Well, the level is set to make it identical to that of the main speakers.
1. What crossover is dividing the signals?
2. Do you have any way to measure sound levels?

Kal

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After sitting in my closet I decided to hook up my Definitive Tech Sub to my system using the sub out from my preamp.

I'm glad you're out of the closet Rich.

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What I would like to better understand is what level to set the Sub at? Too much and it sounds mushy to little and it sounds decent but not great. Also what the difference between an OK sub and a great Sub?

About $800? No, seriously, to answer that question you need to be specific in defining what's meant by 'great sub'.
Great for home theatre or music? Great for big or small room? Great for accompanying satellite or 'full range' speakers?
A sub-woofer that may work well in your room could be a disaster in mine.
A sub-woofer that has built in room analysis and corrections software, such as Velodyne's DD range, has a much better chance of achieving greatness than one without such flexibility. A sub-woofer with a powerful amplifier able to cope with whatever room equalization is asked of it also has a better chance of achieving greatness. There's also a long list of physical and electronic requirements to getting the design of a sub-woofer right and that would take pages and pages to illustrate.
Wandering slightly off topic --- I heard from my tech mate recently that he'd had a large number of damaged sub-woofers over his repair bench. Apparently the increasing number of pre-amps out there that pass DC are killing them. So, if you have a pre-amp that's direct coupled 'make sure your sub-woofer either blocks DC with a capacitor in the input of bypasses DC with servo circuits' (My tech's words which I confess to not really understanding.)
Back to the great sub-woofer quest. There are some rooms, often L shaped that make a sub-woofers job almost impossible to get right without room treatments. This usually involves large, ugly bass traps placed in the corners of your room that have been known to trigger divorces. The careful positioning of a sub gives it a hand-up too. Just dumping a sub-woofer somewhere out of site is usually a recipe for disaster. So, it's a hard question to answer Rich. Someone else will be along soon to make it even more complicated I suspect.

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Thanks JS. I have full range tower speakers (Paradigm 100's) and the room is rectangle. I guess what I am looking for is for the sub to add a little bit more low end as this system is for music only and is two channels.

If you don't play at rock concert levels and the room isn't huge I have a listen to Velodyne's DD12 or any similar model with built in room analysis and correction software.

The fundamental problem with any subwoofer is that at some frequencies, primarily 50-150 HZ, the main speakers and the subwoofers are both putting out energy, and the energy from one is out of phase with the energy from the other; they will be putting out waves that can partially cancel each other, muddying up the sound and varying the output at different frequencies. Many people who have been there throw up their hands and just refuse to use subwoofers, because they think that there is no satisfactory resolution to this problem. Yes and no.

The solution is to put a high-pass filter between your preamp and power amp that "rolls off" the signals below say 80 HZ so that they do not go to your power amp and speakers.
That lets the subwoofer do its job at the lower frequencies without interference.

It is tricky to do this, however, because you need to know the EXACT input impedance of your amplifier to get the correct rolloff frequency, and the amplifier spec sheets tend to be approximate, not always exact. Furthermore, to avoid degrading the sound, you have to use very very high quality capacitors between the preamp and power amp; the only ones that are really great for this are Dynamicaps or Relcap TFT jobs and they cost maybe $20-50 each.

A technician can bench test your amplifier and determine its input impedance. I use a ,01 uF capacitor between signal generator and amplifier and measure the amplifier gain at 10KHZ, then decrease the generator frequency until the gain drops by 30%; this is the rolloff or half-power frequency.
The input impedance is then-

Zin = 1 divided by X, where X = (6.28 x .01 uF x rollof f in HZ)

MIchael Percy or Parts Connexion are my sources for the high quality capacitors, by the way.

The only subwoofer design that I have ever seen that fully addresses the phase issues is the Vandersteen subwoofer. With that sub, the input to the sub comes from the speaker terminals of the power amp, rather than from the preamp, and then a reverse filter in the subwoofer's amplifier re-equalizes the signal for correct output.

For information on this approach, check the Vandersteen website and download the manual for the 2WQ subwoofer.

The formula to calculate the capacitor value to put between preamp and power amp is

C (in Farads)= 1 divided by Q, where Q =(6.28 x Amp Input Impedance in ohms x 80HZ)

Basics - set 3 controls on your subwoofer:
1. Volume (may say level, or gain)
2. Phase (may be a switch for 0 or 180 degrees, or a continuously variable control).
3. Crossover (may be a continuously variable control, or sometimes a multi-position switch relating to other speakers from the same manufacturer).
The manual for your sub should tell you HOW to set it up. If no manual, come back here.

I find that a sound pressure level (SPL) meter is helpful in the setup process, A basic one from Radio Shack is (I think) still under $50. (This presumes your sub doesn't come with a set up microphone etc.)

If you have not yet performed a basic set up procedure to find the best location for the subwoofer, your speakers and your listening position all within the same space, you'll never get anything else right no matter how you go about it. If you or the sub happen to be sitting in the center of a null zone for deep bass, you'll crank the sub for all it's worth and only get more distortion.

