Document 4vamqGaMwda8LxvqaqB9L4Nr1

American Society of Heating and Ventilating Engineers Guide Room loudness = 10 logio 10 = 10 db If the sound absorption in the auditorium had been as small as 200 sabines, the intensity in the auditorium would have been 10 times as great and the noise level auditorium would have been 20 db. ln the If the rest of the auditorium has an area of 20,000 sq ft with a surrounding intensity of 50 db (I" = 10s) the noise level due to all of the noise entering thrm.li!10!Se wall would be found as follows: ou8h the ~ = 10s X 0.00001 = 1 `O -y- = 10 (Through equipment wall) + 1 X = 20 o UUU Room loudness X 10 logic 20 = 13 db --Now-suppose that there is also a duct having 20 sq-ft outlet connecting-the room witlf apparatus having a noise level of 70 db (/" = 10') and suppose that there is an assume ttenua tion in the duct equivalent to a transmission factor of 0.0002. Then, n'M = 10' X 0.0002 = 2 X 10* Jo T on 'j- = 20 (from above) + 2 X 10* X ^qqq = 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 walls and of floor and ceiling partitions are listed in Table 3. Table 3. Average Coefficients of Sound Transmission for Building Partitions* Dbscb&tion or Partition Atebagi Cormcnm Brick panel, Mississippi, 8 in.; plastered both sides gypsum brown coat, smooth white finish; good workmanship Brick wall, 2t^-in. plaster both sides ... ~7~------- Brick wall, 2H-in., 2-in. furring strips, J^-in. rigid insulatipn lath plastered both sides...... ........ .................................................................. .... ........................ ........ Brick wall, 4 in;, 2-in. furring strips and J4->n. rigid insulation lath, plaster, on one side; other side plastered directly on brick Concrete flat slab floor construction, reinforced; floating floor consisting . of nailing strips, rough and finish flooring; H-in. rigid insulation furred out and applied as ceiling--............___________ _________________ _______ Glass, plate fy-in..................... ..... .......... Glass, plate M-in. double glazed, lj^-in. separation.......................................... Metal lath, double, on lj^-in. channels, J-in. gypsum plaster; without cross bracing clips; 4 in., connected at edges only.................. ....................... Tile, hollow clay partition, three cells, 4 in. x 12 in. x 12 in., wood furring strips, J^-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 H-in: 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, J^-in. gypsum plaster; 7 in:; connected at edges only.............................................................................. o.ooooio 0.000032 0.0000016 0.0000040 0.0000020 0.0010 0.0001 0.000016 0.0000050 0.0000050 0.000010 0.000013 0.000040 *ArchitectU`al Acoustics, by V. O. Knudsen, pp. 308-322. 306 Chapter 18--Sound Control location and insulation of equipment room ''Li'nipment room, if possible, should be located at a considerable 'cefrom all rooms in which quiet is required. If this is not possible, cfc^ecessary tQ provide a high degree of insulation against the noise iV-S|r fflay be transmitted through the walls of the equipment room, and vrbic*1, a-^t ^ nojge which almost certainly will be communicated si50 a? tjjC short ducts. (See discussion of Control of Noise Trans- through Ducts, p. 311.) Three wall sections and two floor and sections which are satisfactory for the wall insulation of the nrrient room are shown in Fig. 2. Other partitions, with their sound ^ktine values, are listed in Table 3. The addition of absorptive -I?- eYia)s (such as are described-in Table 2)_to_the inner_walls and.ceiling of ^ die equipment room will not only increase the insulation through the !lis but will also reduce the intensity of the noise in the room. The ^mipment room noise intensity may be figured in the same way as that of the conditioned space, taking 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. ^ 4" BncK Plaster Insulation Value47 db. ?8i ^4* Hollow Clay Tile [ xl'x 2' Furring Strips m| ^ Paper and Metal Lath jjgjj *''' Plaster Insulation Value 52 db. "Absorptive Blanket 1* "2 Fibre Board sStaggered Wood Studs Insulation Value Greater than 50 db. 4Rough and Finish Flooring ^Absorptive Blanket sac-Plaster on Lath Insulation Value - 50 db. Flooring Resilient Chairs Concrete Slab Resilient Hangers Plaster on Lath Insulation Value9 60 db.. or more Fig. 2. Three Wall Sections and Two Floor and Ceiling Sections which are Suitable for the Insulation of Equipment Rooms* Acoustical Problems in the'Heating* and Ventilating of Buildings; by V. O. Knudseti (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 from 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 hair felt between the machinery and the floor of the room. If the machinery 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- 307