Originally Posted by toofast68
So once again I am learning how to interpret everything, but to me, it looks like I do have something going on at 60 hz - I can most certainly hear furnace noise - I will shut down system if my wife does not kill me and measure again....but I have no idea if furnace noise is that low.
Don't know if it'll give you some further thoughts... When my furnace is on, the noise through the floor vents is very low-frequency, and really screws up the lowest end of the waterfall. I can barely hear it really, I just hear the furnace motor and the air flow a bit...getting old, the lowest freqs the subs can reproduce mostly evade me. So yes, I do turn the furnace off when making measurements, it's just too "random" on/off. The noise through the cold air return vent is much louder (to me), I do have one of those in the HT room and put a panel in front of it that helps an awful lot while still allowing airflow. Edit: my furnace and gas hot water tank are *right below* my MLP. Due to new safety/venting building code requirements, the new gas hot water heater I got just before starting with REW is much MUCH louder than my previous one...I can hear it more than the furnace even, the supposedly high efficiency burner makes a very audible LF sound...JIC you have one of those too.
Another thing that shows up for me is the fridge. This shows up as a small bump at 59.something Hz, just like on your graph. I am close enough that I can hear the largest fridge's compressor run, when everything else is quiet. I think part of the picked-up noise is from the very heavy fridge being on a suspended floor, as is my HT room. I thought some of the vibration may be going through the floor, so I tried isolating the mic stand (as I think was suggested in the Audyssey measurement guide, not Jerry's, I use the same stand for both): no diff really. I sometimes turn that fridge off when making more "serious"/baseline measurements like noise floor. I have forgotten to turn the fridge back on too many times as well...did I mention getting old?
Edit: what I meant by my ramblings is we get used to "normal" house sounds, they all make some, so you have to get very critical when trying to determine what some anomalous reading might be.