Document e7g9y1VOqQ4vXRX22N53MDjYp

American Society of Heating and Ventilating Engineers Guide, 1934 -j-- = 10 (Through equipment wall) + 1 X = 20 1 o ^UUU Room loudness X 10 logio 20 = 13 db Now suppose that there is also a duct having 20 sq ft outlet connecting the room with apparatus having a noise level of 70 db (/" = 107) and suppose that there is an assumed attenuation in the duct equivalent to a transmission factor of 0.0002. Then ~*o = 107 X 0.0002 = 2 X 10' 4T on - - = 20 (from above) + 2 X 10* X 1q zuuu = 40 Room loudness = 10 logio 40 = 16 db It may be seen how the energies of noises entering a room are added to obtain the final room noise intensity. The average coefficients of sound transmission (128 to 4096 cycles) for a number of wall and of floor and ceiling partitions are listed in Table 3. Table 3. Average Coefficients of Sound Transmission for Building Partitions* Description op Partition Average Coefficient Brick panel, Mississippi, 8 in.; plastered both sides gypsum brown coat, smooth white finish; good workmanshio. Brick wall, 2)4 in. plaster both sides______ Brick wall, 2^ in., 2 in. furring strips, 3^ in. rigid insulation lath plastered both sides.. ______ ... Brick wall, 4 in., 2 in. furring strips arid 3^ in. rigid insulation lath, plaster, on one side: other side plastered directly on hrirk Concrete flat slab floor construction, re-enforced; floating floor consisting of nailing strips, rough and finish flooring; )4 in. rigid insulation furred out and applied as ceiling..................... .................. Glass, plate ii in............ ................... Glass, plate in. double glazed. 1V6 in. separation . Metal lath, double, on 13^ in. channels, % in. gypsum plaster; without cross bracing clips: 4 in.f connected at edges only Tile, hollow clay partition, three cells, 4 in. x 12 in', x 12 in., wood furring strips, J4 in. rigid insulation, gypsum brown coat, smooth white finish Wood joists, lower side plastered on wood lath; floating floor consisting of nailing strips, rough and finish flooring..................... ...................... ;_______ Wood studs, four-paper plaster board, three-coat smooth finish gypsum plaster........ Wood studs, two kr'n. sheets rigid insulation both sides, joints filled, gypsum scratch and brown coats, smooth white finish Wood studs, 2 in. x 4 in., staggered, metal lath, 3^ in. gypsum plaster; 7 3-4 in.: connected at edges only 0 000010 0 000032 0.0000016 0.0000040 0.0000020 0.0010 0.0001 0.000016 0.0000050 0.0000050 0 000010 0.000013 0.000040 *Architectural Acoustics, by V. O. Knudsen, pp. 308-322. LOCATION AND INSULATION OF EQUIPMENT ROOM The equipment room, if possible, should be located at a considerable distance from all rooms in which quiet is required. If this is not possible, it is necessary to provide a high degree of insulation against the noise which may be transmitted through the walls of the equipment room, and also against the noise which almost certainly will be communicated through the short ducts. (See discussion of Control of Noise Trans mission through Ducts, p. 253). Three wall sections and two floor and 248 Chapter 18--Sound Control ceiling sections which are satisfactory for the wall insulation of the equipment room are shown in Fig. 2. Other partitions, with their sound insulating values, are listed in Table 3. The addition of absorptive materials (such as are described in Table 2) to the inner walls and ceiling of the equipment room will not only increase the insulation through the walls, but will also reduce the intensity of the noise ih the room. The equipment room noise intensity may be figured in the same way as that of the conditioned space, talcing the equipment as the source of noise. In case the equipment is subject to considerable vibration it is advisable to provide a separate or floated floor. 'fi 4" Bnck |jr''! Plaster m Insulation Value = 47 db. ' 4` Hollow Clay Tile M"* 2* Furring Strips sPaper and Metal Lath i" s-A Insulation Value = 52 db. Absorptive Blanket \ Fibre Board l`p Staggered Wood Studs Insulation Value Greater than 50 db. Rough and Finish Flooring -'Absorptive Blanket -Plaster on Lath Insulation Value * 50 db. Flooring gb= Resilient Chairs Concrete Slab Resilient Hangers Plaster on Lath Insulation Value " 60 db., or more Fig. 2. Three Wall Sections and Two Floor and Ceiling Sections which are Suitable for the Insulation of Equipment Rooms51 Acoustical Problems in the Heating and Ventilating of Buildings, by V. O. Knudsen (A.S.H.V.E. Transactions, Vol. 37, 1931). INSULATION OF MACHINERY AND SOLID-BORNE VIBRATION Since mechanical vibrations are readily transmitted through the solid structure of a building, it is extremely important in air conditioning that all mechanical equipment in which vibrations are generated be thoroughly insulated Irom the solid structure of the building. An almost universal notion prevails that the vibrations generated by machinery can be in sulated from a building simply by placing a slab of cork or a layer of hairfelt between the machinery and the floorof theroom. If themachinery is sufficiently heavy, and the cork or felt sufficiently resilient, this ex pedient may suffice. On the other hand, if the machinery is not suf ficiently heavy to load the cork or felt support to the extent that the natural frequency of the machinery on the cork or felt is low in com parison with the frequency generated by the equipment, the cork or felt may be of little avail. Th'e insulation of vibration can be accomplished by means of suitable elastic supports or suspensions, but the design of these elastic supports should be based upon calculation rather than guess-work. The theory of the insulation of vibration was first worked out by 249