A reference dictionary of sound and vibration terms
  • What is machine vibration?
    Most of us are familiar with vibration; a vibrating object moves to and fro, back and forth. A vibrating object oscillates. However, we experience many examples of vibration in our daily lives. A pendulum set in motion vibrates. A plucked guitar string vibrates. Vehicles driven on rough terrain vibrate, and geological activity can cause massive vibrations in the form of earthquakes.

    There are various ways we can tell that something is vibrating. We can touch a vibrating object and feel the vibration. We may also see the back-and-forth movement of a vibrating object. Sometimes vibration creates sounds that we can hear or heat that we can sense. To observe how vibration can create sound and heat, rub your feet back and forth on a carpet.

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    In industrial plants there is the kind of vibration we are concerned about: machine vibration.
    What is machine vibration? Machine vibration is simply the back and forth movement of machines or machine components. Any component that moves back and forth or oscillates is vibrating.

    Machine vibration can take various forms. A machine component may vibrate over large or small distances, quickly or slowly, and with or without perceptible sound or heat. Machine vibration can often be intentionally designed and so have a functional purpose. (Not all kinds of machine vibration are undesirable. For example, vibratory feeders, conveyors, hoppers, sieves, surface finishers and compactors are often used in industry.)

    At other times machine vibration can be unintended and lead to machine damage. Most times machine vibration is unintended and undesirable. This article is about the monitoring of undesirable machine vibration.
    Shown below are some examples of undesirable machine vibration.
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    For getting the undesired vibration, we are often required to do the NVH test. The test equipment includes:
    Analyzers, shakers and controllers, accelerometers, noise dosimeters, octave band filters, transducers for vibration and acoustics, dynamometers, sound level meters, microphones, and analysis software.

    With technology changing every day, focus is shifting more toward the development of PC based analyzers, multichannel NVH data acquisition systems, acoustic holography devices, laser vibrometers, and anechoic test cells. The NVH test equipment manufacturers can be classified as product vendors and solution providers.

    Product vendors supply devices that fulfill certain end users, usually called application specialists, whereas solution providers design products that cater to the clients’ requirements. They often face the end users including aerospace & defense, automotive, industrial, consumer products, and building construction among others, often have a great need of the test equipment.

    The undesired vibration and noise are often solved by the NVH test equipment manufacturer.
  • Who can benefit from NVH test ?
    Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured, Harshness is a subjective quality, and is measured either via "jury" evaluations, or with analytical tools that provide results reflecting human subjective impressions. These latter tools belong to the field known as "psychoacoustics”. And our escalating demands for safety and physical well being mirror our increased awareness of the effects of noise and vibration
    In automatic industry, NVH test deal with both noise and vibration experienced by the occupants of the transportation vehicle and the noise radiated by vehicle, such as drive-by noise testing, the mechanical shocks imposed on them, brake testing etc. The cars are extensively tested to make sure they can withstand the mechanical shocks imposed on them. The noise that cars make will have been analyzed to make sure that it’s comfortable for the driver and passenger and it does not spoil the environment of those around you. There’s no doubt that the customers of automobile industry would benefit directly from the NVH test.
    Definitely, the automatic manufactures who appreciate such measures will benefit from such regulations. As they care about their customers’ requirement and pay more attention to the component design process, the manufactures would beat the competitors during the frenetic manufacturing competition.