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design of cabin noise cancellation


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design of cabin noise cancellation

  1. 1. Design of Car Cabin Noise Cancellation Ong Sin Yee1, ‘Abdurrahman Suratman2, Nurul Shafikah Mohd Zain3, Mohamud Mire4 SET 4722, Section 1, Group No. 4 Basic Microwave Laboratory, Faculty of Electrical Engineering Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia Abstract— According to the increase of long time and distance driving, noise reduction in vehicle cabin becomes a critical problem for comfort improvement. The common purpose of active noise control systems is to reduce acoustical noise in an environment. This paper gives a brief description of designing a cabin noise cancellation system and how this technology is adopted in automotive. The information and research data of the cabin noise cancellation systems was found by searching the published papers from vehicle companies and research authorities. The results of this investigation demonstrate that cabin noise cancellation systems are capable of providing significant noise reduction of car to improve the comfort ability of the cabin. Keywords— Car noise, car cabin noise cancellation, design cabin noise cancellation, reduce car noise, engine car noise. I. INTRODUCTION Cabin noise cancellation, also known as active noise control (ANC), is a method for reducing unwanted sound by the addition of a second sound specifically designed to cancel the first. Sound is a pressure wave. A noise-cancellation speaker emits a sound wave with the same amplitude but with inverted phase to the original sound. The waves combine to form a new wave, in a process called interference, and effectively cancel each other out which is called phase cancellation, as shown in Fig. 1 [1]. Fig. 2 The sources of noise associated with a car Two basic control principles are used widely, that is feedback and feedforward noise cancellation. Feedforward noise cancellation uses a signal from a microphone located in the vicinity of the noise source, and the system filters this sound to produce the anti-noise, as shown Fig. 3 [3]. Obviously, the forward filter needs to be designed so that the sound from the loudspeaker cancels the direct sound from the source at the location of the listener. Fig. 3 Feedforward noise cancellations Fig. 1 The mechanism of active noise control There are many sources of noise associated with a car, as shown in Fig. 2. They can be divided into narrowband harmonic and broadband random noise. Narrowband noise sources include the engine, drive train, air intake, exhaust and auxiliary systems such as the radiator fan. Broadband noise is caused by road tyre interaction and aerodynamic wind noise [2]. The second noise control technique, feedback control, uses control theory to achieve attenuation of the sound level at the location of a probe microphone by means of a linear feedback loop with a large negative gain, as shown in Fig. 4 [3]. This causes the loudspeaker membrane position to regulate the sound pressure towards a silence level. The disadvantage is that the feedback loop can become unstable, and that the feedback loop amplifies microphone probe noise. In practice, feedback controllers can attenuate noise in a limited frequency
  2. 2. band, and the amount of attenuation is limited by gain margins for ensuring stability of the system. pressure level for human ear is 20 µPa. dB of SPL is defined as SPL= 20 log Fig. 4 Feedback noise cancellations system is essentially a loop with-ideallylarge negative gain The noise analysis of the passenger car can be divided into engine induced noise analysis and road induced noise analysis transmitted by tire and chassis system. In this paper, we will focus onto the fundamental source of narrowband noise in a car which is the engine noise. The engine is the main contributor of narrow band noise in a car. The engine RPM gives rise to discrete harmonics which in this context are called engine orders. In a typical setup the aim is to reduce certain engine orders reduce or to give a more pleasant sound. The most suitable processing algorithm is a feedforward structure, and since the engine RPM comes as a tachometer signal, the reference signal can be synthesized from the tachometer data as a pure sinusoidal with the frequency of the engine order to be controlled. Most vehicles with an internal combustion engine utilize materials and passenger compartment designs intended to isolate the vehicle occupants from engine noise. Sound deadening materials can be heavy and expensive though, providing an incentive to find other ways of reducing cabin noise. Using a series of small microphones and speakers inside the cabin, the system is designed to remove tyre, wind and engine noise via anti-noise. A few vehicles employ systems that actively generate an "anti-noise" signal inside the cabin using one or more strategically placed speakers driven by a microprocessor. These systems monitor the noise inside the vehicle using microphones and attempt to cancel the noise by generating an identical signal that is 180 degrees out-of-phase with the detected signal. Fig. 5 shows the basic structure diagram of active noise control system for attenuating engine noise [4]. 𝑃 dB 𝑃𝑜 (1) Where Po=2x10-5Pa. The second parameter is sound intensity level (SL) [6]. Sound intensity level is rate of energy flow across a unit area. The measure of the ratio of the two sound intensities are 𝐼 SL=10 log dB 𝐼𝑜 (2) Where Io=1x10-12 watts/meter2. The last parameter used to asses the sound exposure is sound power level (SWL) [7]. It is use to measure the sound power emitted by a source in all directions. The SPL can be expressed as SWL=10 log 𝑃 𝑃𝑜 dB (3) Where Po=1x10-12watts. II. DESIGN OF CABIN NOISE CANCELLATION The active noise cancellation was design in car cabins to eliminate the unwanted noise [8]. The microphones were used to capture low end drivetrain frequencies that entering the car and send a signal to the noise to the network processing to predict the sound level. The predicted signal is taken as the input reference signal of the control module system. The reference signal that come out from the module is drive to the speaker. Then, the secondary sound is produced which is nearly equal to the noise signal captured by the microphones (primary sound). The sound wave from the speaker meets the primary sound source and cancelling each other. In this case, microphones act as a sensor and speaker as actuator. Active noise control system structure is shown in Fig. 6. Fig. 6 Active noise cancellation in Ford Fusion Hybrid Fig. 5 Active noise control system for attenuating engine noise There are three parameter which are generally used to assses sound exposure to humans. One of the parameter is sound pressure level (SPL) expressed in µPa [5]. Audible According to the theory of active noise cancellation (ANC), the analysis of the noise control system structure [1] shown in Fig. 7. The reference signal is obtained by using engine vibration acceleration to predict the noise in the car. Moreover, the low-frequency noise in a car mainly comes from vibration of the body panels. Three vibration acceleration signals, which come from the engine, the floor vibration and the roof panel are collected. Then, by using a network processing the sound pressure level is predicted and called reference signal.
