School of Mechanical EngineeringEMM 342 Noise and Vibration

Noise Measurement LaboratoryGroup 8

Name: 1. Saw Siong Keat 1046142. Lim Huat Poo 1045973. Nyeo Kok Wooi 1046124. Chng Jin Jun 1045855. Yeap Peng Liang 104627

Date of Summit: 28 May 2012Lecturer: Dr. Inzarulfaisham b. Abd. RahimTitle: Noise measurement in Bilik Persidangan (Conference Room) Objective:1. To determine the characteristic of noise that exists in Conference room.2. To determine the transmission loss, reverberation time , absorption and reflection of sound and noise reduction that occur in Conference room.3. To determine the background noise that exists in Conference room. Introduction:Noise is an unwanted sound in the surrounding. Noise usually is generated by the industrial application which is called as industrial noise. Example of popular industrial noise are sound that caused by compressor, pump, boiler, internal combustion engine and grinding machine. Noise can contribute physical and psychological problem to the people around them like increase blood pressure, stress, lost of hearing and less of rest due the annoying sound. Noise measurement is a very important nowadays, it commonly used to design and improve the machine or indoor in order to reduce the noise generated and enhances the noise quality in the room. Noise quality is important in study or meeting environment especially in lecture hall and conference room. In this project, Conference room has been chosen as our location to measure the noise that exists in enclosed space. It is important to figure out the external or internal sound source which will cause uncomfortable noise that degrading the sound quality in Conference room. The function of Conference room is to carry out an important general meeting which is involved staff and students. The noise has to be reduced to minimum value so that the members can hear clearly from the speaker during the meeting. Experiment carried out include measuring the background noise that exist in Conference room, transmission loss from outside chatting noise to inside conference room and reverberant field from air conditioning sound source. Reverberation time ans noise reduction can be calculated theoretically by taking the dimensions of absorption material and volume of Conference room. From this experiment, we can determine the primary noise and its characteristic that exists in the conference room.

Point 11 under air conditioning 401.3cm 401.3cm

Point 3 and Point 7Point 4 and Point 8 288.5cm 288.5cm288.5cm 288.5cm

Point 1Point 22m 1.5m 401.3cm 401.3cm

401.3cm 401.3cm

Point 5 and Point 9Point 6 and Point 10 288.5cm 288.5cm288.5cm 288.5cm

401.3cm 401.3cm

Figure 1: Measurement points taken in conference room

482cm45cm190cmTable260cm775cm30cm64cm260cm322cm379cmTable 820cm960cm510cm1605cm1154cmTable

Symbol: Represent wooden door Represent chair

Figure 2 The schematic diagram of Conference roomMethodology:

Part A: Transmission loss of chatting noise of people from outside door to inside Conference room It is important to determine whether the disturbance of people chatting noise at the outside of Conference room will transmit through the door into the Conference room. This noise may disturb the members hearing system and lost concentration on the speaking person. The measurement is made when the space is occupied and air conditioning is switch on as background noise. 2 people are chatting outside the door of Conference room. Measurement is taken by using Sound level meter Bruel and Kjaer 2260 and smart phone application. From http://www.moderco.com/kits/standards/ASTM%20E-90-09%20-%20standards.pdf , it state that :A2.2.3 In the source room, microphones shall be more than 2 m from any source. A2.2.4 In the receiving room, microphones shall be more than 1.5 m from the test partition.Therefore, based on figure 1,the first measurement is taken 1.5m from the door inside Conference room while 2 people still chatting outside the Conference room. The second measurement is taken 2m from the door outside the Conference room while 2 people were still continue chatting outside Conference room. The transmission loss of disturbance chatting noise from outside conference room to inside conference room by experiment is the subtraction of measurement data taken at outside conference room to inside conference room. While for theoretical calculation, we need the to measure the thickness of the door that will transmit the chatting noise from outside conference room to inside conference room. We use ruler to measure the thickness of the door and the dimension is 0.035m. From the text book Engineering noise control by A.Bies,the formula for transmission loss is given by: TL=10log ( ), where =sound power coefficient )2 ,where is the impedance of air M is surface density of partition ,which is the impedance of free air at 20 and 1atm.

