Bi-Amping with Active Crossovers - Pros and Cons

Discussion in 'Audio Hardware' started by Soundgarden, Jan 9, 2022.

  1. Roger P

    Roger P Forum Resident

    Location:
    Richmond VA
    I would definitely not discourage at all, that is was drew me to doing DIY etc. It was fun at the time learning and reading and doing.

    Not sure what the OP is trying to achieve, if taking an existing speaker and bypassing the crossover and going dsp and biamping, go for it. I would personally setup up the dsp as close as possible to the existing CO design and work it from there.

    I am all for trying different stuff, hell I burnt up a perfectly good adcom 545 messing around with it many years ago trying to DIY mods others have done. Oops, lol
     
  2. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    I've been of a mind to to stick with an active analog crossover in large part because I've got an all analog vintage system. You're extolling the virtues of digital. Convince me?
     
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  3. jfine

    jfine Forum Resident

    By no means am I a xover expert, but it's my understanding that some passive xover designs can compensate somewhat to flatten the impedance curve. More parts yes that colors it another way. Selection of caps/resistors/inductors/wire, I leave that up to those who know much more about it than me.
     
  4. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    I appreciate your coming to my defense! I do have those things. And persistence. But just as importantly... as I've pointed out... I have a speaker expert on one end and an amp expert on the other. The amp builder will build the actives and the speaker builder will modify the passives. We'd be bi-amping a three way system where the speakers have a simple crossover to begin with. I expect it to take some tweaking and experimenting. So I think I'm going to absolutely nail this.
     
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  5. Roger P

    Roger P Forum Resident

    Location:
    Richmond VA
    While i have never dealt with active analog crossovers, I think that dsp is going to give you much more flexibility in the agility to tweak your crossover preference.

    then again I could be wrong.
     
  6. Roger P

    Roger P Forum Resident

    Location:
    Richmond VA
    I don't think you needed to be defended, you asked for opinions and that is what you recieved.

    We!l if you have someone doing it for you even better! Good luck on your endeavors
     
  7. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    What I'm trying to do is truly understand how this is supposed to be done, options, pros and cons, and then have two true experts produce the mods. I don't want to just say "Here's some money bi-amp my system." Otherwise I won't know what I have, what works, why, or what I might be inclined to try next.

    I've been a scientific researcher, investigative journalist, have built cars, all kind of stuff. I know how to figure things out and get stuff done. Sadly, despite having a genius electrical engineer as a father, a mastery circuitry has always eluded me. In other words, I know my strengths and weaknesses. For an exercise like this, and at least the first time around, I need some help.
     
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  8. House de Kris

    House de Kris VVell-known member

    Location:
    Texas
    If I'm reading your comment correctly, I believe you are referring to the zobel network which compensates for the rising impedance of moving coil drivers. Passive crossovers need this in order to function as planned. I was referring to box tuning resonances imposed on the woofer. If you know of speakers that compensate for that, I'd be interested in learning about them. Every impedance curve I've seen of speakers with passive crossovers still have these box tuning resonances in them, so compensating for them must not be too common. Not saying it doesn't exist, though.

    Going back to the pros of active bi-amplification, we could just ditch the passive crossover (including any zobels), use fat cables from amp to speaker, and effectively eliminate the audibility of this issue completely.
     
  9. Roger P

    Roger P Forum Resident

    Location:
    Richmond VA
    I hear you in that, I have built a couple of classic cars in the past but when I came to DIY crossovers etc you would think I was trying to figure out how to build a dam space craft lol

    I failed several times at that
     
  10. Uglyversal

    Uglyversal Forum Resident

    Location:
    Sydney

    There is no doubt a lot of digital crossovers will give you plenty of flexibility and will be very easy to set up. Some of them will even have the means to connect a microphone and adjust the curve to have a more or less flat response in your room, and with your speakers. The matter is whether such set up will fulfill your expectations or not.
     
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  11. Roger P

    Roger P Forum Resident

    Location:
    Richmond VA
    The person designing the crossovers will more than likely have to do mic'd measurements to design the crossover.

    I think you might also want to visit some DIY forums as well and do some searching and asking.

    That is ultimately how I learned and figured it out. Some of the folks on those forums that is all they do.

    I still do not think I completely figured it out either, while my last set of DIY speakers sounded fine I don't think I achieved what I wanted, that is why they are used in home theater and not critical listening, they took me months and months to build.
     
  12. jfine

    jfine Forum Resident

    I'd be interested in hearing more about the relationship of box tuning resonances imposed on the woofer, due to passive vs active xover designs.
     
  13. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    I would be in the same boat for sure. Thus the experts...
     
