Yeah really, a good subwoofer/speaker should have no problem playing "accurately"(relative term) up to 80hz! I know I've read and heard many many many times where reviewers talked about the sub they were discussing not being able to play as well up to 80 hz! THIS IS MOSTLY NOT AN ACCURATE ASSESSMENT OF WHAT'S REALITY for many situations! Many subs do just fine, even superb at being played hard up to 80 hz and beyond! There becomes problems with dirrectionality and lack of coherence with the main speakers they're crossing over too, as well as poor sub placment in the room, and improper level matching and such at those frequencies however!...Again, user error!
I will conceed that MANY, YES MANY subs are built to be able to take and playback the much more demanding(less accurate musically i'll conceed) dynamic and synthetic sound from movie soundtracks! This becomes a power handling issue. Thus, they are built with a lower "Q factor", or tightness paramater compared to many music woofers built into many speakers!!!...yes! I know that.
Still, there are NUMBEROUS SUBS THAT NOT ONLY HAVE EXCELLENT EXTENSION, BUT ARE VERY TIGHT(high "Q") and accurate as well! Many THX sub's are such, like M&K's superb MX200/350/5000, etc. Paradigms Servo 15 and PS1000(budget) are very tight and extended!! Infact, for the money, you CANNOT BEAT THE SERVO 15 FOR EITHER MOVIES OR MUSICAL ACCURACY AND IMPACT/EXTENSION FOR THE MONEY, PERIOD! I've found no better sub at this price EVER!!! The higher-end Velodynes are ok. But an other turely dynamite all around woofer is the Earthquake...yes! But there are many others out there at different price ranges and budgets, that have no problem(if set up correctly, which is the downfall of most, conceeded).
The reality, regardless, is that, even with some SLIGHT compromises in some "looser" designed subs, FOR MOVIES AT LEAST, the compromises and trade-off's out-weigh the disadvatages of a potentially truely "accurate" bass note at and around the 80hz range! I mean you can still get truely superb results sonically with a lot of care taken. And I think the advantages out-weigh the con's!
Still, that said, you can negate any real aregument in the debate of letting your more "likely" musically accurate bass woofers in your mains vs. crossing down to a woofer in the HIGHLY DEMANDING BASS reigion for HT, by simply getting one of the better subs!
Think about it..if you were building a subwoofer with a built in powered driver, there should be no reason to think you couldn't design a woofer with better control and accuracy than what an equivalent sized woofer in your speakers offered! This is handled much more commonly by powered full range speaker designs, like those offered by Dunlavy, Infinity, NHT, Paradigm, Avantgarde, Phase Tech, Snell, Linn, Klipsch, JBL, and many others! The woofers in those speakers in mention, are very very dynamic, fast, coherent, and well integrated!..there's no reason to think it's not possible to properly set up an external woofer to do the exact same job, with the same results with proper care and know-how!!
Still, again, for what movies are demanding dynamically, even if you are chosing a less than optimally accurate subwoofer design for your system, crossing over the work to the sub still outweighs any dissadvantage you'll likely need to consider for movies!
Now if you like to listen to your much less dynamically demanding music material "full range" through your speakers, then you can always drop the sub, and have no worries! But for what you need for "thill factor", "impact", authority, dynamics, etc from a movie soundtrack, you simply are making a major mistake by not allowing that all to play properly through your system, by not letting the powered sub handle the dirty, and highly demanding bass chores!!...and that includes up to 80hz I'm affraid.
But, if you are affraid, then just go buy one of the better more accurate subs (paradigm PS1000,Servo 15, M&K MX series, Thiel's expensive sub, Velodyne's HGS(OK), Earthquake Supernova's(superb all around), etc, and you'll have no problems if you set up up right!!!!
I must mention something that I've known for years however regarding bass and overall potential "dynamic transparancy" from a speaker system! That being that passive design speakers and external (even high powered) amp set up's really can't reproduce an accurate(again, relative term...as nothings perfect) and "totally dynamically transparent" pressentation!..especially in the bass!!!
I've known for years, as do many speaker makers, that horns, and active drivers do a much better job of reproducting fundamentals closer to "true dynamic transparancy" with all likely sonic info that's likely to pass through the system! True dynamic control, and thus "accurate playback" of info, from say the bass region, requires as much power and as high of a damping factor as possible! Given most passive speaker systems inability to adequately provide control over the rather inadequately "underdamped" passive crossover network/driver configurations, the lister, ESPECIALLY WITH "UNATURAL" SOUND EFFECT RIDDLED MOVIE MIXES, has to listen to a rather less than optimally dynamic and transparent sonic pressentation, due to physical restraints of the playback system! Again, every time I hear a much more realistic and potentially accurate bass program from "active speakers", much more highly efficient speaker systems, and "active powered speakers" in general!!!! It's just the way it is.
So, for me, any time I can get an active woofer/driver in play, I try to do so if the trade-off's don't outweigh the benefits!
I think, for most peoples peice of mind, they would be better running their audiophile speakers full range for their more likely "less dynamic" music needs, and cross over to the sub to handle the "unreasonablly dynamic" digital movie information! Because inevitably, you know people are going to be facing compromises...I just think doing with I mentioned limites the compromises, and maximizes the benefits and effectiveness of the system for the needs!
It's all good though....
