No it is not. Due to the logarithmic nature of the decibel scale, sound levels do not add linearly. For example, if there are two sound sources in a room such as an air handler producing an average sound level of 90.0 dB and a pump producing a sound level of 86.0 dB, then the total sound level is 91.5 dB according to the mathematical rules governing logarithms. If two separate sound sources are producing the same sound level then the overall sound level resulting from the addition of these two sources will be 3 dB higher assuming they are not phase related.

Generically speaking, a person with average hearing would just barely perceive a difference of 3 dB. An increase of 10 decibels is generally accepted as the point at which a sound is subjectively perceived as “twice as loud.” Of course, subjective perception depends on factors such as the person and the nature of the sound.