Acoustic Glossary

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UK Government Environmental Noise Regulations

Aircraft Noise indicators • LAeq,16h • Lday • Levening.
Industrial Noise and Port Noise indicators • LAeq,16h • Lday • Levening.
Railway Noise indicators • LAeq,6h • LAeq,16h • LAeq,18h • Lday • Levening.
Road Traffic Noise indicators • LA10,18h • LAeq,16h • Lday • Levening.

Ultrasound Definition IEC 801-21-04, acoustic oscillation whose frequency is above the high-frequency limit of audible sound (about 16 kHz)

Uncoupled Mode Definition IEC 801-24-18, normal mode oscillating independently of other modes.

See also • coupled modes

Undamped Natural Frequency the natural frequency of a structure.

Undamped Natural Frequency Definition IEC 801-24-09, frequency of free oscillation resulting from only elastic and inertial forces of the system.

See also • natural frequency

Under-range, the input to the sound level meter is too low for the current measurement range.

Under-range %, percentage of time that an under range occurred.