Adding a sub - what will I loose?

It seems that adding another piece of equipment to the audio chain would degrade the sound quality to the main speakers (air, immediacy, the mid range, etc). Or am I way off here??

Currently have a preamp with no sub-out and low output tube amp. Plan to use line level to the sub and then out to the amp. That way speakers would not play full range (above 80hz).

Tghooper

What might you lose?

You might lose your mind if you have too much trouble blending the sub with your mains and the sub doesn't have the controls you need to do the blend. Otherwise, adding a sub or two can be very rewarding, especially with a system based on a low-powered tube amp.

There is a lot of advice on this thread on how to do it, and I think most contributors are advocating for what worked for *them*, but it may not be the best for *you*. I've blended seven different sub configurations in four different systems and they've all succeeded but my methodologies have varied according to several variables:

--The room acoustics
--The bass extension of the main or satellite speakers. on full range I cross over at 40 Hz; on some small satellites you may have to cross over at 70/80 or even 120 Hz.
--The I/Os on the sub--single LFE line level, stereo line level, stereo line level I/O, speaker level, speaker level I/O
--How much phase control the sub has; some have none, many have just a 0-180deg. switch, some have a 3- or 4-way switch (0, 45, 90, 180 deg.) or continuously variable (my latest have 0-360 continuous)
--Crossover control--hopefully continuously variable from around 40 Hz up to 80, 150, maybe 200

Conventional wisdom says that you get more dynamic range and more amplifier efficiency by using a high pass filter to the stereo pair (mains). No doubt this can be true in some cases with careful crossover matching and placement and/or phase setting, but in my own experience I get a better blend by running the mains at full range and blending in the subwoofer at the lowest possible crossover point. If the crossover point is too high it starts making vocals and some lower midrange/upper bass sound thick and murky.

This also flies in the face of conventional wisdom, but I've had a couple of subs that actually sounded better using the speaker connections than the RCAs. Don't know why; on these certain subs (2004-era Mirage LF-100 and LF-150) the subs sounded faster, fuller, more musical and better level-matched with the speaker cables than with the RCA connection.

A month ago I added a single tiny Mirage MM8 sub to my 2-channel stereo with Mirage OMD-15 tower speakers. The MM8 has no speaker level inputs and no outputs at all, so there's no option to sent a high pass signal to the mains. The towers have high handling capacity and are rated down to about 36 Hz, but I wasn't really getting that in-room. The sub, crossed over at about 50 Hz, helped deepen bass extension and kept the sub from murking up the upper bass handled by the towers.

These subs are a good match for the speakers. The subs are sealed, very powerful (1200 watts peak each), and extremely quick, so they easily match up with the mains. As 9" cubes they're made to blend with music systems or add bass to small HT systems, but not to rattle your teeth like a JL Gotham.

Another deal came my way and just yesterday I added a second MM8 to this system. It's just way better with two. The second bass smooths out the bass response (less peaky) and it adds about 6 dB dynamic range.

The funny thing is that somehow the mains (even though I'm *not* running them with a high-pass filter) sound more spacious, more dynamic, more 3-dimensional, more clear.

Right now I'm playing solo acoustic guitar and somehow the sound is simply opened up. Not overly bassy, not murky, but rather airy, more real, more dimensional, more fully fleshed out throughout. I'm a believer now.

But also, where this was previously a somewhat modest system best suited to semi-acoustic pop, rock, small group jazz, vocalists, and chamber music, it's now ready to boogie with big band and full-scale orchestral pieces such as Pictures at an Exhibition, Pines of Rome, and The Planets.

Those who have far bigger budgets who have implemented subs that are linear down to 14 Hz or so testify that the infrasonic information energizes the listening room more like what you sense and feel in a live concert.

I'm well on my way to thinking that if you want a truly fully convincing system that draws you into whatever kind of music you play on it, it could start with the subwoofer(s). In other words, it may actually be beneficial to allocate more money for the subs than the mains. I have no doubt that a pair of JLs costing around $6K could make a $1K pair of speakers sing as never imagined.

Anyway, back to your system, I suspect you'd get your best results by running your main speakers full range and sending simultaneous signal to the sub either via a second set of speaker cables from the amp or a second set of RCAs from the preamp via Y-adaptors. Then use the sub's volume, phase, and crossover controls to blend it (them) with your main speakers.

For blending sub(s) with a 2-channel music system, if you can't afford (or lack the space or floor strength) for a do-it-all sub such as a JL or Velodyne DD+ series, then go for the light'n'lively type of sub with a sealed enclosure, perhaps with passive radiator(s), lots of power, and fully continuous crossover, volume, and phase settings for the best blend with your main speakers.

12-02-11: Tghooper
My plan is to use two small 8" subs. Found a good deal on Sunfire HRS-8 that's within my budget. My listening room is 12x16 with 13' ceilings.

I use a pair of Mirage MM8's, which are 8" drivers and passive radiators in a 9" cube. However, they really don't add much below 35 Hz. Still, they're a good match for my system at this point. And I got them for less than $280 each.

If 14" cubes aren't too big and you want strong performance down into the 20's, you might want to consider these. They're sealed and tight, and the price is right for what they do. I have a local audiobuddy who uses them with his Magnepan 1.7's.

12-02-11: Dbphd
I'm not sure what's meant by fast in the LF range where wave lengths are long. Perhaps it means the sub is farther from the listener than the mains, but most processors let you account for speaker distances during setup.

Fast in the sense of rise time, which--regardless of frequency range--has to do with how quickly the cone accelerates, and perhaps more importantly, how quickly it stops. When you pluck a string bass for example, the fundamental plus its overtones are spread across the subwoofer, woofer, midrange were applicable, and tweeter. For ideal cohesion of just this single note, the cones of all four drivers should accelerate at the same rate; otherwise the overtones arrive at your ears before the fundamental. It stands to reason that a carbon fiber midrange or a beryllium dome tweeter with neodymium magnet is going to reach its excursion point faster than a 15" driver made of conventional materials with an average strength magnet seated in a less-than-rigid stamped frame.

If you look at the evolution of subwoofers, the emphasis has (generally speaking) evolved from cone diameter to absolutely massive magnets, heavy deep excursion cast frames, high excursion surrounds, and way more powerful internal amps powering much lighter, smaller diameter cones.

Even if you argue that rise time of the sub cone is irrelevant (and I think it's *very* relevant), you must at least be able to grasp that the higher amp power coupled with a stronger magnet and lighter diaphragm better controls diaphragm motion and makes the diaphragm stop when it's supposed to with less after-ring. This would result in cleaner bass more in keeping with the acceleration and stopping characteristics of the lighter midrange and tweeter, helping to prevent the sub from muddying the sound.

Also, a sub with a faster rise time also has higher frequency response which can be handy in blending with some L-R speakers. If a sub has a 12 dB/octave slope in its crossover, then if the crossover is set to the Dolby surround standard of 80Hz, its -6dB point is about 120 Hz, so the idea that a sub only need make a 40 Hz wave is simply not realistic.