I have recently moved house and fitted out a top floor room as a studio/monitor room. It is quite small; 12ft 3in wide, 11ft 9in long and 7ft 5in high although, as it is an attic room, the ceiling slopes down on either side to just 3ft 6in at the sides.
I have fitted bass traps wherever I can and the walls and ceilings have plenty of foam attached but I have this annoying resonance that is particularly noticeable at the mix position - about one third the length back from the wall. I can easily hum the note and checking on my keyboard I find it is close to D# below middle C. From the web this appears to correspond to a frequency of about 155Hz and a wavelength of 222cm which is 7ft 3in i.e pretty close to the room height but also not far from a half wavelength of the distance from the mix position to the rear wall.
The resonance is fairly localised to the mix position - if I move my head a foot left or right or back it is gone although it seems to last a bit further as I approach the wall nearest the mix position. It does NOT occur at the same postiion at the other end of the room.
Any suggestions as to how to fix it are welcome.
Cheers
ian