Noise Generated by a Power

By Sadao Aso, Rikuhiro Kinoshita, Heihachi Uematsu and Kiyohumi Sasaki, Members,TMSJ

Faculty of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo Basedon Journalof theTextile Machinery Society of Japan, Transactions,18, T13-19 (1965)

Abstract An investigationwas made to survey the actual noise level generated by a power loom, devise some method to reduce the noise level on the power loom and explorethe possibilityof controllingthe noise generated by loomsin a factory. A power loom was placedin a room, 494M3 in volume,of the workshopattached to our university. The mean value of six room-constantsobtained in variousoctaves band measured 152m2. The noise level and the octave band sound pressure level were measuredwith a sound level meter, an octave band filter and a level meter. Equal-level contours of the noise level and the sound pressure level were drawn with these instru- ments. The noise level at a height of 150cm reached a maximumof 90 phons. The noise within about 2 meters from the loom was louder on the diagonalline, but at 2 meters or a longer distance from the loom it was regarded as a point source. The frequencycharacteristic of the sound pressure level showed a peak value in the 1600-3200c/s band. Sound power in the band was 11 milliwatts. A piece of gum was stuck on the surface of the stopper and a spring was replaced with a suitable one to reduceimpulsive. Then the noise made by the pickingmechanism decreasedby 4-5 dB in a high-frequencyrange. After the gearing was insulatedwith a cover, the noise radiated by the gearing in the driving part decreasedby 4-8 dB in a middle and a high-frequencyrange. This indicatesthat the noise generated by a power loom can be reduced considerablyby a completeadjustment of the loom and by insulating the sound source.

1. Introduction level generated by a power loom and computes sound power. It also explores noise sources, describes a few methods to eliminate and insulate noise and discusses The problem of noise has been around for so many the effects of those measures. years, but it is only in recent years that the need to measure noise by and combat it has been 2. Characteristics of Noise taken up seriously. Tokita's[1] published work of 1963 gave the results of measurements of noise generated by many kinds of and suggested ways to 2-1. Method of Measurement control noise generated by some of the machines. There (a) Loom surveyed is also a published work[2] on noise levels in various Hatsuya's silk loom, having 2 boxes on one kinds of factories. Then, too, there is a published side and capable of 146 rpm, was chosen for our study. general survey of noise[3). The loom's space was 58.5 cm long. This loom An analysis of noise in a weaving factory was was laid on square logs (5.5 cm ><5.5 cm) at a fixed made, too. Hirayama and others[4] reduced the noise place in the workshop which will be described later. A level architecturally and acoustically by covering the motor (1 IF, 3.5 A and 1400 rpm) was also laid on the ceiling of a factory with some absorbents. Nakamura logs. The loom was worked by belt transmission and others[5] studied the acoustical properties of build- through the medium of a pulley on the way. The loom ings in a weaving factory for noise control planning. was kept in a state of perfect balance to be free from We made our investigation to eliminate and pre- shakes during operation. What is referred to in this vent noise generated by machinery proper. This article as a "whole operation" is an operation without article measures the noise level and the sound pressure a vertical motion of shuttle boxes, healds or warp

Vol. 12, No. 1 (1966) 23 and with an empty shuttle having no weft on it. (b) Workshop Our experiment was made in a room of the work- shop attached to the Faculty of Engineering, Tokyo University of Agriculture and Technology. The floor of the room is 81 m2 (9m x 9m) in area and is built of concrete. Its roof is built of wooden boards under sheet zinc. There is no ceiling. The four sides of the room are mortar walls panelled with boards. Two sides have no windows and are trapezoid. The other two have windows and are rectangular in shape. These areas are given in Table 1. The volume of the room is 494m3.

