How do I know if I need a sub woofer?

I am happy with the sound....enjoy listening to music...have an incredible fleshed out sound with delightful micro dynamics that make the music accessible. So why would I need a subwoofer? 

@sounds_real_audio Standing waves can cause bass notes to be cancelled in your room. No amount of DSP or room treatment can fix it since the amplifier power is being cancelled by the standing wave. 

But if you have a sub and especially if you have more than one, you can break up standing waves. Since bass in most rooms is entirely reverberant, you can use a mono signal for the sub if its below about 80Hz or so. This is because the 80Hz waveform is 14 feet long and by the time your ears have figured out its there, its bounced all over the room. 

Many recordings these days have bass well below 40Hz. You can spend a lot of money on speakers that are flat to 20Hz (like mine) and still not have proper bass at the listening position due to standing waves. Its a problem I had to deal with. 

The ear has a sort of tone control built in. If bass is lacking, even though the rest of the frequencies are flat, the system will sound tilted towards the highs. If there is too much bass the highs can sound muffled. So if you get the bottom end right, an immediately audible effect is the system will sound more relaxed and realistic.

That is why subs are so important. 

@atmasphere 

+1. Again.

@sounds_real_audio 

If you decided to get subwoofers, maybe consider Audio Kinesis The Swarm as multiple subwoofers very beneficial to smoothing out room modes.

I use the Swarm subs as well and can also recommend them. That despite the fact my main speakers are flat to 20Hz. That meant I only needed a pair of the Swarm subs to do the job. What I like about them is they are designed to sit directly against the wall to take advantage of the room boundary effect, which allows them to be compact while flat to 20Hz and out of the way.

As do I. Again, extension and a reduction in room modes. I think it is the ultimate approach.