Acoustics and vibrations

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Nowadays we are living in an increasingly noisy environment. We are surrounded by busy roads, railways, and in some places even airports. Some working environments are also more or less noisy, especially in heavy industry. Moreover, we are occasionally exposed to disturbing noise at our homes, both because of the neighbours, as well as because of various sports and cultural events in the neighbourhoods or because of the proximity of heavy industry and transport infrastructure. Daily exposure to excessive noise damages our hearing, so the number of hearing impairments is increasing.

Disturbing noise needs to be measured correctly, so several different instruments for measuring acoustic quantities have been developed. The basic instrument is a sound level meter, which generally measures the sound pressure level in a wide or narrow frequency range. The key element of a sound pressure meter is a measuring microphone, which converts an acoustic signal into an electrical signal with a certain microphone sensitivity. The measurement of acoustic parameters is generally highly dependent on ambient conditions (i.e., air temperature, pressure, and relative humidity), so sound level meters would generally display a different reading depending on the day-to-day ambient conditions compared to a reading measured under reference laboratory conditions. Therefore, the sound level meter must be calibrated under given ambient conditions prior to the use with an appropriate acoustic calibrator that generates a constant acoustic pressure over a much wider range of ambient conditions. Sound level meters measure only sound pressure at a certain moment or. within a short interval, however they do not give cumulative noise, or. sound doses received by a person over a longer period (i.e., several minutes, hours). This acoustic quantity is measured by an acoustic dosimeter.


We talk about acoustics when we are dealing with fluctuations in air pressure, i.e., oscillations of air particles. On the other hand, we are talking about vibrations when we are dealing with the oscillation of solid surfaces. Each rotating or a moving object evokes certain vibrations. Vibrations could be periodic which most often occur because of surface oscillations or as rotation of various motors. The vibrations are measured with vibration meters, which are usually based on accelerometers. Reliable and accurate measurement of periodic vibrations is important since a change in vibration may indicate damage to the machine or engine, so the operator can stop operation even before costly and dangerous mechanical damage could occur. Periodic vibrations are usually sinusoidally shaped, are long-lasting, and generally have a relatively low amplitude of accelerations (i.e., vibrations have small velocities and small displacements). In addition to periodic vibrations, we also know vibration transients (shock vibrations), which occur when there are sudden changes in acceleration, velocity, or displacement (e.g., a car crash, an object falling to the ground, etc.). Proper measurement of such transients is necessary in the modern world mainly due to the increasing number of product testing in accordance with various standards. In the case of vibration transients, the duration of the transient and the amplitude of the acceleration or deceleration.

Calibration of test equipment at SIQ

Sound calibrators

Sound calibrators are calibrated in accordance with IEC 60942. The generated sound pressure, frequency and distortion are measured. The calibration could be performed between 94 and 124 dB and in the frequency range between 31.5 Hz and 16 kHz.


Microphones are calibrated according to IEC 61094-5. For ½ and ¼ inch microphones we calibrate the sensitivity and frequency response (pressure or free field) in the frequency range 31.5 Hz – 16 kHz. On contrary, we could only calibrate sensitivity at 250 Hz for a 1-inch microphones.

Sound level meters

Sound level meters are calibrated according to the IEC 61672 in IEC 61260 standards. The following parameters are calibrated:

  • absolute sensitivity
  • frequency weightings A, B, C and Z (31.5 Hz – 16 kHz)
  • time weightings F and S at 2 kHz or 4 kHz
  • linearity from 0 dB to 100 dB (16 Hz – 20 kHz)
  • electroacoustic filters, levels 0 dB – 80 dB, central frequency 3.15 Hz – 40 kHz

Upon to request we could also perform the following calibrations:

  • self-generated noise of the sound level meter (acoustical and/or electrical)
  • frequency and time weightings at 1 kHz
  • long-term stability
  • C-weighted peak sound level
  • overload indication check
  • stability at high levels


Dosimeters are calibrated in accordance with IEC 61252. We measure all key parameters such as accuracy of sound pressure level, sound dose for different frequencies and levels (31.5 Hz – 16 kHz at 94 dB, 104 dB and 114 dB) and accuracy of time measurement.


We are calibration the sensitivity of charge accelerometers and electronic ICP accelerometers in the frequency range between 10 Hz and 10 kHz can be measured. If required, we could also measure linearity at certain frequency.

Vibration calibrators

The accuracy of the generated level (acceleration, velocity, or displacements), the accuracy of frequency display and distortion are typically calibrated. If desired, we can also calibrate linearity of the generated level for different frequencies and for different loads attached to the calibrator.

Vibration meters

We calibrate the accuracy of acceleration (0.1 m/s2 – 200 m/s2), velocity (0.4 mm/s – 3 m/s) and/or displacement measurement (2 mm – 50 mm) in a frequency range 10 Hz – 10 kHz. The accuracy of the vibration frequency could be also calibrated upon request and if the function is available.

Charge amplifiers

The key parameter of charge amplifiers is its charge sensitivity, which can be measured for all available gain settings at frequencies DC – 10 kHz. We also measure DC offset and RMS noise level. Depending on the type of charge amplifier and according to customer’s requests, the charge amplifier’s sensitivity, integration function, filters and the overload indicators can be also measured.

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  • SIQ Ljubljana