Building systems for_interior designers phần 10 ppsx

CMUs, especially cinder blocks, are slightly porous unless painted or sealed. If sealed, CMUs can reflect all frequencies well. Other forms of masonry vary, but are similar to brick, concrete, and CMUs. Stone, including reconstituted materials such as ter- razzo, can be used for massive, load-bearing walls, stone veneer facing, or paving. Thick, well-sealed stone walls attenuate sound very well. Marble is among the most acoustically reflective materials. Some stone is naturally porous, and therefore less reflective. Plywood has a modest amount of mass, and is relatively ineffective for attenuating sound. Thin plywood furred out from a solid wall is a good absorber of low frequencies. Plywood is quite reflective at high frequencies. REFLECTIVE MATERIALS A smooth, dense wall of painted concrete or plaster absorbs less than 5 percent of the sound striking it, therefore making an almost perfect sound reflector (Fig. 51-2). Applying a skim coat of plaster makes very little improvement on the ability of masonry to absorb sound, except at low frequencies when suspended or furred out from the solid surface. Concrete is a massive material that reflects sound. Resilient flooring, such as vinyl, cork, asphalt, or rubber sheet or tile, also reflects sound, although it is acoustically useful to cushion impact noises. Glass is massive but thin, so its ability to attenuate sound is marginal. Well-separated double-glazing offers superior sound attenuation, as do some types of laminated glass. Laminated glass consists of two or more sheets of glass with interlayers that provide damping as the glass sandwich is flexed. Some types of laminated glass have substantially better attenuation than equal thicknesses of glass alone. Glass reflects higher frequencies almost completely. Because glass resonates, it will absorb good amounts of low frequencies. When designing interior glazing, glass lights with laminated glass set in resilient framing have more mass and offer better damping than plain glass in rigid frames. ACOUSTICALLY TRANSPARENT SURFACES Soft, porous, acoustically absorbent materials are often covered with perforated metal or other materials for pro- tection and stiffness. These coverings are designed to be acoustically transparent except at higher frequencies. With even smaller holes, the higher frequencies can also pass through. Staggering the holes improves absorption. Open weave fabric is almost completely transparent to sound, and provides a decorative cover on absorbent wall coverings. Acoustic Design 407 Massive materials keep sound from traveling from one side to the other. Double brick wall both reflects and absorbs sound Concrete-filled concrete masonry unit reflects and absorbs sound Figure 51-1 Massive materials. Plaster wall reflects sound well. Resilient tile, including vinyl, asphalt, cork, and rubber, reflects sound well. Concrete wall is massive, and reflects almost all sound waves. Reflective materials bounce sound back into the space of its origin. Figure 51-2 Reflective materials. If your noise problem is not coming from outside the room but is a result of the sound inside the room bounc- ing around, you need to address noise reduction within the space. The acoustic treatment of a space starts with reducing the source of the noise as much as possible. Next, try to control unwanted sound reflections. Speech privacy is another major acoustic concern for the interior designer. Sometimes it is also necessary to decrease or increase reverberation time for sound clarity and quality. Noise is reduced within a building by intercepting the sound energy before it reaches your ears. This is ac- complished by changing acoustic energy into heat energy. The amount of heat energy produced by sound is miniscule; 130 dB of sound, which is loud enough to cause pain, produce only one one-thousandth watt of heat. Most of this heat can easily be absorbed by the room contents and wallcoverings, and by the structure of the building itself. The contents of the space control the noise levels within the space, while the structure of the building controls the transmission of noise between spaces. In a normally constructed room without acoustical treatment, sound waves strike walls or the ceiling, which then transmit a small portion of the sound. The walls or ceiling absorb another small amount, while most of the sound is reflected back into the room. The amount of transmission to an adjoining space is determined pri- marily by the mass of the solid, airtight barrier between the spaces, not by the surface treatment. However, the amount of sound that is reflected off the surfaces back into the room is greatly decreased by absorptive materials. When acoustic material is applied to a wall or ceiling, some of the energy in the sound wave is dissipated before the sound reaches the wall, and the portion that is transmitted is reduced slightly. Adding absorptive materials to a room changes the room’s reverberation characteristics. This is helpful in spaces with distributed noise sources, like offices, schools, and restaurants. The acoustics of a space with hard surfaces can be improved by adding absorptive materials. In spaces with concentrated noise sources, the noisy equipment should be enclosed, rather than trying to treat the entire space. ABSORPTION COEFFICIENTS Materials are neither perfect reflectors nor absorbers of sound. The coefficient of absorption measures how efficiently