Ear defenders should sufficiently keep out ambient noise but should not totally blank out important sounds like horns, sirens and machine noises (overprotection).
A residual rating of 75 to 79 dB(A) at the ear is ideal. Noise levels over 87 dB(A) are never permissible.
Ear defenders keep out external noise in different frequency ranges to different extents according to their design. These noise filtering characteristics are referred to as H, M and L (High, Medium, Low). The noise from STIHL chain saws and power tools can be described as mid- to high-frequency. The M value therefore offers the most appropriate hearing protection.