This may be useful in terms of evaluation the context of use. I would suggesting looking at the webpage from the Canadian Centre for Occupational Health and Safety

"What are A-weighted decibels?

The sensitivity of the human ear to sound depends on the frequency or pitch of the sound. People hear some frequencies better than others. If a person hears two sounds of the same sound pressure but different frequencies, one sound may appear louder than the other. This occurs because people hear high frequency noise much better than low frequency noise.

Noise measurement readings can be adjusted to correspond to this peculiarity of human hearing. An A-weighting filter which is built into the instrument de-emphasizes low frequencies or pitches. Decibels measured using this filter are A-weighted and are called dB(A). Legislation on workplace noise normally gives exposure limits in dB(A). Table 2 lists examples of typical noise levels.

A-weighting serves two important purposes:

1. gives a single number measure of noise level by integrating sound levels at all frequencies

2. gives a scale for noise level as experienced or perceived by the human ear"