| 1. |
- Andrén, Linus, et al.
(författare)
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Active Noise Control Experiments in a Fork-lift Truck Cabin
- 2004
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Konferensbidrag (refereegranskat)abstract
- High comfort for the driver in working vehicles is an important feature as well as a demand from the drivers. Low noise level is an essential factor for the manufacturer to maintain a high standard and comfort of vehicles. In many cases the noise inside the cabin can be related to the engine orders. Hydraulic pumps and fans are also related to the engine but not necessarily integers of the engine order. Passive absorbers are not suitable for the lowest frequencies and one approach is to use an active noise control system to solve the noise problem at low frequencies. In the present experiment loudspeakers were mounted inside the cabin of a fork lift-truck to produce the secondary noise field. To sense the residual noise, microphones were installed close to the driver's head. The aim is to create a zone of reduced noise around the head. Since a large portion of the noise inside the cabin can be related to the engine, an active control system based on a feedforward solution is possible. Experimental results from a feedforward solution of active noise control in a fork-lift truck cabin show that the noise level in the low frequency region can be reduced significantly.
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| 2. |
- Johansson, Sven, et al.
(författare)
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A New Active Headset For a Helicopter Application
- 1997
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Konferensbidrag (refereegranskat)abstract
- In helicopters, the low frequency noise generated by the rotors and engines often masks and jeopardizes safe communication. Additionally, pilots are likely to suffer from hearing damages due to the higher sound levels in the headset produced when compensating for the noise by increased speakerlevels. A feasible approach is to reduce the low frequency noise using active techniques, thereby enabling lower speakerlevels. In many Active Noise Control (ANC) applications the primary noise field is either periodic or broadband which simplifiesthe choice of algorithm. In our application, noise up to 100Hz is dominated by tones and in the range from 100 Hz to 400 Hz the noise characteristicsis more broadband. In order to achievean efficient attenuation of the primary noise, a combination of a digital feedforward controller and an analog feedback controller is employed. The feedforward controller is tachometer based and reduces the tonal components, while the feedback controller attenuates the more broadband noise. In this paper, a combination of these two techniques is evaluatedon real data.
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| 3. |
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| 4. |
- Johansson, Sven, et al.
(författare)
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A New Passive/Active Hybrid Headset for a Helicopter Application
- 1999
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Konferensbidrag (refereegranskat)abstract
- In helicopters, the low frequency noise generated by the rotors and engines often masks and jeopardizes safe communication. In addition, pilots are likely to suffer from damage to their hearing due to the high sound levels in the headset produced in compensating for the noise caused by increased loudspeaker levels. A feasible approach is to reduce the low frequency noise by using active techniques combined with a method for reducing the noise in the intercom microphone signal, with lower loudspeaker levels as a result. In order to achieve an efficient attenuation of the primary noise inside the headset, a combination of a digital feedforward controller and an analog feedback controller is employed. Spectral Subtraction is used to suppress the background noise in speech signals. This paper evaluates a combination of the techniques and their application to real data.
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| 5. |
- Johansson, Sven, et al.
(författare)
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Active Control of Interior Noise in a Fork-Lift Truck
- 2003
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Konferensbidrag (refereegranskat)abstract
- Modern fork-lift trucks incorporate a wide range of sophisticated passive techniques to reduce the noise inside the cabin. By using a combination of passive and active noise control technologies it may be possible to further reduce the noise level, thereby improving the comfort for the truck driver. The purpose of the work presented in this paper is to examine whether it is possible to reduce the low-frequency cabin noise by using active noise control technology. The noise situation inside the truck cabin is discussed as well as the active noise control strategy for a practical fork-lift truck installation. The paper presents sound field plots of the cabin noise and preliminary active noise control results from computer experiments based on recorded cabin noise.
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| 6. |
- Johansson, Sven, et al.
(författare)
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Active Control of Sound using the Actuator-Individual Normalized Filtered-X LMS Algorithm
- 2001
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Konferensbidrag (refereegranskat)abstract
- The control algorithm is a central part of an active noise control system. The computational power of the DSP hardware is limited, and therefore algorithms with high computational complexity allow fewer control sources and sensors to be used, often with reduced noise attenuation as a result. This paper presents results from practical experiments using an ANC system based on the actuator-individual normalized Filtered-X LMS algorithm. The algorithm combines low computational complexity with high performance. For that reason the algorithm is suitable for use in large multi-channel systems in order to reduce the computional power required by the control system.
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| 7. |
- Johansson, Sven, et al.
