Appliance Design - August 2008 - (Page 33)

NOISE & VIBRATION CONTROL Silentium provides design engineers with a design and performance evaluation tool for noise and vibration reduction. Called the S-Cube development kit, it consists of an active noise reduction controller board, a calibration unit, two microphones and speaker. The controller allows the designer to create broadband noise and vibration reduction solutions, achieving up to 10 dBA reduction on top of what is achieved with acoustic materials, covering the full audible range. One of the microphones serves as the reference that captures and feeds the noise source to the controller, and the second is an error microphone that measures the residual noise during calibration in order to minimize it. The error microphone is not needed after the calibration process is done. 150 Hz to 1,800 Hz. A key innovation lies in the creation of a virtual microphone to replace the physical error microphone in a feedforward control system. This is accomplished by making a series of measurements with an actual error microphone in place, then applying those measurements to calculate an estimation of error signal that the actual error microphone would produce. Once the estimates are obtained, the actual error microphone is no longer necessary, as it exists virtually in the controller. Eliminating the physical error microphone is highly beneficial, as it makes the active n oi s e control solution product dependent instead of environment dependent. The product equipped with this solution can be placed in any location without the need to install error microphones. It can be easily relocated without affecting noise reduction performance. The potential for this technology to reduce noise from electronic equipment has already been demonstrated. Silentium has introduced solutions that include an IT equipment rackmount enclosure that promotes ventilation and noise reduction at the same time. Measurements by the manufacturer have shown this enclosure to reduce internal noise by the IT equipment and the ventilation system by up to 20 dB(A). Also, an add-on unit that was designed for a new Intel modular server has been shown to reduce the humming noise by 10 dB(A). Residential appliances and HVAC equipment are also targets for Silentium active noise control technology. Typical appliance applications in which active noise control would be particularly pertinent include fans and air ducts/pipes, usually found in cooker hoods, air-conditioners and other ventilation appliances. By adding a duct, one can either improve the functionality of the device (as in the case of an axial fan), or not affect it at all (as in the case of air pipes). For example, Fig. 4 depicts a hybrid active/ passive noise control solution for an axial fan. A 90 mm x 90 mm x 20 mm axial fan was positioned at the midpoint of a 440 mm long duct with a square cross-section that was designed to avoid obstructing the airflow. The duct was lined with acoustic foam to reduce noise in the high frequencies. Two different active noise control systems were used, one on each side of the duct in order to control the noise emitted from the intake and output. The hybrid example illustrates another point about active noise control, namely, that optimal noise reduction results can be achieved by employing both passive and active noise control methods. The passive acoustic absorbing materials handle the high frequency bands of noise while the active system addresses the lower frequencies. < For more information, email: info@silentium.com Fig. 4. Illustration of a hybrid active/passive noise control solution for an axial fan. www.applianceDESIGN.com applianceDESIGN August 2008 33 http://www.appliancedesign.com

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Appliance Design - August 2008 Contents Editorial Shipments/Forecasts News Watch Plastics Switches Noise & Vibration Control Joining New Products Design Marts Association Report: CEA Advertiser’s Index

Appliance Design - August 2008

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