subwoofer to speaker connection

I am a novice and would like to seek advice from fellow Audiogonians. In  reading the forum 128025-84361 (Jan this year) on speaker and sub connection, I am intrigued  by the comment   from rcprince “Virtually every review I have read remarks on how the mids and upper bass from the main speakers are improved when you add a subwoofer…”. I have a pair of Focus Audio Signature Series (Model 78) speaker and one Audio Physic Luna sub. Would connecting these 2 produce improvement in the sound of music? If so , how  can I  best connect my sub and speaker ? I don’t mind buying the high pass filter and inline cross over as mentioned in the above forum, if needed. Moses

Thanks a lot yogiboy.  The information really helps me to understand the connection better. I have now connected one pre-amp output to my amp, the second pre-amp output to my sub. I like to seek opinion of
1.whether it will be better to use the Hsu Research high pass filter so high music tone can be send to my amp when connecting the sound source from the pre-amp. This will allow my sub to provide the base sound, with assumption that the quality of base is better from the sub than my speaker.
2.sub placement: The manual you recommended stated that " If the A/V receiver (AVR) equalizes the subwoofer channel during auto-set-up, corner placement will often provide the best overall performance". For  stereo set up, my amp will unlikely equalize the sub channel. So would it better to place sub on right corner where most base instruments are played from right in an orchestra (I mostly listen to classical music).

Thank you very much

I like when using one sub to place it in the center of the speakers. You can move it around to see which is best for you You should start with changing the adjustments on the low pass filter on the sub until it blends with the mains. If you use a high pass filter you will cut off the low bass on your speakers.You won’t know how it will sound until you try it. BTW, I’ve tried many subs and always preferred my system without them. Give it a go,since you have the sub you have nothing to lose !
I prefer high pass filters as they allow your amp and main speakers work more efficiently while allowing the sub to do what it does best.
I, too, am considering the HSU highpass filter for my HSU subs.
I can't find much info on your amp, but it looks to be a nice one. 
I assume your preamp doesn't have low frequency output, so you are going to need a crossover.
For $100 the HSU is a reasonably priced unit. For my main system I use the Vandersteen M5-HP filters which do the same thing but at a higher fidelity point. 
I will politely disagree with yogiboy regarding the benefit of subs. Every system I have added them was improved. 
Audio Physic has a nice tutorial on placement on its' website, too.

Looking at the Luna manual:
I see you can connect the sub with speaker cables (in parallel with your speakers), and use the subs controls to adjust crossover frequencies.
Though using it this way will mean your main speakers are running full frequency. I am doing this currently in my office, but I prefer using the high pass filter as it lightens some of the work for the amp, but it means the sub and main speakers aren't overlapping frequencies, and thus muddying the sound.

I like to thank both yogiboy and gdnrbob for sharing their experiences. I especially like to thank      gdnrbob for taking time in looking up the Audio Physic sub manual. Although my sub is an older version, with cross over settings 32, 46, 61,80,105 Hz , the overall capability is the same as that in the manual, except the new manual is lot more clear in the directions. My sub has both a volume and roomgain function to adjust the instrument sound. After reading the responses, I like to further seek input and clarification for further understanding

1.       gdnrbob mentioned that you “like using the high pass filter…but it means the sub and main speaker aren’t overlapping frequencies, and thus muddying the sound”. If I set 61Hz above to amp to run speaker and 80Hz below for the sub using the Hsu high pass filter, wouldn’t I have 61-80 Hz overlap? Would you suggest such overlap  or just 80Hz (or another frequency such as 61Hz)above to speaker and below to sub? By the way, your experience on improving the sound with connection to sub (like that express by rcprince that I first read in Jan 17 audiogon forum)  is what prompted me to explore this possibility since I have a decent sub not being used. (I did try to sell once last year at Audiogon, but no takers)

2.       Yogiboy you mentioned that you have tried many subs and always preferred your system without them. What kind of subs and speakers have your tried? May be your speaker is an excellent one and thus no need for sub.(The other day I listened to the demo of Magico speakers with Chord equipment in a store and found such fantastic sound from the set up which further prompted me to explore the improvement on my speaker since I have the spare sub) My speaker, Focus Audio, is an old one about 20 years ago that listed about US$4000 and the sub(Audio Physic)  about US$2000.  My pre-amp is Transcendent , and amp is Lectron HJ50.  I am looking to see if I can improve the sound from the speaker by connecting it with sub properly,  so I can  truly test if there an improvement.

By the way, I am very thankful to the Forum and Audiogonians in sharing and advising inexperienced individuals like me. Really appreciate the help. Moses189

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The reason "the mids and upper bass from the main speakers are improved when you add a subwoofer" is because relieving the main speakers of reproducing very low bass (assuming you are highpass-filtering the signal sent to those speakers and their power amp) can greatly reduce the distortion they are producing. The lower the frequency a speaker is trying to reproduce, the harder it has to work (move air), and the more distortion is creates, generally speaking. If the woofer isn’t having to produce low bass, it can produce upper bass and mids freer of distortion.

That’s why many Maggie owners use subs with their speakers---not just to provide the very low bass that Maggies don’t, but to reduce the amount of upper bass and midrange distortion that results from relieving the panels’ magnetic-planar bass driver of moving far enough to reproduce frequencies below 40Hz or so. The same is true of many other speakers as well.