Table 1 Areas of Various Parts of the Room (m2)

Fig. 1 Measuring points in the room

By substituting reverberation time T, obtained from the reverberations, into the following equation, the average absorption coefficient a in the room was cal-

Table 2 Acoustical Characteristics of the Room culated. Room constant R was computed by a. T= -0.162V/{S log e (1-a) } R=aS/(1-a) where V is the volume of the room and S is the whole surface area inside the room. This equation ignores sound absorption by air. (c) Method of Measuring Noise[7] To know this distribution of noise around the loom, the noise level was measured at various measuring points with a sound-level meter of Rion Co. s' make (comforming to Japan Industrial Standards C1052 and capable of measuring noise levels) by characteristics A, B and C.[8] Next, the sound pressure level in various octave bands was measured by connecting the sound level Table 2 gives the reverberation time, the average meter with an octave band filter and a level meter. absorption coefficient and the room constant of the Because their values fluctuated at each measuring room, which were measured with a sport pistol as a point, i.e., the indicator of the meter vibrated consider- sound source.[6] The pistol was fired at one corner on ably, the mode of greater values was regarded as the one diagonal line on the floor and the sound was re- maximum, the mode of smaller values as the minimum. corded at the other corner. Then the pistol and the Greater or smaller values varied within 3dB and the recorder were replaced and the sound was recorded again. modes were fixed by eye measurement. The sounds of the pistol on the other diagonal line The measuring points are illustrated as the grid in were recorded by the same method. Fig. 1. At each measuring point the height of a micro- Frequency analysis of the sounds of the pistol phone was varied to 50, 100, 150, and 200 cm. A mea- was made with an octave band filter. The reverbera- suring point is described as (e. 9.50) in this article. tions were recorded on a chart by a high level recorder. No measurement was made on the right-hand side or

24 Journal of The Textile Machinery Society of Japan lower side in Fig. 1 because many parts of machines were laid about 30 cm high. A total of 324 points were measured. The measurement was made at night when the back ground noise was small. The difference between the noise generated by the loom and the back ground noise exceeded 10 dB. Therefore, measured val- ues for the back ground noise were not corrected by the JIS method. (d) Results of Measurement The measured values at point (e, 9) are given in Table 3 as an example of the measured results. B - and C - characteristic values of the noise level at each mea- suring point are nearly smilar, but A-characteristic value is about 1 phon bigger than B and C. The dif- ference between the maximum and minimum values of the noise level varise from point to point but is below 9 phon. The difference in the sound pressure level is below 10 dB. The measured values of the noise level were written down at all measuring points in Fig. 1. The points having almost the same values were linked so that an equal-level contour was drawn. Figs. 2-4 show equal-level contours for noise levels differing in height and were drawn from the maximum Fig. 3 Equal-level contours of noise level (phons) value of C-characteristic. i at 100cm height)

Fig. 2 Equal-level contours of noise level (phons) Fig. 4 Equal-level contours of noise level (phons) (at 50cm height) Solid lines are for 150-cm height Dotted lines are for 200-cm height

