Caution: Quieting Loud Equipment after Purchase Weakens Power
Problems arise when loud equipment must be quieted, or modified to reduce noise emission, after the fact. This is where you run into issues of reduced power or capability.
Therefore, it is preferable by far to purchase quiet equipment in the first place. Suppliers are required to deliver both the performance and the sound level limit.
Assessing the Degree of Aftermarket Noise Control Required
It is usually not sufficient to purchase an aftermarket noise control item on the basis of “reduces noise X dbA”.” It is usually necessary to evaluate the reduction in octave- or one-third-octave bands and then calculate the net dBA reduction. This often means involving a consultant.
Resources
Sound and Vibration Magazine 2010 Buyer’s Guide to Products for Noise and Vibration Control 