the material absorbs sound. When all of the 52 Chapter Sound Absorption Within a Space 408 sound energy striking the material is absorbed, and none of it is reflected, the absorption coefficient is 1.0. This is what happens when sound flies out an open window; the window opening is said to absorb (not reflect) all the sound. Rooms are constructed and furnished with a mix- ture of materials, each with a different absorption coefficient. For most common materials, the ability to absorb sound varies with the frequency of the sound. In order to give a useful and general idea of a material’s ability to absorb sound at a variety of frequencies, the absorption coefficients at 250, 500, 1000, and 2000 Hz are averaged together for the noise reduction coefficient (NRC). The NRC is useful as a single-number criterion for measuring the effectiveness of a porous sound absorber at midrange frequencies. It does not accurately indicate the material’s performance at high or low frequencies. Because it is an average, two materials with the same NRC may perform differently. INSTALLATION OF ABSORPTIVE MATERIALS The way materials are installed affects their ability to absorb sound (Fig. 52-1). Installing absorptive materials directly on a wall or ceiling gives the least effective sound absorption. A layer of air between the absorptive material and a rigid surface works almost as well in midrange frequencies as if the same cumulative thickness of absorptive material were used, which is useful to know because air is cheaper than other materials. To get the best low-frequency absorption, you need a deep air space on the ceiling, and you should treat the walls as well. A hung ceiling 41 cm (16 in.) below the structural slab is too shallow to even absorb midrange frequencies well. The absorption coefficient ratings for materials are always given with mountings corresponding to American Society for Testing and Materials (ASTM) requirements. Hanging the absorptive material below the ceiling and supporting it away from the walls works better than attaching material firmly to walls or ceilings. The best way to install acoustically absorbent material is to hang cubes or tetrahedrons from the ceiling. When you use very thick blocks installed at a distance from each other, the edge absorption is very large, especially in the high frequencies. However, these objects become major architectural elements in the space. As this may not be appropriate for all uses, louvers or baffles offer a somewhat less effective but simpler option. For best results, treat the ceiling, floor, and wall op- posite the sound source approximately equally. Treating the ceiling alone may miss highly directive high-frequency waves, which may not reach the ceiling until the third reflection off a surface. Materials absorb high frequencies better than lower frequencies. The amount of absorption is not always proportional to the thickness of the material, but depends on the material and its method of installation. Beyond a certain point, added thickness does little to increase absorption, except at very low frequencies. The lowest musical frequencies can’t be absorbed efficiently by ordinary thicknesses of porous material. Let’s look at how some specific materials absorb sound. FIBROUS MATERIALS Materials absorb acoustic energy by the friction of air being moved in the tiny spaces between fibers. A material’s sound absorption depends on its thickness, density, porosity, and resistance to airflow. Paths must ex- tend from one side of the material to the other, so that air passes through. Sealed pores don’t work for sound absorption, and painting may ruin a porous absorber such as an acoustic tile ceiling. If you can blow smoke through a porous, fibrous, thick material, it should make a good sound absorber. One type of acoustical deck consists of a structural deck of perforated steel backed with an absorptive material, usually fiberglass. Acoustical deck is usually used Sound Absorption Within a Space 409 c o ncret e Nailed to furrin g Suspended from ceilin g and wall s Figure 52-1 Installing absorptive materials. exposed, when it has an NRC of around 0.50 to 0.90. These acoustical panels are available in widths up to 1.22 meters (4 ft) and lengths up to 3 meters (10 ft). Acoustical deck can greatly reduce noise and reverberation in gyms, factories, and workshops. Acoustical deck can also be made entirely of fibrous materials. Fibrous plank is a rigid material usually made of coarse wood fibers embedded in a cementitious mix. Some planks can be used as structural roof decking. The fibrous surface absorbs sound, with performance depending upon thickness. A 25-mm (1 in.) plank has an NRC of around 0.40, with up to NRC 0.65 for 76 mm (3 in.) thick planks. If the surface is exposed to a room, fibrous planks will reduce noise and reverberation in the room. Acoustical foam comes in a number of forms, usually made of polyurethane cells. Acoustical foam can have open or closed cells. Air can be blown into and through open cell acoustical foam. Each cell in closed cell acoustical foam is sealed, and the material is airtight. Acoustical foam is an excellent sound absorber if thick enough. Foam 6 mm ( ᎏ 1 4 ᎏ in.) thick has an NRC of 0.25; 51 mm (2 in.) thick foam has an NRC of up to 0.90. Acoustical foam is used as padding for upholstered theater seats, where it stabilizes reverberation time in the space regardless of whether seats are empty or full. Fibrous batts and blankets of fiberglass