Flanking noise transmission / Structure borne noise

Flanking noise describes the noise that is transmitted through other paths than the direct path between the source and the receiver, as illustrated below.

The flanking transmission presents a problem, when areas with a high noise level are close to areas where a low noise level is anticipated. The upper figure illustrates a scenario, where the sound transmission through the partition wall is suffi ciently reduced by using a construction with a high sound transmission loss.

In this case, the noise level in the receiving room will be influenced by the contribution from the flanking transmission i.e. noise going through the ceiling to the common space above the cabins and then down into the adjacent cabin through the ceiling. The situation can be improved by introducing

draft stops in high density Rockwool, between the cabins in the common space, or by using ceilings with a high sound transmission loss.

The lower fi gure illustrates another type of fl anking noise transmission. In this case, the sending room could be an engine room with a very high noise level. The airborne noise will excite the wall of the engine room, introducing structure-borne bending waves that will be transmitted through the structure. At the

receiver room, these bending waves will excite the surfaces of the room and the structure-borne noise will be re-radiated as airborne noise.

The contribution from this flanking transmission can be reduced by introducing vibration damping of the structure, possibly in combination with an insulation of the wall covered with a steel or aluminium plate.