Part B:Background noiseAir conditioning is determined as the background noise that exists in Conference room. According to the journal of Measurement Method of Background noise in theatre Based on stage machinery:The room has to be divided into a number of squares averagely, which should cover the room completely. Measuring points should be set in the centre of each square. Measuring instrument should be kept 1.2m away from the ground. Measuring result should be the averaging of all the points in room.Therefore, we have divided the Conference room into 4 grids. Based on figure 1,the points 3, 4, 5 and 6 are measured at the center of their grid respectively by using Sound level meter and smart phone application when air conditioning is switched on. Then, air conditioning is switch off and the measurement of points 7, 8, 9 and 10 are taken. The formula used in calculation for averaging the all points in room as below: Volume (total) Sound Pressure Level = 10 log (10Lp1/10 + 10Lp2/10 + 10Lpn/10)The background noise from air conditioning is the subtraction of average sound pressure level when air conditioning turn on with the average sound pressure level when air conditioning turn off. Part C: Reverberation time in Conference room.Since we are unable to measure the reverberation time in conference room due to we do not have instrument to measure the reverberation time. Besides, the reverberation time is too short to measure and it will be inaccurate if we use stopwatch to determine the time in seconds for sound level to decay by 60dB after a sound source is abruptly turned off. Therefore, we can only determine the reverberation time by theoretical only. The dimension of Conference room is measured by using measuring tape. The total numbers of absorption material and its surface area are recorded. The reverberation time and the average absorption coefficient of the Conference room then are calculated by using formula stated in the Result part later.

Part D: Noise Reduction in Conference roomThe noise reduction can be achieved by adding sound absorption to an enclosed space. This can be determined by comparing the sound pressure level in the enclosure after adding the sound absortion to that before the absorption was added. After we have calculated the reverberation time, we desire to reduce the reverberation time by add in some absorption material which is fiberglass board. The formula of noise reduction will be stated in the Result part.

Part E: Sound Pressure Level, Sound Power Level and Sound Intensity level in Conference RoomTo measure the sound pressure level of air conditioning as background noise source, we just put the sound level meter under the air conditioning (point 11) which is switch on. The formula for calculating the Sound Pressure Level, Sound Power Level and Sound Intensity level will be stated in Result part.

Result:Part A: Transmission loss of chatting noise of people from outside door to inside Conference room Based on the figure 1 which is the schematic diagram of conference room:1. Point 1 with the condition: a) Air conditioning is switch onb) People chatting outside the door of conference roomc) Measurement taken 0.3m near the door inside conference roomd) Data taken is: LAeq=68dB

2. Point 2 with the condition:a) Air conditioning is switch onb) People chatting outside the door of conference roomc) Measurement taken 0.3m near the door outside conference roomd) Data taken is: LAeq=86dBTheoretical :.From the website of : www.stanleyhardware.com/default.asp?TYPE=STATICLEFT&PAGE=cht_weight,htm&LEFT=left_cht_weight.htm, the hollow core material of wooden door with 0.035m thickness,2.04m height and 0.83m length, the surface density ,m=9.8kg/m2.

Since the optimum reverberation time is at 500Hz, then the W=2Therefore, the Sound power coefficient, )2 =( 2 =7.268-4Transmission loss,TL=10 log( ) = 31.4dB

Experiment (by using Smartphone application):Tenasmission loss,TL= LAeq point 2 Laeq point 1 = 86dB 68dB =18dBError percentage= 100% = 42.7%

Experiment (by using sound level meter):LAeq location 1 is 59.4dBLAeq location 2 is 61.3dBTherefore , Tenasmission loss,TL= LAeq point 2 Laeq point 1 = 61.3dB- 59.4dB =1.9dBError percentage= 100% = 94%

Part B: Background noiseThe background noise in Conference room is Air conditioning.We have divided the conference room into 4 grids. Each measurement are taken at the center of each grid as stated in figure 1.

