# SI unit: Acoustics

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• The SI unit of frequency is hertz (Hz).
• Sound intensity is the sound power per unit area, the SI unit is Watt per square metre (W/m2).
• Sound pressure is the difference between the pressure caused
by a sound wave and the ambient pressure of the medium it is passing through. The SI unit of sound pressure is pascal (Pa).
• Decibel (dB) a relative unit of measurement widely used in acoustics. However, the dB is not a unit in the sense that a metre is units of length. The decibel is a logarithmic unit used to describe a ratio between the measured level and a reference or threshold level
of 0 dB. The ratio may be sound power, sound pressure, or sound intensity, etc.

## Calibration services for acoustics

We have calibration services for the following equipment: microphones, sound level calibrators, vibration transducers and loggers, and vibration calibrators.

### Microphones

We calibrate ½ (LS2P) and 1 (LS1P) inch condenser microphones described in the standard IEC 61094-1 (Table 1). The calibration method depends on the ac-curacy required by the customer. The smallest calib-ration uncertainties can be achieved by using the re-ciprocity method. In many cases, a comparison with a reference microphone by a sound level calibrator is adequate.

### Sound level calibrators

The most common devices calibrated at MIKES acoustics laboratory are sound level calibrators and pistonphones. We calibrate the sound pressure levels at fixed frequency points. At the same time, the distortion and frequency of the sound source is measured

### Vibration transducers and loggers

We calibrate vibration transducers, loggers and vibration measurement devices in the frequency range 1 Hz – 10 kHz. Typical nominal acceleration is 10 m/s2. The calibration gives the magnitude and the phase of the sensitivity of the vibration trans-ducer. The uncertainty of the calibration depends on the transducer under calibration. Typical uncer-tainties for the magnitude are 1–3 % and for the phase 1–2° depending on the frequency.

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