# Active Crossover Questions.



## JCD (Apr 20, 2006)

If someone were going to build a system using an active crossover, what issues would you need to consider.

I can pick up some of the obvious ones:

Crossover point
Assuming a traditional rectangle, the delay to offset the radiation pattern tilt
Amp gain adjustments between the drivers
Order (e.g., 1st, 2nd, 3rd, 4th, etc) and Alignment (Linkwitz-Riley, Butterworth, Bessel, etc) type of crossver
Amp choices

The answers I have for the above would be --

Dependent on driver choice of course, but rules of thumb would be to choose a crossover point that has at least 1 or 2 octave overlap between the two drivers. In a three way system, the rule of thumb I've seen is to have the lower crossover in the 200-350Hz range, with the higher crossover in the 2,000-2,500Hz range.
Still a little sketchy on this one, but do you just have to calculate the delay based on the horizontal offset of the voicecoils? Or is it also alignment dependent?
I'd assume this one is just a matter of running test tones through the drivers independently and calibrating the levels with your rat shack spl meter.
Most of the active crossovers don't offer much in the way of variety here. You're pretty much limited to 4th order Link-Riley. Other than one of the units from Behringer I saw, everything from Rane, Ashly and Behringer only had a 4th Link-Riley option.
All I have are rules of thumb on this one -- tweeters don't need as many watts as mids and mids need less than woofers. If you were going to put just one tube amp in the mix, the tweeter may be the best choice.


So, for the folks that actually know what they're talking about (because, it ain't me), do I have it right for the "stuff" I've mentioned? And what am I missing?

Can you tell I've been rading my Loudspeaker Design Cookbook again?

JCD


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## F1 fan (Jul 6, 2006)

Your answers are pretty much bang on but I will add a couple of things.

With a 4th order LR an octave of overlap should be fine but the drivers response should not have any nasty response problems in the crossover region or the ideal slope will not be realized.A peak in a drivers response can be EQ'ed to flat with a notch filter but this is probably only possible with the Behringer or a DIY design.
Also aligning the voice coils either by slanting the baffle or electronically with an all pass network will work for all aligments.The amount of delay needed is determined by the relative offset of the voicecoils.

The 4th order LR is popular because it has so many advantages over other alignments.

Here is a link to an excellent manual for a DIY unit that is a good read. http://www.delta-audio.com/Active_Filter_Four/Active_Filter_Four_manual.pdf

Regarding power requirements here is link to an active speaker using 6watt tube amps for mid/tweet and 100 solid state for the woofer. http://www.aurumacoustics.com/integris_300B.html

Here is a review of the speaker. http://www.soundstage.com/revequip/aurum/index2.html

Hope this is helpful.
Fred


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## JCD (Apr 20, 2006)

Thanks for the info and links.

Good to know that I'm on the right track there.

Thanks again.

JCD


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## kingdaddy (Nov 3, 2006)

Try Marchand, they have an electronic crossover that will do anything under the sun (XM-44).


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## jmprader (Apr 19, 2006)

I thought I'd resurrect this thread and ask a related question. 

I am interested in using an electronic crossover, Behringer, Marchand or otherwise, in connection with a DIY speaker project. 

Generally speaking, what can some of you smart guys tell me, plus and minus, regarding the use of inexpensive electronic crossovers versus more "traditional" passive crossovers. Are there any "typical" sound quality tradeoffs going to an electronic xover? Any big caveats, for example, if I want to drive some ribbon tweeters, which apparently might be better served by a steep crossover, are there any known issues with electronic crossovers that I might need to be aware of?

When I look at some of the inexpensive crossovers (Behringer cx2310...two way stereo, three way mono with a sub output to boot, for example), coupled with low-cost high output "pro" amps (Behringers, Nady's, Crowns, etal) and some DIY infinite baffle subs, mid-bass woofers, midrange drivers and tweeters, it almost seems too easy to assemble a fairly low cost, extremely flexible, high output and high power handling set of 5.x speakers...assuming a cooperative spouse and minimal in wall location issues. 

Burst my bubble or tell me something good, guys. I can take it, either way.:daydream:


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## F1 fan (Jul 6, 2006)

IMO for DIY projects I think the active approach is the best way to go.Both the CX2310 and Marchand units would be good choices with the CX 2310 being a real bargain (around $100) and has lots of flexibility with its front panel adjustable crossover frequency settings which have steep 24db per octave slopes.As long as care is taken in the choice of drivers and crossover frequencies etc,I can't think of any tradeoffs in using active filters other than the increased complexity due to the need for additional channels of amplification.In fact there are many performance advantages.


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## Danny (May 3, 2006)

Passive crossovers soak up lots of power from the signal.
Active crossover - need separate amps for each driver (low, mid, high)
I'd probably go for a more expensive crossover (or even a digital unit) like a lab gruppen, turbosound etc. Generally the more expensive ones will have more options you can customise


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## JCD (Apr 20, 2006)

The main issue I've heard about with "inexpensive" electronic crossovers is they can infect the signal with some "noise".