(författare)
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ACTIVE HEADSET FOR ENHANCED SPEECH INTELLIGIBILITY IN INTERCOM SYSTEMS
- 2001
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Konferensbidrag (refereegranskat)abstract
- Low frequency noise has a masking effect on speech, which significantly reduces the speech intelligibility. Usually, in order to overcome the masking effect the sound level of the communication signal is increased. Exposure to the communication system then causes hearing damage. A feasible approach is to reduce the low frequency noise by using active techniques combined with a method for reducing the noise in the intercom microphone signal. In order to achieve an efficient low frequency noise attenuation inside the headset an active hybrid headset is proposed, and in order to suppress the background noise in speech signals spectral subtraction is used. Improved low frequency noise attenuation enables lower communication levels and reduces the risk for hearing damage.
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| 8. |
- Lagö, Thomas L, et al.
(författare)
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AVIIS, ACTIVE VIBRATION ISOLATION IN SHIPS : SOURCE IDENTIFICATION AND ANVC APPROACH
- 1997
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Konferensbidrag (refereegranskat)abstract
- Engine induced sound and vibration levels in boats for professional and leisure use is in many cases unacceptably high in term of comfort and the environment. Classical methods for passive treatment are normally less effective due to the low frequency content and often leads to an increase in weight. This contradicts the requirements for lower weight for increased speed. More efficient vibration damping methods must therefore be found. With active engine mounts, it is possible to achieve a decrease in the vibrations even when the hull is not very stiff. This is especially important in marine applications since the engines are mounted on weak and light structures. The AVIIS project aims at investigating the effects of a combined passive/active engine mount for use in boats. A Storebro 36 Royal Cruiser with two Volvo Penta engines has been used in the project. Four different approaches have been appraised, the results of which are presented here: 1. passive engine mounts, with and without thrust bearings, 2. optimized passive engine mounts, 3. passive engine mounts, rigidly mounted, 4. A combined active/passive engine mount. This paper reports the key data from the measurements and how the different primary sources have been estimated from the analysis. This analysis has then been used to select the ANVC approach.
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| 9. |
- Maillard, Julien, et al.
(författare)
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Active control of pressure pulsations in piping systems
- 1998
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Fluid-borne vibrations in piping systems remains a serious problem in applications such as marine vessels where mechanical fatigue and radiated noise are critical factors. In the case of pumps or hydraulic engines, the main source of vibrational energy is in the fluid axisymmetric plane wave associated with the system pressure pulsations. Due to fluid/structure coupling, this wave propagates in both the pipe wall and fluid. For high levels of pressure pulsations, the resulting radial and axial wall motion can then cause mechanical fatigue and unwanted radiated noise. Passive pulsations dampers have been used traditionally to reduce the fluid pressure pulses. The use of such passive devices is limited however in critical applications due to the resulting static pressure loss which decreases the system performance. This report describes the design and testing of a non-intrusive fluid wave actuator for the active control of pressure pulses. The actuator consists of a circumferential ring of PZT stacks acting on the pipe outside wall to generate an axisymmetric plane wave in the fluid through radial motion coupling. After briefly describing a simplified model of the actuator along with predicted performances, experimental results will show the control performance of the actuator applied to the discharge line of an oil driven hydraulic engine.
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| 10. |
- Maillard, Julien, et al.
(författare)
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Fluid Wave Actuator for the Active Control of Hydraulic Pulsations in Piping Systems
- 1999
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Konferensbidrag (refereegranskat)abstract
- Fluid-borne vibrations in piping systems remain a serious problem in applications such as marine vessels where mechanical fatigue and radiated noise are critical factors. In the case of pumps or hydraulic engines, the main source of vibrational energy is in the fluid axisymmetric plane wave associated with the system pressure pulsations. Due to fluid/structure coupling, this wave propagates in both the pipe wall and fluid. For high levels of pressure pulsations, the resulting radial and axial wall motion can then cause mechanical fatigue and unwanted radiated noise. Passive pulsations dampers have been used traditionally to reduce the fluid pressure pulses. The use of such passive devices is limited however in critical applications due to the resulting static pressure loss which decreases the system performance. This paper describes the design and testing of a non-intrusive fluid wave actuator for the active control of pressure pulses. The actuator consists of a circumferential ring of PZT stacks acting on the pipe outside wall to generate an axisymmetric plane wave in the fluid. Experimental results estimate the control performance of the actuator applied to the discharge line of an oil driven hydraulic engine.
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