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Thread: Biamp crossover question

  1. #1
    Steve Gonzales
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    Biamp crossover question

    While I run my system in full triamp mode, I've often wondered what the effects of an electronic crossover being used in a biamp configuration are?. Here is an example: JBL 4343 in biamp configuration: Low pass into an amplifier, then into the LF input terminals of the 4343's crossover, then the HP is routed to an amplifier and then hooked to the top end terminals which then divides the signal passively. So what type of interaction between the electronic crossover and the passive is taking place?. If the electronic crossover has a 12db/oct slope and the passive circuit has a 12db/oct slope, what happens to the phase?. I have assumed, that since they add, a 24db/oct slope will be the outcome and remain in phase with the LP/LF section, assuming that the LP was an even order too?. What are the other effects going on here?. What can a pure passive crossover of high quality do better than a good electronic crossover and vice-versa? Another question I've wondered about is if a stock passive crossover can be easily modified to suit a completely different driver. Here is an example: An N220 passive is engineered to work with an LE5-9 midrange. Can just the midrange section of the network be modified to work with an LE85/H92 combo without touching the HP/LP filter sections in the network? It seems to me that it would effect the whole thing. Thank you for the information, Steve G.

  2. #2
    Senior Member Ian Mackenzie's Avatar
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    information overload.

    in the case of biamping a JBL monitor, the woofer low pass passive filter is usual completely bypassed and the high pass filter to the mid/horn etc is also bypaased so you only get the slope of the active filter (the 4435/35 is the exeception where the active and passive high pass filters do combine

    As a rule electronic active filter do intrude on the tonality of loudspeakers for hifi use with soe rare exceptions.

    To be continued:

  3. #3
    Steve Gonzales
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    Are you sure?

    It seems to me that if a 4343's passive section was completely bypassed, the midbass,midrange and UHF wouldn't get filtered. Say you were to use an M552 and cross over at 250hz. I believe that the passive is still engaged because how else would the 10" midbass, 2307/2420 and 2405 "self filter" with respect to each other?.

  4. #4
    Senior Member Ian Mackenzie's Avatar
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    Sorry but only only had one minute to reply.

    I don't have time to upload a schematic but what happens is the mid cone high pass passive filter elements are bypassed so there is no series capacitors or inductor shunted across the signal. Nor does the woofer have a series inductor or a capacitor shunted across the signal. Normally the horn and tweeter continue to use their passive filter elements. In the case of the 3143 network as I recall the horn and and uhf signals were via the mid filter to provide better protection from amplifier transients.

    Getting back to your question.

    In th case of JBL engineered systems, the filters are tailored especially for the system at hand so either active or passive will provide nearly identifcal acoustic response.

    Note this is seldom the case when a diy person attempts to bi amp an existing passive crossover..

    The prime benefit is better performance from the woofer in most home brew active systems. In professional applications like monitoring it results in greater dynamic range and reduces power loss in the use of passive networks.

    Active crossovers however do not necessarily mean a handshake for improved fidelity for home listening. It depends on the standard of your other equipment and that of your speakers.

    Sorry I do not have time to consider your other questions and i am not sure how you have your system currently arranged. This would require a complete re design of the crossover network and is best left to an experienced / qualified person with test equipment such as Clio / Leap

  5. #5
    Administrator Robh3606's Avatar
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    Hello Steve

    To keep it simple when you biamp a 4343/44 you remove the Low pass filter on the woofer and 1/2 of the bandpass filter on the 2121/22. You still have the other half of the bandpass filter in line for the 2121/2 to provide a smooth transition to the compression driver as well as the rest of the crossover.


    Rob

  6. #6
    Steve Gonzales
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    Right.

    Kinda already knew that stuff, gents, thanks anyway. I want to know what's going on between the passive and electronic, is there something special about the blending of them that gives the speaker it's tonal quality or a compromise for the obvious reasons?. I just used the 4343 as an example. What I should have asked was: is it that difficult to achieve the same tonal quality in a 4 way with an all electronic crossover? I've had great success with my triamped system, so it doesn't seem a stretch to do it with a four way, I need to hear from someone that has heard both, picked one, and why. There is not a bi-amp capable passive crossover in the JBL inventory that is exactly what I need. I've considered having some built but don't want to go through that much trouble if I can expect the same performance from a quality electronic. Is there something particularly better about the way a passive sounds vs. an electronic of equal quality?

  7. #7
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Steve Gonzales
    What I should have asked was: is it that difficult to achieve the same tonal quality in a 4 way with an all electronic crossover?
    That is a very broad question.

    Let me try to explain. If the passive network has asymmetrical slopes, overlapping slopes, slopes that are not textbook for any other reason, additional filters to tame resonance, compensate for HF fall off or any other unusual aspects you may not be able to duplicate it with just any crossover. There are some that can be tailored to match most or all of these conditions, but if you don't FULLY understand what the passive network you are trying to emulate is doing, you will never really duplicate it's sound.


