How do you know if you need to add a sub (without auditioning one, I mean)?

With all the speakers I auditioned before buying, I tried both with and without a sub. With some speakers -- big towers like the Focal 948 and Martin Logan ML 60 Xti, the single large driver REL sub I had didn't do all that much, not even for imaging, etc. If I had had a sub which could really reach down there -- 14 hz or 20 hz, then what @simonmoon said about atmospherics would probably have become evident.

That said, every other speaker I listened to was improved by a single sub. Bass notes appeared, image and soundstage enlarged and got more definite, and (most surprising) the tonal richness of mids and upper frequencies were altered in a good way. I'm now on my way to stereo subs before, one day, going with a swarm.

As for price, I think there are good options out there and some have been listed already. I think you could likely get set up pretty nicely for under $2k for two.

hilde45,


Did you run your mains full range or with a cut-off?  Are you running room correction?   If so, the mains may have been driven less hard with the subs reducing distortion.

Which subs have high pass filter outputs that go to the speakers, to relieve them of reproducing very low frequencies?  I could see how that would reduce distortion.  An extra active crossover is too much cost and complexity for me.

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!

Sound meter (you can use an app on a smartphone) and white noise as a source ( available to stream via internet).

If you do not see response down to 20 hz, you are missing the lower octaves that you should be able to hear and a proper sub would be the remedy.

Use the same app and white noise to adjust the sub to proper level and crossover frequency if you get to that point.