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

You don't NEED a sub, but you may want one. Suggest that you buy a Hsu VTF 15H Mk 2 in plain black for under $1,000 (costs another $150 fro wood veneer finish) and see how you like it. Strongly advise that you add a second one when you can afford it.

The ATC SCM40s have low frequency extension as good as any three-way speaker of their size and better quality bass than than nearly all at that price point. I know that model. The specifications ATC provides is a bit misleading because their speakers are tested or the specs published differently than others.

I too would recommend an audiokinesis system if you want to go down that route. I have heard it. It is very good, affordable and lends itself to setup success rather than frustration. Otherwise a sub would be way down on my list of rabbit holes.

So what does anyone think of the idea of using a Loki as a very inexpensive experiment to see if more bass even suits me. I know it won’t be the lower register bass and there are plenty of other differences between this and a sub.

Think you just answered your own question. Why even bother? You’ll be missing many of the benefits of adding a sub(s) so really what’s the point, especially when you can try actual subs in your system absolutely risk free? I frankly don’t understand the hesitation.

To the OP, mild curiosity has now reached the point where you NEED four subs and people just don't understand why you're hesitating.  


If you want more bass, then EQs can do the job.  If you want deeper bass, then a subwoofer is your tool.  Keep in mind that there really isn't much musical content below 40Hz on most recordings.  On most popular recordings over the last 60 years, bass was in the 50 to 160Hz region.  The lowest note on a 4 string bass guitar is 41Hz, but it's fine if your loudspeaker doesn't go that low because the low E note has a large amount of overtones that fill for the fundamental.  Reading into many of the comments above I suspect people are setting the level on their subwoofer(s) so high that they can hear the subwoofer.  It's can be impressive, but it's not very accurate.

It is simple, 99.9% of systems improve with subs.