Active Feedback-Controlled Boom Noise Damping/Absorption in Large Vehicles

Large vehicles, such as SUVs (Sport Utility Vehicle) and minivans, exhibit body boom phenomena during multiple source excitation events including rough road/impact and powertrain induced events. The main cause of the boom is the low-frequency acoustic/vibro-acoustic modes of the cavity being excited via the high acoustic transfer functions at multiple paths, due to an inherently weak body structure and/or existence of popular features such as tailgates with their corresponding dynamics. Abating the boom noise by modifying the response is the more viable and less costly option than body changes.

DEICON’s active acoustic damping/absorption system has been used successfully to do such modification, cost-effectively. More

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Vibration Isolation of Large Transformers

In a recent application, DEICON was asked to further improve the structure-borne noise reduction of two large transformers (9000 pounds, each) installed in a multi-story residential building. The transformers were housed in sound proofed rooms and isolated from the floor via mounts (compressed fiberglass mounts for one transformer and cork/neoprene mats for the other). In a preliminary study including some laboratory tests it was concluded that the compressed fiberglass mounts had too much damping deteriorating their high frequency vibration isolation and the cork/neoprene mounts were too stiff to effectively isolate the transformer. It was decided to change the isolation schemes from compressed fiberglass and cork/neoprene to air. More

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Active Tuned Acoustic Damper

Active Tuned Acoustic Damper The application of DEICON’s patented, active acoustic damper/absorber in adding low-frequency modal damping to small rooms (listening rooms, recording studios, home theaters) is licensed to Modular Sound (the reputable manufacturer of Bag End professional grade speakers). Bag End manufactures electronic bass traps, with the trade name E-trap (TM), based on this technology. The industrial applications of this technology, due to their uniqueness and need for customization, are being implemented by DEICON.

 
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Active and Semi-active Vibration Isolation

The conflicting nature of vibration and shock isolation requirements, necessitates design compromises in realizing mounting schemes for systems subject to both vibration and shock perturbations. To avoid making such design compromises, one needs to pursue active and semi-active isolation solutions.

One approach to active isolation is combining an active scheme with a traditional passive isolation system. In such an approach a passive, but adjustable mount (such as an air spring) is used in mounting the machine. The control scheme takes advantage of the adjustability of air as the mounting medium and through the use of controls does on-demand adjustment of the parameters (damping and stiffness) of the isolation system. Such a system uses no additional actuators to exercise the control. Such active system can switch its parameters, promptly, from being an ideal vibration isolator to an ideal shock isolator, depending on the nature of the instantaneous perturbation (vibration or shock). More

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Vibration and Shock Isolation

DEICON, Inc. was invited to make a presentation on shock and vibration isolation at the global superyacht forum in Amsterdam. The following is an excerpt of the talk.

There exist a number of different isolation schemes, e.g., single mounting, double mounting, active isolation, semi-active isolation, air mounting, etc., with different pros and cons. Either one of these schemes can use rubber, air, or even metal (steel) as the isolation medium. Each one of these schemes and media have their own pros and cons. Shock and vibration isolation schemes are required to:

  • reduce the propagation of base vibration to the isolated object (machinery),
  • abate the transmission of vibration energy of machinery to the hull, and
  • lower the impact of shock from the hull to isolated object or vice-versa.

By varying the two main attributes of an isolator, i.e., its stiffness and damping, as well as the mass of the isolated machine, one can either emphasize the achievement of one of above mentioned isolation requirements at the expense of others, or optimize the achievement of all the requirements with moderate levels of effectiveness. The latter is the commonly used approach by designers. The following web page provides a good overview of ‘vibration isolation’ http://www.deicon.com/vibration-isolation .

The metric for measuring the performance of an isolation scheme is what is known as ‘transmissibility’ which is a measure of how much of the vibration force is being transmitted from the isolated machine to the base (hull of a yacht) at various frequencies. ‘Transmissibility’ is also the measure of how much of the motion of the base (support structure, e.g., the hull in a watercraft) will be transmitted to the machine. The goal is lowering the transmissibility at the frequencies where the vibration energy lies, as much as possible, without causing the machine to experience excessive motion.

As indicated in the vibration isolation page (http://www.deicon.com/vibration-isolation ), softer isolators with negligible damping will have the lowest transmissibility at off-resonant frequencies. Their excessive transmissibility at resonance is normally addressed by having the resonant frequencies well below the vibration excitation frequencies. Thus, the softer and the more underdamped the mount, the higher is its vibration isolation erformance. Unfortunately, the improved isolation using soft and highly underdamped isolators is achieved at the expense of excessive low-frequency motion of the isolated machine in response to shock disturbances; we all have seen how a Diesel engine experiences excessive undesirable motion during start up and shut down, straining all the plumbing and wiring connections to the engine. On the other hand, stiffer mounts with high damping are good in tightly holding the isolated machine and thus avoid excessive motion, but they transmit most of the vibration to the support structure.

No one passive solution quite satisfies all the requirements of an ideal isolation system. The common practice used by isolation system designer has been centered around a compromise design which satisfies all the requirements to some degree, but not to the highest possible degree. A number of enhancements to the plain passive isolation have been proposed over the years but again none satisfies all the requirements of an ideal isolation. For example double (two-stage) mounting, while effective at high frequencies, has no better low-frequency isolation effectiveness than a single mounting system. Shock isolation of double mounting is also inferior to that of single mounting. In addition, double mounting imposes unfavorable weight and space penalties.

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