Understanding airborne sound and impact sound, and how to measure each type of sound

1. How do Airborne Sound and Impact Sound differ?

Airborne sound (Airborne Sound)

Airborne noise occurs when sound travels through the air, such as music, speech, and television. This type of noise is quite common, so it is usually what you think of when considering noise.

Impact sound (Impact Sound)

Impact noise occurs when sound vibrations travel through a medium other than air and happen when two or more objects collide. Examples of impact noise include construction jackhammers, a ball bouncing on the floor above you, or water rushing through your pipes. Impact noise can travel through structures, and therefore it is sometimes called structure-borne noise.

2. How to test?

Below is a brief description of the acoustic testing types we typically perform:

Airborne Sound Testing

Airborne sound testing is performed on walls and floors. First, a controlled noise is generated by an amplifier and speaker over a wide frequency range. The generated noise is very loud and typically exceeds 100dB. Initial measurements are made using a class 1 sound level meter in the 'source room', followed by subsequent measurements in the 'receive room' on the other side of the wall or floor being surveyed. The speaker position in the source room is then changed and measurements are repeated on both sides of the partition under test. Background noise measurements are then made using a class 1 sound level meter in the receiving room and used to apply appropriate corrections for external sounds such as traffic noise.

Similarly, the reverberation time (reverberation time (RT60)) is measured in the receiving room using a sound source and sound level meter to determine corrections that must be applied to account for the room's absorption characteristics and capacity. The difference between the two airborne noise levels (for walls and floors), corrected for background characteristics and reverberation, determines the airborne sound insulation performance of the wall or floor. A larger airborne noise difference between the source room and receive room determines a higher airborne sound insulation performance.

Impact Sound Testing

Impact sound testing is typically performed only for floors. This testing is different; a calibrated Norsonic "tapping machine" consisting of five "hammers" driven up and down by a cam and electric motor is used to "tap" the floor surface by applying a known force to the floor structure. The machine is placed in several predefined positions. The resulting noise is measured in the dwelling below using a sound level meter. Background noise measurements are then made using a class 1 sound level meter in the receiving room and used to apply appropriate corrections for external sounds such as traffic noise.

Similarly, the reverberation time (reverberation time (RT60)) is measured in the receiving room using a sound source and sound level meter to determine corrections that must be applied to allow for the room's characteristics and absorption capacity.