Experiment (by using Smartphone application)Based on figure 1,When air conditioning is switch on, LAeq for point 3 is 61BLAeq for point 4 is 62dBLAeq for point 5 is 62.4dBLAeq for point 6 is 61.4dBFrom the text book of Engineering Noise control by David A.Bies,Volume (total) Sound Pressure Level = 10 log (10Lp1/10 + 10Lp2/10 + 10Lpn/10)=10 log [(1061/10 + 1062/10 + 1062/10 + 1061/10 )/4]=61.5dB

When air conditioning is switch off,LAeq for point 7 is 41dBLAeq for point 8 is 43dBLAeq for point 9 is 43dBLAeq for point 10 is 44dBVolume (total) Sound Pressure Level = 10 log (10Lp1/10 + 10Lp2/10 + 10Lpn/10)=10 log [(1041/10 + 1043/10 + 1043/10 + 1044/10 )/4]=42.9dBTherefore, the background noise from air conditioning in Conference room = 61.5dB-42.9dB = 18.6dBExperiment (by using Sound Level Meter)We have divided the conference room into 4 grid. Each measurement are taken at the center of each grid.When air conditioning is switch off,LAeq for point 3 is 57.2dBLAeq for point 4 is 57.2dBLAeq for point 5 is 57.4dBLAeq for point 6 is 57.4dBFrom the text book of Engineering Noise control by David A.Bies,Volume (total) Sound Pressure Level = 10 log (10Lp1/10 + 10Lp2/10 + 10Lpn/10)=10 log [(1057.2/10 + 1057.2/10 + 1057.4/10 + 1057.4/10 )/4]=57.3dB

When air conditioning is switch on,LAeq for point 7 is 59.4dBLAeq for point 8 is 59.4dBLAeq for point 9 is 59.5dBLAeq for point 10 is 59.5dBVolume (total) Sound Pressure Level = 10 log (10Lp1/10 + 10Lp2/10 + 10Lpn/10)=10 log [(1059.4/10 + 1059,4/10 + 1059.5/10 + 1059.5/10 )/4]=59.45dBTherefore, the background noise from air conditioning in Conference room = 59.45dB-57.3dB = 2.15dB

Part C: Reverberation time and absorption in Conference room.We had taken several absorptive materials in the conference room into consideration. The absorption material that exists in conference room are as below:From website http://www.sae.edu/reference_material/pages/Coefficient%20Chart.htm,125 Hz250 Hz500 Hz1000 Hz2000 Hz4000 Hz

Carpet0.010.020.060.150.250.45

Seats (fabric-upholstered, empty)0.490.660.80.880.820.7

Seats (fabric-upholstered, Fully Occupied)0.60.740.880.960.930.85

Brick (Painted)0.010.010.020.020.020.03

Plaster Ceiling0.010.020.020.030.040.05

wood table 0.150.110.10.070.060.07

people 0.2320.2790.3250.3530.3720.353

Table 1 absorption coefficient chart

The dimension of the room is 16.05m in length, 11.54m in width, ad 2.75m in height.Therefore, the volume of the room, V = 16.05m x 11.54m x 2.75m= 509.35m3And the total surface area of room, S = 2 x (11.54x 2.75 + 16.05 x 2.75 + 11.54 x 16.05) = 522.18m2=18440.613 ft3There are 49 seats provided in the conference room, we assume that it is 2/3 fill up like there are 33 people in that room. The surface area of the seat is approximately 0.5m2.The total surface area of the wood table in the conference room is approximately 18.62 m2.In order to find out the average absorption coefficient of the room, we apply

For 125 Hz, the average absorption coefficient is

The total absorption of the room is given by

The reverberation time is

The room constant is given as

125 Hz250 Hz500 Hz1000 Hz2000 Hz4000 Hz

Carpet0.010.020.060.150.250.45

Seats (fabric-upholstered, empty)0.490.660.80.880.820.7

Seats (fabric-upholstered, Fully Occupied)0.60.740.880.960.930.85

Brick (Painted)0.010.010.020.020.020.03

Plaster Ceiling0.010.020.020.030.040.05

wood table 0.150.110.10.070.060.07

people 0.2320.2790.3250.3530.3720.353

29.4937.6751.3672.2192.05129.74

Average sound absorption coefficient, 0.0520.0670.0910.1280.1630.230

Absorption, A30.28738.98453.84577.257100.472147.387

Reverberation Time, T 2.7762.1571.5611.0880.8370.570

Room Constant R131.11340.35956.49382.785109.954168.386

Table 2 Reverberation time and room constant calculated in conference room

Part D: Noise Reduction in Conference room.From the references we obtained,

Figure 3 Optimum reverberation time for different size and type of roomThe speech is the primary function in the conference room. Therefore the required reverberation time at all frequency is 0.7 seconds. If we desired to reduce the reverberation time of the conference room, we need to add in some absorptive materials.

