Hi vivek,
Only dipole surrounds produce a true "null". The woofer/midrange drivers on a dipole surround are out of phase, so that if the drivers face fore and aft (sorry, I just sold my sailboat and I can't shake these nautical terms)--to the front and rear of the room, and you are sitting to the side, the output of the front and rear drivers more or less cancels at your listening position. But because a great deal of the sound is reflected from various room surfaces before it reaches your ears, the content from the dipoles is a mix of in-phase and out-of-phase sound waves. Subjectively, this results in a diffuse soundfield that can't be easily pinpointed to a particular source. Since this was the original goal of Dolby surround for home use, dipole surround speakers are used to to mix 5.1 Dolby movies in small control rooms, to simulate the diffuse and enveloping soundfield produced by rows of sidewall-mounted monopolar surrounds in large movie theaters.
The Axiom QS series are "multipolar," a mix of both dipole and bipolar radiators, so there isn't as specific a null created.
Nulls also occur at low frequencies in all rectangular and square listening rooms, resulting from the cancellations and reinforcements dictated by the room's standing waves and dimensions. That's why when you listen to deep bass from a subwoofer and walk around your room, you'll pass through nulls where certain bass frequencies will disappear and, a few feet farther, will suddenly be boomy.
Regards,