or mineral fiber are commonly used for acoustical or thermal insulation. They may be exposed to the room as a wall finish behind fabric or an open grill, or as a ceiling finish behind perforated pans or spaced slats. Fibrous batts and blankets absorb sound to reduce noise and reverberation in the room. Their performance depends on their thickness and the properties of the facing. The NRC rating can be as high as 0.90. Fibrous batts and blankets improve attenuation when used between the two faces of a partition in a stud space, or above a suspended ceiling between the ceiling and the floor above. They absorb sound as it passes through the partition’s cavity. Their ability to absorb sound is limited when the wall is tied rigidly together with wood studs, but sound transmission loss is signif- icantly improved with use of light gauge steel studs. The performance of fibrous batts and blankets depends on their thickness. Fibrous batts or blankets should never completely fill a cavity. Fibrous board works like batts or blankets, but has a higher density. Rigid or semirigid boards, especially those made of fiberglass, offer excellent absorption. They are available with a variety of sound-transparent facings, including many fabrics, and are used as wall or ceiling panels. Ratings for 25-mm (1-in.) fiberglass board are around NRC 0.75, and around NRC 0.90 for 51-mm (2-in.) board. Fiberglass comes as batts, blankets, and boards with excellent sound absorption. The manufacturing process for fiberglass creates consistent, very fine sound- absorbing pores. Fiberglass is used for many applications, including insulation in stud walls and ducts, and for industrial noise control. Compressed blocks or sheets are used to form resilient supports or hangers, or as joint fillers instead of rigid ties. The absorption of fiberglass depends on the airflow resistance, and is af- fected by the material’s thickness and density, and by the diameter of the fibers. The thickness of the board or blanket is usually the most important element. Loose acoustical insulation is similar to fibrous batts and blankets, but is blown or dumped in place. Loose insulation reduces sound transmission through the partition. Cellulose fiber is a sound absorbing material that is the basis of acoustical tile, wood wool, fibrous sprays and other acoustical products. Fibrous sprays include a variety of spray-on insulation materials that are often specified for fire resistance, instead of asbestos fibers. Fi- brous sprays are inherently porous, and therefore absorptive. Their performance depends on their thickness and on the application technique used. A well-applied 25-mm (1-in.) thick coat can achieve an NRC of 0.60 or higher. CEILING TREATMENTS The ceiling is the most important surface to treat for sound absorption. Some of the fibrous materials we discussed above are used for ceilings, either openly or covered with acoustically transparent fabrics or perforated panels. There are also products designed specifically for the acoustic treatment of ceilings, the most common of which is acoustical ceiling tile. Acoustical Ceiling Tile Acoustical tiles are excellent absorbers of sound within a room, where they help lower noise levels by absorbing some of the sound energy. Their extreme porosity and low density, however, offer no reduction in the passage of noise from room to room through a ceiling or wall. To improve resistance to humidity, impact, or abra- 410 ACOUSTICS sion, tiles are available factory painted, or with ceramic, plastic, steel, or aluminum facing. Acoustical tile is made of mineral or cellulose fibers or fiberglass. Mineral fiber tiles have NRC ratings between 0.45 and 0.75. Faced fiberglass tiles are rated up to NRC 0.95. Acoustical tiles are both lightweight and low density, and can be easily damaged by contact. Con- sequently, they are not recommended for walls and other surfaces within reach. The main purpose of acoustical tile is sound absorption. Membrane-faced tiles absorb less high-frequency sound than porous-faced tiles. Tiles are available in a variety of modular sizes: square tiles range from around 31 cm (12 in.) to 61 cm (24 in.). Rectangular tiles are often 61 by 122 cm (24 by 48 in.). Tiles are also available based on 51-, 76-, 122-, and 153-cm (20-, 30-, 48-, and 60-in.) dimensions. Typ- ical thicknesses include 13, 16, and 19 mm ( ᎏ 1 2 ᎏ , ᎏ 5 8 ᎏ , and ᎏ 3 4 ᎏ in.). The thicker the tile, the better the absorption. Edges may be square, beveled, rabbeted, or tongue-and- groove. Acoustical tiles come in perforated, patterned, textured, or fissured faces. Some tiles are fire-rated, and some are rated for use in high-humidity areas. Acoustical tile is usually suspended from a metal grid, but can also be glued or otherwise attached to solid surfaces. Suspended applications absorb more low- frequency sound than glued-on tiles. Suspended grids create space for ductwork, electrical conduit, and plumbing lines. They allow lighting fixtures, sprinkler heads, fire detection devices, and sound systems to be recessed. The grid consists of channels or runners, cross tees, and splines suspended from the overhead floor or roof structure. The main runners are sheet metal tees or channels suspended by hanger wires from the overhead structure, and are the principal supporting members of the system. The cross tees are secondary sheet metal supporting members, carried by the main runners. The grid may be exposed, recessed, or fully concealed. Most systems