system noise floor management is complicated. (1) it starts with complete elimination of outside noise, including building mechanical noise, and also the effects of ground noise. (2) next is HVAC; you need an air box isolated, low flow, high volume air flow, and -3- 90 degree turns between your air box and the room outlet.....and sufficient air returns. (3) the room has to be quiet, but lively. it should not muffle voices when talking. (4) power grid should be isolated in some form or fashion. (5) signal path well sorted out according to taste. (6) gear decoupling or grounding according to taste. (7) resonance/acoustical feedback eliminated, but life not squeezed out either.
the test for 4, 5, 6 & 7 is whether you can maintain the low noise yet not strangle the musical expression. the goal is not absolute quiet, the goal is that the most delicate musical nuances are alive, and that the space promotes extended listening.
many superb listening rooms are compromised in terms of perfect noise control, but do enough of the right things to allow the nuance to be alive. having a lively room is more important than just a quiet room. we can listen around a bit of noise to hear the good stuff, but if the room is stifled then some of the musical life is restricted. and gear with the objectively lowest noise is not the goal, it's what happens next. does that low noise allow for more musical truth?
but if you can have it all, quietest room, and most musical truth revealed, then that is best.