That being said, I've listened to a DIY setup with an active crossover using a Behringer DCX2496 that was AMAZING. For a tweaker, it's got a LOT of stuff for not much $$. The owner of the system I mentioned did say that he had to mess around with the gain to get rid of some noise caused by the unit, but once he got everything dialed in, it was totally quiet.

Another brand to throw in the mix are the crossovers from Ashly. The reputation I've been able to pick up is that they're a really good product at a fairly reasonable price. I think you could find the 3 way stereo version for $350 (used?).

Rane is another brand I'd look at.

As for the benefits -- my understanding is that they're huge. 

At the very least, you're going to get an extra 3db going with an active system. 
Designing an active crossover is a LOT easier
You can change the time delay of the various drivers with a digital crossover to get the drivers in phase and time coherent (can't remember the correct term right now)

From everything I've read so far, the only downside is that you have to pay more for the amps. Even there, you can spend less than you think. You need relatively low wattage amps for the tweeters, medium for the mids and a little more for the low end -- however, all of these amps can have less wattage than an amp that would drive all of the drivers in a passive system. Also, you can look for amps that work well in certain frequencies rather than working well across the spectrum.

Getting back to the crossovers, my "feeling" for the hierarchy of crossovers I'd go with would be:


If I were going with a simple, low cost crossover I'd go with Rane
If I were going with a simple, upgraded system I'd go with Ashly
If I wanted a crossover with a lot of flexibility and was low cost, I'd go with the Behringer 2496 (Since I'm a tweaker, I'm going to use this one when I build my next set of speakers)

No real world comparisons for this list, just what I've been able to accumulate through my wanderings on the web.

JCD


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## cobyh (Jun 7, 2006)

thylantyr said:


> DCX2496 has more pros than cons for a DIYer. Everyone should own
> one to learn more about tweaking audio. For best performance, have
> this unit at arms reach from the listening position to allow proper
> listening and tweaking in real time. The rest is easy, turn the knobs
> ...


Hi....stumbled across this thread in my search for info on the system I'm building for my HT/living room. Where can I find more info on folks using the DCX2496 in their setup? I'm planning on using 4 of them for 7 3way speakers and I'm in the process of designing the system now....currently in the driver selection stage. Here's the link to my current post on it, if you'd like to look: http://www.hometheatershack.com/for...rossover-would-love-discussion.html#post32496

In terms of driver selection, I know the 2496 allows for some pretty impessive EQ'ing options, so I'm assuming that it opens some doors for using drivers that are hard to use with passive eq's....do you or anyone else know of some that might fit that bill? Perhaps cheaper because of the need for notch filters but otherwise high quality? I think I'd like the t-m crossover point to be around 3500hz, the m-w crossover to be between 500 and 200hz...know of any drivers you might recommend that have high sensitivity, good power handling, and wide dispersion within those bands? Currently I'm leaning towards the Morel dome midrange but the price is a bit high.


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## reed.hannebaum (Apr 21, 2006)

dbx is another brand you may want to consider. I use the dbx 223, which is an LR 2-way (they also have a 3-way version), to crossover between my front speakers and my front stereo subs. My situation is not quite the same as yours since I retained the passive crossover in my front speakers, but none the less I have had excellent results with this versatile unit, and I was able to buy it used for $85. 

Before the dbx, I tried the Paradigm X-30, but it introduced some low level hiss into my front speakers, and it did not allow for stereo sub output. The dbx unit does not have adjustable phase alignment, but I discovered with the X-30 that with my speaker/sub placement I didn't need it.

From the issues you raise above it certainly looks like you have been doing your homework. I might add that the delay needed to compensate for voice coil offset should be calculated at the crossover frequency for the 2 drivers. In the case of an LR alignment, you will then preserve phase coherence as you crossover from one driver to the next. Also, when choosing a crossover you may want to consider whether you need baffle step compensation. Marchand offers this as an option on some of their crossovers.

Also, I found the best way to choose the crossover frequency, is to set it close to middle of the overlap range between the 2 drivers and then adjust for the flattest response from REW. I did this as a first step before any adjustments with the BFD.


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## cobyh (Jun 7, 2006)

reed.hannebaum said:


> dbx is another brand you may want to consider. I use the dbx 223, which is an LR 2-way (they also have a 3-way version), to crossover between my front speakers and my front stereo subs. My situation is not quite the same as yours since I retained the passive crossover in my front speakers, but none the less I have had excellent results with this versatile unit, and I was able to buy it used for $85.
> 
> Before the dbx, I tried the Paradigm X-30, but it introduced some low level hiss into my front speakers, and it did not allow for stereo sub output. The dbx unit does not have adjustable phase alignment, but I discovered with the X-30 that with my speaker/sub placement I didn't need it.
> 
> ...


