Volume. How does it work???

[allapologies]

if for example microwave oven (A) produces 25 decibels, Microwave (B) produces 25 decibels and Microwave (C) 25 decibels, and they were all located next to each other on the same work surface in the kitchen would they produce a combined output of 70 decibels, or would the volume still only be 25 decibels?...apologies for this seemingly pointless question, but i would like to know an answer.

[moonacre]

Decibels are on a logarithmic scale not linear. This means that for every increase of 3 (I think!) the sound doubles. My physics was never that good but this would mean that adding the 3 sound sources of 25 decibels together would give a maximun decibel level of around 29 (25+3+1point something).