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Old 22nd November 2004, 05:15 AM   #1
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Default PA vs DIY active crossover

Is there a performance difference between a DIY and PA active crossover?

More specifically:
* a 4th order LR active crossover such (Elliot Sound Products)
* Behringer Active crossover (the main difference that I can see is that it has variable crossover points, but still has the same types of filters

Behringer CX2310 2 way active crossover with subwoofer crossover included

Behringer 3 way version which has limits to each channel

The 2 way Behringer is comparable in cost to what it cost to DIY. I have sent questions to them to see if the sub uses 4LR filters as well, and if the mid driver is rolled off at the sub xo point.

I want to use it to drive my 2 way mains and stereo subs. With the 2 way unit the subs would be mono, is this a significant loss?
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Old 22nd November 2004, 05:39 AM   #2
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I've heard from some whom I consider to be a VERY reliable source that it's not worth DIYing active crossovers. He (a gifted analog engineer) builds his own amps, and encourages me in my persuit of speaker design- but says that active crossovers are good enough as a commodity component. He prefers Rane brand- I never found out which model- but the general point is that you can find it for $100 used, so its probably not worth your time to make your own PCBs and spend the time on it.

I asked him if the 90 db SNR was a concern, and he looked at me like I was new. He said that was the least of our worries- and to be honest, anywhere I've ever lived has had highway/road/computer/breathing noise above 20db.

I guess that you really need to decide what you mean by "performance difference". The performance differnece that matters most for DIY is probably flexibility and convenience, not SNR or THD.

As for your subs being mono... what's the crossover frequency? If it's below 100 hz, it might even be beneficial that it's mono.
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Old 22nd November 2004, 06:00 AM   #3
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Crossover is between 60-80 Hz, higher is preferred but may be influenced by localisation issues as I intend to place the subs next to the listening position.
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Old 22nd November 2004, 06:27 AM   #4
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It sounds like you might want to look into getting some delay- assuming your mains are 5 or so meters farther than the subs, that's a bit over a millisecond of delay you'd want to align the subs with arrival of the main signal.

Many pro crossovers will allow this option, so that's an added benefit of purchasing this particular link in the chain. The Rane crossover I looked at (not personally endorsing it, just had it recommended to me) had this feature, and their website mentioned that an internal modification allows the delay to be applied to any of the three channels of output.

My present outlook is that a happy medium could be found with a pro 3-way crossover with a nice chassis, built in power supply, limiting, delay, and rumble filter- and active filters such as notches and other compensation for dipole effects or linkwitz transform done on small DIY PCBs on the line between the crossover and the amplifiers. My grand 5 year plan involves something like this.
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Old 22nd November 2004, 10:41 AM   #5
Hans L is offline Hans L  Netherlands
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There's one major difference between 'diy' and 'pro' active filters: the first is tailor made and the second is not. If you are serious about designing speakers, I don't see how you could use a generic active xo. But is you're not too fussy about the resulting acoustical slopes, I suppose a second hand active filters is hard to beat costwise. A viable alternative to a diy active filter would be a digital filter which is much more flexible than the average retail active xo.
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Old 22nd November 2004, 11:57 AM   #6
Toaster is offline Toaster  United Kingdom
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I took the Behringer 3-way ready-made option myself for a friends system currently under development. This was only possible because of the very flat acoustic in-box response of the raw mid-bass driver, an Audax HM130CO, and the acceptably flat response of the Morel MD32S tweeter. Another important factor was quite a broad overlap in the usable frequency response of the two drivers. The two major problems with using a stock crossover were thus avoided- a lack of provision for equalising the drivers response to deal with- for example- diffraction loss, and the inhierant acoustic roll-off of the drivers cascading with the active crossovers roll-off to muck up the shape and rate of the resultant acoustic crossover between the drivers.
Building (say) an ESP croosover would probably've been a waste of time in this application, although arguably it might sound better if higher quality parts were used. In practice it sounds fine.
Much to my annoyance I can't easily use the same approach in my own system, which presently uses the Morel MW144 mid-bass. A nice drive unit, but there is a significant 'bump' in the response in my box from about 1.5kHz up to the 4kHz crossover point. I'll probably need to build from scratch or build a kit in order to get the necessary flexibility. Unfortunately it's quite rare to be able to 'get away' without driver eq, but if you can, crossovers like the Behringer do a good job. As noted above, the best off the shelf option for experimenters will be a digital crossover.
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Old 22nd November 2004, 12:17 PM   #7
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Default Re: PA vs DIY active crossover

Konnichiwa,

Quote:
Originally posted by paulspencer
Is there a performance difference between a DIY and PA active crossover?
In many ways and in others no.

