Method > Method for reducing noise
The overall noise is an additional result of some partial noises. Then, it’s often just one origin of noise which provides major noise, sometimes two.
In fact, the additional result of noise levels is not done by arithmetical mode (10+10=20), but logarithmic mode (10+10=13).
That’s why major source is very often responsible of total noise for a large part.
For example :
There are 3 active noise sources as :
The overall noise is 66.5dB in this case.
If Source 2 and source 3 are switched off in same time, overall noise will decrease to 65dB ( reducing of 1.5dB the overall noise).
If Source 1 is switched off, overall noise will decrease to 61dB ( reducing of 4dB the overall noise).
By Mobile Sound Viewer, it will be possible to see source 1, your actions taken to reduce noise will be most efficient on source 1, so cheapest things.
In summary, scientific method explains that major source level must be decreased in the way to be the most efficient and cheapest.