allow acoustical tiles to be removed for replace- ment or access. In addition to absorbing sound within a room, many acoustical tiles also attenuate sound passing through to adjacent rooms. This can be critical where partitions stop against or just above the ceiling to create a continuous plenum. Tiles for sound attenuation in this use are usually made of mineral fiber with a sealed coating or foil backing. An integrated suspended ceiling system includes acoustic, lighting, and air-handling components. The grid is typically 152 cm (60 in.) square, with flat or cof- fered acoustical panels. Air handling can be integrated into the modular luminaires to disperse conditioned air along the edges of the lighting fixtures, or it may be part of the suspension system and diffuse air through long, narrow slots between ceiling panels. Metal-Faced Ceilings Perforated metal pans backed by fibrous batts (Fig. 52-2) are an alternative to acoustical tile ceilings. Sim- ilar panels may be used on walls to absorb sound. Per- forated metal-faced units are available for use with suspended ceilings. The metal panels have wrapped mineral wool or fiberglass fill, and receive somewhat lower NRC ratings than acoustical tile. They are available in sizes from 31 by 61 cm (12 by 24 in.) to 61 by 244 cm (24 by 96 in.). Baked enamel finishes are available in a variety of colors. Metal panels are easy to keep clean, have a high luminous reflectivity, and are in- combustible. With the acoustic backing removed, a perforated unit can be used for an air return. The size and spacing of the perforation—not just the percentage of openness—affect the performance. Depending on the perforation pattern and type and on the thickness of the batt, the NRC of perforated metal pans can reach 0.50 to 0.95. If the batts are encased in plastic, as required in some states, the high-frequency absorption is impaired. Metal pans won’t reduce sound transmission unless they have a solid backing. Linear metal ceilings consist of narrow anodized aluminum, painted steel, or stainless steel strips. Slots Sound Absorption Within a Space 411 Perforated metal panel Gypsum board backup stops sound from traveling through panel Mineral fiber or fiberglass acoustic insulation Figure 52-2 Perforated metal ceiling panel. between the strips may be open or closed. Where they are open, a backing of batt insulation in the ceiling space allows sound absorption. Linear metal ceilings are usually used as part of a modular lighting and air-handling system. Slats and Grilles Wood or metal slats or grilles in the ceiling are often be- lieved to have acoustic value, but in fact serve only to protect the material behind them, which is typically absorbent fiberglass. The absorption value is maintained if the grilles or slats are small and widely spaced. Increas- ing the size of the dividers or reducing the space between them will cause high frequencies to be reflected. Acoustical Ceiling Panels Acoustical ceiling panels (Fig. 52-3) or boards of treated wood fibers bonded with an inorganic cement binder are available in a range of sizes, from 31 by 61 cm (12 by 24 in.) to 122 by 305 cm (48 by 120 in.). Available thicknesses range from 25 to 76 mm (1–3 in.), and they come with a smooth or shredded finish. Acoustic ceiling panels are installed in ceiling suspension systems or nailed or glued to walls and structural ceilings. They receive NRC ratings from 0.40 to 0.70. Acoustical ceiling panels have high structural strength and are abuse resistant. They have an excellent flame-spread rating. Panels can be used across the full span of corridor ceilings, or as a long-span finish directly attached to the ceiling. They are appropriate for wall finishes in school gyms and corridors. Although they are usually resistant to humidity, check high- humidity use with the manufacturer, especially for panels with reveal edges. Acoustical lay-in panels are fabricated of steel or aluminum with textured and embossed facings to give a cloth-like appearance. With acoustical fiber fill, the panels offer sound absorption as high as 1.10 NRC and meet fire safety standards. Acoustical ceiling backer is available in 61 cm (2 ft) square or 61 by 122 cm (2 by 4 ft) sizes. Ceiling backer can easily be placed on top of an existing ceiling tile system that is not providing enough sound attenuation. The barrier material is a reinforced aluminum and fiberglass construction. Perforated steel or aluminum panels with finished edges provide both absorptive and reflective surfaces for environments where a variable reverberation time is desirable, such as music rooms, concert halls, performing arts centers, and restaurants. The units are 61 cm (24 in.) wide closed and hinge open to 122 cm (48 in.) wide for additional absorption. Acoustic baffles are available in 51 mm (2 in.) fiberglass and a variety of standard heights and widths. These panels are designed to acoustically upgrade existing spaces such as cafeterias, auditoriums, pool areas, and anywhere where high ceilings and poor acoustics require more sound absorption. The facing of the baffles is stretched to provide a smooth surface free from wrin- kles or other distortion. Cloud panels are used when ceiling heights are too low for traditional baffle installations, and perform the same acoustical functions without sprinkler or lighting interference. A 25 or 51 mm (1 or 2 in.) fiberglass core acts as an absorber and is contained within an extruded aluminum frame. The panels are available up to 122 cm (48 in.) square, and are finished with fabric. Perforated galvanized steel or aluminum panels that can be individually attached to ceilings or walls offer an economical sound absorbing and fire-resistant approach to acoustic control. The panels are hung on metal brackets and backed with high performance acoustical fill. Panels can be cleaned in place without removing the acoustic fill. Optional protective plastic or fiberglass wraps are available. Perforated metal panels are appropriate for gymnasiums, swimming pools, weight rooms, and similar facilities, and can be used in auditoriums, theaters, libraries, and food service operations where noise is a problem and cost is an issue. They are also appropriate for industrial applications. 