In order to increase the sound absorptive of the room, we suggest using 1 inch thick fiberglass board with 90m2 attached to the wall to increase sound absorption.125 Hz250 Hz500 Hz1000 Hz2000 Hz4000 Hz

Fibreglass board0.530.990.990.990.990.99

33.9954.77108.06151.4175.75215.14

Average sound absorption coefficient, 0.0600.0970.1910.2680.3110.381

Absorption, A35.05557.608119.927176.222210.498270.760

Reverberation Time, T 2.3981.4590.7010.4770.3990.311

Room Constant R236.16460.646133.598206.780255.042347.323

Table 3 Fiberglass is added to increase sound absorptionThe noise reduction is calculated using

125 Hz250 Hz500 Hz1000 Hz2000 Hz4000 Hz

Room Constant R131.11340.35956.49382.785109.954168.386

Room Constant R236.16460.646133.598206.780255.042347.323

Noise reduction, NR0.6531.7693.7383.9763.6543.144

Table 4 Noise reduction after fiber glass is added

Part E: Sound Pressure Level, Sound Power Level and Sound Intensity level in Conference RoomThe measuring point 11 is under air conditioning which is switch on. Assuming the room temperature as 25 degree and frequency of 500 Hz is taken as reference. Sound Pressure Level,Lp=10log46.55dB=10logPrms=4.2510-3PaIntensity of sound,! = = =4.36-8 W/m2Intensity of sound in decibel, Li = 10log[]dB = 10log[]dB =46.39dBIntensity of sound = 4.36-8 W/m2 = Sound Power = 8.07Sound Power level,Lw = 10log[]dB = 10log[]dB = 69.1dB

FrequencySound Pressure Level (dB)Sound Intensity Level (dB)Sound Power Level (dB)

