Low frequencies below 150 Hz are omni-directional; that is, they seem to come from all directions. Hence it would not be possible to locate  the subwoofer no matter where it is placed in your room. This, however, does not necessarily mean that the placement of the subwoofer is not critical. Each room, depending on its shape and dimensions, has a number of resonant frequencies that react with each other. Thus, the level of perceived bass may vary across a room depending on where source of sound is placed.

 Suggestions on placement are given in the Figures below. It is important to note that every reflecting surface increases the low frequency level by  3 dB. Hence, when you place your subwoofer up against a wall, you get a higher level of low frequencies than when it is placed further away from any wall. Similarly, when you place it in a corner, the three reflecting surfaces further increase the level. However, this may result in uneven distribution of bass across your room, as discussed before. Hence, experiment with the placement and monitor its bass while sitting at your favorite listening spot. It may take a while before you finally arrive at the optimum location.

One experiment that usually works is this. Start out by placing your subwoofer where your favourite listening spot is (you will have to take the trouble of vacating your armchair, but only briefly!) Then, turn on your subwoofer and move across the room to  find a spot where bass response is best. This is the optimal position of your subwoofer with reference to your favourite listening spot.