Why I prefer to sub. Compare a standard 2-way mid/woofer to a dedicated sub's woofer. The difference is plain. The driver which puts bass and midrange on the same cone to meet its ~2kHz tweeter isn't a beast-mode specialist for just bass. It's a more generic do-it-all. Being passively driven, it then inserts a filter between itself and the amp; plus speaker cables and their connectors. The active sub's woofer direct-connects to its amp for superior control and power transfer. Its filter precedes the amp. With a passive speaker, the choice of amp comes down to best overall performance. With a sub, its amp is optimized for just bass. That tends to mean very high power, very low impedance and high damping so routinely class D. When bass activates and its driver/amp combination allows, the designer can apply EQ to get more bass extension/linearity from a far smaller box than a passive speaker could. The vast majority of active subs also include a separate volume control. This allows end-user tailoring of relative bass balance to room and taste. But there's more. If the main speaker gets actively high-passed, we remove LF stress from its mid/woofer's or woofer's voice coil. Less voice-coil heat means lower voice-coil impedance. That means less dynamic compression. Particularly with 2-ways but in my experience even 3-ways, this demonstrably opens up their main driver, in the case of 2-ways all the way up to their tweeter. That's a lot of bandwidth. Because large bass excursions no longer factor, neither do typical distortions associated with them. In short, bass-filtered main speakers play cleaner, bigger and more dynamic.
The bass reach of instruments and drums. Synthesizers and very large church organs can go lower.
The obvious proviso is that the sub's high-pass filter—if there is one—may be of insufficient quality. Now the discerning shopper learns that outboard analog crossover options are scarce. Also important to consider is the aforementioned DSP latency of modern subs. As an often dark spec, it tends to go unpublished so must be ascertained by direct query. Some subs account for this with selectable mains delay. You enter the placement difference between sub/mains into a menu and DSP delays the analog high-pass signal for perfect time alignment regardless of setup. Of course now you're committed to using's the sub's A/D-DSP-D/A path to filter your mains; or an equivalent pre/pro's. This may or may not be attractive. It's why I opted for external pure analog filters.
The musical benefits of properly integrated subwoofers often surprise novices. They only expect the obvious lower louder bass; and often in garish excess to boot. More bass is actually a lesser of the attractions though certainly figures particularly with synth bass that's often beyond the full grasp of passive speakers. That's especially so when it's been recorded at very low levels for more felt-than-heard moodiness like infrasonic pedals.
The actually most significant improvements I hear are bigger more audible space which determines music's subjective scale and gives more venue cues for higher realism; superior dynamic expression and contrast all the way into the midrange when the mains high pass; and more listening satisfaction and fullness at far lower volumes.
A side but very real benefit is that because the main speakers no longer need to do real bass, they can be a lot smaller. That tends to be cheaper—or better relative to a more full-range equivalent for the same money—look better and create fewer psychological barriers. Now there's less visual mass obscuring the soundstage which our ears insist is peopled by musicians but our eyes know is occupied by speakers which front certain performers. Our brain is very clear that two physical objects can't possibly occupy the same space at once. To my mind, small speakers cause less fuckery to be a sterling example for when less really is a lot more. Subs can shrink our speakers.
Of course if you go after a stacked dual 21" 260kg carbon-concrete sub monster scaled like a fridge—hello Betonart Tyrexx—that notion shatters despite the suggestive female worship in their photo. Now today's compact becomes far more practical particularly when set up as designed. Firing up, the SB1's profile is a real low rider of which you'll see quite little from the chair. It certainly won't obscure virtual performers. So there's a lot to be said for compact subs that can traverse the terrain at the required SPL down to 20Hz to deserve the subwoofer prefix. HT fans may demand lower but as the above graphic showed, for music it's only occasional synths and the largest of pipe organs which dig past 28Hz. [Above left, docking between the LS1 legs.]
I wasn't kidding about a subwoofer shrinking the mains.