412 ACOUSTICS Acoustical panels made of wood fibers in a cement binder can span lengths up to 3.66 meters (12'). Figure 52-3 Acoustical ceiling panels. WALL PANELS Acoustical wall panels are used in offices, conference rooms, auditoriums, theaters, teleconferencing centers, and educational facilities. Wall panels have wood or metal backing and mineral fiber or fiberglass substrates. Fabric coverings are usually fire-rated. Fabric covered panels are available from 25 to 51 mm (1–2 in.) thick. The NRC ratings vary from 0.5 for direct-mounted 25-mm mineral fiber panels to 0.85 for strip-mounted 38-mm (1 ᎏ 1 2 ᎏ -in.) fiberglass panels. Panels are available from 46 to 122 cm (18 to 48 in.) wide, and up to 305 cm (120 in.) long. Re- veals at the ceiling and base help assure a good fit. Open- ings for wall plates and thermostats can be field cut. Acoustical wall panel systems can also include tack boards that are used as accessory panels in cubicles, conference rooms, break rooms, reception areas, and lob- bies. Tack boards may be attached using hook and loop attachments. At least one European designer has created a collec- tion of acoustic wall panels made of felt-like recyclable molded polyester fiber or molded plastic. Easily installed and adjusted with self-adhesive hook and loop tape, the panels can be used as room dividers or mounted on walls. CARPET Carpet is the only floor finish that absorbs sound. Car- pets in almost any degree of density, looping, and depth, especially when used with additional padding depth, produces a high degree of absorption in the middle- to high- frequency range. Carpet can be glued to a floor or installed over an underlayment of hair felt or foam rubber. The absorption is proportional to the pile height and density, and increases with the thickness of a fibrous pad, unless the carpet has an airtight backing. Carpet earns an NRC of between 0.20 and 0.55, mainly for high frequencies. Carpet is sometimes installed on walls where drapery is not feasible and wall panels are impractical. It should be installed on furring strips with an enclosed air space behind to increase absorption over the entire acoustical spectrum, especially in the low frequencies, where glue-down application performs poorly. Carpet on walls may have different fire-rating requirements than carpet on floors. Carpet does not reduce the passage of sound from room to room, but it can prevent noise that originates when an object makes hard contact with the floor. Us- ing a thick carpet with pad, along with a resilient layer within the floor construction, will reduce impact noise. DRAPERIES, FABRICS, AND UPHOLSTERY Curtains absorb sound if reasonably heavy—at least 500 gm per square meter (15 oz per square yard)—and, more importantly, if the resistance to air flow is suffi- ciently high. The curtain fabric must severely impede but not stop the airflow through the material. Drapery fabrics at 100 percent fullness vary between 0.10 and 0.65 NRC, depending on the tightness of the weave. A light curtain has an NRC of around 0.20. Heavy flow- resistant drapery covering up to one-half of the area can achieve an NRC greater than 0.70. Sound absorption at all frequencies is increased when the drapery encloses an air space between the wall and the drape. Venetian blinds, by comparison, have an NRC rating of 0.10. Cur- tains do not reduce the passage of noise from room to room through a ceiling or wall. Fabrics attached directly to hard surfaces don’t absorb sound. However, fabric that is not airtight and is stretched over fiberglass or other absorbent materials creates an excellent finish that fully preserves the absorption of the underlying material. Deep, porous upholstery absorbs most sounds from midrange frequencies upwards. OTHER FINISH MATERIALS Acoustical plaster is a less well-known, porous, plaster- like product that was originally intended to create joint- free surfaces that absorb sound. Acoustical plaster consists of a plaster-type base with fibrous or light aggregate material on top. It is useful for curved or nonlinear surfaces and can be applied up to 38 mm (1.5 in.) thick. It is fire-rated. Unfortunately, the performance of acoustical plaster depends upon the correct mixing and application tech- niques. Under controlled conditions, acoustical plaster can achieve an NRC of 0.60. Field installations are usually much less effective, however, so acoustical plaster can’t be relied upon as a sound absorber. Acoustical plaster is very easy to abuse, and not resistant to humidity. As mentioned earlier, resilient tile made of vinyl, asphalt, rubber, cork, or similar materials, is almost as sound reflective as concrete. If it is foam backed, resilient flooring can attenuate