I am impressed. True it's been a while (over a year) since the last JVC projector was here for review, but it definitely seems to me - specs notwithstanding, that this year JVC managed to make their projectors quieter.
I have no doubt that the DLA-RS4910 is quieter at full power than the Epson 5030UB, and also the Sony VPL-HW55ES, although to a lesser degree.
The Bottom line though is that few will have any issue at all with the JVC running full tilt - maximum brightness, as it is still fairly quiet. Not once did I ever (sitting 3-4 feet from the JVC) feel the need to switch to Eco, due to the audible noise.
The JVC is very quiet in Eco mode - you won't find many projectors that can do better.
JVC doesn't seem to be publishing a spec for audible noise this year, at least not in the manual, or in the brochure we have here. That leaves me to guess.
I would estimate that at full power, the RS4910 and it's siblings are probably in the 26-28 db. range. Nicely done JVC!!!