Sound is caused either by rapid vibration of materials or fluctuations in air flow. Sound moves through the air as a longitudinal pressure wave and propagates through gases, liquids and solids. A pure tone is characterised by its frequency, measured in Hz (Hertz) (indicating the rate of vibration), and its pressure level in dB (Decibels) (indicating the intensity).
The irreversible change of material properties during exposure to a deteriorating environment, for a specified time interval.
Measurement of the air flow through a sample at constant air resistance of 200 Pa for a test surface of 20 cm².
Air resistance (acoustics)
Air flow distance, calculated from the measurement by the air velocity to reach a pressure drop of 1 inch water column (unit: N.sec/m³).
Air resistance (sealing)
Measurement of the air resistance at a fixed air flow through O-ring sample compressed at 75%.
The function of the foam is to prevent accumulation of electrostatic charge, which can damage electronic components. To reach the function, one enhances the electronic conductivity of the foam by a factor 10 to 100.