Silencer causing HRV inefficiency

I have a Fantech SH704 ventilator installed going into 2x4 silencers (the type with fiberglass panels inside a wooden box). The silencers are causing the motor of the ventilator to overwork and produce a loud noise. I believe that my ventilator is not powerful enough for the silencers. How can I solve this? I could remove the silencers, but then I would get sound from inside the room traveling outside through the ducks. Are there methods of silencers that don't require so much air pressure? By the way, I need the silencers for stopping noise inside the room getting outside, not really for fan noise getting inside the room. Thank you, Andrew

There's also this thing on "equivalent duct length" that I'm unsure of. Is this required for every ventilator unit? I'm not quite sure on how to do this, but I do know that if it is required for my unit then it could be the solution.