Thanks for the responses so far. Is there a consensus as to how much one
needs to spend to get a decent sub that really makes a difference? I’m
not saying I want to spend the bare minimum, I’m just interested in a
basic parameter.
There are plenty of great subs. In smaller systems I've really enjoyed the SubX from Goldenear.
But one thing you'll run into right away in most rooms is standing waves which will make the use of one sub hard to do and likely causing the sub to be inconveniently placed. These are bass notes whose wavelength is significant- under about 80 Hz they are over 14 feet long. Such a wave can bounce off of the wall behind you; at certain frequencies when it comes back to the listening chair will cause a loss of bass energy as it can be out of phase with the incoming waveform.
I know Erik gave advice about using room treatment and room correction for this problem. In a nutshell, it will make little difference if bass is being cancelled by standing waves!. When bass is being cancelled, room correction will ask the amp to make more power at that frequency, and of course that power will be cancelled- you'll have the same problem and the amp will run out of gas. Room treatment won't fix it either, unless you're able to have the bass traps actively move about the room as the bass notes change :)
But there is an elegant solution, and one of the best ones isn't all that pricey. I'm referring to the use of a Distributed Bass Array (and the best example of this is the Swarm from Audiokinesis.com). A DBA uses four subs placed asymmetrically in the room. Because the wavelengths are so long, bass below 80Hz is omnidirectional- you can't tell where its coming from. Its the harmonics of the bass notes from your main speakers that allow you to place the source in front of you. So in a DBA, with the bass coming from a variety of directions, the standing waves are broken up, causing the bass to be evenly distributed around the room.
The Audiokinesis Swarms are designed to be placed directly against the wall so as to take advantage of the room boundary effect, which is +3dB per octave going down from 100Hz or so. In this way the Swarm subs can be fairly compact as they are designed to roll off at 3dB/octave over the same range. The result is flat response to 20Hz. They need a subwoofer amp but Duke at Audiokinesis can guide you on that- its not expensive.
As long as the subs are not making any output above 80Hz they will not attract attention to themselves. So they should be crossed over lower, maybe at 50Hz or so. In most rooms this is insanely easy to set up.
After this is done then Erik's suggestion of room treatment and the like is useful but not before!
