I'm in the unique position of maybe being able to help shed some light on this long running debate once and for all, as I actually have both at the same time now. I know there have been others also. I know Faster did, and I think I saw where dholmes or airplay (or somebody) did too. I'm sure that there are probably a few others as well that I either do not know about, or am not thinking about right now at the moment. However, I can do a fully subjective review with them both, in my home on my equipment, and with no emotional attachment or involvement either way to either one to defend or try to justify a buying purchase decision I made, most of all to myself (as some here may very well have even if they don't want to admit it or even realize it or not), because, well, let's face it, I've bought them both, and I can call it like I see (or a better word would be hear) it.
To me, when I audition a speaker, I do it first and foremost as a 2 channel music speaker (unless it's a fxi or something like that). I know some people here say "Well if you take a 70, high pass it and add a SVS, and if you do this, and if you do that, and yadda yadda yadda, blah blah blah blah blah, and freakin' blah", but to me, any speaker I consider to be worthy should be able to stand up on it's own as a good 2 channel music performer before anything else.
So, with that said, I took a pair of the 70s and set them up right beside of the 150s. Then I unhooked the Adcom GFA 5400 amp (125 watts per) from the 150's tweeter/midrange set of 5 way speaker wire binding posts and hooked it up to the 70s. Then I reinstalled the jump straps on the 150's, and left them powered by the Adcom GFA 5500 amp (200 watts per). Now, admittedly, the 150s had more power driving them, but the fact is, they need it. If anything, the 70s probably had even more power driving them based on actual needs and requirements than the 150s did. Also, one other factor to consider is that the 70s don't have as many hours of break in time on them yet. I know some people here may or may not put a lot of stock into that theory, but I personally do myself. However, I will admit though that I could very well be wrong here, as it may just simply be a case of someone's ears adjusting or adapting to a certian speaker's sound over a period of time. I then tried to adjust each set of speaker's placement to get as good of sound as I possibly could out of the both of them, while keeping them side by side. Ultimately, setting the 70s right beside of where I originally had the 150s proved to be the best. The 70s were both to the immediate right of each of the 150s, about 6 feet apart, angled in slightly, approx. 3 feet from the rear wall, and approx. 7 feet from each side wall. Also, I adjusted the SPLs as close as I possibly could with a Rat shack meter to A/B compare them to each other. CD player and preamp were both also Adcoms. Some CDs I used were some of my old standbys, such as AC/DC, Ted Nugent, Pink Floyd, etc. I also even grabbed one of the old lady's Carly Simon Cds just for something different.
Well, all I can say is , WOW! Man, some of you you were right all along. The 70 is so much superior it was unreal! It really is the world's greatest speaker of all time! Having that extra passive mid range driver truly was such a big, huge, dramatic, mind bending, orgasmic, earth shaking, jaw dropping, unbelievable, drastic, night and day difference that is almost like a religious experience where you can almost see GOD (somehow, I now know how Chocolate Thunder Darryl Dawkins must have felt when describing one of his dunks)!
Sorry, I just couldn't resist. In all total seriousness, I felt that the 150 was the better of the 2 (not that the 70 was bad though, as I want to clearly point that out). The 150 obviously had much, much better bass. That aspect of it wasn't even close. It was a landslide difference of Nixon in the '72 election type proportions on bass output. The 70 may have had slightly better mid range dynamics, but I really couldn't notice it all that much if it did. I know some people here have said that they think the 70 is brighter, but I really couldn't tell it when trying to concentrate just on the highs. I think maybe it's just more of a case that people notice the 70's highs more because they are clearly accentuated more than the 150's because of the difference in the bass output. I will also concede though that I have probably lost some high frequency hearing over the years after being exposed to much, much loud rock music, gunfire, jet engine noise, and wind noise from riding a Harley. To my ears anyway, both speaker's tweeters are silky smooth, and IMHO, a big improvement over the old Tri-lams.
Bottom line, the 70 may have slightly better mid range dynamics, while the 150s defintely have much more obvious better bass. To me, in a 2 channel (full range or large) music set up, the 150s are the best speaker that Polk makes in that particular series. It just has the best balanced sound over the full spectrum. The new 12 should have the best of both worlds, the mids of the 70s AND the bass of the 150s.
Another bottom line though, and this is simply stating the obvious, this is really more of an apples to oranges type of comparision. The 150s very well should be the better "large" speaker, if you have enough power to properly drive them (as I most definitely do). The 70 is obviously the better choice if you have a receiver in the 100 watt or so per channel range and can run the 70s high passed along with a good subwoofer. Only a Stupid, Idiotic, Dumbass (which, coincidently, also happens to be Sid's intials) would buy the 150s and then run them high passed IF IT WASN"T OUT OF SHEER NECCESITY BECAUSE THEY DON'T HAVE A POWER AMP CAPABLE OF DRIVING THEM (I capitalized that to make it clear so that I wouldn't offend anyone who is running the 150s high passed out of sheer neccesity, however, if you are doing that when you do have a suitable amp, then you deserve to be offended). As a side note, I'll bet that if Sid had 150s, he would high pass one of them, bi-amp the other, and then stack one 35 on top of one of them.
So, even at the closeout prices on the 150s, unless you already happened to have enough amp power for them (as I did), it still might not have been worth it if you then had to then go out and buy an adequate amp for them that could run into hundreds of dollars more. I think it's safe to say that in most (but not all) cases, the 70 is the better choice. I think the 70 is more of a high passed, receiver and sub based speaker, while the 150 is more of a 2 channel seperates based speaker. Again, that is pretty much just stating the obvious. However, bottom line, as a 2 channel music speaker with enough power to properly drive them, the 150 is better than the 70 to my ears, and frankly, I don't see how anyone else who heard what I heard would say otherwise. Either way though, 70 or 150, you have a quality speaker that you can be proud of!