Hello jazz99,
For your situation, I'd suggest the SVS SB1000 (12"driver in a sealed box) would be the better choice than the SVS PB1000 (10" driver in a ported box) although either would provide a dramatic improvement over not using any sub with your Focal Aria 906 speakers.. They're both priced at $499 and are powered by the same 300 watt class D amp.
The PB1000 is slightly larger and generally considered better for movies and the SB is slightly smaller and considered better for music.
Your Focal bookshelf speakers on stands are only reproducing bass down to about 55Hz. The human audible hearing range is 20Hz to 20,000Hz, with 20Hz being the lowest audible frequency and 20,000Hz being the highest audible frequency.
Your current system is reproducing none of the frequencies on your music between 20Hz and 55Hz. Adding either SVS sub to your system will fill in this gap and you'll be amazed at what you were missing. I believe the SB1000 sub will reproduce bass frequencies in this missing frequency range more accurately and integrate more seamlessly with the sound frequencies reproduced by your Focals than the PB1000 sub can.
For best bass response in your system and room, it's also very important to properly and precisely position the sub in relation to your listening seat. Here's my suggestion of how to do this:
1. Disconnect your Focal speakers and place them and their stands temporarily outside your room. You can mark the positions of the stands on the floor (colored tape works well) or just optimize their positioning as a final step in this procedure.
2.Hook up the sub and place it at your listening position.
3. Play some music with good and repetitive deep bass.
4. starting at the right front corner of your room, walk counter-clockwise around the perimeter of your room and determine the exact spot where the bass sounds best to you. This is a critical step, so take your time and walk the perimeter multiple times if needed to find the precise spot that the bass sounds best to you (natural and detailed without being over-emphasized or attenuated).
5. Reposition the sub to the exact spot the bass sounded best.
6. Sit on your listening position seat and replay the music with good and repetitive bass. Verify the bass now sounds just as good here as it did at your identified spot. If it does, your sub is optimally positioned within your room. If it doesn't, you'll need to repeat this procedure from step#2.
7. Reconnect your Focal spkrs and place them on the stands at the marked positions or reposition them again in relation to your listening seat for optimum tonal response and imaging. I'd recommend running your Focals full range and connecting them to your amp as usual rather than connecting them to the SVS sub. There's also no harm in trying both methods and using whatever method you prefer.
8. Set the desired low frequency cutoff frequency on the SVS sub. This is an important step with the goal being the smooth and continuous blending of the sound from the sub and your Focals. This will probably require some experimenting with the ideal cutoff frequency likely being somewhere close to 55Hz.
I believe an ideal cutoff frequency setting could be determined mathematically if we had all the relevant data but you're likely to arrive at a setting that's very close just doing it by ear and what sounds most seamless to you. Try to avoid creating any holes in the combination's frequency response.
My opinion is that, when you have everything positioned and configured properly, anyone listening to your system from your listening seat will just assume you have the best sounding pair of bookshelf speakers they've ever heard.
Lastly, I want you to realize that this system will sound great from your listening seat but there is a compromise that cannot be avoided when only a single sub is used; the bass response will not be optimized at multiple other specific spots in your room. Less discriminating listeners will probably not even pick up on this unless they're sitting at a spot in the room where a bass mode exists.
Bass modes are specific spots in any given room where the bass will sound exaggerated, attenuated or even absent. I can explain bass room acoustics in more detail but I'd like to avoid turning this post into an even longer book.
There are bass systems that eliminate the vast majority of bass modes existing in a given room which results in very good bass response throughout the entire room but they're more expensive and require more subs. I use one of these systems, called a distributed bass array system, but I think it's too expensive ($3K) for your budget, more elaborate (4 SVS SB1000 sized subs with a separate 1K watt amp) than is practical for a small room like yours and not necessary if you're content with optimized bass response at a single listening position.
Hope this helped a bit,
Tim
