Impact/Impulse Noise is defined as:

• A. A continuous steady noise
• B. A short burst of acoustical energy with a rapid rise to maximum intensity followed by a slower decay.
• C. Noise below 85 dB
• D. Noise lasting more than 1 second

Answer: (B)

Impulse noise is a brief, high-energy burst of sound that rises to a peak almost instantly and then decays more slowly. The defining feature is the very short duration and abrupt onset, so the peak sound pressure level is what matters rather than a long-term energy average. This is why describing it as a short burst of acoustical energy with a rapid rise to maximum intensity followed by a slower decay is the best fit. It isn’t continuous noise, which lasts for a longer period and is described by time-averaged levels, and it isn’t noise that lasts more than a second, which would place it outside the impulsive category. In practice, examples include hammer blows, gunshots, and explosions, all of which produce a sudden spike in sound pressure, followed by a decay.