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
I think you laid it out very well Sean. Just one thing added, if you use something like a 6 db slope the transition will be very smooth but you may find out that you may negate part of the effect of the subs because the satellites are still active for too long and the sub sounds muddy because it extends too high. As Sean said, then you definitely want the crossover point to be different between the subs and the satellites.
In my system the processor does both the high pass and low pass.Your advice if I understand it correctly is to use the processor to xover the ported monitors and a seperate xover to xover the sub ? I use Paradigm Mini MK3's as mains and center.The extra goes to the ES ch.The subs both sit in the same corner stacked.Funky stuff happens when I try to seperate them.The manual for my EAD say it uses a 24db/oct linkwitz riley.Seems steep enough to do the job ? The room has a very robust sound with films.I am very happy with it but my mini's tend to not like the lows of HT.80hz just didn't cut it.Oh well.
No, not two separate crossovers just different frequencies for each section. If you could you would leave the subs at 80 hz but crossover the monitors at lets say 100hz. Twenty -four db is pretty steep. That should be a fast enough slope. If your monitors don't like 80 hz try raising the crossver gradually upward. The higher the bass the more likely it is that your sound will get muddy.
Yes, use the processor to cross the monitors (high pass), then use the crossover on the subs (low pass). The gap between will simply be 'lost' as a tiny amount of heat in the circuitry. Anyway, as usual, Sean has given the best and easiest-to-understand description of crossover gapping I've ever seen...just wish I had seen it before I went through hell setting up my subs : )
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
All of the above is good advise and sound theory. Give it a try. However, my experience has led me to a somewhat different approach.
First, turn off the main speakers and, with the crossover set to 90 Hz or thereabouts, listen to some music. "What music" you say. Yes it's true that most of the time nothing will be coming out of the subwoofer. (Dirty little fact).
Secondly, search through your recordings and find one that does have signal below 90 Hz. How does it sound? Do you really want that in your mains?
Thirdly, think about the high frequency capability of your subwoofer. Is it really all washed up at 100Hz?
Obviously what I am driving at is the suggestion that the 50Hz subwoofer crossover frequency often suggested is too low, at least for my particular system. My subwoofers are my own design, and include 15 inch JBL drivers which are good to 800 Hz, so 90 Hz is a walk in the park. (The somewhat deficient range below 30 Hz is filled in with 12 inch specialized subwoofer drivers). Although most commercially available subwoofers don't claim to go higher than 200Hz or so, limiting them to 50 Hz is unnecessary.
IMHO no aspect of audio exhibits greater disparity between theory and practical tweeking based on listening than does the subwoofer. I am not alone in noting that precisely measured (with a warble tone) flat response to 20 Hz often sounds deficient when music is played.
Finally, with regard to overlap/gap of crossover frequency: I have obtained Marchand electronics modules which have an interesting feature. It is a control that provides a bandpass boost or cut at the crossover frequency. This is supposed to take care of the problems around crossover noted by sean. I have not got the things wired up yet, but I am anxious to see how this feature works.
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
OK.What I did was run the mains and rest of the system ie. center and surrounds xover at 80hz.With the sub off I listened to a few well known sound tracks.Trying to ignore the unbalance sound it did not have that chesty sound I disliked before.It was tight and free from the peaks in the bass.It would appear that is my starting point.It also had tons of head room and only began to show signs of distress above 100db,well above my usual listening.Setting the xover higher also yeilded the same results.Gave me more headroom and my 6.5 inch drivers were very happy.I will go rent a pro xover this weekend and ease the subs into the system until I feel they are making a contrabution not an over statement.I never tryed to solve this problem from up high first and then the subs.This makes so much sense.Keep in mind I am stuck with the 24db high pass coming out of the processer.Thanx I'll keep you guys posted.
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
Problem #1 : My processor will allow me to adjust xover freq. but,that freq. is the hi pass and low pass.It won't let go of the LFE channel to adjust out board with out doing it it self.The unit is an EAD Ovation-8.I can run the front three large but that would entail three outboard xovers.I can't remove the low pass xover for the sub and fear redundence of cascaded xovers.I can run the high pass at 80hz (which means the bass has that freq.at the xover point ) And try to roll the bass off with an out board third octave eq. .But we are still cascading eq's.Rane makes that cool THX44 that eq's the 80-800hz for the front LCR ,to tame the xover bump.I'm going to sleep on it.Thanx.
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
Sean..."Versatility"? My Rotel 1066 is so damn versatile that half the time I can't figure out what it is up to. And the manual isn't much help. I do hear a lot of complaints about "bass handling", so perhaps the solution is what I have done...set all the speakers to "large" and get some separate crossovers for the speakers which aren't. I am in the process of wiring up three Marchand crossover modules and power supply in a decent chassis. The modules and the power supply are completely assembled so the wiring job is pretty easy, and the whole rig, including $40 chassis and gold plated connectors will end up costing me about $150 (three channels). For another $60 it could have been 5-channel. My old Audio Control Richter scale (2 channel) will do the rears. Of course, if you have more money than time there are plenty of crossovers available for sale complete.
Lions and tigers and bears oh my.Since the problem is in the sub woofer and associated electronics and the monitors seem to be doing fine on their own this is where I will begin.I will use the parameteric to tame room modes and an eq ( third octave ) to roll it off.Who the heck knows.I wish my processor had more bass management.........
To whom it may concern.Problem solved.The problem with switching xover freq. on the fly is that the room modes increase in amplitude as xover freq. increase in frequincy.Example...I switch from 65hz to 80hz and I now have to take into account the new freq. the sub is producing.One of them is an octave above the killer 42hz mode, smack dab in the middle of the xover point.Once I ran some sweeps with the trusty testocilator (thats not a joke,its a tone generator)and the rat shack meter I quelled some junk at 80hz and above.Alls well again and the system has gained some headroom with the new higher xover point.Nemo sounded outragous.