Two subwoofers for two channel music listening

More than 2 SUBS, SWARMS. Sacrifice Directionality for Extension?

People who want very/extremely lows produced cleanly will use more than 2 subs, sometimes multiple ’Swarms’ which has been discussed here. I’ve never heard that except a swarm of bees chasing me, and that is directional, i.e. run this way.

Swarms, more than 2 subs get super lows, however the results are MONO BASS, even the upper bass will be mono because the fundamentals and overtones emanate from too many locations, and reflect off too many surfaces..

Some use ported mains and/or ported subs. I recommend only front firing ports, again to retain directionality.

I much prefer decently low bass with imaging than a bit more bass.

In my exuberant youth, I, with help from Electro-Voice Engineering department, designed these enclosures with optional ports, to squeak more bass from these 15", which I measurably got.

However, they are rear facing ports. Less pressure in the enclosure, the front 15's go lower. Additional output from the tuned port and rear surface of the woofer, that gets to rear wall/corners. Even more extension, but they muddy the directionality of both the extended bas, also all it's output, fundamentals and overtones muddy everything else.

It's a trade off. I keep the ports closed. Why sacrifice directionality of a lot of low content for most of my music to get more bass infrequently or rarely?.

Martin Logan makes a couple of lines of subwoofers and they recommend the line level option over the high impedance connection where possible, though to be honest, I doubt that you or I  would ever be able to hear the difference.
I'm no audio engineer, but I did stay at a Hollywood Express last night :)

It's interesting that the SVS 1000 has both line level and speaker level inputs.  I have the SVS SB 3000 and it only has line level.  But it does have a terrific Bluetooth app to manage volume, xover point, slope remotely. No more continuous getting out of your listening position to tweak the sub controls.  Really comes in handy for music that's recorded a bit this as the Bluetooth app also allows user preset settings.

@ozzy621 - thanks for commenting that the speaker level input doesn't result in an amp driving an amp. Inherently we all should know this can't be as the sound would be horrible. I still don't understand how 'the main amp sends a low level signal to the sub amp' and not full range signal as the main amp speaker terminals are designed to do.
Perhaps someone out there could explain how this main amp speaker output to sub amp speaker input works.

Remote Control of Sub(s) sounds terrific, initial setup from a few listening spots. After that, remote volume would be very nice.

A crossover has to exist somewhere, to separate low bass from everything else. Home theater receivers have built in, and the content coding has separate bass.

2 channel amps for music systems typically do not have crossovers built in. You can use a self powered sub’s built in crossover, that is the method that makes it easier for the amp and mains because they do not have to produce low bass.

A separate external crossover does the same thing, except you have more control of the quality of that device. And you do not need to get any signal back from the sub. Crossover sends lows to sub, everything else (easier job) to the amp(s) which send signals with no low bass (easier job) to the mains. 

http://www.acousticfrontiers.com/three-ways-to-add-a-subwoofer-crossover-to-your-two-channel-system/

Many subs have crossovers built in, some line in, some speaker wires in, some both. If via speaker wires, the amp is still producing low bass, then the sub filters that for itself, and sends speaker wires to your mains. This gives the mains a break, but does not give the amp a break.