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Experiencing Impact Noise and Walking Noise
Everyone probably has experience in the notion of impact sound transmission when woken up by the heavy steps of the occupant upstairs or simply by the steps of someone in another room within the same flat. One may even have observed that according to the nature of the floor, the walls, and the dimensions of the room, the perceived impact noise was different.
One has probably also observed that according to the nature of the floor covering or floor constitution, the noise of the steps inside the room where one is walking may sound quite differently (e.g., a wooden floor on joists will sound more hollow than a plain concrete floor).
Impact Noise of a Floor
The impact noise of a floor is measured in a laboratory that features a heavy slab with a framed 10 m2 opening in the middle. Due to the constitution of the walls, flanking transmissions can be considered negligible, and the sole contribution to the sound levels measured in the receiving room comes from the radiation of the test floor. The floor under test is excited using an impact machine (also designated the tapping machine).
The impact noise Ln is given by
where L1 is the mean sound pressure level in the reception room, expressed in dB, S is the area of the floor specimen under test, expressed in m2, and A is the equivalent absorptive area in the reception room, expressed in m2.
The standard describing the measurement procedure is usually ISO 140-6  or ASTM E492 . Those standards typically consider either the 100-3150 Hz range (ISO) or the 125-4000 Hz range (ASTM). More recently, EN/ISO standards have attempted to extend the range in the low-frequency region  down to the 50 Hz third octave band.
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