Put "subwoofer placement" in a search engine. After proper set up is accomplished, the rest is a piece o'cake.

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The fundamental problem with any subwoofer is that at some frequencies, primarily 50-150 HZ, the main speakers and the subwoofers are both putting out energy, and the energy from one is out of phase with the energy from the other; they will be putting out waves that can partially cancel each other, muddying up the sound and varying the output at different frequencies. Many people who have been there throw up their hands and just refuse to use subwoofers, because they think that there is no satisfactory resolution to this problem. Yes and no.

The solution is to put a high-pass filter between your preamp and power amp that "rolls off" the signals below say 80 HZ so that they do not go to your power amp and speakers.
That lets the subwoofer do its job at the lower frequencies without interference.

It is tricky to do this, however, because you need to know the EXACT input impedance of your amplifier to get the correct rolloff frequency, .......

Thats a fascinating explanation of effective sub woofer use I've never encountered before, specifically this idea of having to determine the EXACT input impedance of an amp etc.
It leaves me wondering if I'm deaf, as I'm more than happy with they way my 2 Velodyne DD12's manage to appear to blend perfectly with my main speakers which are large electrostatics. Maybe I just got lucky Commsysman?

As the man said to the little kid sitting on the edge of freeway eating dirt..."son, whatever suits you just tickles me to death..."

But seriously...if I am not correct about this problem, why would a respected designer like Richard Vandersteen spend hundreds of hours designing a product in such a way as to solve the problem? I suggest you look at the owner's manual for the Vandersteen 2WQ subwoofer, posted on the Vandersteen website.

As for your situation; I suspect that the overlap between your electrostatic speakers and your subwoofers IS less pronounced than with many other situations; that has certainly been my general experience.

I think that any of the experienced reviewers at Stereophile will tell you that the overlap between subwoofers and main speakers is very definitely a problem that often, if not always, makes integration of the two problematical.

I would say that you WERE indeed lucky, since you apparently do not have enough overlap for it to be a significant problem; that hardly makes your case typical.

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I would say that you WERE indeed lucky, since you apparently do not have enough overlap for it to be a significant problem; that hardly makes your case typical.

Looks like I did get lucky Commsysman. There's another problem sub-woofers can present that I haven't seen addressed in any forum or audioporn magazine. My Dynaudio 'Evidence' Masters worked brilliantly in a hall sized room when I had them. These monsters go down so low you can validly claim they include their own sub-woofer. Now it's known that placing a sub-woofer in the wrong location can degrade performance in a particular room. When I attempted to get the Dynaudios to work in my next house I faced nightmarish problems. If I positioned them so that the sound-staging came together, the bass was hiddiously boomy. If I positioned them so that the bass was more tolerable, the sound-staging fell apart. So, I got rid of them. I wonder if anyone else has had a similar problem?

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I wonder if anyone else has had a similar problem?

Not exactly since the room I'm in now has only contained LS3/5a's and my current full range speakers. Neither of those sets of speakers descend deep enough on their own to cause problems in the room. However, either situation - too much bass or insufficient bass extension - gives a good argument for the viability of satellites and subwoofer over the problems of balancing the demands of a single cabinet.

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I would say that you WERE indeed lucky, since you apparently do not have enough overlap for it to be a significant problem; that hardly makes your case typical.

Looks like I did get lucky Commsysman. There's another problem sub-woofers can present that I haven't seen addressed in any forum or audioporn magazine. My Dynaudio 'Evidence' Masters worked brilliantly in a hall sized room when I had them. These monsters go down so low you can validly claim they include their own sub-woofer. Now it's known that placing a sub-woofer in the wrong location can degrade performance in a particular room. When I attempted to get the Dynaudios to work in my next house I faced nightmarish problems. If I positioned them so that the sound-staging came together, the bass was hiddiously boomy. If I positioned them so that the bass was more tolerable, the sound-staging fell apart. So, I got rid of them. I wonder if anyone else has had a similar problem?

This is not unusual and, imho, one of the best reasons for a using a subwoofer, even with such full-range speakers. The optimal position for imaging and overall performance rarely coincides with that for optimal bass and the odds of coincidence decrease with the bass capabilities of the main speakers.

Kal

I think I got pretty lucky too. I bought a single subwoofer, to supplement nearly full range speakers. I've got the added extension and slam that I needed (wanted), and after some futzing around, with settings and positioning, I have very good integration between the sub and spkrs. There's no audible clue to the sub's physical location, I just hear the main speakers as stronger and deeper in the low bass. Sub affects nothing in the vocal range. But when I turn the sub off, with full range music, I miss it. It surely helps that I could set the crossover point pretty low.

Just to provide some additional information that might clarify my setup, FYI:

The Vandersteen 3A main speakers I am using are supposed to go down to about 35 HZ, but in my room they do not give one the impression of having a lot of really low bass, when used solo, without the subwoofers or filter in the system. The room is 15 feet by 35 feet, with a ceiling that slants from 12 feet high at the left to 8 feet high at the right.

