Bi-Amping with Active Crossovers - Pros and Cons

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

  1. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    [​IMG]
    So here's what I figure is the next logical question that any non-engineer in my position would ask. How do you turn this passive crossover design into an equivalent line-level crossover? I don't expect a detailed answer, that's what the builder is for. But how is such a task approached?

    The added twist of course is that the line-level crossover only has to separate the lows from the mids/highs. And the speaker needs to be adapted so that lows go directly to the woofer and the mids are separated from the highs before going to the mid-range driver and tweeter respectively.
     
  2. Phil Thien

    Phil Thien Forum Resident

    Location:
    Milwaukee, WI
    There isn't a 1:1 conversion. Some passive crossovers include some degree of baffle step compensation (google it), they may include additional components to tame resonant peaks, etc.

    You can start with crossover frequencies and slopes, but if you're using an aluminum woofer or tweeter (for example), you may find a need to add some equalization or to revert to adding some passive components back via a speaker-level filter.
     
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  3. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    I suppose that gets back to the point that several have made of build, listen, adjust, repeat...

    But are you saying that the crossover schematic may not contain all the components that are actually included in the crossover design?
     
  4. Phil Thien

    Phil Thien Forum Resident

    Location:
    Milwaukee, WI
    Pretty much. The more suitable the drivers, the faster you're going to get to the finish line.
     
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  5. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    So one way to do this might be to start with a tunable, custom-built, analog, active crossover. Once that's dialed in, I can take some measurements and have one built using fixed components.
     
  6. Davey

    Davey NP: Portishead ~ Portishead (1997)

    Location:
    SF Bay Area, USA
    You would remove the strap, short the 0.4mH inductor in series with the woofer, and short the 6uF and 24uF caps in series with the midrange, and (I think) open the 0.4mH inductor across the midrange, apparently the midrange doesn't have an extra electrical crossover with tweeter, that gets rid of the lower crossover, which will now be implemeted at line level. The impedance of the high end section on its own may be a bit wonky, though, you'd have to model it or measure it.
     
    Last edited: Jan 11, 2022
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  7. Randoms

    Randoms Aerie Faerie Nonsense

    Location:
    UK
    I have only ever compared manufacturers passive set up to their own active set up.

    Some Meridian M2 and M3 active only designs (which only required a line input) were still around, as were some Arc speaker / Nytech amplification systems, but most of my early experience was from Linn (speakers) / Naim amplifiers and active crossovers.

    Whereas original the Linn Isobarik had passive (DMS) and an active (PMS) versions, the last versions had no built in crossovers.

    [​IMG]


    The passive crossover fitted inside the speaker stand:

    [​IMG]

    Here is an early Linn active crossover for their Isobariks:

    [​IMG]
     
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  8. Jim Hodgson

    Jim Hodgson Galvanically Isolated in Greenpoint

    Location:
    Brooklyn, NY
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  9. SandAndGlass

    SandAndGlass Twilight Forum Resident

    I would venture a guess that since I had been running the 100-dB. sensitive Altec’s with a 3.9-Watt tube amp, I think it would be fair to assume, that by the time that border is crossed, it would well be into hearing damage!

    Quite true, but another member would have the forum believe that iron core inductors are inherently evil and that every one of them will saturate, perhaps just by looking at them?

    I guess that the same thing applies to evil iron core transformers, being that they are also just coils of wire (inductors) wrapped around an iron core?

    I guess this would mean that all tube amps, except for OTL's, will saturate and therefore are bad imperfect designs.

    Also forgot to mention that the ALK crossover in the photo has a transformer looking object on the far left. This is actually an autoformer, which is an iron core inductor with various taps.

    Not to mention that the ALK crossover in the picture clearly violates his rule #4, due to the inductorts not having a heavy gage wire that would make them the size of large donuts...

    I should also notify Al Klappenberger, who is the ALK in ALK Engineering, that his designs are apparently all wrong. Apparently three decades as a microwave engineer are clearly not sufficient to learn him about the flawed logic of using iron core inductors in crossovers.

    [​IMG]
     
  10. SandAndGlass

    SandAndGlass Twilight Forum Resident

    The issues are those that originate with aftermarket changes by individuals who have little knowledge of the design concepts and engineering.