12530.163052.68

1603534.8457.52

20037.136.9459.62

25040.1139.9562.63

31542.6742.5165.19

40044.6944.5367.21

50046.5546.3969.1

6304847.8470.52

80048.9548.7971.47

100049.3649.271.88

125049.5349.3772.05

160049.2449.0871.76

200048.7848.6271.30

250048.1447.9870.66

315047.3147.1569.83

400046.446.2468.92

500045.3645.267.88

630044.3344.1766.85

800043.6543.4966.17

1000042.542.3465.01

1250042.2942.1364.81

Table 5 : Compiling data from point 11 at different frequency

Graph 1: SPL,SWL and IL versus frequency in conference room

Discussion:1. We identify the air-conditioner as the primary noise exists in the conference room.2. From the http://soundproofing.org/infopages/air_conditioner_soundproofing.htm, older air condition units are more likely to emit noise compare to newer unit. Compressors make more noise than fans and when the unit worn out, it can be very difficult to quiet down and replacement is the only option. Fan blades can make a lot of noise if coated with dirt through long use and can become imbalanced, causing bearings to go bad aggravate the noise. The noise came from the compressor and integral fan noise as well as vibration is hard to soundproof them directly with material installed to them. 3. The type of noise came from the air conditioner may attributed to fans, and compressor. Therefore, this type of noise is category as discrete frequency noise. Discrete frequency noise is mainly generated from rotating machinery. 4. Beside the noise generated from the air conditioner, we also want to eliminate the noise from outside of the room, like chatting noise, to prevent interference to the conversation inside the conference room. 5. Thus transmission lost through the conference door is investigated to determine the effectiveness of the soundproof of the conference room towards the disturbance from outside.6. The experimental data (smart phone application ) shown 18dB losses when the conversation is taken outside. In other words the door provides an insulation barrier of 18dB. However, theoretical data shown 31.4dB loss through the door. 7. While by using sound level meter, there is only 1.9dB transmission loss, which is much smaller than theoretical value. We suspect that the sensitivity of sound level meter become low since it has been used for many years ago.8. Theoretical value shows that the loss is higher than experimental .This may due to the slit or door gap make the sound permissible into the conference room which make the experimental data differ from the theoretical data.9. For background noise topic,when the air conditioner is turn off the background noise is 43dB which is dubbed as a quiet office or room. There shown a vast sound pressure level difference between the air conditioner is on and off. 10. When the air conditioner is switched on the background noise is 61.5dB which shown an increment of 18.6dB by using smart phone application. Again, by using sound level meter, the background noise caused by air conditioning is only 2.15dB. Sensitivity of sound level meter is again suspected low and broken. 11. The 61dB of the conference room make the chatting noise from outside (68dB) rather insignificant which means that the conversation inside the conference room will not be disturbed by the noise emitted from outside the room unless it is a big noise like radio music. 12. When we tested the sound pressure level at 0.03m away from the air conditioner vent, we found out that it gives a data of 86dB and showing a decreasing value as the distance from the vent get bigger as shown in the graph. 13. But it has shown a trend of approaching asymptote of 61dB as the distance get further away. 14. Therefore, for a distance of 0.9 m away from the air conditioner vent, the noise from air vent is diffused into the enclosed space and turn into a background noise.15. The reverberation time calculated from theoretical data is 1.561 seconds at 500Hz for 2/3 occupied room.16. The optimum reverberation time for a conference room is 0.7 second for a room size of 18440.613 ft3 by referring to Figure 3.17. Therefore by considering improving the reverberation time of the room, we propose a 90m2 area of 1 inch thick fibreglass board added to the wall to increase the average absorption coefficient of the room. 18. The data shown improvement of reverberation time up to 0.701 seconds. 19. The noise reduction after added the fibreglass board to the wall shown a decreasing of 3.74dB. 20. We are unable to determine the transmission loss from speaker to audience because the microphone in each seat is come together with speaker itself, meaning that microphone and speaker are in 1 set. Therefore, every audience can listen clearly from their position as each microphone set is just in front of them.21. From the website http://www.engineeringtoolbox.com/nc-noise-criterion-d_725.html,

Figure 4 : Recommended NC level in conference roomit stated that for conference room, the recommended NC level is between 25 and 30 and the equivalent sound level in dBA is between 35 to 40dBA. Comparing to our experiment calculated result, taking 500Hz as a reference, the sound pressure level in conference is 46.55dB while in the website, the recommended value is 35dB. Therefore, we have to add in some absorption material to decrease the sound pressure level in conference room so that the sound pressure level will more likely to 35dB. 22. There are several errors exist when taken the data i. There is some noise like accidentally tap table emitted when data is taken causing it to fluctuate. ii. Some people are walking outside the corridor of conference room which will affect the value of data when the measurement is made near to the door or wall.iii. Weak battery power will affect the data taken.

23. Precaution stepsi. There must be less people around the room when the experiment is carried out to decrease the probability of noise making.ii. Many data should be taken to average out the errors and improve the data accuracy.iii. Make sure the battery power is full.

Conclusion1. The transmission loss through the door is 18dB by using Smartphone application and 1.9dB by using Sound level meter.2. The background noise when air conditioner is switch off is 43 dB and when the air conditioner is switch on, it is 61dB by using sound level meter. While by using sound level meter , the difference between air conditioning switch on and off is 2.15dB.3. The reverberation time is 1.561seconds theoretically. References 1. Machinery noise measurement. By S.J. Yang and A.J. Ellison from Oxford science Publications.2. http://soundproofing.org/infopages/air_conditioner_soundproofing.htm3. www.stanleyhardware.com/default.asp?TYPE=STATICLEFT&PAGE=cht_weight,htm&LEFT=left_cht_weight.htm4. http://www.sae.edu/reference_material/pages/Coefficient%20Chart.htm5. Text book Engineering noise control by A.Bies,4th edition.6. Measurement Method of Background Noise in Theatre Based on Stage Machinery by Hui Ren, Jingjing Zhang, Wei Jiang, Zhibin Su from School of Information Engineering, Communication University of China Beijing, China7. http://www.moderco.com/kits/standards/ASTM%20E-90-09%20-%20standards.pdf ,

Figures of Measurement data

Point 1 dataPoint 2 data

Point 3 dataPoint 4 data

Point 5 dataPoint 6 data

Point 7 dataPoint 8 data

Point 9 dataPoint 10 data

Point 11 data