With the terms ‘vibration’ and ‘noise’ regularly being used interchangeably, there is often confusion surrounding the precise definition and difference between the two. This ambiguity leads to many questioning what is the difference between vibration and noise?
Despite their common confusion, vibrations and noise differ quite significantly. Vibrations are mechanical oscillations or the intermittent motion of a particle or body, resulting when it is moved from its equilibrium condition. Oscillations can be motions that repeat periodically or randomly and vibrations can be both desirable or undesirable. There are two different types of vibrations – free and forced.
Types of vibration
Free vibrations occur when the system is briefly disrupted and then allowed to move freely. The force is applied and then the object is left to vibrate at its natural frequency. In contrast, forced vibrations manifest when the system is repeatedly disrupted, subsequently forcing the object to vibrate at a specific frequency and resulting in a transfer of energy from the object to its environment.
Vibrations can also be damped or undamped. Undamped vibrations are oscillations that do not get consumed by the object’s environment due to the absence of external resistive forces. Damped vibrations are vibrations that lose energy to its surroundings through the use of external resistive forces. The external forces make the object resist which results in the loss of energy and, as a result of this, the magnitude of vibrations decrease.
How to measure vibration
Vibrations can be measured by displacement, velocity or acceleration. In order to measure vibrations, an accelerometer in the form of a piezoelectric accelerometer, dynamic pressure transducer or geophone is required. An accelerometer is a sensor used to sense the vibration and to measure the acceleration of the device. Accelerometers are commonly used on high-frequency objects and can measure high-frequency elements and shock. Accelerations may be static or dynamic. Static acceleration measurements will help you identify the angle of the device whereas dynamic acceleration can highlight the movement of a device. A high sensitivity accelerometer will measure low amplitude signals and a high sensitivity accelerometer will measure low amplitude signals.
Noise is defined as being unwanted sound and is made by pressure variations resulting from vibrating air particles and pressure waves. Sounds and noises can travel through solids and liquids through pressure waves to the human ear. As long as the sound is an acoustic noise and can, therefore, be detected by the human ear, it is here that the brain decides whether or not it is perceived as a (wanted) sound or (unwanted) noise.
How to measure noise
Noise is measured in frequency and amplitude using decibels (DdB) and Sound Level Meters. By measuring the amplitude of noise, you can identify the precise force or energy of the sound wave and the measure of amplitude indicates the intensity of noise. The pitch or frequency of noise can also be measured in hertz (Hz). Sound Level Meters such as condenser microphones are used for acoustic measurements. The instrument required for noise measuring will vary dependent on the environment in which the noise occurs. For example, noise dosimeters are used to measure noise in work and office buildings whereas noise monitors are more suitable for noise, vibration and harshness (NVH) studies in which environmental noise such as cars and lorries are analysed.
ACSoft supply high-quality acoustic sensors and instrumentation for the professional engineer to suit all Noise, Vibration and Harshness (NVH) projects. You can view our wide range of products here or, alternatively, you can get in touch with us by calling 01234 639550 or emailing us.