According to the Usher web site these speakers are -3 dB down at 42 Hz, which is low enough to not need a sub.

--Ethan

Will you need a sub? That's a very personal judgement. According to the spec, they are 3 dB down at 42 Hz - the lowest note of a bass or bass guitar. That's plenty for some folks.

Have you read the review?
http://www.stereophile.com/standloudspeakers/508ush/index.html

Unless you listen to a lot of pipe organ or certain types of electronica (both of which can go lower) you should be set.

It all depends on what you consider to be adequate bass. Many folks happily live with speakers that range in the 35-45hz range, while others feel that a good portion of the music is missing and is not being recreated.

I am a big fan of a full range coverage, however, I have never heard a well integrated subwoofer system. I think it's very difficult to effectively integrate a sub within the music system without it having to sound unnatural and drawing undue attention to itself and having a smooth integration/hand off of frequencies to the sub.

I prefer to have full range speakers that go from about 25hz to 20khz and deliver not just deep, but articulate and detailed bass. Given a choice between speakers that don't quite deliver the 20hz range and adding a subwoofer, I would choose the former. I'd rather miss those frequencies than deal with the sub issues, which I find more distracting.

I hope this helps.