If one doesn’t highpass the signal going to the main speakers and their power amp, that advantage of bi-amping is lost.

subs also fill in the "nulls" making the main speaker sound cleaner and clearer.
Thanks both  bdp24 and stringreen for providing the "scientific" reason in having bi-amp. I will for sure buy the Hsu high pass filter and will be looking forward to detect the difference. 
On a sonewhat separate but related question I wonder if you can help to advice. There  is another Lectron amp JH50 tube (50watt) amp available from a store possibly selling for $1500. Would there be any major advantage in having 2 rather than just one such amp to drive the 2 speakers I have? (With one such amp,  I normally turn the pre-amp volume control to half way to produce adequate volume to listen in my small room, 12 ft wide, 13ft long, 8 ft high). Moses189
If you can use them as monoblocks, then yes, it would be an upgrade.
Possibly less so if you want to drive upper and lower frequencies separately.
One of the best things about monoblocks is that you can put the amps close to the speakers. Thus, using short speaker cables.

Thanks for your comments, gdnrbob.  I wonder if anyone would like to further comment on future upgrades of my system since spending $1500 for  another Lectron JH50 amp will not provide any tangible gain in the sound (to be used as monoblocks) after adding my sub+high pass filter, what would be the next upgrade that you would recommend: change  my  Audio focus (Signature series model 78) speaker, or Transcendent Grounded Grid Preamp, or  Linn sondek LP12  turntable with Karma cartridge?
Why not try out what you have and see if it makes a difference before you make your next move?
 I have tried the sound with and without  the Hsu bass optimizer.  I found that  combining my subwoofer with Hsu bass Optimizer with cross over at 60 Hz  to my amp,produced the music a fuller range.  The base part is especially better when listening to organ music  and a clearer voice when listening to Pavarotti singing. Any suggestion as to what would be a further worthwhile upgrade to explore with my system. 
I just ordered a Hsu high pass filter. I'll let you know what I find. It may be what you are looking for.
Without knowing what sound quality you like makes it almost impossible to give you suggestions.
If you are near local dealers, I would suggest listening to as many speakers as you can, so you can get a handle as to what you are looking for sound-wise. Then we can work out what electronics you need.
I wish I heard Audio Focus, but I never have.
I am glad to hear the improvement with the connection of my subwoofer +high pass filter. I am happy with the improvement and not in a hurry to further upgrade, assuming the next upgrade will be expensive. Will look forward to hear your experience with the high pass filter. Moses189

Nature and live music have low frequency ambience that is something you won't have in your listening room if you can't get low frequencies in there. REL subs (like mine) for example are generally used as an addition to main speakers left unmolested running in their designed range, so they're (the mains) still simply doing whatever they do but seem to sound better with subs…I think the sort of low frequency "room charging" is what makes everything sound better, with the bonus of being able to actually hear the groovy musical low stuff on a recording.
Thanks. What is the cost? The basic connection is similar to Hsu high pass filter.  I wonder if anyone has compared both and give an evaluation.Moses 189
@ Moses 189,
You can search the forum for "minidsp", there are a lot of info, YouTube also a good source.
I believe the miniDSP is more flexiable and not cost a lot more.  
Thanks for the suggestion. I am glad that it is not expensive. I already have tried the Hsu high pass filter which is working out well. I would be interested to compare this MiniDSP. I wonder if anyone has experience comparing these 2? Moses189
Successful sub integration is an extremely misunderstood topic. By far the best way to integrate them is to install some RTA software on your computer (room eq wizzard, true rta) get a decent microphone and a test CD with uncorrelated Pink Noise- then measure your system’s response at your listening position.
Chances are that your main speaker will show an acoustic high pass response.
Set the sub crossover at the dropoff frequency for starters. Then do the following-
Place the sub at the manufacturers recommended position. It is not necessary and often sub optimal to put the sub "in the middle".
Set the sub to polarity inverted.
Get a sub with continuous phase angle adjustment- e.g. JL Audio D110, Some REL, etc. This is a critical adjustment.
Also critical is high level (speaker level) inputs.  Run the cables in parallel with your main speaker cables.  Integration is more successful when the sub input sees the same signal and signal timing at the amplifier- not the preamp. 
Play the sub at a louder level than the mains and measure again. Is the sub showing it’s dropoff frequency that correlates to your preciously measured main speaker? If not, adjust the crossover.
Now look for peaks and valleys through the useable bass range- e.g. 20 to 125 Hz.
Adjust the phase angle in steps (e.g. 1/4 turns) until you measure the smoothest response with no peaks and valleys.
Adjust the sub level to match the mains.
Do the ear test- and only adjust the sub level to taste.
I have successfully integrated a single sub into many systems this way including recently JL Audio D110 with KEF LS50s and Harbeth C7s. In each case my response at the listening position was flat from 20Hz through the entire bass region and it sounds phenomenal. You simply cannot hear the sub- all the bass is perfeclty centered with the main speakers.

Done right there is no need for additional processing or filters.

Thanks avanti1960 for your sharing of your experience

of achieving good base sound without purchasing a high filter. I wonder if using an inexpensive high filter would achieve similar effect as what you have used, except simpler and easier. In addition, by connecting the sub parallel with the speakers to the amp terminal, the advantage of the improving mids and upper base as per comment from bdp24 and filling in the “nulls” as per comment from  stingreen would be lost. Since I am a novice to this and do not have sound engineering or electronic engineering background, I hope all those with more experience and knowledge can help to understand better, so we know what would be the specific advantage of each. Moses189