@quanghuy147 , Do you have carpet on the floor? Wall to wall with a pad underneath? You have a vertical node problem not a horizontal one.
I have noticed that media rooms with wall to wall carpeting have less of a problem with this. The other solution is to get speakers that do not radiate up and down, vertical line source speakers.
I have noticed that media rooms with wall to wall carpeting have less of a problem with this. The other solution is to get speakers that do not radiate up and down, vertical line source speakers.