    If a crossover is designed by the speaker manufacturer, it doesn't matter where or how that crossover is implemented. Crossovers can be on the inside or the outside of the speaker cabinet.

    Crossovers can also be line level, prior to the power amplifiers, that's perfectly fine. Active or passive line level crossovers, both are completely workable. This is because they are part of the overall speaker design and function as the manufacture engineered them to.

    The main thing is, that in a home environment the passovers are integral to the speaker design. To open up the speaker cabinet and bypass the original crossovers, is simply far from being a good idea.

    Bi-amping by itself using the crossover networks already in place is perfectly acceptable, as long as the particular is designed to accommodate this modification.

    Some speaker manufacturers are going to have a single pair of speaker terminals. This arrangement makes a clear statement that that particular speaker is not designed for bi-amplification.

    Many speakers have two pair of speaker terminals that are bridged. This is so that particular speaker can be bi-amped, if the owner desires to do so.

    By removing the jumper wire, you then have both the option to bi-wire and the option to use dual amplifiers.

    Another little fallacy that has worked its way into the thread is the absolute requirement to use two identical amplifiers when employing bi-amplification.

    While you certainly are welcome to do so and it may simplify level matching a bit. But to consider it some kind of mandate is silly. To allow the woofer plenty of power and headroom, you might decide to use a 500-Watt amplifier on the woofer and use a 100-Watt amp on the midrange and tweeter.

    Often individuals will use a powerful SS amp for the bass and use a tube amp for the mids and HF.

    You can crank 100-Watts through a large speaker like a K-Horn and the super-tweeter is only using a Watt or two of that power.

    While a manufacturer may opt for a line level crossover approach, such a design is limited to the factory implementation. This does not allow the end user the degree of flexibility in choice of amplification.

    If a speaker manufacturer closes shop, I'm not all that distressed. Passive speakers will likely last many decades. If the manufacturer has many units sold, spare drivers and such are usually able to be sourced on eBay. If the electronics go south, then it becomes a much larger issue.
     
  11. Funky54

    Funky54 Coat Hangers do not sound good

    You’re not hearing what I’m hearing… since I’m here first hand and not theorizing from what my best friends dentists roommate said about British people in 1980… I’ll go with my opinion.


    Here’s another trick you’re not considering.. if my Left Channels of each stereo amp are connect to the LF woofer I can go with tubes that highlight stiff bass. Since the right channels of each stereo amp is connected to the Mid/High F’s.. I can roll for the beautiful holographic soundstage. My amps are EZ-bias so I don’t have to run identical valves from the left to right channels.. so as long as I match left with left, right with right.. do that with mono blocks and let us know.
     
  12. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    It sounds to me like you’re saying that issues with bi-amping in a home audio environment typically arise because someone with little knowledge of design concepts and engineering is doing the work. Correct? If so yes that makes perfect sense and I would imagine just about anyone on this thread would agree.

    But it my case I’ve got a speaker with a fairly simple crossover design. I’ve got a guy who just finished an expert rebuild of those speakers willing to work with me. And I’ve got the expert who builds my amps ready to do a custom analog active crossover. Which is something he’s done for many of his customers.

    So doesn’t it stand to reason that this can actually go quite well? Because both are engineers with tremendous knowledge of the design concepts involved.
     
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  13. House de Kris

    House de Kris VVell-known member

    Location:
    Texas
    That's is a very simple first order crossover which you can easily replicate before the amps. Don't remove the inductor across the midrange. I'd also add a fourth terminal and move the black wire from the woofer to it. I wouldn't feel comfortable connecting the returns of two dissimilar amps together.

    One of the faults of this design is that the crossover frequency shifts when you change the level controls. You could try to mimic this behaviour, or you can set out to improve this speaker - your choice.
     
  14. House de Kris

    House de Kris VVell-known member

    Location:
    Texas
    I have never witnessed such a violent defense of mediocrity. Really, whatever path you choose is fine. You can pass alone the fact of Rule 4 violation to ALK, but they've made their choice as well as to what compromises they're willing to live with. And no, a properly sized inductor would be MUCH bigger than a large donut. If you replaced all those inductors with no compromise coils, you'd be looking at over $10,000 just for the inductors alone. This would all be done to make the passive crossover perform almost as good as a multi-amped system. But, I can understand that is not your goal, and I'm fine with it. Really.
     
