Crossover question(s): internal, external, mono vs stereo

[TWB]

Hello
I have spent quite a bit of time learning from this forum and have begun putting a system together. I have tried to answer my question via this forum but haven't found quite the information I am looking for, so thanks for your patience!
I have recently acquired some PA mains on the cheap, with the intention of buying an amp and building my own subs as I have time, but running the mains on their own while the subs are being constructed time (15", 200w)
This will be a strictly personal rig, running solely off a behringer DDM400 (DJ mixer with a built in crossover) so there are 3 XLR outs (L, R, and sub, where you can set the crossover frequency).

My question is in several parts: first of all, it seems like running 2 subs and 2 mains off one amp is something that people do, but is this only possible in mono, with 2 subs in one channel and 2 mains on the other? (And in this case, it would seem like running 2 mains and one sub - before the 2nd is finished - would work well, am I correct here?) Or is there a way to run 2 subs and 2 mains in stereo off of one amp?
As a second part of this question, would an amp with a built-in crossover be redundant (xti, Behringer EPQ), or would there be any benefit to having one built in?
And thirdly, running everything off a DJ mixer (solely pre-recorded music with the ability to adjust all my EQ's, ect internally), is a DSP unit still necessary or would things sound fine running straight into my amp?

Thank you for your help and I hope I'm not being too redundant!

[Sydney]

Or is there a way to run 2 subs and 2 mains in stereo off of one amp?...

( The assumption is that "one amp" has 2 channels of amplification. )
If the amp has 2 channels of amplification ( A & B ) AND you are using a passive crossover in each channel to do the required filtering from the sub cab to the main top.
But practically it is NOT a viable approach.
Instead use 1 amp chl. for L, 1 amp chl. for R, and a summed mono signal feeds for sub.
At the minimum 3 chl of amplification required ( or a 2 channel amp given the same summed mono sub signal )

"Real Pros Go Active"

Syd

[Greg Plouvier]

it seems like running 2 subs and 2 mains off one amp is something that people do, but is this only possible in mono

Yes unless you have self powered subs or, subs with built in low pass crossovers(not optimum) You still need at least 3 amp channels - 2 for stereo tops - 1 for subs; not necessary to run subs stereo

it would seem like running 2 mains and one sub - before the 2nd is finished - would work well, am I correct here?

It would work probably not the greatest.

would an amp with a built-in crossover be redundant (xti, Behringer EPQ), or would there be any benefit to having one built in

Not redundant if fact a much better way to go. You really need proper processing to protect your speakers - the Berry mixer does not offer that with it's meager crossover section although it does look like a cool mixer

running everything off a DJ mixer (solely pre-recorded music with the ability to adjust all my EQ's, ect internally), is a DSP unit still necessary or would things sound fine running straight into my amp?

I would seriously consider at least a Crown XTI amp to run a mono setup with subs on 1 ch and tops on the other.

[SeisTres]

I'm going to assume you mean the ddm4000 since using 400 gave me no results.

Took a look at the manual and, it will no cut it. Sure you might be able to get away with for emergencies, but that's it. You need a proper high pass and low pass with at least a 24db/octave slope. Then, you need to able to pick different crossover frequencies for subs and tops. Also, the eq's on the mixer are pretty much to give it "your own feel" but you will still need a proper EQ. And don't forget about limiters, too. So in short, and xti sounds good. However, if you must have stereo tops, you could get a small xti for tops and a bigger one for subs; or get a separate all in one processor and two amps. Keep in mind that with two amps, you can run four tops and even six subs.

and yes, you can run one sub, it'll just be lower volume than two.

BTW, don't forget to check out the old xls series on musiciansfriend - really cheap.

[TWB]

Thank you for your many quick responses!

As for using the mixer (yes, a DDM4000, my mistake) as a crossover, that was really an afterthought. I had no intention of doing so when I purchased the mixer but realized that was an included feature that might solve some issues when I started building a sound system... I hadn't really expected it to work as a good alternative.

BTW, don't forget to check out the old xls series on musiciansfriend - really cheap.

As far as I can tell, the XLS series include neither crossover nor processing- which would pretty much negate the savings over an xti if I had to sort that out some other way, am I correct?

I do understand that building a good system is an expensive proposition and am thinking about an xti even though it really is over my budget- used on ebay would be that route. I am really attracted to the Behringer EPQ series, however, as it offers crossover, 4 channels so I could properly run sub(s) off the same amp in stereo, and a limiter. It only lacks compression and EQ, and I am really questioning how necessary these are. I absolutely understand that BFM equipment is top-notch audiophile gear and it's easy to say that doing something perfectly is THE way to do it- but I want to make sure that it's what would work best for me.

In the foreseeable future, this setup would be a portable party rig, so minimizing complications is key along with price and and volume- hence my question about running a single sub. I know that it wouldn't be as loud, but are there any good reasons why running a single sub is a bad idea? I've seen several popular speaker kits (B-52 matrix, for example) with a single sub. From what I gather, that's exactly the sort of intended application that I'm shooting for. So of course setting an EQ would make things sound better, but is an EQ alone worth the $100 extra of the crown over a behringer (and also loss of 2 channels and reduced power)? Another way to phrase it: is it going to sound BAD at a raging houseparty?

I really do appreciate all the input here. I was very tempted to try and simply find something ready-to-go (like the B-52) rather than building my own setup from scratch, but decided to do it the hard way and learn a lot and hopefully end up with something that's louder, sounds better, and ends up significantly cheaper than a factory unit!

Just for reference, my target here has been $500-600 for getting a system up and running (200 for speakers, 150+ for at least the first sub, and as little as possible for an amp that will keep things bumping nicely for a while.... so I cringe when I hear things like

you could get a small xti for tops and a bigger one for subs; or get a separate all in one processor and two amps. Keep in mind that with two amps, you can run four tops and even six subs.

Maybe in a few years....

[TWB]

Just wanted to say I ended up going with the xti. Seems like that was overwhelmingly the proper choice and I'm pumped! Thanks again for the advice.