I looked at the dbx stuff but if I can get a DCX2496 new refurbed for $200, then it's comparable per channel with a lot more features...I haven't really found anything else in this price range that does digital crossover and the eq'ing (dynamic too...that aspect looks very interesting), as well as phase control and time delay for time coherency. 

Oh, quick question...the speakers will have no baffle area to speak of...they'll protrude out and only be the diameter of the driver. So, I should be able to acheive a nice, gentle -6db slope into the lower freqs, right? When manufactures rate their drivers for efficiency, I'm assuming they're not taking baffle loss into account, right? As in, a tweeter rated 92db efficient will NOT match a woofer rated 92db efficient...is this correct? 

REW...I haven't played with that at all yet. Need to; I've a BFD for my sub and haven't set it up yet. Does REW model drivers as well? Is it pretty effective?


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## cobyh (Jun 7, 2006)

thylantyr said:


> I posted a reply on your other thread. Based on my DCX experience and seeing
> what you need, there is a very low % chance that you will use the phase control
> and time delay found on the DCX2496.. because most of these issues are more
> theoretical than practical. The real rewards from the DCX are LR 8th order
> ...



I'm actually looking at 21 channels of amplification. Blah. I'm really not keen on 2 channel audio; ever since listening to my dad's Dynaco Quad back in the 70's, I've thought that multichannel is the way to go, hence the effort to do equal 7 channel setup. 

The amps and speakers don't justify the 'complexity', the criteria I've established do. I've got more cables and amps to buy, but ultimately I get a lot more flexibility. And instead of designing a crossover with all the inherent compromises, the active setup lets me tinker...it's a bonus, not a hindrance. If I get it wrong, I can go back and redo it, without throwing away a bunch of components, and resoldering. 

I haven't decided on the drivers, or the amps, but I have decided on active digital crossover, and 7 equal channels, so the complexity really isn't an issue at this point. It's time to play... 

:T


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## reed.hannebaum (Apr 21, 2006)

cobyh said:


> I looked at the dbx stuff but if I can get a DCX2496 new refurbed for $200, then it's comparable per channel with a lot more features...I haven't really found anything else in this price range that does digital crossover and the eq'ing (dynamic too...that aspect looks very interesting), as well as phase control and time delay for time coherency.
> 
> Oh, quick question...the speakers will have no baffle area to speak of...they'll protrude out and only be the diameter of the driver. So, I should be able to acheive a nice, gentle -6db slope into the lower freqs, right? When manufactures rate their drivers for efficiency, I'm assuming they're not taking baffle loss into account, right? As in, a tweeter rated 92db efficient will NOT match a woofer rated 92db efficient...is this correct?
> 
> REW...I haven't played with that at all yet. Need to; I've a BFD for my sub and haven't set it up yet. Does REW model drivers as well? Is it pretty effective?


If I understand you I think you’re correct on all accounts. Once the wavelength exceeds the diameter of the driver, then the response falls off at theoretical rate of -6db/octave. With a baffle, this drop off occurs at lower frequencies and is complicated by the shape of the baffle.

From what I have read, manufacturers measure the efficiency of their drivers when mounted to a very large baffle. So yes, the actual efficiencies will be different for similarly rated woofer and tweeter when mounted to a narrow baffle.

REW is an excellent tool for measuring the frequency and time domain response of your room + system. The software is very flexible and has powerful analytical tools to help identify and correct problems.


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## F1 fan (Jul 6, 2006)

cobyh said:


> Oh, quick question...the speakers will have no baffle area to speak of...they'll protrude out and only be the diameter of the driver. So, I should be able to acheive a nice, gentle -6db slope into the lower freqs, right? When manufactures rate their drivers for efficiency, I'm assuming they're not taking baffle loss into account, right? As in, a tweeter rated 92db efficient will NOT match a woofer rated 92db efficient...is this correct?


If you intend to mount the drivers in close proximity to a wall behind them then their response will be much like it would be if mounted on a large baffle,so they will not have 6db of diffraction loss.


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## cobyh (Jun 7, 2006)

The wall behind them will be over three feet...still an issue? 

I guess easiest thing to do is to build it, drive it and measure it...I'm curious. I am expecting some boundry effect from the screen above the speakers. It's a hellova big flat reflector.


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## F1 fan (Jul 6, 2006)

cobyh said:


> The wall behind them will be over three feet...still an issue?
> 
> I guess easiest thing to do is to build it, drive it and measure it...I'm curious. I am expecting some boundry effect from the screen above the speakers. It's a hellova big flat reflector.


3 ft from the wall would mean that they would get very little boundry re enforcement.

Although if you plan to crossover in the 500hz range then much of the diffraction loss 
will be filled in by the woofer when it is level matched with the midrange.

But like you mentioned you need to do some measurements to get the full picture of what is really going on.


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