Q's about the acoustics of fans
First a little background, I live in a downtown apartment, 9th floor with two windows that swing out, hinged on left side for one window (south) and on the right for the north window. This causes the north window when open to direct sound from the freeway, which is directly to the south right into my apartment. Average level about 71dB, yes it is ridiculously loud, no a/c, 
In the summer both windows need to be open 24 hrs a day with fans on. Of course 71dB of road noise is not condusive to hi-fi listening, so to combat this I bought a huge squirrel cage blower and will be putting it into a box the size of the window opening (24"X56"). Blower on bottom, opening on top its going to be radiused up top to smooth out the flow and keep the velocity low (mainly and air exchanger).
The internal shape I was contemplating, to minimize turbulence was 5"X9" at the fan output expanding linearly to 24"X12" (Box width X box depth). Then I got the weird idea that this might act like a rear loaded horn. Now I know I will get maximum airflow from this shape but dont horns act like acoustic transformers? Would this only affect certain frequencies? would this make the fan/bearing/road noise louder despite the lowered velocity
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