Am using the mini DSP microphone UMIK-1 -
https://www.minidsp.com/products/acoustic-measurement/umik-1 with REW..
This microphone is rated at 20Hz - 20Khz, i use the provided calibration files and this microphone seems to be most used for acoustic measurements across most forums..
Ok.. I will put it from my understanding of room modes.. I use a 80Hz crossover on my AVR..
Below 80Hz, there are 3 room modes per the above chart.. 1st width mode at 40Hz, 1st length mode at 51Hz, 1st height mode at 59 Hz and 2nd width mode at 81hz, just after the crossover..
If i put it on the floor, i need to put them at 1/4th (to minimise 1st width mode at 40Hz), 3/4 (to minimise 2nd width mode at 81hz ) in the room width & 1/2 the length placement in the room (to minimise the 1st length mode at 51Hz).. Am unable to place them on the floor in the right locations as it is a small living room.. But i thought of placing it on ceiling space, which remains unused in a listening room..
Since i used ceiling, i was able to mount them at the right locations as mentioned above..
i also have the liberty to minimise the height room mode (1st height mode at 59 Hz) if i can place the sub at room midpoint between ceiling/floor.. This way, there is all the probability that it will minimise all the room modes below 81Hz in my room, post which i can cross it to mains.. Pic below of what i planned earlier..
I have suspended the sub from ceiling as much as i can.. The down facing driving on the enclosure is at 44 inches from the ceiling.. If i can have it near 57 inches (midpoint between ceiling/floor), it should minimise all the room modes below 81Hz..
If you look at the above graphs and the room mode chart, 1st width mode at 40Hz, 2nd width mode at 81hz, 1st length mode at 51Hz, is all minimised (almost flat, no peaks).. With the exception being 1st height mode at 59 Hz, which i have minimised to the extent possible..
Had it been a dedicated HT room, i would have placed the subs at 57 inches from ceiling (room height midpoint) on either sides of my listening position and every possibility that i would have minimised all the room modes below 81Hz with two subs..
I still have a minimised peak at 60Hz, have been suggested to use a crossover of 60Hz, so that it is passed on to L/R speaker..