Vol. 12, No. 1 (1966) 25 In the light of these figures, we may say that the noise generated by a loom is the compound of the sounds generated by many parts of the loom. The noise level contour of a plane 100 cm high shows directivity distinctly. Noise within a about 2 meters from the loom is louder on the diagonal line. Noise at a distance of more than 2 meters is regarded as a point source. The maximum value of the noise level at the level of the human ear is about 90 phon. The equal-level contours of the sound pressure level were made by the same method as the noise level. To cite an instance, Fig. 5 shows the equal-level contours of the sound pressure level in the 1600-3200 c/s band and on a plane 50 cm high. The sound pressure levels in each octave band at the point (e. q) closest to the front of the loom are given Table 3. All the equal-level contours of the sound pressure level showed that the sound was the loudest in the 1600-3200 c/s band, the second loudest in the 3200-6400 c/s. The sound pressure level decreased in the other bands as frequency became small, but the sound in the 50-100 c/s band was slightly louder than in the 100-200 c/s band. The characteristic of the sound pres- Fig. 5 Equal-level contours of the sound pressure level (dB) sure level as to the height from the ground had the (in 1600-3200 c/s band at 50-cm height) same tendency as the noise level in each octave band. 2-2. Sound Power Where the sound power of a source is known, loud- coefficient is known, or when the source is put with ness when the source is put in a room whose average other sources in a room, is calculable by the sound power. Therefore, sound power is a value necessary to control noise from the standpoint of architectural Table 3 Measured Values of Noise Level and the Sound acoustics. Properly, sound power should be calculated Pressure Level in Various Octave Bands at the by the sound pressure level of the source put in a free Measuring Point (e, 9) space. Since it is difficult to place a loom in a large space, we calculated sound power by the sound pressure level measured in the room of the workshop mentioned above. Assume that sound power is expressed as a sound power level (PWL) 10-12 W for 0 dB, and that a source is put in the center of a room having room constant R. Then the relation between the sound pressure level (SPL) at r meters from the source and PWL is given by the following equation : C9] SPL=PWL+l0 log (0.25rc-1r-2+4R-1) In our experiment the loom was assumed to be placed in a 1/4 free space from the equal-level contours of the noise and the sound pressure level. Therefore, SPL=PWL+IOIog (,r-'r-2+4R-1) The value measured by C-characteristic of the sound level meter can be used as the SPL, but it has to be a mean value calculated not by an arithmetical mean but by the decibel unit from values measured at several points r meters distant from the loom in three different dimensional directions. The center of the

26 Jourmal of The Textile Machinery Society of Japan loom was regarded as 50 cm above the floor, and 5 measuring points nearest r=2m were chosen. The sound pressure levels measured at those points in each octave band, the mean sound pressure levels (SPL), the PWL and the sound power computed by the PWL are given in Table 4. The SPL was calcul- ated by this equation : 5 FL= 10 log log- , (SPL) i 10 -10 log 5

3. Partial Sound and Noise Control

3-1 Picking Mechanism To control noise, we have, first, to define the char- acteristic of a sound generated by each part of a loom. This is impossible, however, because no one part of a loom can be operated independently. Since the main noise of a loom is generated by the picking mechanism, we took the alternative of measuring the noise level and the sound pressure level of the sonud issuing from the picking mechanism. The measurement was made Fig. 6 Sketch of picking mechanism under the conditions described in what follows. (i) Stopping the picking stick Ratch C and catch D in Fig. 6 for the picking mo- tion were not meshed with each other. In other words, a signal was sent to rod 0 that a shuttle was held in the opposite shuttle box, so that lever M might be lifted to free ratch C from the movement of arm F and catch D. 11) and (e, 8, 9 and 11), all nearest the loom. The (ii) Stopping the whole picking mechanism sound pressure levels were measured at heights of 50, Picking cone J was lifted and tied to the frame 100, 150 and 200 cm at each point by the same method of the loom to be put out of contract with picking as the whole operation. tappet K. This stopped all motions for the picking. Part of the measured results are shown in Fig. 7. Measured points were (c, 7, 9 and 11), (d, 7 and When the picking mechanisms on both sides of the