high frequencies. Relatively thin finishes of wood boards or panels, usually attached to furring, are generally little better than a basic wall. Wood paneling absorbs low frequencies by resonance, and can result in a serious bass Sound Absorption Within a Space 413 deficiency in music rooms unless it is thick or attached directly to the wall without an airspace. RESONATOR SOUND ABSORBERS Sound can create a resonance in hollow constructions whose natural frequencies match that of the sound. Air within the hollow acts as a spring, oscillating at a re- lated frequency. Because a resonating body absorbs energy from the sound waves that excite it, resonating devices can absorb sound energy. Resonators are easiest to construct for lower frequencies. They are often used in modern concert halls, and are constructed as concealed hollows in the walls. Volume or cavity resonators, also known as Helm- holtz resonators, consist of an air cavity within a massive enclosure connected to its surroundings by a narrow neck opening. Sound causes the air in the neck to vibrate, and the air mass behind causes the entire construction to resonate at a particular frequency. The result is almost total absorption at that frequency. Cavity resonators can be tuned to different frequencies, for example to 120 Hz for electrical transformer hum. Concrete blocks can be used as cavity resonators by tuning their openings and adding absorptive materials. The use of a fibrous filler in the block increases high-frequency absorption. Resonator sound absorbers come in a wide variety of shapes and sizes. Some are manufactured in standard sizes, but most are tailored to a specific job using standard designs. They are generally large, and must be integrated into the architectural design of the space. Panel resonators consist of a membrane of thin plywood or linoleum in front of a sealed air space that usually contains an absorbent material. The panel is set in motion by the alternating pressure of the sound wave. The sound energy is converted to heat. Panel resonators are used for efficient low-frequency absorption, and when middle- to high-frequency absorption is not sought or is provided for by another acoustic treatment. They are often used in recording studios. SPECIAL ACOUSTIC ABSORBERS Space units are blocks of fibrous and porous material made of mineral fibers or fiberglass. They look much like acoustic tile and are typically 50 mm (2 in.) thick. Space units are applied to hard wall and ceiling surfaces. They absorb sound efficiently, helped by the exposure of their thick sides. Functional absorbers are free-hanging cylinders used in industrial applications. They employ both surface absorption and tuned resonances to absorb sound and help reduce noise and reverberation in a room. Quadratic-residue diffusers consist of a series of narrow wells of unequal depth separated by even narrower plates. Typical depths are 10 to 41 cm (4–16 in.) or more. This results in an attractive ribbed appearance. Quadratic-residue diffusers work by spreading the sound reflections over a wide arc at an angle to their wells. They are used in broadcast and recording studios, control rooms, and wherever specular reflections off plain surfaces are to be avoided. They can be made of any hard material and may be engineered to work over a wide range of frequencies. 414 ACOUSTICS Remember Harry and the hair salon he designed? The shampoo sink wasn’t the only difficult design issue. When his client explained that it cost $1 every time he sent a towel out to a commercial laundry service and that the salon used hundreds of towels a week, Harry understood why the client wanted a commercial-size washer and two dryers on site. Fitting the huge machines into the tight space was hard enough, but Harry knew that they would be noisy, and their exposed location (the only possible one) could be readily seen by cus- tomers and made acoustic control a serious issue. Not only that, but staff had to be able to get to the machines frequently throughout the day. Harry decided to install heavy curtains from the ceiling to near the floor. He selected an inherently flame-resistant velvet fabric in a soft green. Working with the curtain fabricator, he decided on a hospital cubicle-type curtain track mounted on the ceiling just in front of the machines. The track had to jog hori- zontally around the machines. Because of ductwork soffits and structural beams, the curtain was made in several panels, with some shorter where the ceiling was lower. The curtain was lined to provide extra sound absorption. The final design not only camouflages the machines, but also effectively reduces the noise level. It also provides a lovely, soft vertical surface in an otherwise hard-surfaced space. Sound travels through other materials as well as air. It can be transmitted through steel, wood, concrete, masonry, or other rigid construction materials. The sound of a person walking is readily transmitted through a concrete floor slab into the air of the room below. A metal pipe will carry plumbing noise throughout a building. A structural beam can carry the vibrations of a vacuum cleaner to an adjacent room, or the rumble of an electric motor throughout a building. Buildings generate their own sounds. Rain and sleet pound and clatter on building surfaces. Doors slam and old wood floors creak. Heating and plumbing systems, elevator machinery, and machines like garbage dispos- als produce mechanical noises. When the structure