  3. 3. The reference signal which comes from the network processing is modulated and amplified through the power amplifier. Then, the secondary sound source produced the sound wave from the speaker and will cancel the noise. Thus, in the system, engine, roof and the floor are the input acceleration signals and the speaker is taken as the output. IV. RESULT The data is divided into three categories that are small cars have CC less than 1000; medium cars have CC between 1000 to 2000 and large cars have CC greater than 2000. The data of CC, number of cylinder and torque is gotten from the catalogue for each type of car, as shown in Table 1. A poundfoot (lb·ft) is a unit of torque. One pound-foot is the torque created by one pound force acting at a perpendicular distance of one foot from a pivot point [12]. TABLE 1 THE CAR SPECIFICATIONS BASED ON CATEGORY OF CAR Category of Car Type of Car Produa Kelisa Produa Viva Produa Kancil Honda City Medium (1000<CC Toyota Vios <2000) Proton Persona Volvo XC90 Large Toyota Mark X (CC>2000) BMW 7Series740i Sedan Small (CC<1000) Network processing Fig. 7 Schematic diagram of active noise control system in car cabins. 1engine vibration acceleration sensor, 2-floor vibration acceleration sensor, 3roof vibration acceleration sensor, 4-error sensors, 5-secondary sound source, 6-controller III. METHODOLOGY This research paper is about designing of car cabin noise cancellation, In order to design an engine for a particular application, it is helpful to determine a various terms such as horsepower, torque, rpm and cubic centimetres (cc). The terms horsepower torque, and rpm are used in engineering to design transmission shafts as well as. When designing a transmission shaft one must consider the power (watts or horsepower), and speed of rotation (rpm or frequency) to choose the proper material so that the maximum shearing stress allowable will not be exceeded. When speaking of automobiles torque is defined as a force around a given point, applied at a radius from that point. Horsepower (hp) is the name of several units of measurement of power, the rate at which work is done. A revolution per minute (rpm) is a measure of the frequency of a rotation. It annotates the number of turns completed in one minute around a fixed axis. It is also used as a measure of rotational speed of a mechanical component. A cylinder is the power unit of an engine; it’s the chamber where the gasoline is burned and turned into power [9]. This is the simplest set of equations that use in order to find horsepower, torque, rpm produced by an engine. As folows: 𝑁 𝑓(𝐻𝑧) = 𝑍(60) (4) 2 Where f is frequency, Z is number of cylinder and N is value of RPM [10]. 𝐻𝑜𝑟𝑠𝑒𝑝𝑜𝑤𝑒𝑟 (ℎ𝑝) = 𝑇𝑜𝑟𝑞𝑢𝑒 𝑥 𝑅𝑃𝑀 5252 Where RPM is revolution per minute [11]. (5) Size of Cubic No. of Torque Centimeters Cylinder (lbft) (CC) 847 55 850 3 56 850 46 1497 107 1497 4 104 1600 109 2521 236 2500 179 5 3000 245 A. Relationship between Revolution per Minute (RPM) with Noise Frequency The value of RPM and number of cylinder is used to find the value of noise frequency with equation (4). The value of noise frequency is recorded in Table 2. TABLE 2 THE VALUE OF NUMBER OF CYLINDER, RPM AND NOISE FREQUENCY FOR EACH TYPE OF CAR Category of Car Type of Car Small (CC<1000) Produa Kelisa Produa Viva Produa Kancil 3 Medium Honda City (1000<CC<20 Toyota Vios 00) Proton Persona 4 Volvo XC90 Toyota Mark X BMW 7Series740i Sedan 5 Large (CC>2000) No. of Cylinder RPM 800 1300 1900 2400 3000 800 1300 1900 2400 3000 800 1300 1900 2400 3000 Noise Frequency (Hz) 20 33 48 60 75 27 43 63 80 100 33 54 79 100 125
  4. 4. TABLE 3 THE VALUE OF SOUND POWER LEVEL (SWL) AND NOISE FREQUENCY BASED ON TYPE OF CAR Category of Car Type of Car Produa Kelisa Small (CC<1000) Produa Viva Fig. 8 The graph of noise frequency (Hz) versus RPM The Fig. 8 shows the graph of noise frequency versus RPM based on the value of noise frequency calculated and value of RPM from Table 2. From the graph, if the value of RPM increases than the noise frequency increases. The increases of RPM mean the increases speed of the car. The speed of car increases will affect the noise frequency to increases. Produa Kancil Honda City B. Relationship between Sizes of Car Engine with Noise Frequency. Medium (1000<CC <2000) Toyota Vios Proton Persona Fig. 9 The graph of noise