Hello, I am moving into a new house, remodeling, etc. & am installing a new A/C compressor and radon fan. Being that low frequency noise highly bothers me & affects my insomnia quite a bit, I am trying to look at all considerations regarding acoustics, mechanical sound propagation properties, standing wave issues, etc. with regards to the fan locations & models. I will share the work I've done so far with my physics major friend - it has been fairly easy to determine the fundamental frequencies that these two systems generate. I'm not sure how to figure out the amplitude in dBLs or otherwise, nor the more complex mid range and high frequency harmonics that create rattle, etc., however it is really the fundamental frequency (the low freqs) that I'm primarily concerned with. What is a major mystery to me is how to determine with any degree of accuracy how these low frequencies will resonate within the walls, creating unique standing wave patterns that I can't predict. I will be living in a house with brick veneer, but of course the guts are still wood, and wood has this resonant quality to it, like a tuning fork being constantly struck by mechanical hums - so I wonder about mitigation of this tendency.. (sound moves much faster through wood and concrete than air). How do I determine how it will propagate through my house? (through wood, concrete, sheetrock, ceilings, floors, attics, closets, defined spaces, etc?) I also don't know how the decibels fall off over distance because of this resonance problem; it adds a bit of a wildcard to the mix. Are there other considerations I haven't thought about here? I do know that parallel surfaces are the worst acoustic problem, that sound waves move in a sphere, and orthogonal angles should be considered. This stuff isn't installed yet obviously, so I can't just bring a microphone and try to determine these things practically, it's all theoretical at this point. The main concern is the location of the A/C compressor - if I put it in the most aesthetically pleasing and logical location, it will be the farthest from my bedrooms, however it will be in a prime place to propagate LF sound through parallel surfaces and resonate into said bedrooms (it will be located on a concrete platform on the opposite side of the house). If I instead install it on the side that is perpendicular to the orientation of the bedrooms and aforementioned parallel surfaces, technically the compressor will be closer to one of the bedrooms, but it will not be making noise through parallel surfaces, nor will I likely be in the 'line of fire' of the standing wave it generates. The standing wave would more likely fall in that case to somewhere in the front of my house, the living room or garage. It has a relatively low RPM speed, which I suppose is why air conditioner compressors make so much annoying low frequency noise and can propagate such a long distance. If I install it in the location where it will be oriented in a parallel fashion, I have thought about putting old mattresses in the garage on the walls to mitigate A/C noise, as a sort of baffling, or maybe even using rubber or another type of foam since sound moves the slowest through it. The radon fan looks as though it is higher frequency than the A/C compressor, and will be far enough away from me on the other side of the house to not experience the LF standing wave frequency that it creates, in my bedroom anyway. We determined the fundamental frequency both of these generate from looking at the fan RPMs. I bet fan radius and blade shape also determine plenty about the sound of the fans, as do other factors I've probably forgotten about, but wouldn't the most annoying aspect of the mechanical noise (IMO the low frequencies) probably be determined by the RPMs? I'm hoping we're right on this one.. Trane XR13 A/C compressor outdoor fan fan RPM = 825 13.75 Hz = fundamental tone wavelength of sound propagation = 81 ft (halve this to get harmonics) 40.92 ft - distance of 2nd harmonic 27.28 ft - 3rd 20.46 ft - 4th 16.37 ft - 5th 13.64 ft - 6th 11.69 ft - 7th 10.23 ft - 8th 9.09 ft - 9th harmonic Fantech HP 190 radon fan RPM = 2541 42.35Hz = fundamental tone wavelength = 8.1m 26.57 ft 13.28 ft - 2nd harmonic 8.86 ft - 3rd 6.64 ft - 4th 5.31 ft - 5th 4.43 ft - 6th These were determined in Wolfram Mathematica via wave equations. Much thanks in advance for your help!