You sure about that? 10dB means that that the 636 is 100x quiter than the 877.
For comparison purposes, if one sound source is 50% quiter than another, it is 3dB quiter, or louder depending on which way your are comparing (quite to loud / loud to quiet).
Lets say that you do a further 50% reduction on the first one. You once again reduce it by a further 3dB.
So a 50% reduction, and another 50% reduction? A total savings of 6dB.
Cheers.
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