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?
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?
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.
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.
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.
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.
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.
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.
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.
Konnichiwa,
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.
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.
Sayonara
paulspencer said:
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.
paulspencer said:
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.
Sayonara
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.
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.
Konnichiwa,
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....
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)....
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
paulspencer said:
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....
paulspencer said:
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)....
paulspencer said:
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
Hans, I'm not sure what you mean when you say that electronic crossover slopes won't work with the average drive unit. There's not really anything you can do with a passive that you can't do (better?) with an active crossover. The reverse is not true! As to the 4LR, opinions differ of course, but it's a valid alternative with it's own advantages and disadvantages. IIRC, Linkwitz specifies the use of all-pass time delay networks for proper implementation.
Re-reading Paul's posts, if it's just a sub to main speaker two-way crossover you need, you may well be able to use a commercial crossover. The first step would be to measure the unfiltered in-room response of the sub and main speaker to see how much overlap you have either side of your desired crossover frequency. If you have ambitions to go to a full three-way active system, and especially if further projects are likely, the Behringer DEQ is well worth stretching to. I suspect I'll be investing in one fairly soon, even if in the long run it's just used as a development tool...
Re-reading Paul's posts, if it's just a sub to main speaker two-way crossover you need, you may well be able to use a commercial crossover. The first step would be to measure the unfiltered in-room response of the sub and main speaker to see how much overlap you have either side of your desired crossover frequency. If you have ambitions to go to a full three-way active system, and especially if further projects are likely, the Behringer DEQ is well worth stretching to. I suspect I'll be investing in one fairly soon, even if in the long run it's just used as a development tool...
The only thing I'm saying is that you need a huge overlap of two drivers , bith with a flat response of their own in order for the electronic filter to turn out the way it was supposed to. But normally you don't have this luxury and you want all kinds of correction in order to obtain for instance true LR4. Maybe you need a low Q 2nd order filter on the HP and something similar to a butterworth 2nd order on the LP, including some bafflestep. And that's still assuming the drivers themselves measure flat...
I wasn't aiming at Paul initial post, so it was just a general remarks about retail xo's.
I wasn't aiming at Paul initial post, so it was just a general remarks about retail xo's.
Hans,
Anything is possible with an active crossover, but the distinction between dedicated active crossovers and commercial LR24 crossovers with state-variable topology needs to be made clearer.
A typical example would be the Marchand XM-9. With this unit it is not possible to have different xover frequencies of the low and high-pass filters and it doesn't support asymetrical slopes so your examples would be a problem for it. However, there are other options....XM-44, DIY dedicated, DSP-based, etc.
The driver requirements, with regards to overlap, for an active crossover system are no different or more stringent than for a passive crossover.....assuming the crossover is flexible and the proper topology can be created.
Davey.
Anything is possible with an active crossover, but the distinction between dedicated active crossovers and commercial LR24 crossovers with state-variable topology needs to be made clearer.
A typical example would be the Marchand XM-9. With this unit it is not possible to have different xover frequencies of the low and high-pass filters and it doesn't support asymetrical slopes so your examples would be a problem for it. However, there are other options....XM-44, DIY dedicated, DSP-based, etc.
The driver requirements, with regards to overlap, for an active crossover system are no different or more stringent than for a passive crossover.....assuming the crossover is flexible and the proper topology can be created.
Davey.
Hans L said:
I think your post was repeating, not clarifyingDavey said:
But aparently I wasn't clear enough, so here it is again: commercial active xo's are often inflexible, which renders them pretty much useless imho. Those who are not cost more, so in that case you might as well skip them and go straight to DSP's which are generally extremely flexibel.See my first post.
Konnichiwa,
Well, I would argue that frequencies and slopes should be settable accuratly and such, that when the resulting outputs should be re-integrateable into a squarewave if such is present on the input, they actually do (most state variable X-Overs have by far too wide a tolerance to ensure that BTW, even if the Filter is LR4).
Further, it should be fundamentally transparent sonically and allow the equalisation of driver imperfections/frequency response aberations.
In case non-conicident drivers are used one MUST be able to "time-align" the drivers.
Anyway, what comes to mind on short notice.
Sayonara
Bricolo said:
Well, I would argue that frequencies and slopes should be settable accuratly and such, that when the resulting outputs should be re-integrateable into a squarewave if such is present on the input, they actually do (most state variable X-Overs have by far too wide a tolerance to ensure that BTW, even if the Filter is LR4).
Further, it should be fundamentally transparent sonically and allow the equalisation of driver imperfections/frequency response aberations.
In case non-conicident drivers are used one MUST be able to "time-align" the drivers.
Anyway, what comes to mind on short notice.
Sayonara
YMMV
It now seems pretty obvious that an "entry level" active like the Behringer CX3400 is a 'blunt tool' that may give you approximately want, quickly for a pretty modest outlay.
