Frequency Range - Bookshelf Speakers

For a 2-channel stereo system, which consists of a pair of bookshelf speakers and a powered subwoofer, what difference does it make if the bookshelf speakers go down to 70Hz vs. 30Hz (or anything else in between)?
my experience with totems and morels is that the less`you rely on the sub the better. sounds fuller to me. however, your electronics effect it alot. the integration question looms as does quality of sub at higher frequecies.
In my experience, the lower your speakers can go, the more flexibility you will have in adjusting the sub's crossover. This can be really important for good integration of your system with the accoustics of your listening room.

This applies to floor standers as well as stand mounted speakers.
I'm not sure too many bookshelf speakers can go down to 30Hz. If they can, and you are just using them for mostly 2-channel stereo music listening, I think it would be better to skip the subwoofer altogether.
I have Usher S 520's and a Outlaw LFM 2 (8") sub. The Usher's bass starts to roll off around 70hz and goes down to about 50hz. I set my LFM's crossover at about 60-65hz and thus achieve a smooth transition from the Ushers to it for the lower bass. I don't have a "bass gap" iow.

BUT: I usually don't even use a sub with my Usher's unless I'm watching a concert DVD or movie. Because even though the Usher's "only" go down to about 50hz, I find that more than enough. I am using them in a fairly small room, but they in no way have trouble filling it or sounding thin.

And it's good that the Usher didn't try to force the 520's bass lower, because then it would be a "fake" bass that won't sound right and start to mess with the musicality and clarity or the "real" bass. You'd have the lower mid range and upper bass more pronounced to try to make the speaker sound like it has more bass than it really does, and then you will undermine the accuracy of the bass articulation. I'd rather hear the growl of the bass guitar and tight beat of the drums that isn't overpowering but honest than a warm mush of false bass that sounds big and bloated since it's really just overdone lower midrange and upper bass. You can't alter physics iow.

So I'd be wary of any bookshelf speakers that claim to go down below around 50hz, or at least below 40-45hz. They might be playing with specs, or they might be comprimising sound quality in an effort to attract more "bass heads".

My advice: don't worry about how low bookshelfs might go, worry about how well they sound. Then choose the best sounding one (tested yourself or from reviews) and if it doesn't go low enough or produce enough bass for your preferences, then add a sub. This may be more expensive than buying all-in-one bookshelfs that supposedly go from very low frequencies with a 5" or 6" or possibly 8" woofer to very high frequencies with their tweeter, but the system will likely sound much better.

You might also find you are satisfied with just your bookshelfs, I am. If I could go back I wouldn't have spent the money on a sub, since I don't use it much. And I thought, at least, that I was a bit of a basshead. Guess not, I'm a "faithful musical reproduction and balance" head lol.
The differences are that,
* the (purported) 30 Hz model's performance will be much more stretched
* the 30Hz bookshelf may interfere with the subwoof, thereby compromising integration.
* bookshelves reproducing 50 Hz & lower, in tune & time & as loud as the rest of the spectrum, are. Go for the 70Hz model.

There are many more differences, but these seem simplest. Regards
I've tried, TRIED, I tell you! ... to properly integrate a sub with bookshelf speakers. In my experience (for what that's worth... not much), you don't want a monitor going lower than around 60hz or you start messing with serious room modes, etc. around the speaker/sub crossover and it's near impossible to get a good result.

The best scenario I've found is to get some good monitors that go reasonably deep and forget the sub; unless you're a fan of pipe-organ music, of course. Deep isn't the only criteria - they must go deep enough (~45hz) and be articulate in that region.

The Usher X-718's (-3db @ 42hz) I currently run fit this bill exactly and I don't miss the sub at all with rock nor jazz.
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Bob is right, again. I personally like subs. You can put the bass anywhere you want for the best integration and let the monitors handle the rest. It will depend on the monitor's drivers and crossover as to the quality of the midrange. Better that way than to try to make a monitor play frequencies below 60 Hz. The sub may be localizable if it plays much above 80 Hz or is too loud. I prefer a monitor that is allowed to play full range and a sub that you can change the crossover, and phase. Its your best chance to integrate it without it being noticed.
Agree with Bob, again.
Vinyladdict said "If I'm sending everything below 60 or 80hz to ONE sub (essentially mono'ing below 60 or 80hz... probably 80) should I have no problems with "woofer pumping" and subsonics?"

Did eliminating the subwoofer affect/help this problem? Do you still have rumble or subsonics without the sub? Could this be another reason not to use a sub? To eliminate modal response problems and inherent vinyl "noise" (subsonics and rumble).

much of this depends on room size and musical genre. imo using l/r monitors that on their own can't do a pretty good job on fairly deep bass, say @50 hz is not logical. depending on who you rely on for info, most bass is non directional below @150 hz. a speaker so small that it cannot produce lower harmonics without relying heavily on a sub is gonna sound off without some incredible fine tuning. if you know of a small spkr that plays flat down to 30 hz let us know because unless you have a BIG listening room or crank pipe organ and tuba you have eliminated the need for most subwoofers. i love my sub but just set it at low x-over...monitors with no decent bass just do not cut it in the realism dept with me.
My AAD 2001 do.
Excellent monitors but need muscle ( I would say 100wpc minimum - quality too ).
The bass is quite amazing for its size. Speed is another area where AAD 2001 excel. Having Martin Logans for almost 8 yrs can leave permanent hunger for speed and transparency. They are very comparative with ML in that department tho.
My priorities have change as well as amps around my house (SET, Low power PP tube and SD speakers).
They do not get much use lately for lock of space and adequate amplification ( I've nice vintage SS Accuphase integrated but needs some work).

I have a pair of Totem Mani-2's that reproduce deep bass very well with proper amplification. Actually it is amazing how clean and deep they go but I find that integrating my Sunfire sub crossed over quite low so that I cant "hear the sub" adds to the overall sound of the music. If I turn up the crossover it becomes a set of speakers and a sub, much less coherent. The room size is 20x14 and that has a lot to do with bass reproduction, as was mentioned.
Acoustat6 - wow, took me a minute to figure out what you were talking about! FYI - for anyone else, the quote Acoustat6 attributes to me is from an old post unrelated to this one.

The short answer is that I've never really had any problems with subsonics and rumble. In fact, the phono preamp I now use (PS Audio GCPH) has built in subsonic filtering so I don't even think about it. The old post you quote was simply me "thinking out loud" and curious.

That being said, I've found there is rarely much musical information below around 40hz unless, as I originally stated, you're a pipe-organ fan.

In measuring in my room, I found that introducing a sub impacted other areas of the musical spectrum in a negative way even when I had it crossed over in the 30hz range. I simply could never get good results. I'm not saying others may not be able to in their rooms, just simply speaking from experience in a small squarish room.