Table 4 Sound Power of the Loom

Vol. 12, No. 1 (1966) 27 loom were stopped (condition ii), the sound pressure level on the right-hand side was larger than on the left side by 3-5 dB in the middle frequency range. The reason is that the gearing and the belt in the driving mechanism were on the right-hand side. When the sticks were stopped (condition i), there was a big difference in sound pressure level between the two sides in the high-frequency range. The fact shows that the sounds generated by the picking mech- anism are not the same on both sides but are louder on the right-hand side. When the sticks were stopped, the sound pressure level on the left side was smaller than in the whole operation by 6-7 dB in the high frequency range. This difference is presumably the loudness of the noise ge- nerated by sticks. Fig. 7 shows that, even with the sticks (which seemed to generate the loudest noise) stopped, high- pitch sounds were generated by the picking mecha- nism. An examination of their source showed that they were generated by the following motion : Catch D in Fig. 6 is pulled up, together with arm F, by strap G, motivates stick A and is then returned by spring I. Fig. Sound pressure level of sounds generated by At this time, catch D is stopped by stopper E, but D picking mechanism and E, both being made of metal, produce a high-pitch sound. This sound is generated every time the crank revolves. Therefore, the noise level changes periodically. It is clear from Fig. 7 that this sound is louder on the right-hand side than on the left. Besides, this sound is not generated at the same time by the picking mechanisms on both sides. Accordingly, the picking mechanism on the left side was stopped and the noise level and the sound pressure level of the sound gen- erated by the picking mechanism on the right-hand side was measured under the condition (i). After that, a piece of hard gum 3 mm thick used as a packing ma- terial for machines was stuck on the surface of stopper E to relax the impact of catch D and stopper E. The noise level and the sound pressure level in this condi- tion were measured by the same method as above. The results of the measurement of the sound pres- sure level are shown in Fig. 8. Even after treatment with the hard gum, the sound pressure level decreased by only 2 dB in the high frequency range. The max- imum and minimum values of the noise level measured by C-characteristic were 90 and 80 phons before the Fig. 8 Effect of treatments for reducing noise treatment. They were 86 and 81 phons after the generated by picking mechanism treatment, showing that the miximum value decreased by only 4 phons. noise was effectual. We then examined other sources The high-pitch sound produced by the metallic and learned something. Picking cone J in Fig. 6, being shock softened as we listened to it, but it does not beaten hard by the nose of picking tappet K, did not seem that the treatment with hard gum for reducing follow on the curved surface of K but departed from it.

28 Journal of The Textile Machinery Society of Japan When returned by spring L, the pickig cone knocked with both picking mechanisms stopped and the gearing against the surface of K and generated the impulsive covered and uncovered. sound. The reason was the weakness of spring L. The Part of the sound pressure level measured is shown spring was, therefore, replaced. After that, the sound in Fig. 10. The gearing being covered, the noise level pressure level was measured, found to be 84 phons at the maximum value, and was added to Fig. 8. After the gum was stuck and the spring was replaced, noise in high frequency range decreased considerably. This shows how important a complete adjustment of a mac- hine is as the first step to controlling the noise of machinery. The loom used in our experiment was equipped with a picking mechanism which generates a loud noise because it is as loom of the pick-at-will motion. Since the stick of a loom having a single shuttle box never throws the shuttle continuously on the same side, this noise is out of the question. The noise in the shuttle box is caused by the pick-at-will motion. When a shuttle enters a shuttle box, it is reduced slightly in speed by a swell, runs against a picker to generate an impulsive noise, and is then stopped by a buffer through the medium of the picker. If the time of the collision of the shuttle with the picker is long, the impulsive noise is small. Fig. 9 The cover to insulate the noise generated Since, however, the shuttle box has to move up by the gearing and down because of the pick-at-will motion, the picker stops the shuttle instantaneously at a certain place but must depart from the shuttle at once so as not to hin- der the up-and-down motion of the shuttle box. To help this movement of the picker, the buffer approaches the entrance to the shuttle box when the shuttle runs in the shuttle box, stops the picker in a short time and retreats at once. At the same time, the picker is sep- arated, together with the stick, from the end of the shuttle by spring H in Fig. 6. The impulsive noise is, therefore, unavoidable. The noise in the shuttle box is the loudest when the shuttle strikes against the picker; the second loud- est when the picker returns after picking and collids with the buffer ; slight when the picker throws the shuttle. So long as the pick-at-will motion is used, the buffer is useless for noise control. 3-2. Gearing in Driving Part As we have said, considerable noise was generated by the gearing in the driving part. The sound source was, therefore, insulated with a cover the simplest and, we believed, an effectual method of noise control. Fig. 9 illustrates the cover placed over the sound source. The surface, seen in the photo, and the invis- ible side are made of asbestos boards 5 mm thick which are hemmed with plywood. The inside of the playwood octave aana is pasted with a glass fiber board 5 cm thick. Meas- Fig. 10 Effect of cover placed over the gearing in urements were made at points (c,11), (d, 11) and (e, 9) driving part

