Outdoors, the problem is you have a lot of area to energize. There is no room gain. But you don't have standing wave modes within the walls to worry about either. Just the nodes that might setup between subs, if placed over 1/4λ apart.

Inside a room, the problem is room modes. These are determined by room size and proportion, subwoofer number and position and listener position. Large rooms are typically less problematic where room modes are concerned, because modes shift down in frequency. The larger the room, the more it acts like open space. Smaller rooms generally have more noticeable room mode problems. One solution involves using multiple subs strategically placed to partially cancel peaks and fill in the holes caused by standing wave nodes within the room.

Welti suggests four corner placement or four subs placed at wall midpoints. Geddes prefers random placement. I tend towards a staggered symmetrical approach, one placing subs in different places in all three planes but symmetrical with respect to the listener. Each placement method has its strengths and weaknesses, and many of them are room specific.

What works best for you?

What would you consider to typically be the best location for a single sub in a mid-sized room?

Dave

With three subs you could get a comparable quality, but placement became more critical. One in a corner, one along a side wall and the last one 2/3 the way up to the ceiling along another side wall. This worked pretty well.

In this same study I allowed each of the woofers a totally independent amplitude and phase and let a computer find the "ideal" for each sub. The most interesting thing was that if I took the three woofers and made the amplitude and phase at two of them completely random, I got about the same result as the complex adaptive one. But think of the advantage. The complex adaptive one has to be set for each room, but the random approach works the same in any room.

I'll leave the concept of making a random filter as a task for the reader (Here is a hint: its called a decorrealtion filter).

In Welti's study, several placement configurations were tested. A single sub was used and placed in various locations. Pairs and groups were also tested, with group sizes of 3, 4, 5 and even large groups like 10 or 20.

The results were pretty clear, that the most uniform response was obtained with large random placement, subs in each corner or subs at the midpoint of each wall. The large random group placement was found to be good, but no better than the placement in each corner or at the midpoints of each wall.

I think it is important to notice the large random placement had two unique features, one being the number of subs and the other being their random placement. In this case, I think the high number was more important than the placement because there was just so many of them.