Thanks for the feedback guys! I'm sure you guys are just as tired of hearing about this issue as I am tired of, well, hearing it
Fred, it would appear the the Panasonic fan is a "blower" while the Fantech fan is a centrifugal fan. The difference is subtle and relates to the pressure they develop. It may be a case of the manufacturer being loose with their wording, though. WIth regard to the tone generated by the fan, it would certainly seem that it would be higher frequency than what I'm hearing. Of course, I don't have a lot of experience with this sort of thing, so who knows what frequency I'm hearing, but it does seem to be in the lower frequency range to me.
I have listened to the fan in free air, but the noise was dominated by the wind noise.
BIG, thanks for the link. My interpretation of that is it comes back to velocity. However, now that I can adjust the volume of air between my equipment closet and my theater, I would expect a big difference in noise when I reduce the air into the theater. I'm just not seeing the sort of change I would expect.
TMcG. As usual, you are correct. A custom fab'ed piece would likely provide a more gradual bend. However, I think that with such a drastic change in the shape of the transition I would expect to have at least changed the character of the noise. That doesn't seem to be the case, which leads me to believe that the source is something different.
I suppose there is a little more good news. Now that my soffit duct is nearly complete, there doesn't seem to be any wind noise. Even with the equipment vent nearly closed I don't hear any velocity noise from the duct. Just the low droning.