of the building is pushed and pulled by the wind, heat, or humidity, the building creaks, groans, and crackles. CONTROLLING BUILDING SYSTEM NOISE A lot of the noise in a building comes from mechanical systems. Machines cause noise by vibration. Enclos- ing the noise at the source with materials that reduce noise by absorption and block airborne sound limits the problem. The equipment supplier can often provide prefabricated partial and full enclosures. Curtains and panels may also help isolate the machinery. Laundry machines, mixers, bins, chutes, polishing drums, and other machinery with sheet metal enclosures that vibrate can create a lot of noise. The vibration can be dampened by permanently attaching a layer of foam to the vibrating metal, which converts the noise energy to heat. Adding a heavy limp barrier material to the outside of the foam creates a composite damping barrier material and further reduces the noise. The first step in quieting machine noise is to select quiet equipment and install it away from inhabited parts of the building. Mount equipment with resilient fittings to eliminate structure-borne noise, and house noisy equipment in sound-isolating enclosures to cut down on airborne noise transmission. Damping is accom- plished by rigidly coupling the machine to a large mass, called an inertia block. Decoupling the vibration from connections that would carry it throughout the building can reduce airborne machine noise. Breaking the connection from the vibration source to the building structure will also keep noise from spreading. Using flexible joints in all pipes and ducts connected to the machine accom- plishes this. Flexible conduit connections are used for 53 Chapter Sound Transmission Between Spaces 415 all motors, transformers, and lighting fixtures with magnetic ballasts. Elevators, escalators, and freight elevators are local- ized sources of noise, and generally run at fairly low speeds. If the spaces around them are located judi- ciously, their noise should not be a major problem. However, the motors and controls can be noisy. Higher-priced upper floors in a building may be near noisy elevator machine rooms, mechanical equipment rooms, and cooling towers. An acoustic expert should be called in during the equipment design phase, as these problems are almost impossible to solve later. Plumbing and Mechanical System Noise The piping for a building’s plumbing system can also be a source of noise, both from the normal sounds of water rushing through uninsulated pipes and from water ham- mer in improperly designed systems. Pipes and flushing toilets should be kept away from quiet areas. In many buildings, 40 percent of the construction budget is spent on the mechanical system. Mechanical equipment in the building has many noise-producing components. The air-handling system includes fans, compressors, cooling towers, condensers, ductwork, dampers, mixing boxes, induction units, and diffusers, all of which can either generate noise or carry it to other locations. In one east coast hotel, the roof-mounted chiller causes clearly audible vibration in the meeting room chandeliers below. Systems also include pumps and liquid flowing through piping. Roof mounted heating, ventilating, and air- conditioning (HVAC) units are very economical but very noisy. The vibrating equipment, short duct runs, and acoustic sound reflections all lead to problems. Use of vibration isolators, sound mufflers, and careful location of equipment all help. Electrical System Noise Most noisy electrical equipment produces a low- frequency 120-Hz hum that is difficult to reduce. Mounting the transformer on vibration isolators, hanging it from a wall with resilient hangers, or placing it on a massive slab can minimize electric transformer noise. When transformers are located near acoustically reflective surfaces, the sound can be amplified. Sound- absorbent material behind the unit is not useful at 120 Hz; only cavity resonators will work at that low frequency. Flexible conduit connections should be used. Be aware of transformer locations so that they don’t end up adjacent to or immediately outside quiet areas or directly below a window. Magnetic lighting fixture ballasts for fluorescent and high-intensity discharge (HID) sources also produce a 120-Hz hum. Magnetic ballasts are being replaced by electronic ballasts in fluorescent sources, but are still used in HID fixtures. When the ballast is attached to the fixture, the sound is amplified. A large number of fixtures in a plenum can lead to a serious noise problem. Absorbent materials in plenums, flexible conduit, and resilient fixture hangers can help. Ballasts can be remote mounted if necessary. Weatherstripping on windows and doors will reduce wind noises. This will also cut the transmission of out- door noises into the building, and reduce heat loss as a bonus. Rain and sleet noises can be reduced with heav- ier roof and window construction. Structural noises in a building may be inevitable and are difficult to remedy, as building components slip past each other during sporadic releases of built-up stresses. If the source is precisely located, the compo- nent can be nailed or bolted more tightly. Blowing graphite particles into a moving joint as a lubricant sometimes helps. AIRBORNE AND STRUCTURE-BORNE SOUND Airborne sound originates in a space with any sound- producing source, and changes to structure-borne sound when the sound waves strike the room boundaries. The noise is still considered airborne, however, because it originated in the air. Structure-borne sound is energy delivered by a source that directly vibrates or hits the structure. In practice, all sound transmission involves both airborne and structure-borne sound. When airborne sound hits a partition, it makes the partition vibrate, generating sound on the other side (Fig. 53-1). The sound will not pass through the partition unless an air path exists. If the partition is airtight, then the sound energy causes the structure itself to become a sound source by vibrating the partition. The partition vibrates mostly in the vertical plane, but also causes some energy to pass into the floor and ceiling, resulting in structure-borne sound. When a mechanical contact vibrates or hits a struc- 416 ACOUSTICS [...]