  15. House de Kris

    House de Kris VVell-known member

    Location:
    Texas
    Oops, my bad, do remove the inductor. Seems when the changed the midrange they lowered the cutoff and made it a second order at the same time. If I were doing this, I'd make the low-pass on the woofer second order as well, thus making both second order, not first. Sorry for the early morning gaffe.
     
  16. Gibsonian

    Gibsonian Forum Resident

    Location:
    Iowa, USA
    You bet! It's all about the implementation. Both passive and active can work very well.
     
  17. monte4

    monte4 Senior Member

    Location:
    Ontario Canada
    I'm biamping with active crossovers, but everything's been done for me as I'm running an Activ Linn system. There are active crossover cards installed in my power amp and the passive crossovers in the speakers are disconnected. I ran the system as a normal setup for 20 years then when to an active crossover set up and the difference was night and day.
    As far as just biamping without external crossovers, my Linn dealer has always maintained that one great amplifier will sound better than 2 lesser amplifiers biamped provided that a single great amplifier has enough headroom for the speakers that it is driving.
     
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  18. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Thanks for sharing that. Who did the work installing the active cards and disconnecting the passive crossovers? And are all your components Linn?
     
  19. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Thinking about the impact that gain has on first order crossover behavior... in theory one could add crossovers even earlier in the signal chain, like prior to the pre-amp volume knob. That would require multiple pre-amps to process the separated frequency ranges. And of course a power amp for each pre-amp.

    I can't imagine that this is ever done for quite a few very good reasons. One reason being that it unless it was also adjustable the pre-amp would be hardwired to a single speaker design. Sorry, just musing about this over first cup of coffee. Not a serious consideration.
     
  20. Randoms

    Randoms Aerie Faerie Nonsense

    Location:
    UK
    Definitely agree that two lesser amps passive bi-amped is less good than a single better amp.

    Nice. Yes, I did the Keilidh passive / active demonstration on numerous occasions, the improvement is "very obvious"!

    BTW, if you ever want to upgrade again in the future, the Linn Ninka use the same Aktiv cards as the Keilidhs, so you can literally simply swap loudspeakers. I recommended this to a friend who I sold a 2 x LK140 / Keilidh Aktiv system back in the nineties.
     
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  21. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    @SandAndGlass I'm genuinely interested in your response. Just trying to clarify your hang-ups with bi-amping in a home setup like mine.
     
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  22. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    This begs the question of whether you think two lesser amps can be better than a single better amp if actively bi-amped!
     
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  23. monte4

    monte4 Senior Member

    Location:
    Ontario Canada
    Yes, my system is all Linn (see my profile). My Linn dealer who sadly and suddenly passed away a year and a half ago did all the work. I originally was only using a Linn 2 channel power amp in my system. I purchased a slightly used Linn 5 channel power amp from my dealer plus new Linn Activ cards. He installed the cards into the amp then brought the amp plus more speaker wire and interconnects over to my house. He then opened up my Linn speakers and disconnected the passive crossovers. He hooked everything up, there is some daisy chaining of interconnects on the back of the 5 channel amp as I'm only using 4 channels. Then he tri-wired to my speakers (they have 3 sets of binding posts ready for being run active) as my speakers have two mid/woofers and one tweeter. Also the installed active cards (one mid/bass and one treble) in my amp have adjustable gain to help match to your system/room acoustics. He stayed for about an hour after he finished and listened to parts of about 5 LP's setting up the gain adjustments on the active cards (they can be adjusted using a small screwdriver from the rear of the power amp). The sound is night and day from when I was running the non active setup. Right of the bat I noticed more bass extension, and everything just 'came alive'. It was like there was a curtain over the front of the speakers being taken off.
     
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  24. Randoms

    Randoms Aerie Faerie Nonsense

    Location:
    UK
    Dozens of customers who I did the demo for back in the nineties know the answer!

    Like other dealers, I installed a fair few active systems.....
     
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  25. Soundgarden

    Soundgarden Forum Resident Thread Starter

    Location:
    Bend, Oregon
    Sounds like a very worthwhile improvement. Do you feel he got the gains dialed in properly based just on that initial setup exercise?
     
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