Strategies:
Passive Sound & Vibration Control
Active Sound & Vibration Control
Semi-active Sound & Vibration Control

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.

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.

Passive Sound & Vibration Control

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.





Active Sound & Vibration Control

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. Not to mention that active systems can potentially provide increased effectiveness in controlling sound and vibration compared to passive approaches. And, some applications do not lend themselves to have large passive vibration control appendages, such as a tuned mass damper, attached to them. Active damping and cancellation control can address these two concerns.

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.



Active, Feedback Controlled Electronic Bass Trap (PDF)
Musical Articulation Enhancement Using Electronic Bass Trap (PDF)
Active, Feedback-Controlled Boom Noise Absorption in a Large Vehicle (PDF)
A Kalman Estimator-Based Active Vibration Isolation Strategy (PDF)



Semi-active Sound & Vibration Control

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.



Computer Controlled Air Isolation System
Air Suspended Tuned Mass Dampers (Semi-active)
Self-tuning of tuned dampers (semi-active tuned dampers) (PDF)
Combustion Driven Oscillation Mitigation (PDF)


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Sound and Vibration Control