your opinion on subwoofers in two channel

postive or negative...should you buy better amps, cables, players, speakers and not put the money on subs?
If you are using monitors as speakers, adding a sub is a must in my opinion. You would get a bigger soundstage and more weight and body with instruments and voices. A sub adds the bottom frequency which in turn helps your middle and upper frequency sound more natural.
I added a sub when I had JM Lab Mini Utopia and could never turn back without a sub. Have fun.
Depends on your two channel audio objectives, for each objective my suggestions are;

Balance of esthetics, quailty & function: get small moderately priced speakers (6" woofers or less, 6 db at 60 to 100 Hz) and a reasonably priced mid-size sub (8" to 10" woofer to cover 30 to 100 Hz). Great sound and looks good.

Pure high end audio: spend your money to upgrade to large expensive accurate LF range speakers (12 or 15" woofers, 6 db generally between 30 and 50 Hz) before ever considering a sub to complement the extreme low end (12 to 15" woofer at least to cover 20 to 50 Hz). Incrementally better sound than above with the drawback of big imposing boxes and significantly higher cost.
interesting thoughts and knowledge thanks i understand what both of you are saying...thanks
I think good subs that can be tweaked in to mate with your room & system do make sense and can add to the enjoyment in a meaningful way. Less adjustable subs or trying to do to much from a single sub can be more of a distraction than a benefit. And it depends on your taste in music. If there is little to be heard then a sub adds little (duhh, ok so that ain't such an epiphany).
To answer your question directly, if I had to choose between better sound overall or adding a sub, I'd take the former, but if I could afford the additional extravagence of one or two good subs I'd go for it. IMHO, YMMV, DEYS.
Can be a good thing if you like the sound of your system for 2 channel music and just wish it had more sub bass. You can enhance the lows without messing up the rest of the system. Also if you don't have the room for large floor standing speakers.

If the smaller speakers have great mids and highs, a really good sub can make them sound like larger speakers costing much more than the cost of the 2 speakers and the sub if you can get them to integrate well. REL subs are pretty easy to integrate.

Back in the 90's a lot of people would match two of the small B&W Matrix 805 speakers with the Matrix 800 sub. It would come close to the performance of the Matrix 801s for those with smaller rooms and/or those who could not afford the M801s. A pair of M805 plus the Matrix sub was about half the cost of the M801s. Probably is still the case with the current B&W 805s and subs.
Sugabrie is right but prices are pretty high,Wouldn't go with a B&W sub or Velodyne etc for music.REL,Martin Logan etc get excellent speed and pitch accuracy by using multiple small drivers.I think that the Vandersteen 2weQ is oine of the best valuies in High fi$800 for one used $1200 (?) new.Has three small drivers that are muiscal where ars unless you spend meha bucks on large driver sub it will be too slow.Cool thing about Vandersteen as well is it's x-over which is designed for you to hook wires together with your satelites at speaker posts'X-over "see's" whole waveform of muisc not just what is low passed under 150 (or what ever) Hrz and results a a suipperior product at a bagain price.Never was big fan of their well selling 2Ci m(* though big ones are good and costly) but subs are so good that many folks get and at the price end up with a apair.I knwo it shouldn't make sense because you are not supposed to localize bass beneath 150 hrz and therfore only need one but hoowk two of them up and you won't want to give it up.NHT made a good two chanell sub.Depending on your speakers subs are worth it oenor two remeber but way to many folks foget the name is SUB woofer and turn them up to loud and set the crosover too high so they "hear what they paid for".You shouldn't "hear" the sub.It should provide a foundation.If you chosee a value amp don't get sucked into cable snake oil and hav smaller two way spoeakers you'll have better imaging than a larger cabinet.Some of the best b\valuies in Hifi seem to be the hybrid integrateds by companies lie Unison and Pathos.Digital get's better and better so my mind is save there and update that when finaces allow.
Hi,, there can be a problem with full range speakers in some rooms because the proper spot for imaging etc may not be the best location for the speakers low frequency performance,,,similar to how a sub has to located in a particular for smooth response.
I second Butsy: full range floorstander may offer you a real placement issue between imaging and bass response (room nodes and standing waves). With a sub, placement is way more flexible and you get the advantage of monitor imaging. $ for $, I would think monitor + sub is a better deal unless you start spending over $7-8k on large full range speakers IF AND ONLY IF both monitors and sub are well integrated (you need a friend and some patience). In the budget category, Martin Logan - even the Grotto ($750 used) is a sweet deal, then REL. If you do not have monitors yet and have $5,000 to spend for both (price new), combo ProAc 1SC and their new sub. Amazing.
I tried for 3 weeks to get two Velodyne DD 10's with room correction built in to seamlessly mix with my Martin Odysseys. Went so far a to hire a professional. It was just wasn't good enough. Sold the subs and the Odysseys, bought the Martin Logan Summits with powered bass. My though not ruler flat is very very good.

My two cents but the money into the best full range that meets your budget.

Save the subs for movies.
I have a pair of PMC GB1s 29Hz-25kHz. Heaven in the mids and highs, just need a tad more low end. I have limited space 15x11 and limited budget, 700.00. What specs in a sub should I be looking at? This is something I do not understand when reading the many threads on 2 ch sub matching...
The main problem with subs is that they are extremely dificult to locate, you can be playing around with them for the longest time, and when you think everything is in order, you turn off the sub while playing music and you realize how much music is being "blocked" by the sub, a lot of information on bass and midbass that is being cancelled by the sub in order to get the whuum dull sound of the subwoofer.
I will try to draw an image of what I am saying, Imagine your sound is like a graph with crests and valleys, when you add a sub you get a line in the center (lower maybe) and from that line you have mids and highs going up and lows going down, but everything around the line is blurry, When I finally located the sub in a "good" position I would get deeper sound, the line was erased and the valley seemed now deeper (a good thing) than with no subwoofer, but beware, I had masking tape all around the subwoofer marking 1/8" movements!!!
My opinion today is that a subwoofer should be crossed higher than 100 hz so you can listen clearly to what they are doing, and be aware if they are messing everything up.

If you are willing to get into this, get subs, with the price a good sub is going for, and the terrible resale value they have, I would recommend changing main speakers for more bass capable ones...
If you use subs the smartest thing you can do is make bass traps for each corner. This will help considerably. No modal ringing plus it flattens the response. Without them bass normally isn't nearly as musical in my experience.

Electronic equalization with a sub is also good as the bass region is where the very large dips and peaks occur. Digital equalization like the Behringer DEQ 2496 will help alot especially if you cannot install bass traps for whatever reason.

Without all of the bass music doesn't have it's foundation. To my ears something is obviously missing and I find it distracting. Honest bass can make a good system much better.