  14. Roger P

    Roger P Forum Resident

    Location:
    Richmond VA
    Box resonance and tuning was a problem I ran into as well in the low frequencies, never completely figured it out.
     
  15. jfine

    jfine Forum Resident

    Good ideas here

    Identifying Enclosure Resonances
     
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  16. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    That's an awesome thread. Really lays bare the negative impact of enclosure resonances on impedance. No resonances = better bass!

    @House de Kris and @jfine I'm not sure if this is a dumb question or not. It probably is. But are you saying that passive crossovers are in some ways/some cases designed to compensate for enclosure resonance? If so, then if the passives are replaced by active crossovers, does that then mean that pre-existing enclosure resonances become more of an issue?
     
  17. SandAndGlass

    SandAndGlass Twilight Forum Resident

    You are right. Not in a vintage system. Or in any system where you intend to keep the chain all analog.
     
  18. TheVinylAddict

    TheVinylAddict Scientist's have opinions too

    Location:
    AZ
    I think you already know the answer partly here - the first part of it is that a good, well implemented crossover (active or passive) is the key :) and that just because you go active crossover does not guarantee improvement, especially if replacing a very well engineered passive crossover. All the assertions of "active always better" assumes a lot of things.
     
    Last edited: Jan 13, 2022
  19. Davey

    Davey NP: Björk ~ Homogenic

    Location:
    SF Bay Area, USA
    The passive crossover becomes part of the box alignment since it effects the Q of the woofer (I think the DC resistance of the inductor effects mostly Qes), so when you remove that series inductor from the woofer circuit, the box tuning and hence bass response will change.
     
  20. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Exactly. But what I don't understand is whether the passive crossover itself is either designed to or has the effect of compensating for enclosure resonance induced impedance issues in any of the drivers.

    If it does? Then yes, this is a potential negative of going to active crossovers. Which isn't a reason not to do it per se. But a possible unintended consequence to put in the "con" column and something that needs to be considered.

    @Davey's response suggests that yes this can be a real issue.

    One way to address such an issue, I suppose, would to be to avoid cabinet resonance in the first place. Efforts to accomplish that need to be done very carefully to avoid creating even more unintended consequences.

    But I think there's my main question: Is there a clear need to/way to compensate for this in the design of the active crossover?
     
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  21. Davey

    Davey NP: Björk ~ Homogenic

    Location:
    SF Bay Area, USA
    All I said is that removing the series inductor from the woofer circuit will change the box tuning, not increase resonances. The bass response will change, maybe for the better or maybe for the worse, depends how it was originally tuned and whether you liked it that way.
     
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  22. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Thanks for clarifying. Sorry, didn't intend to put words in your mouth :)
     
  23. House de Kris

    House de Kris VVell-known member

    Location:
    Texas
    No, not at all. The linked thread, while quite good, is about resonances in the enclosure. Box tuning is a much huger, and completely different issue. It has to do with that huge spike on the impedance plot (in the linked thead) at 45Hz or so. That suckered shoots all the way up to 90ohms. This is the resonant frequency of the tuning of the box. Ported speakers have two huge spikes, one at the box tuning, and one at the port tuning. They are the nature of the beast, they are just there. Their presence is part of the definition of resonance, and everything in the known universe resonates. Neither active or passive (that I know of) address these box tuning issues. But, only passive crossover exacerbates their contribution, and not in a good way.

    The resistance in the path between amplifier output and speaker voice coil determines how much the variation in impedance across the spectrum will have an impact on the flatness of the frequency response produced by the speaker because the driving voltage across the voice coil will no longer have a flat frequency response.

    If you have an active crossover and amp connected directly to the woofer, you will have a certain small amount of error. Double the length of the cable, and the error doubles. Keep the length the same and reduce the cable gauge by three gauges and the error doubles. Switch over to passive crossovers and the DCR of the inductor is so huge that it becomes the dominate source of this error. First and second order passive crossovers would have a similar error. Third and fourth order crossovers have even more, as they have two inductors in series with the woofer.

    There will be some, no make that many, who poo-poo this whole discussion. Alas, this is not some subjective wishful thinking, this is objective science. Most will insist that these errors are not big enough to matter since they don't hear them in their speakers with passive crossovers. They will insist that passive crossover speakers are good. Yes, they're not just good, they're good enough. But, if you want to go beyond good enough, and shoot for superior audio, then throwing out the passive crossover is just one step in many to take.
     
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  24. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Then I suppose I'll consider speaker box construction one matter and crossovers another.
     
  25. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Sorry to bug you but I'm curious how removing the series inductor would change the box tuning. Would you mind offering a super simple explanation?
     

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