    Quote Originally Posted by Steve Gonzales
    Is there something particularly better about the way a passive sounds vs. an electronic of equal quality?
    Not inherently, but... See above....

    That said, I've posted this before but bear with me. Adding an active crossover is the same as adding a second preamp. If you have a good system (one that doesn't use ANY LSI chip based receiver, processor, or integrated) you should try to get one of the very few crossovers that are as good as your preamp. All of the affordable semi-pro and pro models that we are familiar with don't cut it. Some are better than others, but they all add a sonic signature that ideally wouldn't be there. Forget the subtlety of changing wires... we are talking sonic signature.

    An example of whether or not it is possible to match the sound of an active and passive network. I use my active as a tool in designing my passive filters. I can quickly compare a 1st, 2nd, 3rd order etc. at any frequency with my digital active and when I hear what I like I build the passive... I build the passive for the actual impedance not the label and it sounds and measures surprisingly similar to the electronic one I liked.


    Widget

  8. #8
    Senior Member Ian Mackenzie's Avatar
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    Steve,

    In my view the most improvement comes from biamping.

    To tri or quad amp addsa lot of complexity and issues of S/n ratio can arise with horns unless great care is taken.

    For example you might have a nice SS amp for your woofers and a nice sweet SE Triode for your horns. Provided the active crossover is up to the task you will reap the rewards. In some cases where your Valve amp has a high input impediance say 1-2 megohms a simple high level passive RC network b/n the pre amp and the power amp is all that is required with a buffered low pass filter for the low end.

    As Widget say, particularly if you are dealing with unknwn drivers some experiementation of slopes and crossover points is required for the best blend just asa designer would tailor a passive network. 9/10 times most drivers are not plug and play!

    Ian

  9. #9
    Administrator Robh3606's Avatar
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    There is tailoring in the passive neworks that an M552 or M553 cannot duplicate. One of the more flexible digital loudspeaker management systems can do tailoring like a passive network. I have an active 4 way and my biamped 4344's both sound great, well to me at least. But like Widget and Ian say drivers are not plug and play. You may get a peak hear or there depending on where your crossover points are and what the individual driver responses are. With a typical active you don't have to worry about attenuation and you have flexabillity of moving the crossover point. In a simple analog 24db like the ones we are using you can't do different slopes or assymetrical ones. Your stuck with only those 2 variables. With a pasive network you have no limitations. As long as you recognize what you can and cannot do you should be fine using common sense your ears and some basic measurement tools.

    Rob

  10. #10
    Steve Gonzales
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    Good

    Thank you all, for your opinions. Widget, what do you mean when you say that one of the reasons you use a passive is because of the impedence?. Is it not better to filter the signal, i.e, have the amp deal with the driver's reactive load than an LCR network?. Also, what experience do any of you have with electronic crossovers that manipulate the signal in the digital domain? I'm considering a JBL DSC 260 or 280, they have the ablilty to equalize and I believe time correction too. I realize that my M553 is not the end-all. What it has allowed me to do is get my feet wet and experience the ease and flexiblity an active crossover can offer. When I start upgrading things, I like to be informed about the choices and the pros and cons of those choices. Your answers will help, thank you.

  11. #11
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Steve Gonzales
    Widget, what do you mean when you say that one of the reasons you use a passive is because of the impedence?.
    I didn't say that! I said pay attention to what the impedance really is.

    I'd avoid those two older JBL digital units... digital is changing fast... anything older than the last year or two isn't very good... yeah, that is a generalization, but reasonably true.


    Widget

  12. #12
    Steve Gonzales
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    gotcha

    What is your active crossover of choice?

  13. #13
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Quote Originally Posted by Steve Gonzales
    What is your active crossover of choice?
    Analogue, or digital...?
    bo

    "Indeed, not!!"

  14. #14
    Steve Gonzales
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    Both

    Since I'm gathering info for an upgrade, I'd love to have some recommendations. Maybe your take on what the best overall, as far as type, is.

    BTW Bo, I've often wondered how the short conical 2307 w/2420 is so good in the 4345.

  15. #15
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Steve Gonzales
    BTW Bo, I've often wondered how the short conical 2307 w/2420 is so good in the 4345.
    Since Bo answered a question I thought was directed at me, I'll butt in and give an answer posed to him.

    The 4345 uses the 2421 not 2420... that helps and the 1200Hz crossover also helps. In Bo's case he further helps out his 4345s with careful EQ.

    As for the crossover question.

    I really like the DEQX PDC 2.6P I am using. It is quite transparent and not at all digital sounding. If you do some searches we have discussed actives quite a bit... there are several that have been recommended.


    Widget

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