Greetings,

            I have a pair of bookshelves with 5.25 drivers  and a 12" powered subwoofer that I am trying to integrate correctly.  The purpose of this exercise is to ensure that I have my sytem calibrated and integrated properly to its fullest potential so that I can make a better decision as to whether an upgrade in speakers is actually necessary.  It may just be that if I integrate my curent system accurately and it satisfies my tastes then I may have no need to upgrade, ever!

Steps I have completed:

1. Set sub to default volume level
2. Determined optimal placement by using the poplular "Crawling for Bass Technique"

http://www.audioholics.com/tweaks/speaker-setup-guidelines/crawling-for-bass-subwoofer-placement

1. Set my intial speaker levels with Avia test tones and Radio Shack SPK

Now I have come to a crucial crossroad that I fell will either make or break my Sattelite/Sub integration (I think it's OK to call Bookshelves with 5" woofers a sattelite speaker?).  Keep in mind I am bypassing the Subs onboard crossover by setting it to direct mode.

I have done some reasearch and have come up with two theories that make the most sense to me.  Keep in mind that the most popular theory is set it to 80HZ and forget it.  I threw that one out the door because it is just a generatlization and doesn't take into account any unique factors that make up my system.  In other words it is not scientifical enough for me.

So here are two theories that seem to make some sense scientifically.

1.  Set the Crossover a the -3DB rating of the bookshelf which would be 75HZ

2.  The bass of the main speakers must be flat to one full octave below the subwoofer crossover point.  However this is not mentioned in articles as frequently as step 1.   (http://www.soundstage.com/maxdb/maxdb021999.htm)

1. Setting the crossover with the -3DB theory I went with 80HZ on my receiver, which is what I have been using since I've had the setup (4 months or so).  I was never really happy with this crossover setting.  Music did not reveal great uniformity. It appeared as if there was some gap between the sub and the sattelites and upper frequencies 200HZ + did not sound organized, a bit muddy when I turned up the volume.  For a test I used Avias low pass sweep test in it reavealed dips and gains of +- 10DB on the SPL throughout the range and extreme dips at 180HZ, 120HZ and 60HZ.
2. Setting the crossover 1 full octave above the -3db mark of 75HZ of the bookshelf (150HZ) appeared to yield better results.  Material appeared more organized, sounded much cleaner at higher volumes and appeared to integrate better with the subwoofer (I did not appear to get much localization as most people would suggest). The SPL meter and low frequency slope showed that the dips and gains weren't as severe throughout the 20-200HZ frequency band but it did still reveal some, but not as many, dips of +/- 10 DB.  I would think that the cleaner sound in the 200hz + range would be due to the lightened load placed on the AVR.  This has confused me because according to my subwoofer manual (http://www.velodyne.com/products/manuals/dps%20manual_english_web.pdf ) the subs 12" sub  starts its roll off around 120 HZ +/-3db. And from everything I have read frequencies above 80 HZ on the subwoofer can be localized.   However, we just can't go by the cutoff because crossover frequencies is a game of slopes and unfortunately I don't know the crossover slope of the AVR (onkyo HTR 550) .  But I do know the passive subwoofer on the Subwoofer is a +/- 6 DB. Not sure if this comes into play if the crossover on the sub is defeated or if it just means that the frequency will roll off above 120hz at a rate of -6DB per octave?  Can anyone help explain this better?

Ultimately I am left confused on using the crossover for better system integration. Although it appears the 150HZ setting has tightened up my system it goes against 90% of the things I am hearing.  Most sources state  the crossover should be between 100-80HZ, including the instruction manual for my speaker.  This leads me to some closing thoughts:

1. 80 HZ may be correct but I don't know how to setup my subwoofer or my subwoofer is a piece of junk.  But that wouldn't support the increased clarity I get from the bookshelves by setting the crossover higher.  If 80HZ was the correct setting than it should sound just as good if not better on my bookshelves when compared to the 150HZ setting.
2. Acoustical conditions in my room and slopes between my equipment  may not be good for a 80HZ crossover setting
3. 150 HZ or 1 octave above the -3db point is the correct crossover frequency for these speakers.

If it is #3 then I clearly think I am left with some issues I can do nothing about:

If the 120HZ is the +/- 3DB rating on the high end of my subwoofer then that would mean, using the 1 octave rule that the subwoofer is only flat up to 60 HZ.  If this is the case then since my bookshelves are flat down to 150HZ and the sub up to 60HZ then I have some uncertainty going on between 60 and 150HZ in my system and this is where my SPL and low frequency sweep test pattern show the most movement.

In the end does it go against all common logic to set a crossover frequency of 150 HZ for a bookshelf with a rating of 75hz @ +/-3db and a 12" woofer with a high pass of 120 @+/- 3db?

Thanks for listening.