From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Technical bulletin explaining noise measurement with a comparative chart of decibel levels for various sounds.
| Identifier | ExFiles\Box 104\2\ scan0228 | |
| Date | 1st March 1936 | |
| Noise and How It Is Measured Left Chart: Decibels : Relative Energy Scale Sections (from top to bottom): Deafening Noise Distracting Noise Range of Conversation Extreme Quiet Sound Proof Chambers Decibel Scale (and examples): 110 - Threshold of painful feeling, Thunder, Artillery firing, Unmuffled airplane engine 100 - Large steam whistle, Boiler factory, Structural steel riveter at 15 ft., In subway car 90 - Pneumatic Jackhammer drill 10 ft. away, Newspaper press room, Noise in untreated airplane cabin, Elevated trains from street 80 - Automobile horn at 23 ft., Noisiest street corner, New York, Fire siren at 75 ft., Large public address system, Police whistle at 15 ft., Average machine shop 70 - Interior of electric interurban train, Snow shoveling on cement walk, Motor truck without muffler, Noise in a stenographic room 60 - Average factory, Busy street traffic, Full volume of modern home radio, Noisy ventilating system, grille 3 ft. away, Average busy street, Congested department stores 50 - Average public building, Church bells at 1200 ft., Average store, Moderate restaurant clatter, Noisy residence 40 - Average office, Quiet automobile, Satisfactory high school ventilating system, Ordinary school class room, Public library 30 - Average residence, Quiet office, Silent-movie theatre, Quiet residence 20 - Legitimate theatre, Private office acoustically treated, Planetarium, Rustling paper, Average whisper 10 - Quiet church, Underground vault, Broadcasting studio, Sound-film studio, Breathing through nose 0 - Very quiet studio for making sound pictures, Threshold of audibility Main Text: Noise is undesired sound. The famous philosopher, Schopenhauer, said, “Noise is a torture to all intellectual people.” Noise may consist of many kinds of sounds. The pitch, tone, or frequency of vibration of the sounds may range from the lowest note of an organ to above the highest note of a piccolo. Before noise can be suppressed it must be understood and also measured. Tone Scales Acoustic engineers use two scales for measuring sound, one for the tone and one for the intensity level. The first is the familiar tone scale as represented by the notes of the piano. The individual notes are indicated with letters like C, D, E, F, etc., and also in terms of vibrations or cycles per second. Thus middle C on the tone scale is 261.626 cycles per second. High C, two octaves above, is 1046.5 cycles per second. Nearly every one is familiar with musical tones, and we may refer to high pitched sounds or high audible frequencies as notes having vibrations ranging from approximately 261 cycles per second up to 5000 or 20,000 cycles per second; beyond 20,000 cycles the average human ear cannot distinguish vibrations as a sound. Noise usually consists of a jumble of sounds that combine many different tones. Our ears are most sensitive to sounds ranging from 261 cycles per second to shrill notes in the region of 5000 or 6000 cycles per second. Thus, noises in this wide range become the concern of acoustic engineers, air conditioning engineers, architects, motor car builders, industrial engine manufacturers, and even of communities where noise abatement commissions operate. More important, however, than the frequency of a noise is its loudness — especially to the acoustic engineer who must suppress noises in air-conditioning systems, in the exhausts of engines, or in cabs of motor trucks. Any tone or noise may be loud or soft. For the lack of a popular comparative scale of loudness most people say, “It sounded like a boiler factory,” or “It was as quiet as a tomb.” These expressions are descriptive, but not scientific. Intensity Levels Acoustic engineers have discovered a relationship between the energy which produces a sound and its effect upon the human ear. Our ears respond to different intensities of loudness in a peculiar manner. They are very sensitive to feeble sounds, such as the buzzing of a fly, while extremely loud sounds, representing millions of times the amount of energy produced by the wings of an insect, do not have a proportionate effect on our hearing. Nature has wisely arranged our hearing so that the ear compensates for extremely loud sounds by not responding to them as well as to very faint sounds. Referring to the large chart on the last page, the scale on the left represents the approximate response of the ear to sounds of varying intensities, while the scale on the right shows the relative energy required to produce these sounds. Thus, it may be seen from the scale that doubling the amount of sound energy makes but a slight difference in the impression made upon our ears. Footer: Printed in U. S. A.{Mr Adams}—March, 1936, 10M Licensed under C. F.{Mr Friese} Burgess Laboratories, Inc., Patents BURGESS BATTERY COMPANY GENERAL SALES OFFICES, 111 W. MONROE ST.{Capt. P. R. Strong}, CHICAGO Battery Division—FREEPORT, ILL. Engineers and Manufacturers of Acoustic and Electric Products Acoustic Division—MADISON, WIS. Bulletin 111 Index BS{A J. Barnes - Assistant Manager}/800A | ||