If you want to really the speakers you need something with the ability to fine tune, like a DCX-2496 for a quick result, or more effort - say Speaker Workshop/ SoundEasy & do your own.
How far do you want to go? How many Speakers might you do?
I have a CX3400 (still in box, hope to use within a week actually), but I'm just after quick indicative answers.
I'm wanting to do several speakers, with some more challenging but hopefully rewarding drivers, so am probably getting SoundEasy. Though I’m balking at the cost of the sound card!
Cheers
It now seems pretty obvious that an "entry level" active like the Behringer CX3400 is a 'blunt tool' that may give you approximately want, quickly for a pretty modest outlay.
If you want to really the speakers you need something with the ability to fine tune, like a DCX-2496 for a quick result, or more effort - say Speaker Workshop/ SoundEasy & do your own.
How far do you want to go? How many Speakers might you do?
I have a CX3400 (still in box, hope to use within a week actually), but I'm just after quick indicative answers.
I'm wanting to do several speakers, with some more challenging but hopefully rewarding drivers, so am probably getting SoundEasy. Though I’m balking at the cost of the sound card!
Cheers
Hans (is that you Hans Laros from the DIY speakers list?),
I don't follow why it would be necessary for a 4LR to have two octaves flat on either side. I would have thought that a steeper slope decreases the need for a flat response either side.
One thing that appeals is the impact of the steeper slope on the output of the tweeter and midbass. I'm interested in using the Vifa XT tweeter, which I understand prefers a 3rd order @ 2.8k when passive. With active, I could go a little lower due to the higher slope and avoid overstressing it. Likewise, the midbass drivers if crossed at 60-80 Hz with a 4LR should gain significant output potential and headroom, as well as midrange clarity - they achieve what I preceive to be useable output down to perhaps as low as 25 Hz in room.
I'm very interested in Behringer Ultracurve DEQ. Ultradrive has interested me for some time, but I'm putting it off due to cost (approaching the cost of the speakers themselves). I have a chance to get DEQ cheap. I could actually do a DIY active xo to just divide up the frequencies, then do everything else with DEQ. Later I could add DCX when I get a good deal on it, or save up some more.
This would have to be better than my current passive xo, which is crossed probably too high (2nd order @ 3.5k) and the tweeter was a bit over-done so I padded. It's a 2.5 way xo.
Using DEQ I can actually assign digital delay to a 2nd output (all other settings being the same). I could use this to time align the subs or the tweeter to the mids. For some crazy reason the 3 way Behringer active analogue xo only assigns delay to the bass, when it is probably better for the tweeter! In PA speakers I imagine one would want to time align the mid and tweeter the most as they have considerable offset in the case of most compression horns!!!
I don't follow why it would be necessary for a 4LR to have two octaves flat on either side. I would have thought that a steeper slope decreases the need for a flat response either side.
One thing that appeals is the impact of the steeper slope on the output of the tweeter and midbass. I'm interested in using the Vifa XT tweeter, which I understand prefers a 3rd order @ 2.8k when passive. With active, I could go a little lower due to the higher slope and avoid overstressing it. Likewise, the midbass drivers if crossed at 60-80 Hz with a 4LR should gain significant output potential and headroom, as well as midrange clarity - they achieve what I preceive to be useable output down to perhaps as low as 25 Hz in room.
I'm very interested in Behringer Ultracurve DEQ. Ultradrive has interested me for some time, but I'm putting it off due to cost (approaching the cost of the speakers themselves). I have a chance to get DEQ cheap. I could actually do a DIY active xo to just divide up the frequencies, then do everything else with DEQ. Later I could add DCX when I get a good deal on it, or save up some more.
This would have to be better than my current passive xo, which is crossed probably too high (2nd order @ 3.5k) and the tweeter was a bit over-done so I padded. It's a 2.5 way xo.
Using DEQ I can actually assign digital delay to a 2nd output (all other settings being the same). I could use this to time align the subs or the tweeter to the mids. For some crazy reason the 3 way Behringer active analogue xo only assigns delay to the bass, when it is probably better for the tweeter! In PA speakers I imagine one would want to time align the mid and tweeter the most as they have considerable offset in the case of most compression horns!!!
Kuei Yang Wang said:
What is needed for a squarewave output? I assume that LR4 isn't enough, because a rapid spice simulation of my active XO project shows something awfull at the output (both outputs summed) when I inject a squarewave. And that was for a LR4 alignment. (squarewave at the XO frequency)
Time aligning the drivers, can this be done with a delay like this all pass?
http://www.linkwitzlab.com/filters.htm#4
And, when you mentionned equialisation of driver imperfections/frequency response aberations. Isn't this getting away of the active xo's role? You're talking about a parametric equalizer, aren't you?
