Do I need a subwoofer?

@jerryg123 , You are right in that the volume of a point source system drops of at the cube of the distance at all frequencies. You are also right that a room can increase bass at certain frequencies at various locations depending on the room. However, drivers have a frequency response range, a range where they can effectively radiate the frequencies they are responsible for. What is the low frequency limit of a woofer?  Woofers do not have electronic high pass filters. They will vibrate at 10 Hz even though they are incapable of radiating that frequency usually because they are too small or they can not move far enough. If you stick the microphone right up to the driver say 1/2 inch away you will be able to see 10 Hz on an oscilloscope at some volume. As you move away that volume will drop of rapidly way faster than the cube of the distance.  By a meter you will not be able to measure it at all. As the woofer gets larger (in an appropriate enclosure) and moves farther you will pick up 10 Hz louder until finally the volume is up to the rest of the frequencies at one meter. But at distances farther away the lower bass limit will rise or rather the volume at 10 Hz will fall off faster then the rest of the frequencies. This is why the specification for frequency response is so misleading. Just because a speaker's 3 dB down point is at 28 Hz at 1 meter does not mean it will be 3 dB down relative to the other frequencies at 4 meters. Under most circumstances the 3 dB down point will head north. At 4 meters it might be up at 40 Hz.

@jerryg123 , that is certainly the easy way out. You will just have to live with more distortion in your main speakers and very little if any bass below 40 Hz and please don't quote specs. 1 meter is a lot different than 12 feet in a residential room.

For many this is the better way to go. Without digital bass management integrating subwoofers can be a real PITA and commercial subwoofers other than Magico's Q subs and perhaps one or two others are pretty bad. I listened to a smallish monitor system last weekend and it was surprisingly good excepting there was no low bass. I can understand why many people would stop there. Those monitors were better than any tower speaker I have heard.

@jerryg123 , the QLN Prestige 5s are down 3dB at 26 Hz at 1 meter which means in a normal sized room at 3 meters they are down somewhere around 10 dB. You still need subwoofers if you want to try duplicating a live performance. 

@olfac87 , two subwoofers is the minimal requirement for decent bass. Cindyment made a very important point. Most people do the cheap and dirty method of integrating subs by using only low pass filters on the subwoofers. Using a full two way active crossover and putting a high pass filter on the main speakers will decrease distortion in the main speakers and add a significant amount of head room to the system.  The ultimate way of integrating subwoofers is with a digital bass management system such as you find in MiniDSP units and digital preamps such as the DEQX Premate, Anthem STR and Trinnov Amethyst. These allow you to adjust your speakers in time so that the sound of the subwoofers gets to your ears at exactly the same time and phase as the main speaker. Using a high pass filter and time correction allow you to put the subs where they work best, in corners or right up against a wall, and allow a higher crossover points further lowering distortion and increasing head room. With the 801s I would not want to cross over any lower than 80 Hz. 

The only commercial subs I like are the Magico Q series units. If you are decent with tools you can build a fine pair of subs from Dayton Kits (partsexpress.com) and save enough money to get a proper crossover, measurement microphone system and a vacation in Tuscany.