Okay. So are many people just wrong to have their setup with two subs in their front wall in between their mains and straddling a center console?
Wrong? In many ways, yes. In some other ways, no.
They are wrong because they are not likely getting the best performance from their subwoofers and very often they are putting more subwoofer in the room than is necessary.
The best location for placing sub(s) producing a mono signal is very rarely easy to predict and is often not on the narrow wall. Given the limitation we all tend to put on placement - that they have to be on the floor - the ideal location for a single sub is most often in a corner as it fully excites every single room mode equally and gets the most energy in the room as possible. However, exciting all the room modes also means getting the deepest nulls in the response. So, where there are no nulls, the output in significantly increased, but the nulls are equally as deep.
Placing a subwoofer 2/5ths from a side boundary reduces the nulls from the walls to the side of the sub, but it also reduces the modes where the energy is increased. It also does nothing for the modes from the other dimensions in the room, front to back and top to bottom.
Putting two subs on the same wall 2/5th from the sides does nothing new in the room but increase the peak output by 6dB SPL because there are two subs instead of one. Having two subs in this arrangement when one sub will never be utilized to even half of its potential is simply a huge waste of money. If, however, you are pushing one sub very hard, adding a second will reduce the distortion increase the dynamic potential.
No, they are not wrong, because the characteristics above can get you a smoother response because of the 2/5ths placement on the wall (and that distance is very important - it serves no purpose to move the sub out of the corner if you are going to place 1/3rd or 1/4th of the way in from the side. It could get a smoother response in the room.
However, if you are going to put two subwoofers in a room using the theory of placing them 2/5ths from the side walls, it is WAY WAY WAY better to put the second subwoofer on a different wall than the first. That would energize the room modes differently and address the nulls from the other horizontal dimension. The top to bottom nulls will still be 100% present, but the side to side and front to rear nulls will be reduced just as the side to side and front to back modes will be reduced.
All of that said, the 2/5ths theory only works if the room is a perfect rectangle and the doors and windows are all closed. Once you introduce variations like a vaulted ceiling, cove, L-Shaped room, or whatever, you cannot merely measure a distance 2/5ths from the side wall and place a sub there and get real benefits. Instead, you need to purchase a solid modelling software package and calculate the best placements, or you need to experiment with various placements you are willing to live with and choose the best one(s).
The one HUGE caveat to all of this is the necessity that both subs are being fed the same exact signal, as in a mono 0.1 LFE channel and redirected bass from the other channels. If you are running true stereo subwoofers, the two up front placement is more ideal - but they would present a more natural stereo effect if they are outside the mains speakers, not inside.
So, in most cases those aesthetically attractive rooms where the owner puts two subs up front inside the main speakers are usually not a good setup - and rarely are they half as good as that system could be if the subs were better placed or if the funds spent on the second sub were instead spent on acoustic treatments.