Konnichiwa,
I think what people are alluding to is that the LR4 X_over has certain theoretical advantages over traditional (other) active X_Over structures, mostly that it can combine back into a phase, pulse and amplitude "perfect" response. Of course, this simplies accurate slopes, given the fairly high order of the filter (4th) the circuit is rather sensitive to component tolerances.
My suggestion for this, when using an active X-Over would be an inverting (Rauch/Multiple feedback) 3rd order Highpass combined with a subtractive section for the Mids. Using such an approach is much more resilient to component tolerances and the two responses always integrate back.
You might find that first building such an X-Over and adding the neccesary equalisation (you can estimate what is needed quite well from datasheets and simulations and then finetune by ear) for the Woofer/Midrange to the feedback return of the subtraction circuit will make for a very simple and good active X-Over.
The Highpass for the Mid/Woofer section can be applied in two 1st order sections, one before the actual X-Over and one after the subtraction amp, as long as the load is then buffered or a defined output load can be assured. The resulting X-Over can be build with just two quality Op-Amp's and at the maximum two buffers (not unity gain Op-Amp's please) per channel.
The Subwoofer X-over I would actually suggest you consider something more usefull than a direct X-Over.
My suggestion would be a variation of the subwoofer EQ rod Elliott shows, plus a suitable variable and finetunable X-Over and continouslyt variable phase.
This approach suggested here is much more likely to actually work in practice giving excellent results than LR4.
You may overestimate the gains. The biggest gains are when you insert the 1st order HPF, going up gives more headroom up to a point, a a lot of LF intensive instruments (Kick Drum, Bass) tend to have their main output when played above or around the 80Hz you quote.
Behringer equipement is quite affordable and usually well discounted below list. Similar digital X-Overs exist from other manufacturers, I would strongly suggest to consider saving a little and going for the DCX, it is just muchj more flexible and easy to configure than what you have in mind. If you have the chance to compare you may very well find that X-Over slopes other than LR4 sound considerably better.
Don't. The second output is really low quality and I mean REALLY LOW quality.
Actually, Behringer is not crazy. In PA Speakers the Mid/Tweeter tend to be horns which have their acoustic centre well behind the woofer when put into conventional cabinets. Thus the woofer output will arrive earlier than the tweeter one and needs to be delayed. In HiFi Speakers the whole situation is of course the reverse.
Sayonara
paulspencer said:
I think what people are alluding to is that the LR4 X_over has certain theoretical advantages over traditional (other) active X_Over structures, mostly that it can combine back into a phase, pulse and amplitude "perfect" response. Of course, this simplies accurate slopes, given the fairly high order of the filter (4th) the circuit is rather sensitive to component tolerances.
paulspencer said:
My suggestion for this, when using an active X-Over would be an inverting (Rauch/Multiple feedback) 3rd order Highpass combined with a subtractive section for the Mids. Using such an approach is much more resilient to component tolerances and the two responses always integrate back.
You might find that first building such an X-Over and adding the neccesary equalisation (you can estimate what is needed quite well from datasheets and simulations and then finetune by ear) for the Woofer/Midrange to the feedback return of the subtraction circuit will make for a very simple and good active X-Over.
The Highpass for the Mid/Woofer section can be applied in two 1st order sections, one before the actual X-Over and one after the subtraction amp, as long as the load is then buffered or a defined output load can be assured. The resulting X-Over can be build with just two quality Op-Amp's and at the maximum two buffers (not unity gain Op-Amp's please) per channel.
The Subwoofer X-over I would actually suggest you consider something more usefull than a direct X-Over.
My suggestion would be a variation of the subwoofer EQ rod Elliott shows, plus a suitable variable and finetunable X-Over and continouslyt variable phase.
This approach suggested here is much more likely to actually work in practice giving excellent results than LR4.
paulspencer said:
You may overestimate the gains. The biggest gains are when you insert the 1st order HPF, going up gives more headroom up to a point, a a lot of LF intensive instruments (Kick Drum, Bass) tend to have their main output when played above or around the 80Hz you quote.
paulspencer said:
Behringer equipement is quite affordable and usually well discounted below list. Similar digital X-Overs exist from other manufacturers, I would strongly suggest to consider saving a little and going for the DCX, it is just muchj more flexible and easy to configure than what you have in mind. If you have the chance to compare you may very well find that X-Over slopes other than LR4 sound considerably better.
paulspencer said:
Don't. The second output is really low quality and I mean REALLY LOW quality.
paulspencer said:
Actually, Behringer is not crazy. In PA Speakers the Mid/Tweeter tend to be horns which have their acoustic centre well behind the woofer when put into conventional cabinets. Thus the woofer output will arrive earlier than the tweeter one and needs to be delayed. In HiFi Speakers the whole situation is of course the reverse.
Sayonara
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