... manager paging systems for the cast offstage Productions communications systems are provided for lights and sound technicians, projection rooms, and similar functions These may be special intercom systems with mobile wireless remote stations The sounds of an organ can be produced electronically in buildings without pipe organs, but since organ pipes can produce sounds as low as 16 Hz, few sound systems will... to the system The amplifier is rated to deliver sufficient power to produce 85 to 90 dB for speech, 95 dB for light music, and 100 to 105 dB for symphonic music, in situations where the background sound level is 60 dB Systems for rock bands produce sound pressure levels above 110 dB, and exposure to this level of loudness for extended periods will damage hearing The amplifier’s power can be reduced in... small systems without much equipment, or in a separate sound control room with a large operable sound control window Using a monitor loudspeaker or working from a remote location control room produces unsatisfactory results for live performances Many performing arts sound reinforcement systems use control facilities located entirely within the audience area SYSTEMS FOR SPECIFIC SPACES Interior designers. .. that not only incorporate wireless systems for office communication, but also include sound systems that deliver sound masking, paging, and music simultaneously, without shutting off the masking sound All three modes are delivered through the same set of speakers that blend invisibly into the ceiling plane This eliminates the need for redundant systems The Public Building Service of the U.S General... the rear of the screen Special Sound System Installations Paging and voice alarm systems are used in power plants and other industrial facilities, where high levels of ambient noise and long reverberation times overwhelm public address systems Paging and voice alarm systems also cost less and are smaller than public address systems Lights or sirens are used for simple messages, and headsets can be used... acoustic concerns that affect the health, safety, and enjoyment of the public is an important part of your role as a member of the building design team Your knowledge of all the systems that make a building work will enhance the quality of your design work, the value of the building to those who use it, and your own enjoyment of your work as an interior designer ... loudspeaker systems (Fig 55-2) offer flexibility in seating arrangements and reinforce sound from any position in the room, even when the room is divided by movable partitions Distributed systems provide flexibility in spaces where the source and the listener locations vary according to the use of the space They don’t provide directional realism, but offer very good clarity and intelligibility Distributed systems. .. high ceilings Distributed loudspeaker systems use a series of small low-level speakers, 10 to 31 cm (4–12 in.) in diameter, located throughout the space These are often ceiling mounted or recessed in the ceiling and send sound directly down, so that each speaker covers a small area Speakers may also be located in the backs of seats or pews Distributed loudspeaker systems are used in areas with low ceilings... and standards for the design, specification, and evaluation of systems and components for open office spaces in federal buildings The GSA’s speech privacy potential (SPP) rating is a summary of background sound level and attenuation between typical source and listener locations You may encounter this rating when doing work in federally owned buildings, and when specifying materials that are marketed to... sound-transparent ceiling panels As we discussed earlier, open offices usually have masking sound systems for speech privacy High-rise office towers may include a sound system designed for life-safety announcements and transmission of warning signals Emergency sound systems are normally separate from other systems and use fire-rated equipment, wiring, and installation materials Auditoriums and Lecture . removed, a perforated unit can be used for an air return. The size and spacing of the perforation—not just the percentage of openness—affect the performance. Depending on the perforation pattern. structure of the building is pushed and pulled by the wind, heat, or humidity, the building creaks, groans, and crackles. CONTROLLING BUILDING SYSTEM NOISE A lot of the noise in a building comes. should be at least 3 meters (10 ft) apart, which increases to 3.7 meters (12 ft) for normal privacy and 4.9 meters (16 ft) for confidential privacy. Check desk locations for speech path privacy;

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