What is resonance in vibration

Glossary - key terms clearly explained

Vibration engineering, vibration isolation, vibration damping - no matter what you want to call it, Bilz is your expert in this field. So that you too are in the picture, we have put together some key terms relating to the topic for you and explained them in an understandable way.



Vibrations are changes in state variables over time (e.g. paths, accelerations, speeds, etc.), based on a mean or equilibrium value or a position of rest. There are different types depending on the nature of their course.


Types of vibrations

Periodic oscillation: With this type of oscillation, the course can be predicted precisely based on the previous regularity, e.g. for the harmonic oscillation, the course of which corresponds to a sine function. Also called deterministic oscillation.

Stochastic oscillation: These are also called non-deterministic or random oscillations and cannot be foreseen.

Vibrations / shocks: The essential characteristics of the shock are its duration, its course and its intensity. In shock isolation, the interference pulse, which consists of a high force peak acting over a short period of time, is transformed into a longer-lasting pulse with only small residual forces due to the elastic deformation of the isolator.

Structure-borne noise are mechanical vibrations that propagate in a solid body. You can hear the radiated airborne sound.

Vibrations are periodic mechanical vibrations of bodies.


Vibration isolation

Vibration isolation means the decoupling of disruptive forces and vibrations. This effect always works in both directions, i.e. from the machine to the environment as well as in the opposite direction (see also types of insulation). The terms Vibration damping and Vibration damping (not to be confused with damping!) are often used synonymously.


Damping D

is the physical property of an insulator to extract energy from the vibration system, which is converted into heat. This limits the vibrations to a permissible level. The attenuation D is a dimensionless quantity.



Important with the Selection and calculation of the suitable vibration isolation is the nature of the burden. This is made up of two components:

  1. static load caused by the weight of the machine and the workpiece
  2. dynamic load caused by the movement of the vibration. Unit: Newton (N)



Maximum deflection of a harmonic oscillation from the rest position (1). Peak-to-peak (2). RMS value (RMS = abbreviation for Root Mean Square, square mean; 3), period duration (4)
Units: 1, 2 and 3: meter (m), 4: second (s)


Frequency f

is the measure of the number of oscillations per second. The unit is Hertz (Hz).


Natural frequency = resonance frequency

is the frequency with which a body swings freely around its equilibrium position after a single stimulation.


Excitation or interference frequency

is the frequency with which a system is excited in the event of a forced oscillation. It is often the same as the machine speed or the number of strokes.


Voting ratio

The ratio of the interference frequency to the natural frequency is called the tuning ratio. In general, it can be said that the lower the natural frequency of the isolator, the better the efficiency of an insulation, i.e. the greater the ratio of the interference to the natural frequency. As a rule, a voting ratio between 3 and 4 is aimed for.


Resonance / resonance amplification

If the natural frequency is close to the excitation frequency or is even the same (tuning ratio = 1), one speaks of resonance. The oscillating system consisting of the machine and the isolator reacts with particularly large amplitudes. The oscillation is not reduced, but amplified (resonance amplification).



are elements that convert an input signal into a different output variable. Usually mechanical work is converted in the process. You thus actively intervene in the control system and / or specify target values.


Active / passive vibration isolators

Passive vibration isolators have an amplification of the oscillation amplitude when excited in the range of the natural frequency. This amplification of resonance depends on the damping properties of the isolators.

Active vibration isolators generate a counterforce that is phase shifted by 180 ° (see also phase shift) by means of a suitable control system, with the isolators acting as actuators here. This minimizes the resonance gain in the range of the natural frequency of the isolators.
Isolators are often colloquially referred to as Vibration damper designated.


Degrees of freedom

Degrees of Freedom (DOF) are the possible directions of movement of a system. A solid body has 6 degrees of freedom, because the body can be moved in three mutually independent directions (X, Y, Z) and rotated around the three axes.


COG = Center of Gravity = focus

The position of the machine's center of gravity is important for the static storage and selection of the installation points for vibration isolation.


Types of isolation

Source isolation is the vibration-isolated mounting of a machine, the vibration forces of which are thereby reduced. The environment, such as neighboring machines, the building and people are also protected from the disruptive forces.

In the Receiver isolation It is important to protect machines that are sensitive to vibrations (e.g. measuring machines) from disruptive floor vibrations.


Phase shift

The physical term phase shift means that two harmonic oscillations are phase shifted from one another if their period durations match, but the times of their zero crossings do not. A phase shift of 180 ° is used in active isolators (e.g. Active Isolation System ™) to isolate vibrations and minimize resonance amplification.


Direct isolation

Direct isolation means that vibration isolators are installed directly under or in the machine, usually in the same place as the existing installation points. The direct insulation assumes that the machine bed or the base frame has sufficient inherent rigidity and does not twist due to the elastic mounting.


Indirect isolation

In the case of machines whose inherent rigidity is insufficient for direct insulation, a correspondingly rigid intermediate structure must be inserted between the machine and the insulators, e.g. a steel platform, cast plate or a block foundation made of concrete (foundation insulation).