Vol. 12, No. 1 (1966) 29 at a 50 cm height decreased by 6 phons. As the figure inside the building have yet to be considered. The shows, the sound pressure level at a 50-cm height de- noise analyzed in this article is the noise of a loom creased by 4 dB in the 800-1600 and 1600-3200 c/s having no heald or warp. It is not the noise of cloth bands, by 8 dB in the 3200-6400 c/s band. These weaving. However, sounds generated by healds and results show that covering a source is useful for insu- warps are a frictional, low-pitch sounds which matter lating a sound. However, the sound pressure level in little and may be left out of consideration in noise the low frequency range increased by 3 dB. The control. Nevertheless, the noise characteristic of a reason presumably is that a vibration of the loom is weaving factory at work can be estimated from the transmitted to the cover and makes a sound source. For various values given in this article, and it is hoped noise control, sound in a high frequency range had that they will help in building an architecturally and betterbe reducced even if sound in a low frequency acoustically quiet factory or rebuilding an existing range increases slightly. factory. The authors are deeply grateful to Masaru Koyasu, of Kobayashi Institute of Physical Research, for his 4. Conclusions suggestions and advice. Grateful acknowledgment is due also to Shunichi Nakamura, of the same institute, Generally, a vibration and a sound are unavoidable for his help in the measurement of the reverberation if a machine is run. However,if the noise is a high- time. pitch sound like that generated by the loom and is fairly loud, it has great physiological effect on workers. Sato[lo) says many workers in mills have dif- References ficulty in hearing. Our measurement of noise gene- rated by a spinning machine showed that sounds in the middle frequency range (300-1200 c/s) were 85 dB in [1] Y. Tokita : J.Acoust. Soc. Japan : 20, 270 (1964) sound pressure level and were the maximum of all [2] C. M. Harris : Handbook of Noise Control ; (1957) sounds. Sounds over 4800 c/s were below 60 dB when New York, McGraw-Hill Book Co. measured in a circumference 50 cm away from the [3] S. Morita : Noise and Noise Control ; (1961) To- spinning machine and 1 meter in height. kyo, Ohmu-sha. Since workers even in mills equipped with such [4] T. Hirayama and A. Koda : at a meeting of spinning machines lose the power of hearing, it is Acoust. Soc. Japan (1954) easy to imagine that the auditory nerve of the worker [5] S. Nakamura, F. Kenmachi, Y. Tokita, M. Koyasu can be hurt by noise in a weaving factory, especially and Y. Kohashi ; Bulletin of Kobayashi Institute high-frequency noise, which is louder than in a spin- of Physical Research, 12, 172 (1962) ning factory. [6] Acoustic Material Association of Japan : Architec- Even if the noise characteristic of a loom is minu- tural Acoustical Engineering Hand Book ; p. 140 tely investigated, it is difficult to take steps which will (1963) Gihodo, Tokyo. immediately reduce noise measurably. For example, [7] J. Igarashi ; J. Japan Soc. Mech. Eng. ; 57, 437 the buffer had better be replaced with a damper, but (1954) this is difficult for many reasons. [8] JIS Z 8731 (1957) Method of Sound Level Measure- Since the whole building of a big weaving factory ment is usually sealed up, noise is insulated nearly perfectly [9] Y. Kohashi : Acoustical Engineering. p. 40 (1956) and does not spread to the outside of the building. Tokyo Nikkan Kogyo Newspaper Co. However, in most factories, measures to control noise [10] K. Sato : J. Ja pan Soc. Mech. Eng. ; 59, 81 (1959)

30 Journal of The Textile Machinery Society of Japan