Cross over frequency ???

Several factors come into play here.

1) What type of speaker are you using for the mains i.e. vented or sealed ?

2) Are you running the mains full range or rolling them off ? If rolling them, are you doing this actively or passively ?

3) How much overlap is there between the mains and the sub i.e. what freq are the mains crossed at if crossed at all ?

4) Where is the sub placed in the room ?

5) What is the proximity of the sub to the mains ?

6) What does your in-room frequency response look like without the subs energized ?

Lot of questions here, but there are a lot of variables involved.

As a general rule, if you are running the subs to supplement the bottom end of a large full range speaker, cross it over as low as possible. If using the sub to take over the bass chores of a smaller speaker, you want to cross the smaller speaker over at a point that is slightly above resonance and bring the subs in at a point that is slightly below that resonance. In other words, if the smaller mains ( aka "monitors" ) resonate at 65 Hz, cross them at 80 Hz and bring the sub in at about 45 or so.

While one would think that there would be a gap there due to neither of the woofers directly covering the range between 45 - 80 Hz, what happens is that the lower output from the sub and the mains sum together to create a relatively even balance. If you don't create a "gap", you'll end up with too much overlap i.e. where both drivers are covering the same range, producing too much output in that region. The end result is bass that sounds very "one note", slow and sluggish.

Obviously, this was just a "generic" description. What frequencies you should use and the amount of "gap" that you should create will vary with the crossover slopes and speakers being used. The only time that one would not want to use such an approach is if you were using "brick wall" type slopes. While some may consider 24 dB slopes relatively steep, you'll still have a considerable amount of "blending" between drivers taking place. In order to minimize blending / driver overlap, you have to have REALLY sharp slopes. Going active is really the only way to achieve good results doing this in my opinion. I'm sure that Jeff Joseph would argue this point with me though : ) Sean
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Kg: If you cross your monitors over at 80 Hz @ 24 dB's, that means that the signal is down -24 dB's at 40 Hz, -12 dB's at 60 Hz, -6 dB's at 70 Hz and "flat" at 80 Hz. At the same time, your sub is running at full output at 70 - 80 Hz, so the monitors are adding to what the subs are already contributing there. Even though the monitors are "sloping down", the amount of output that they can contribute may be too much for the room when combined with the subs. On top of that and as you can hear by ear, the amount of output that the speakers are required to make with that crossover frequency selected is still putting a strain on them.

If possible, you might want to select "small" speakers for the monitors and then tinker with the crossover point for the subwoofer. This should roll the monitors off a little quicker and clean them up while letting you fine tune the contribution of the subwoofers to a greater extent. I don't know if your Pre / Pro will allow you to take this route, but it might be worth checking out.

As a side note, placing the subs in the corner will give you the most reinforcement at low frequencies. While i've no doubt that you can shake the room like this, bass transients, pitch and definition typically suffer in such an installation. I would encourage you to do some further reading on the subject and do some personal experimentation with your installation. If you are using this system primarily for HT, it may be fine the way that it is with the subs in the corner. If you are using the subs to listen to a lot of music, i'm near certain that you can do better. Whether or not where the subs need to be place is convenient is an entirely different matter : ) Sean
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El: The Marchand "blending control" or "damping" adjustment as Phil calls it works fabulously. I'm sure that you'll be happy with this once you get it running. Sean
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Kgveteran: Glad you are making progress. It's always good to hear that someone is willing to experiment and learn on their own AND the results that they obtain from doing such are to their liking. This can only encourage that person and others that may be sharing those experiences through forums like these. It is stuff like this that makes me happiest when it comes to various threads in these forums. Well, that and people sending me boxes of money : )

As a side note, any professional crossover that you get is likely to use either XLR's or 1/4" ( mono headphone ) jacks. As such, you'll probably have to stop by the "Shack" and grab some 1/4" male mono headphone jacks to female RCA jack adapters. You might also be able to find these at a store that sells musical instruments ala Guitar Center, Sam Ash, etc.... It's quite possible that wherever you go to rent the crossover may have adapters that they'll lend you.

By the way, find out what the slope is on the crossover that you end up renting is. Some have variable slopes along with hinge frequencies. You'll probably find that a higher frequency crossover requires a sharper slope and that a lower frequency with a shallower slope can work too. Strictly a matter of trial and error here to see what works best with your gear, room and ears. Sean
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That is the problem with many HT processors i.e. the lack of bass management. They want us to run a million speakers for all this surround stuff, but they won't provide us with the actual versatility in these units to do so properly. The only alternatives are to run TRUE "full range" speakers all the way around, which is obviously costly, or get into very costly and confusing crossover / multi-amp / rat's nest of wiring installations.

Sorry if i wasn't more help, but i'm just not familiar with a lot of that stuff. Due to using large towers with multiple woofers all the way around, i've never had to tinker with bass management very much. Have you thought about all new, monster sized speakers all the way around ??? : ) Sean
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