Active Noise Control quiets offensive noise by using cancellation techniques, or anti-sound. Signal Systems Corporation's mission is to help quiet irritating noises so you can have a more peaceful life as well as tactical noise reduction and hearing loss prevention.
Abstract: The modern vehicle has evolved into a multimedia hub, becoming a vital integration and delivery point for a panoply of media and devices. However, the resulting in-vehicle noise pollution created by this multitude of services has significant potential to become annoying to all vehicle occupants. This problem motivated the authors to build a system that enables the configuration of in-vehicle personalized audio zones (PAZs) that don't require earphones. The PAZ system comprises a novel user interface, custom-designed headrests, and an infotainment noise-control subsystem. The performance evaluations of PAZ in a BMW 5 series sedan delivered approximately 20 decibels of isolation, which resulted in an overwhelmingly positive subjective experience for the occupants. PAZ not only ameliorates noise pollution, but also provides a unique solution to sound personalization via configurable audio zones and individual media selection that doesn't require headphones.
Many people have heard of active noise control, but with the exception of headphones, few people have experienced its benefits. Why has this happened?
The short answer is cost. Unlike over-hyped technologies, active noise control works. The obstacle has been to make active noise control a cost-effective solution to noise problems. This obstacle has been far more difficult than many people expected. When a technology is more expensive than its benefits are generally worth, only a small market exists for the technology.
Now, new technologies are usually expensive to start out. Early users of a technology pay a higher price for being first, with a competitive advantage as the benefit. Technology developers gain valuable experience working with early customers. This experience and know-how yields product improvements that provide more economical solutions for future customers. In this way, the technology spirals into wider and wider use, as the cost for implementation falls.
So, what happened to active noise control? Why don't we see active noise control technology in our daily lives? The answer lies in the fact that most consumers are reluctant to pay more than 100 to 2000 dollars for noise reduction solutions. This cost range has been difficult to achieve with effective active solutions. The notable exceptions are noise canceling headphones and some dishwashers.
The result is that other applications of active noise control have been in industrial situations, where the benefit for active noise control is driven by hearing safety concerns. In some cases, improving speech communication has been important enough to use active noise control. Even in industrial markets, active noise control technology spirals have been rare. The result is that the pervasive use of active noise control still waits for the "killer-app" that can propel it out of the one-of-a-kind, custom project cycle that best describes how much of active noise control technology is applied today.
So, where has active noise control been successfully applied? A partial list:
These products are successful because they have taken active noise control technology and reduced it to practice. Another common element is that with the exception of cabin noise reduction, the solution is 'simple'. By simple, I mean that the solution does not require an extensive number of microphones, sensors, cables, etc. In many cases the controller that produces anti-sound commands can be built with analog circuits, leading to lower costs and portability.
The exception to this rule is aircraft cabin noise reduction. In this case, numerous speakers (or headsets) and microphones are used. In the noise reduction system built into new Boeing aircraft, it appears that the noise reducing apparatus has been integrated into the entertainment system. This has the benefit of reducing the cost of the noise reducing system, since it is being added to an existing acoustic system. The existing entertainment system uses headphones, signal processors, and cabling that can be leveraged by the active noise control (ANC) design.
So where should we go in ANC technology development? I think that continued development of simple solutions is best done through education. Present commercial efforts are mired in patent issues and return on investment questions. Through education, engineers can be trained in the use of active noise control. When these engineers are confronted with design problems, they will be equipped to find niche solutions using active noise control.
Researchers in this field should focus on two approaches. The first is the development of integrated active control solutions for complex noise problems. Automobile audio systems, with integrated personal communications systems and active noise control technology could improve driving enjoyment and safety. A second approach is the search for the 'killer application'. As an example, are there new ways of communicating that rely in a fundamental way on ANC technology? We will have to wait and see.
SSC developed a MEDEVAC Active Noise Cancellation Acoustic Pillow (MANCAP) featuring active noise cancellation (ANC) and passive noise reduction measures to create a quiet zone around injured personnel's ears during evacuations in and around noisy military vehicles. The MANCAP concept allows access to the patient's face for respirators and medical treatment while installed on any standard NATO litter. The MANCAP will reduce the local noise level of the patient to less than 80 dBA in a military helicopter by leveraging our ANC algorithms, real time software, hardware and headrest technology previously developed under commercial and DoD sponsorship, including Army, Navy and Special Forces efforts.
Noise levels in crew compartments below the flight decks on Navy ships during flight operations have traditionally been extremely noisy due to jet engine noise as well as launch machinery transients. Levels exceed Navy desired levels by over 10 dB. Current state of the art materials do not work well at low frequencies. SSC proposes to develop an active noise solution that consists of a modular, fully integrated smart material that can be applied to the interior compartments of ships. The smart acoustic panel will reduce radiating noise by employing advanced smart materials such as polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT) actuation materials, embedded MEMs based acoustic and vibration sensors, and polyurethane foam for passive vibration absorption. A method to use smart acoustic materials to provide local noise control of manned spaces will also be investigated if global control proves to be unfeasible.
Benefits of this project include: development of acoustic smart panels and quiet zone generation will enhance habitability on aircraft, and in high noise manufacturing areas. It will also enhance vehicle stealth applications.
We are developing noise cancellation software for use in Army battlefield robotics. This software will eliminate unwanted signals from microphones mounted on an unmanned vehicle. We have recently tested our system on the Demo III Experimental Unmanned Vehicle (XUV) built by General Dynamics Robotic Systems Technology. Our noise cancellation software achieved over 40 dB narrowband cancellation while eliminating over 30 tones from the robots' background noise level.
Some of these results are presented in the Air Coupled Sensor Workshop Presentation Slides (Adobe Acrobat PDF Format 437 kB)
We have been developing active noise cancellation systems for acoustic composite tiles for several years. We have developed a real-time 48 channel controller using programmable DSPs. This system was integrated into a smart skin that was demonstrated underwater. Our control system designs are based on hierarchical approaches.
We are currently investigating on-line evolutionary techniques for fully adaptive control systems that change sensor and actuator configurations as well as filter coefficients. These systems promise to define the state of the art in affordable and effective controllers for intelligent materials.
We are currently developing an 80 channel active noise control system using programmable DSPs networked together. The active noise control system contains processing resources with over 16 Billion Operations Per Second capability.
A related publication is: L. Riddle and J. Murray, 'Smart Structure Active Sonar Echo Cancellation Using Frequency Scheduled Control,presented at the 1998 SPIE Conference on Smart Materials
A technical review of our progress appears in the Smart Skin Demonstration Presentation Slides (Adobe Acrobat PFD Format 159 kB)
A full length paper describing the trade-offs involved in making a cost effective ANC system for complex problems is described in:
L.Riddle, J. Murray and S. Lease, 'Active Noise Control Architecture for the Smart Skin Demonstration,' ACTIVE-99, International Symposium on Active Noise Control, Dec 2-4, 1999.
We have developed a new MATLAB™ based Active Noise Control Simulation Toolbox. The simulation offers finite element modeling interfaces, sensor, filter and hardware models, and state-of-the-art multi-channel adaptive LMS algorithms.
Christopher E. Ruckman,wrote an useful ANC FAQ in 1994-1999. It provides a solid introduction to the technology.
An edited list of active noise control web sites is maintained at the Open Directory Project.