frequency (Hz) versus number of cylinder The Fig. 9 shows the graph of noise frequency versus the number of cylinder based on the value of noise frequency calculated, value of RPM is fixed at 3000 and the number of cylinder from Table 2. The number of cylinder increases means the size of car engine increases. From the graph, if the size of the engine increases than the noise frequency increases. C. Relationship between Sound Power Level (SWL) with Noise Frequency The first step to calculated sound pressure level is based on the data of torque and RPM from Table 1 and use it to calculate the value of horsepower using equation (5). Next, convert horsepower to watts using equation (6) is the most common conversion factor, especially for mechanical power [13]. 1ℎ𝑝 = 746 𝑊𝑎𝑡𝑡𝑠 (6) The value of sound power level is calculated using equation (3) and the value of SWL is compared to noise frequency based on the value of RPM, as shown in Table 3. Volvo XC90 Large (CC>2000) Toyota Mark X BMW 7Series74 0i Sedan Sound Power Level (SWL) (dB) 158 160 162 163 164 158 160 162 163 164 157 159 161 162 163 161 163 165 166 167 161 163 164 165 166 161 163 165 166 167 164 166 168 169 170 163 165 167 168 169 164 167 168 169 170 Noise Frequency (Hz) 20 33 48 60 75 20 33 48 60 75 20 33 48 60 75 27 43 63 80 100 27 43 63 80 100 27 43 63 80 100 33 54 79 100 125 33 54 79 100 125 33 54 79 100 125
  5. 5. [6] [7] [8] [9] [10] [11] [12] [13] Fig. 10 The graph of sound power level (SWL) versus noise frequency (Hz) based on type of car The Fig. 10 shows the graph of sound power level (SWL) versus noise frequency based on the type of car from Table 3. From the graph, if the value of noise frequency increases than the value of sound power level increases. V. CONCLUSIONS The noise frequency increases will affect the RPM to increases. The number of cylinder increase linearly with frequency due to the increases size of engine. The results of this investigation demonstrate that cabin noise cancellation systems are capable of providing significant noise reduction of car to improve the comfort ability of the cabin. ACKNOWLEDGMENT We would like to express our deepest gratitude and appreciation to our laboratory instructor Ir. Dr. Mokhtar bin Harun for his excellent guidance, caring, patience, suggestions and encouragement who helped us to coordinate our project, especially to design the link. We would also like to acknowledge with much appreciation to all those who gave us the possibility to complete this project. A special thanks goes to the crucial role of the staff of the Optic Communication Laboratory. Last but not least, again we would like to say many thanks go to our laboratory instructor, Ir. Dr. Mokhtar bin Harun who are given as full effort guiding in our team to make the goal as well as the panels, especially in our project presentation that has improved our presentation skills by their comment and tips. REFERENCES [1] [2] [3] [4] [5] Chu Moy, “Active Noise Reduction Headphone Systems“, 2001 Reese, L. Active sound-profiling for automobiles. Doctoral thesis, ISVR, Southampton, UK, 2004. “ Active Noise Control”, Retune DSP ApS, May 2013 Jari Kataja,” Development of a robust and computationally efficient active sound profiling algorithm in a passenger car”, VTT Technical Research Centre of Finland, 2012 P. Aarne Vesilind, J. Jeffrey Peirce and Ruth F. Weiner. 1994. Environmental Engineering. Butterworth Heinemann. 3rd ed. B. J. Smith, R. J. Peters, Stephanie Owen Addison Wesley Longman, 2nd edition, 1996 ISBN 0582088046 Comprehensive introduction to the principles and practice of acoustics and noise control William Hamby. "Ultimate Sound Pressure Level Decibel Table". Archived from the original on 2010-07-27. Hou Chenyuan “Hardware-in-loop Simulation of Active Noise Cotrol in Car Cabins,” ©2009 IEEE. Beer, Ferdinand P., Johnston, E. Russell Jr. Mechanics of Materials. New York: McGraw-Hill, Inc., 1981. Nobuyuki OKUBO,,"Noise Reduction in Truck Cabin by Design Change of Floor Panel",Proceedings of the IMAC-XXVII February 912, 2009 Orlando, Florida USA. Heywood, J.B. "Internal Combustion Engine Fundamentals", ISBN 007-100499-9. Arthur Mason Worthington (1900). Dynamics of rotation: an elementary introduction to rigid dynamics (3rd ed.). Longmans, Green, and Co. p. 9. Division, P. (n.d.). Units and conversion factors