Sound and Vibration Control Strategies
Noise control and vibration control treatments are not one-size-fit-all solutions. Different control mechanisms and strategies should be used to solve different problems.
DEICON has the experience and the know-how to provide the most suitable solutions to variety of industrial, architectural and marine noise and vibration problems.
The common approach to mitigate sound and vibration caused by acoustical/structural resonance, is adding damping to the acoustic plant and structure. Damping dissipates some of the sound/vibration energy by transforming it to heat.
Passive, semi-active, and active control methods can be used for Sound & vibration damping. The traditional passive damping methods include the use of broadband dissipative solutions such as sound absorbing material (for sound), viscoelastic, viscous, and friction dampers (for vibration), as well as narrowband reactive solutions (tuned dampers) such as Helmholtz resonators (for sound) and tuned mass dampers (for vibration). Active damping involves the use of actuators (e.g. speakers for sound and motors for vibration) along with sensors and controllers (analog or digital) to produce an actuation with the right timing to counteract the resonant oscillation.
When the disturbance(s) is(are) at certain frequency(ies), i.e., a forced sound/vibration problem, then damping treatment may or may not be effective depending how close the disturbance frequency(ies) is(are) to the resonant frequency(ies) being damped. In this case, passive or active cancellation solutions should be used to quiet the system. Passive sound/vibration cancellation is normally achieved by appending the oscillating system with a tuned absorber, e.g., Helmholtz resonators and quarter wave tubes (for sound) and dynamic absorbers (for vibration) with the natural frequency similar to the disturbing frequency.
As in sound/vibration damping, passive, semi-active, and active treatments can be used for sound/vibration cancellation. Active cancellation involves the use of active elements (actuators) along with sensors and controllers (analog or digital) to produce an out of phase actuation to cancel the disturbance causing the noise/vibration.
Frequently, the goal of control is not abating sound/vibration at/of the source, e.g., a noisy mechanical room (for sound) or a vibrating structure (for vibration), but is to prevent its transmission to the surrounding. Such control schemes, known as ‘isolation’, are used extensively to isolate a noisy environment from a quiet one (in sound control), as well as machinery (industrial and marine), civil engineering structures (base isolation in building, bridges, etc.), and sensitive components from the foundation/base (in vibration control).
As in damping and cancellation, passive, semi-active, and active control techniques can be used for isolation. The most common passive isolation method is is the use of sound barriers (in sound control) and mounting the vibrating structure/machine to the base via resilent elements, e.g., rubber, (in vibration control). Active isolation involves the use of actuators along with sensors and controllers (analog or digital) to create actuation with the goal of lowering the transmission of sound/vibration from one body to another. Click here for more detail on Vibration isolation.
The most commonly applied sound and vibration control techniques are based on the use of passive technologies. The majority of these applications are based on passive damping using viscoelastic materials for vibration control and sound absorbing materials and Helmholtz resonators for sound control.
Although most passive damping treatments are inexpensive to fabricate, their successful application require a thorough understanding of the vibration problem in hand and the properties of the damping materials. Viscous dampers (dashpots), tuned-mass dampers, dynamic absorbers, shunted piezoceramics dampers, and magnetic dampers are other mechanisms of passive vibration control.
Passive sound and vibration control has its limitations such as: lack of versatility, large size and weight when used for low-freqeuncy sound/vibration control, and de-tuning of tuned treatments.
Due to their lack of versatility, passive damping and cancellation strategies become ineffective when the dynamics of the system and/or the frequencies of the disturbance vary with time. And, some applications do not lend themselves to have large passive vibration control appendages attached to them. Active damping and cancellation control can address these two concerns. Moreover, active systems are more effective in controlling sound and vibration compared to their equally-sized passive counterparts.
Due to remarkable advances in sensor, actuator, and more importantly computer technologies in recent years active systems have become cost effective sloutions to most sound and vibration control problems.
Semi-active (also known as adaptive-passive) control is an adjustable passive sound/Vibration control scheme. That is, the passive treatment can adjust itself, in response to changes in the acoustic system/structure. For example, the stiffness, damping coefficient or other variables of the the passive control scheme can change, automatically, so that optimal sound/vibration mitigation is induced. These variable components also known as ‘tunable parameters’ of the control system, are re-tailored via a properly developed semi-active control algorithm.
Being more versatile than passive control techniques and more affordable (in terms of cost and energy consumption) than active control schemes, have made semi-active control methods very popular.