Alright, in all humbleness and humility here, I'm going to pipe in here, adressing many of the views expressed here on the subject. I've built many-a-high-end custom theater over the last 10 years, and have probably hooked up more systems than 99.99% of the people ever to post on this sight. I do consider myself quite accomplished and dedicated regarding making systems sound even to world class standards, and have just plain been an HT junkie for many years, as well as high end guy all around. Needless to say, i like to think I'm somewhat the expert on making things sound better than anyone I've meet when it comes to putting systems together correctly.
Anyway, my input on the whole "which crossover setting is best" issue is that, yes unfortunately, it does often depend on a lot of varriables you have to work with!
I'll start with some considerations that are really mandatory, and which in a round about way get to the issue here none-the-less.
First, You really need enough subwoofer(s) or ACTIVE bass woofers for the room/system you're putting together! This will have a lot to do with what bass is going where, in regards to proper bass output. That being said, I find most people "under-sub" in modest sized rooms, or they have their(likely) "underpowered/undersized" sub playing higher than it comfortably can! The answer there is either to get more sub(s)(and learn how to place and set them up to be coherent and balanced in the system their in), or place the smaller sub towards/in the corner to get more boost and efficiency from it by letting the room boundaries help(considering EQ'ing in that situation is a big plus indeed!).
Now, let's say you have that issue adressed, and have enough(very necessary) sub(s) for your room, there are other concerns that are magnified by the fact that most people out there are at the very least using lower powered receivers driving passive speakers! But even when considering separates driving even larger FULL RANGE monitors in most peoples systems, still, the inefficiency in most any amp to drive most lower efficiency/sensitivity home speaker makes it even that much more critical to do some BASS MANAGEMENT AND PROPER ALLOCATION!
To simplify, I find that it becomes mostly mandatory to take the bass and dirrect it where a more capable ACTIVE SUBWOOFER(S) can better handle the very demanding bass that's recorded on these digital movies!
There are many many many people out there who are running there FULL RANGE SPEAKERS as LARGE on their pre/pro's, quite contrary to what THX dictates. Yes, it's loosened up a bit over the years, but WHAT WORKS WORKS! (See: "if it ain't broke, don't fix it!"). THX spent hundreds of thousands of hours finding out what works best, and there's a reason for their 80hz crossover! Even with very high sensitivity passive speakers (like horn jobbies), getting proper control over the bass driver is better handled by an ACTIVE SPEAKER!(OR WOOFER RATHER)! letting your passive monitors(no matter the size) play only a the top bass portion for speed and ease of handling by your amp/receiver/whatever, and letting the subs handle bellow 80hz, makes for a much more dynamic potential in a sound system!(note: they even use this setting in large commercial theater!). So, in short, if you do run most domestic home speakers full range passivly, and just have the sub "filling in the bottom octave", you're most likely encountering mushy, slow, distorted, bloated, rather "less dynamic" bass response, all things being equal...that's what I tend to find. And I've dealt with just about everything you can imagine, in every setting!
Now the exceptions to this would be where just don't have dedicated woof's, and need to do full range from your speakers, or you are running much more efficient ACTIVE SPEAKERS!(I.E, powered subs built in already, and they're big enough to fill the room with the bass it can handle).
I think if people will just take the time (or hire someone) to properly set up their systems, crossover at 80hz, get the speakers in the right spot for coupling with the room at that 80hz crossover(including subs), and have enough sub to hanle the bass in the room it's going into, they would have some of the most amazingly fast, dynamic, powerefull, hardhitting, coherent, and solid bass they could imagine!!!
Again, I find most people problems stem from first, poor set up, room, and tweeking/calibrating, and second ill conceived equip!
Now, to adress many peoples findings(especially in smaller rooms with lower ceilings, or even very very tall ceilings) where they get a rather weeker bass problem at the "crossover" setting from their subs and satalites, what that problem is a "poor coupling" with the speakers (including sub) at that frequency in the room!!!(This is very often the problem many people get with smaller THX SEALED BOX MONITORS, that need to be carefully placed to play down to 80hz in a room) If you just get those speakers COUPLING WELL at the CRUCIAL CROSSOVER POINT, you will have no such problem!(note: this is easier for most people to get in extremely large acoustic spaces, such as commercial theaters and giant rooms!). Still, if you just play your test tones and/or fiddle around with speaker placement and listening, you can solve this issue! At first try, many poeple will stick their speakers in ANY OLD SPOT, and find they don't sound good crossed over in certain settings! So, they lower the crossover till they get more bass. Again, if you just get the speakers to couple to the room correctly at 80hz, you'll have no such issues!(i.e, "the hole in the bass syndrom"!) Of course the sub needs to play strongly right up near 80hz as well.
The last point brings another issue, and that's that your subs should play strongly up to 80hz efficienltly, and blend well! However, I find most subs, when set up carefully, can blend up that high, as long as you can blend em coherently with your speakers.
Thankfully, most powered subs are efficient enough, and fast enough up at 80hz to do the trick. Blending the sub with the mains(at the very least, all though not the last word on perfect blend with ALL THE SPEAKERS) up front can handle any of the coherence, localization issues most might encounter as well(then you gotta balance, equalize and tweek!)
Still, in a round about way, as you can tell, I gleen towards tHX's recommendations when it comes to bass managment! I think this set up gets too bad of a rap with most novices because they know NOTHING ABOUT PROPER SPEAKER SET UP IN A ROOM!!!! They stick speakers where they THINK THEY SHOULD GO, instead of where they sound the best!(bass is the single most placement critical element for speaker and seating placment!) I've played way way too long with many other set-up's, and however it does sometimes vary depending on gear/room/system, etc. Still, not deviating from this in a proper set up system(sadly, most peoples system never is) is the best way to go with most all combinations of gear and room settings most people will ever deal with!
Receiver/sub/sat systems, floor standing speakers/receiver/sub systems, even separates/full range/sub systems will all have the best potential dynamic range most offten if you set em up right in the room, and have enough ACTIVE SUBS to hanle the bass chores! Trying to get more bass being handled by passive speakers playing full range from each channel, will yeild a less controlled, fast, and authoritative bass sound to your sytem...overall, weaker! That's what I find anyway...too each is own however.
I, as an audiophile also, know far too many people who still insist on running their audiphile full range speakers, well, full range for movies with no sub!!! It's never as good, trust me. Yeah, your sub may not be as fast for less dynamically demanding music material as is the bass woofers in your expensive audiophile main speakers, but then those can't handle the EXTREMELY demanding dynamic digital bass recorded in such movies as THE HULK, Lord of Rings, Matrix, Dare Devil, whatever!
Try what THX recommends, and do what I recommended, and I think there's reall no way you can't like what you hear!..especially all you people running receivers with full range speakers!...really gotta cross over...your system will become that much more efficient and dynamic
Peace
