The Journal of the Acoustical Society of America

A general formulation is presented for the optimum controller in an active system for local sound control in a spatially random primary field. The sound field in a control region is selectively attenuated using secondary sources, driven by reference sensors, all of which are potentially remote from this control region. It is shown that the optimal controller is formed of the combination of a least-squares estimation of the primary source signals from the reference signals, and a least-squares controller driven by the primary source signals themselves. The optimum controller is also calculated using the remote microphone technique, in both the frequency and the time domains. The sound field under control is assumed to be stationary and generated by an array of primary sources, whose source strengths are specified using a spectral density matrix. This can easily be used to synthesize a diffuse primary field, if the primary sources are uncorrelated and far from the control region, but can also generate primary fields dominated by contributions from a particular direction, for example, which is shown to significantly affect the shape of the resulting zone of quiet.

/pdf/modeling-local-active-sound-control-with-remote-sensors-in-2attfuuyfn.pdf

Modeling local active sound control with remote sensors in spatially random pressure fields

A survey on active noise control in the past decade–Part II: Nonlinear systems

The aim of this paper is to provide an overview of the existing industrial practices used for cabin noise control in various industries such as automotive, marine, aerospace, and defense. However, emphasis is placed on automobiles and armored vehicles. Generally, automobile cabins usually constitute of thin structural panels, where the fundamental frequency typically falls below 200Hz. If a specific structural mode couples with a specific acoustic mode of the cabin, booming noise occurs. As such, discomfort may be felt by the occupants. Fundamentally, vibroacoustics problems may be minimized if the acoustic modes and the structural modes are decoupled, which is achieved usually by structural modifications or acoustical treatments. However, if excessively performed, the weight limitation of an automobile design will be exceeded; not to mention the adverse effect of increased weight on several factors such as fuel efficiency, mileage life of tires and acceleration of the vehicle. Moreover, current solutions...

https://www.worldscientific.com/doi/pdf/10.1142/S1758825116500721

Acoustic Metamaterials: A Potential for Cabin Noise Control in Automobiles and Armored Vehicles

A normalized frequency-domain block filtered-x LMS algorithm for active vehicle interior noise control

Experimental investigation of different active noise control concepts applied to a passenger car equipped with an active windshield

Full-scale experiments on the reduction of propeller-induced aircraft interior noise with active trim panels

Passive structures are augmented with actuators, sensors and control to implement the task of active noise or vibration reduction. Such systems are considered smart because they have advanced functionalities compared to conventional structures. A smart aircraft lining is able to reduce the low-frequency cabin noise induced by tonal or multi-tonal external noise sources. Such noise sources are for example fuel-efficient rotor engines like counter-rotating open rotors. Research on smart systems starts on a laboratory scale by using low-noise sensors and high-performance rapid control prototyping systems. The replacement of such costly and bulky laboratory hardware is one important precondition for the commercialization of smart structures. The increased internal noise, the reduced computational performance and other restrictions of low-cost hardware must be taken into account during the design of a smart system. Experimental results on the noise reduction of a smart lining with low-cost hardware show that a replacement of laboratory hardware will not lead to a loss of performance. The smart lining achieves tonal interior sound pressure level reductions of up to 25 dB with a mass increase of only 2 percent. Even a mass neutral implementation seems possible, if conventional loudspeaker-driven passenger announcements are realized with smart linings.

/pdf/aircraft-lining-panels-with-low-cost-hardware-for-active-58hhlchg0a.pdf

Aircraft Lining Panels with Low-Cost Hardware for Active Noise Reduction

Typical challenges in the design of active systems for noise and vibration reduction applied to large lightweight structures are complex material systems under distributed and stochastically varying loading. Having a limited set of actuators and sensors available, it is required in the pre-design process to derive an optimal system performance with respect to above mentioned boundary conditions. Therefore, a pre-design tool has been developed that numerically computes an actuator placement based on a structural model derived from either finite-element models or experimental system identification. It furthermore accounts for flat and simply curved plates with loading of multiple point forces or diffuse sound fields. A model for piezoceramic actuators is implemented and a modal correction method applied to account for its effect to the structural model. Subsequently, a genetic algorithm is utilized for actuator placement with respect to sound radiation or average vibration level as well as the actuators power consumption. Based on the derived actuator placement, the patches are applied on a stiffened carbon fiber reinforced plastic panel mounted in a transmission test facility. Control objective is the reduction of sound transmission by manipulating vibrations of the panel. Different feed-forward and feedback control concepts are considered and implemented.

Development and Experimental Application of a Pre-Design Tool for Active Noise and Vibration Reduction Systems

The efficiency of future aircraft has to be increased because of the CO2 restrictions layed down by
the European Union. Two key technologies to reach this ambitious goal are a consequent light-weight
design of future aircraft and new engine concepts like the Counter-Rotating open rotors (CROR).
However, the combination of lightweight materials like carbon-fibre-reinforced plastics (CFRP) with
CROR is acoustically demanding because of the very high sound pressures emitted by this type of
engine and the poor transmission loss of CFRP structures in the lower frequency range.
Therefore, this work conducts a preliminary study to improve the transmission loss of a CFRP panel
excited by a synthesised CROR pressure field in lower frequency range. As a first step, a typical
aircraft fuselage panel mounted in a sound transmission loss facility is equipped with actuators
and sensors to implement multiple-input multiple-output (MIMO) feedforward control of flexural
vibration. The CFRP panel is excited via a CROR pressure field synthesised by a 112-channel loud
speaker array. The active vibration control (AVC) system is realised by accelerometers and inertial
exciters. A considerable vibration reduction of the flexural vibration on the accelerometers is achieved.
The local attenuation around the accelerometers leads to a new controlled vibration pattern that
radiates sound in a different way than the uncontrolled one. The difficulties in reducing the radiated
sound power through the AVC system are due to low observability, the “pinning” effect, and the
restructured vibration patterns. All of these effects are studied in detail through surface vibration
scans and sound intensity measurements. Additionally, the radiation resistance matrix is used to
analyse the controlled vibration patterns.

Malte Misol

Papers

Experimental investigation of different active noise control concepts applied to a passenger car equipped with an active windshield

Full-scale experiments on the reduction of propeller-induced aircraft interior noise with active trim panels

Aircraft Lining Panels with Low-Cost Hardware for Active Noise Reduction

Development and Experimental Application of a Pre-Design Tool for Active Noise and Vibration Reduction Systems

Experiments on Active Control of Counter-Rotating Open Rotor Interior Noise