Sounds like a Fun Project
Pumps and therefore pump rooms need ventilation so they don't overheat.
Vents and soundproofing don't go together very well.
There are two types of noise source in the pump room. 1) the pumps 2) room reverberation. In general, for bare rooms, the sound level due to reverberation is easily 10 dB louder than the noise from the pumps at the openings, unless the pump is close to the opening.
Add sound panels to the room that are thick enough to absorb the full range of sound put out by the pump. If the room is 12x10 by 8' high, we have 1000 cuft volume and the room constant is 1000/20 = 50 Sabine seconds. The room has a surface area of 600 sqft and an absorption coefficient of maybe 5%, for a total of 0.05 x 600 = 30 Sabines of absorption. The room has 50/30 = 1.7 seconds of reverb time. A dead room has less than 1/2 second reverb time. For this room to have 1/2 second RT60 you need total of 50/0.5 seconds = 100 Sabines (sqft of 100% absorption). You have 30 already so buy 70 Sabines of probably 2" thick sound panels. Each panel is usually 2'x4' = 8 sqft. You need at least 9 of them. Couple extra won't hurt. Distribute them on walls and ceiling. Should cost maybe $8/sqft, or 70 x $8 = $560 to $600. Buy 2" Air Conditioning Duct Boards in 4x10 sheets, two of them will do, cut them down to size. Don't breath fiberglass dust. Spray paint any cut edges. This part of the project will cut the room gain problem down to a practical minimum. Noise reduction is 10 Log 70/100 = about -5 dB.
Next build large, loose fitting, open ended dog houses that will go over each pump. You want one that slides easily on the floor over or away from the pump. It is open at both ends. Add 2" sound panels to inside the dog house. Now you've blocked and absorbed 2/3rds of the noise being dumped into the room (-5 dB) and more importantly, hopefully blocked the line of sight sound path between the pumps and the louvers.
Next make a large panel out of plywood and add a 2" sound panel to both sides of it. Make the panel about 1' bigger on all sides than the louver opening. You want to mount the panel away from the wall so air can low around the panel into and out of the louver. Calculate the minimum amount of air flow at the edge of the panel by dividing the open area of the louver by the edge perimeter of the panel. Typically the panel will have 6 to 8" air gap to the wall. This is also good for about -5 dB. Total job is -15 dB and what is also good here is that you've muted the noise, caused it to not be clear, more like a distant hum.
Remember you can never get rid of sound. You can only reduce it enough that it will hopefully get lost in the noise floor. If not, raise your own noise floor help cover the intruding noise. Nothing is better than an old fan, fish tank or a modern gurgling water feature.
Art Noxon
Acoustic Engineer