The speakers are sensitive to placement, and want to be over 3 feet from the rear wall, and about 4 feet from the side walls, for best overall sound.

This placement does not do much for the bass either. The Vandersteen 2WQ subwoofers only work well in one place; right in the rear corners of the room (actually, because of the baseboards, they are about 2 inches from the rear and side walls).

The input impedance of my Bryston main amp is 30K ohms, and putting a .068 uF capacitor between the preamp and amp to properly roll off the amplifer output gives a -3db rollof point of 80 HZ.

The system has VERY well-defined bass with this setup, at all frequencies.

By the way; the lowest-frequency bass notes I have ever heard on a recording are on the Delos CD "King of Instruments", on the track entitled "Rain Over the Quaker Graveyard" . I have not measured the actual frequency, but it is certainly in the neighborhood of 20 HZ. It's a hell of a test!

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By the way; the lowest-frequency bass notes I have ever heard on a recording are on the Delos CD "King of Instruments", on the track entitled "Rain Over the Quaker Graveyard" . I have not measured the actual frequency, but it is certainly in the neighborhood of 20 HZ. It's a hell of a test!

If that was a 20HZ note, without harmonic overtones, you should have felt it, not heard it! Given the mixtures organists indulge in though you probably felt that 20HZ and heard whatever other register was coupled to it . Just a guess from a retired organist and audiophool.

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The fundamental problem with any subwoofer is that at some frequencies, primarily 50-150 HZ, the main speakers and the subwoofers are both putting out energy,

IMO, a speaker that operates in this range of frequencies (50-150 Hz), is NOT a subwoofer, but a bass speaker. Sub-woofer means below the woofer. Not, in place of a woofer. I feel that a lot of confusion in this area is caused by the use of the term (subwoofer) when what is being discussed is adding a bass speaker to bass deficient speakers.

I feel that a subwoofer should not be used to reproduce tones above 30-35 Hz. I think that this misuse of subs is what gives so many people so many problems.

It is right at that frequency where it is barely audible and you do feel it just about as much as you hear it; right at the low limit of audibility.

Richard Vandersteen advises that input to the main power amp should be down 3db at 80 HZ, plus or minus 20 HZ; that is the characteristic he designed his subwoofer amplifier around. 80HZ seems to work very well in my system; that is how it is set up. It is very free of any audible problems; excellent bass definition at all frequencies.

To integrate the subwoofer and main speaker, it is virtually impossible to avoid an overlap in operating frequencies. With most main speakers and subwoofers, there is considerable overlap, especially between 50 and 90 HZ.

The filters used inevitably start to roll off the output of the subwoofer somewhere between 40 and 60 HZ, which means it will have significant output up to at least 80 HZ in most cases, while the main speakers will certainly have output down into this range. If one tried to have the output of the subwoofer stop dead above a certain frequency, and the output of the main speaker stop dead below that frequency, that would be ideal; unfortunately no one has figured out a practical way to implement this. The design problems are formidable.

When a subwoofer is used with small stand-mounted speakers, as is often the case, those speakers tend to have seriously reduced output starting at 50 or 60HZ; to be of much use with those speakers, the subwoofer obviously has to have significant output up to, and above 60 HZ, and that is how they are designed.

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To integrate the subwoofer and main speaker, it is virtually impossible to avoid an overlap in operating frequencies. With most main speakers and subwoofers, there is considerable overlap, especially between 50 and 90 HZ.

The filters used inevitably start to roll off the output of the subwoofer somewhere between 40 and 60 HZ, which means it will have significant output up to at least 80 HZ in most cases, while the main speakers will certainly have output down into this range. If one tried to have the output of the subwoofer stop dead above a certain frequency, and the output of the main speaker stop dead below that frequency, that would be ideal; unfortunately no one has figured out a practical way to implement this. The design problems are formidable.

Are you referring to difficulties in crossover design, speaker behavior or both? I should imagine that if the crossover could be implemented in the digital realm things wouldn't be so difficult or am I missing something? Either way, I sure don't detect any gap between my subs (2 Velodyne DD15's) and my main speakers (Soundlab ULPX's) with the crossover set at 70Hz. In fact, on my system I have to run the crossover above 85Hz or below 60Hz before I hear any problems. Below 60 HZ the main speakers run out of grunt, above 85 Hz I start to hear differences between the electrostatics and the dynamic sub's that's impossible to ignore.
I've heard electrostatics crossed over much higher with no audible problems on another system http://aca.gr/pop_coulson.htm but as other audiophools tell me, I'm easy to please.

Both

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After sitting in my closet I decided to hook up my Definitive Tech Sub to my system using the sub out from my preamp. What I would like to better understand is what level to set the Sub at? Too much and it sounds mushy to little and it sounds decent but not great. Also what the difference between an OK sub and a great Sub?

Why were you sitting in your closet? Does that help you to think? I find that the shower works much better.

I think it is his own personal business whether he wants to come out of the closet or not....