PA Type X-Overs tend to be made highly adjustable, which has a sonic cost in complexity and part quality. A dedicated, preset X-Over frequency DIY Unit build to the highest possible standards tends to be superior.

If adjustability is important it may be worthwhile going for a digital X-Over.

Quote:
Originally posted by paulspencer
I want to use it to drive my 2 way mains and stereo subs. With the 2 way unit the subs would be mono, is this a significant loss?
Depends. Can be.

If you want a real active system, with the ability to correct Driver/Room problems etc you should consider the Behringer DCX-2496.

Otherwise consider making a DIY subtractive X-Over for the 2-Way speakers and tailor the subwoofer filter such that you only use a 1st order highpass (electrical) for your main speakers HPF, with a sealed enclosure (in case the speakers are commercial close the port) and a 1st order HPF you usually get a nice 3rd order acoustic slope HPF which can be easily integrated with a sub having a 3rd order LPF, without requiring more than a high quality caoupling capacitor somewhere in the chain to produce the HPF, much better than using a PA Electronic Box in most cases.

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Old 22nd November 2004, 01:51 PM   #8
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I'm looking at using Behringer Ultracurve DEQ, which I can use to also perform all other functions not otherwise performed by the active crossover in dealing with the response of the drivers.

Ultradrive looks very appealing, however the cost is prohibitive at this stage. I'm interested in this as a future option.

I can come up with a DIY active xo for AU $100

The Behringer 2 way is $169,
3 way RRP is $300 but can probably get it for more like $250

My mains are transmission line. At the point I wish to cross I don't have the rolloff to use a first order slope. Why not just use a 4th order LR? As linearity, headroom and output are major design concerns, I'm crossing fairly high - possibly as high as 80 Hz.

Regarding delay to my subs, the path difference is about 2m or slightly more, which is equivalent to about 6msec. It seems debatable if this is necessary for a subwoofer. With a fairly crude setup I found the subs did a pretty good disappearing act, not quite perfect, but very good considering I haven't build proper inert boxes and haven't calibrated and set it all up yet.
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Old 22nd November 2004, 02:44 PM   #9
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Konnichiwa,

Quote:
Originally posted by paulspencer
I'm looking at using Behringer Ultracurve DEQ, which I can use to also perform all other functions not otherwise performed by the active crossover in dealing with the response of the drivers.

Ultradrive looks very appealing, however the cost is prohibitive at this stage. I'm interested in this as a future option.
Actually, the DCX-2496 is only 100 Oz Bucks more expensive than the DEQ-2496. So it gives you pretty extensive EQ funcionality AND a highly flexible X-Over for the same as your DIY X-Over and DEQ....

Quote:
Originally posted by paulspencer
My mains are transmission line. At the point I wish to cross I don't have the rolloff to use a first order slope. Why not just use a 4th order LR?
The 4th order LR is a theoretically perfect filter, which means it only works in situations where the speakers conform to theoretical perfection (as in flat response at least 2 octaves above and below x-over point, completely conincidental sources etc)....

Quote:
Originally posted by paulspencer
As linearity, headroom and output are major design concerns, I'm crossing fairly high - possibly as high as 80 Hz.
Well, you might find that removing the organ pipe resonators and making the box sealed might give you a good compound rolloff at a given frequency you can choose fairly freely. Anyway, your choice.

Sayonara
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Old 22nd November 2004, 04:33 PM   #10
Hans L is offline Hans L  Netherlands
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Quote:
Originally posted by Kuei Yang Wang
The 4th order LR is a theoretically perfect filter, which means it only works in situations where the speakers conform to theoretical perfection (as in flat response at least 2 octaves above and below x-over point, completely conincidental sources etc)....
Not only are we dealing with electronic crossover slopes, which tend to not work on the average driver, even if the drivers are sufficiently flat in and outside the bandpass, the LR4 so often seen on retail active xo's aren't necessarily the best filtering around.
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