Document VqY7YNn4Lz5YNbgOeMreEd4j

American Society of Heating and Ventilating Engineers Guide, 1936 fan in a certain high school auditorium was nearly as loud as average speech in a large auditorium. Such an amount of noise is devastating to good acoustics; in fact, it is impossible to hear speech in the presence of such a noise. db. 100 -Boiler Factory 90 -Electric Power Substation 80 - Ventilating Room for Large Hotel (Very Noisy) Average Loudness of Music in Room-* 70 -Inside of Duct, near Large Low Speed Fan Conversation in a Small Room-* -Equipment Room t Average Condition 1 ' 60 -Fan Room for School Building i Rather Quiet 1 Speech in a Small Auditorium-* -Guest Room. Large Hotel on Noisy Street (Windows Open) bO Speech in a Large Auditorium-* ^_Near Outlet of Ventilating Duct in High School Auditorium 1 Very Noisy, no'Filters* in Duct 40 *- Fan Noise in Theater < Poor Control of Norse) 30 20 -Fan Noise in Theater < Proper Control of Noise) 10 < Near Outlet of Ventilating Duct in M. G. M. . Sound Studio < Planned Control of Noise 1 Fig. 1. Chart Showing the Equivalent Loudness (in Decibels) of Speech, Music, and a Number of Noises Incident to the Ventilating of Buildings3 Acoustical Problems in the Heating and Ventilating of Buildings, by V- O. Knudsen (A.S.H.V.E. Transactions, Vol. 38, 1932). In every problem of noise reduction in buildings it is necessary to know how much noise can be tolerated. The noise levels given in Table. 1 may be regarded as completely inoffensive. They represent what might be' termed ideal conditions, not often realized in existing buildings. How ever, they represent conditions which can be attained by proper control of noise, and heating, ventilating and air conditioning engineers should aim to provide the degree of quiet specified in the table. In considering the tolerable room noise level due to heating, ventilating, or air conditioning apparatus, not only must the absolute value of the noise be considered but also its relation to the room noise level without the apparatus running. This is necessary since a large increase of noise subjects the apparatus to serious criticism even though the level may be low. It must also be borne in mind that the noise produced by the ap- 328 Chapter 18--Sound Control paratus is additive to that of the room without apparatus.. ;Thus.if . the two are equal, when combined the noise level.will be 3 ,;db higher; For, these reasons the room noise caused by the apparatus should not exceed the other room noise. Noise Control ; , ; ......... . ,.. . Essential to the design;of :a satisfactory system are:;first, a;knowl edge of the nature and intensity of the noise generat^d by the 'various parts of the equipment; second, a knowledge of how to vary the noise level' between ;the apparatus .And the. conditioned-room. if (need be; third, a knowledge of the acceptable level of apparatus'' noise in ;the con ditioned. room. Besides these, the. engineer rnust be able to deal With other noises. which might efiter the rpbm wheh;op6nings;arb;madb.intq,i|:,i such as cross talkbetween rooms connected with common ducts, and noise irx. .. Table!.Acceptable Noise Levels:.: ai ___ ____________________________ . . ; *\ ....... ' -V.i :i .L 'u.JT Talking picture, stu'dioS;::..'!!..'.'.;.--........ .............. 6 to ;.8"db` Radio broadci4sttog-ittiidi<)S!:LviL.:Lu:u;;.;L.jLva-L.cu..L;Lj:uj:i..-.-._^i..L. ,; 8 tdiXO/db , 8 to 12:dh Music studios.-.,--;------ ...................... ------- ....................... .............................. ,. 10 to 15 dl> ; , Apartments, hotels, homes, small,'private offices . 10 to 20 db '", Theaters, churches/ auditoriums, 'classrooms, libraries; ... 12 to 24 dB- 5; Talking picture theaters, sttiall clothing stores..-...;..;.__ _____ i......... ,15 to,25 db : i General:P0i<ies.j:...^l^-LL^C-:-+:~-4;.-- ;;;2P tO:30dbl;:I Large ;pablic . offices;; banking rooms, upper stories of; department, Stores, restaurants; -barber shopsy ............ ' 25 to 35' <ili Grocery stores.'drug:stores:..... 30; td 50 db ri Accounting and(typewitingi6ffices..-:-:.:.L-.'--;;..:--.i..;.;.. x ,% 35 to 45 db: n Main floor of department stores.......;. ...... ; * - _ , d0 t(?.50;db. transmitted to portiohs of duct systems' outside the cohditidhedroonVand' thence to its interior. * ' 'V! The problem of apparatus iioise ig-iecdivirig' the study of equipment manufacturers wh6 are aiming at; both ndise reduction and standardiza tion: Some manufacturers' now' have noise ratings available for their equipment, while some pass each unit of equipment of - Certain types through-sound tests durihg the cOurSe of manufacture.11 ' ';~0 ROOM NOISE LEVEL, COEFFICIENTS OF ABSORPTION The problem of noise reduction from apparatus to room must take into consideration and treat separately thethree modes of travel of noise to the room from the apparatus through the air'to the walls of the room and thence to its interior; iecoiid, ;through'thebuilding structure to the room; third, through ducts Or openings to; the-room; Because the noise entering-by- each of- these -'three channels is susceptible^ to-quantitative analysis,.solutions are' available. -Along with-the transmission of- sound through the building structure, the engineer must also consider the transmission;Of vibrAtionywhich may also be objectionable.- The solution' is not complete, however,' until the effect of the noise entering- the rdom'oh- the roommOise: levehis determined. ' ' y y! : .T.; One of the most effective means'Of reducing riOises In ventilating equip ment is accomplished by the proper covering of the interior walls and 329