve seem equally loud to a listener (even if of different energy content) energy impression Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Hearing Phenomena Directivity People can fairly accurately place the source of a sound [as a result of bi-aural (2-ear) detection] Masking One sound can cover (or mask) another sound; this effect can be selective when sounds are of similar magnitude [you can, to some extent, pick which sound to hear ] Memory The ability to imprint a sound/voice in one s memory [so you don t have to ask who s this on every phone call] moodtexas.com Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 The Magnitude of Sound Sound power A property of a sound source; independent of surroundings; not affected by the environment (i.e., by building characteristics); used in architectural acoustics Sound pressure The effect of a sound source (or sources) at a particular location is affected by the environment; used in architectural acoustics Sound intensity An alternative to sound pressure (same concept, different units); typically not used in architectural acoustics Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Measuring Sound Pressure reading is a single value A or C weighting scale setting integrating sound level meter (we have several) gives a single-number (frequency-weighted-average) value for sound pressure level (in dba or dbc) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 The Weighting Scales most commonly used for architectural acoustics C weighting is essentially flat; has little effect on result; A weighting is not at all flat and weakens effect of lower frequencies Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Basis of the A Weighting Scale the A weighting scale emulates the frequency response of the human ear Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 Measuring Sound Pressure octave-band sound level meter (we have one!) gives values of sound pressure level at specific octave bands (in db) reading is a series of values (shown graphically) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Grateful Dead: Wall of Sound ( Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14

15 Boise, Idaho: green building, constructed circa 1900, cooling energy use = 0, no purchased heating energy; plug loads = 0, locally-sourced materials; if LEED was around back then, this would get a Platinum rating Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Boise, Idaho: green building, constructed circa 2005; LEED was around back then, and this building received a Platinum rating Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15