Let's look at a the situation with a single sub first. The primary bass issue in most rooms is the inevitable peak-and-dip pattern as the subwoofer interacts with the room boundaries. We can shift this peak-and-dip pattern by moving the sub or the listening position, but we cannot make it go away for any listening position without equalization (which can actually make things worse elsewhere in the room). The smaller the room, the farther apart (and more audible) these bass region peaks and dips; and the larger the room, the denser the peak-and-dip pattern. If the peaks and dips are dense (close together), the ear tends to average them out - giving smoother sound. So in general the larger the room, the smoother the bass.
Another way to get a smoother and denser peak-and-dip pattern is to use a second subwoofer, located asymmetricaly with respect to the first. This way each sub will produce a unqiue, dissimilar peak-and-dip pattern at any given listening position. The sum of these two dissimilar peak-and-dip patterns is considerably smoother than either one alone. This is the main advantage of using two or more subs. There are other possible advantages as well, but I won't go into them now.
Since your room is fairly large you probably start out with a smoother than normal peak-and-dip pattern anyway, but that doesn't mean you wouldn't benefit from a second sub.
I disagree with what your local shop told you. There is no magic location where a single sub will produce smooth in-room bass. There will be a "best" locaton where the peak-and-dip pattern is the least objectionable. One minor advantage of using multiple subs is that their positioning is relatively non-critical compared to positioning a single sub.
Duke
dealer/manufacturer
Another way to get a smoother and denser peak-and-dip pattern is to use a second subwoofer, located asymmetricaly with respect to the first. This way each sub will produce a unqiue, dissimilar peak-and-dip pattern at any given listening position. The sum of these two dissimilar peak-and-dip patterns is considerably smoother than either one alone. This is the main advantage of using two or more subs. There are other possible advantages as well, but I won't go into them now.
Since your room is fairly large you probably start out with a smoother than normal peak-and-dip pattern anyway, but that doesn't mean you wouldn't benefit from a second sub.
I disagree with what your local shop told you. There is no magic location where a single sub will produce smooth in-room bass. There will be a "best" locaton where the peak-and-dip pattern is the least objectionable. One minor advantage of using multiple subs is that their positioning is relatively non-critical compared to positioning a single sub.
Duke
dealer/manufacturer