Various sound values are quoted in your machine Instruction Manual under the heading of "Specifications". You will find values for both the sound pressure level and the sound power level.
The sound pressure level is measured at the user's ear according to standards applying specifically to the machine and provides information about the stress on the user's hearing. The sound power level is a measurement of the noise produced by the machine in the vicinity. This is measured on an envelope around the machine according to the relevant standards. The sound pressure level is used to assess the best way to protect your hearing.
Sound levels are quoted in dB(A). Unlike other familiar units of measurement like meters and kilograms, the dB(A) scale for sound is not linear. So 100 dB(A) is not twice as loud as
50 dB(A). In terms of subjectively perceived volume approx. 10 dB(A) is equivalent to doubling the volume. Sound pressure is a physically measurable value and here an increase of 6 dB(A) is equivalent to doubling.
What Should I Take Intro Account When Choosing Hearing Protection?
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.
Maintenance and Storage
Ear defenders need regular maintenance and cleaning to prevent skin irritation and other ear problems and to keep them working effectively. The user information supplied with the product includes cleaning instructions which you should follow carefully. Damaged pads should not be reused. In particular with combined hard hat + ear defenders take care not to squash the pads in the ear defenders when storing them away after use.
Source: http://en.stihl.ca/hearing-protection.aspx
