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External Crossover for Passive Bi-Amping

Discussion in 'Audio Hardware' started by yanquiuxo, Jan 2, 2021.

  1. yanquiuxo

    yanquiuxo Well-Known Member Thread Starter

    I know the subject of bi-amping is asked about frequently, but I have a question I don’t see raised in many posts. I currently run B&W 704 towers off a Marantz SR7009. I want to upgrade my amp to something like two Rotel RMB-1552 or two Marantz MM7025 for horizontal, passive bi amping. I’m not looking to get flamed over the benefits (or non benefits) of passive bi amping, so be nice!

    My question is, should I be looking at an external crossover to go between my pre and power amps? In the research I’ve done I believe this may improve some sonic quality if the signal being fed to the power amp is already filtered to - (forgive me for not wording this correctly) help the speakers’ internal crossover not work as hard? Is there a reason I should NOT use an external crossover?

    Curious any opinions out there or recommedations for an effective crossover to do this! TIA
  2. Is there a reason for passive? Active don't cost much, although they're often in rack form factor. The best passive options might be speakers that are bi-amp capable themselves. I am running JBL 530s biamped (passively), with Hegel H90 to woofer/mids, and Hood 1069 Class A for tweeter, with 2 powered subs.
  3. yanquiuxo

    yanquiuxo Well-Known Member Thread Starter

    If I understand your question, the reason for passively bi-amping is because I don’t want to physically modify the speakers from how the manufacturer built them by removing the internal crossover, but I still want to gain any potential benefits from running additional power to them.
  4. Ingenieur

    Ingenieur Forum Resident

    I would let the speaker crossover do the work.
    You are right, the line level section will see the whole signal bandwidth and modulate the output power transistors but the respective lo/hi frequencies will see a higher impedance and be attenuated. There are designed to do this. They work the same bi-amp'ed or not.

    You can get inexpensive active crossovers but it's just another source of distortion.
    Passive would have to be adjusted ~ the same as your speakers crossovers. Adjustment might be messy to avoid humps and holes.

    Something like this might work for you.

    Rolls Stereo Two-Way Crossover - SX45 | Sweetheart Deals | Reverb

  5. okc_craft

    okc_craft Just Another Budgetphile

    I’m not sure what the effects of this would be. I guess the benefits would more likely be with the amps not having to produce the frequency that aren’t needed by their drivers. I do agree with @ampguy that active is probably easier to implement. If you were curious I would suggest start with something like a miniDSP, easy to setup and tweak for not a lot of money.

    For what it’s worth I do think bi-amping alone will offer significant sonic improvement.
  6. I looked up your speakers, and it looks like you have dual binding posts for high and low, so one way with two amps would be to use one amp to power the lows, and the 2nd amp to power the highs, or horizontal biamping.

    I'm not sure how you could change the crossover point externally without altering the speakers, but perhaps you are trying to optimize power, so full range from the two amps isn't mostly wasted by utilizing the crossovers in the speakers? I presume the speaker posts are at or near the crossover point of the speakers when used with the jumper bars, but not sure. Perhaps contact these folks, for suggestions: electronic crossover, PLLXO, passive crossover, active crossover, custom amplifier

    Let us know how it works.
  7. fireprix

    fireprix Forum Resident

    Greenville, PA
    As mentioned above, your speakers need to be bi-amp capable. Are the 2 inputs on the back of your speakers labeled as low frequency and high frequency? If so remove the jumpers and put a signal to the LF terminals and see if you only get low frequency sound. Do the same for the high frequency terminals and see if you only get high frequency sound. If so, you don’t need a line level crossover. You can just run a Y cord from the preamp out to your amps inputs.

    Sorry you got 3 answers as I was typing.
  8. Ingenieur

    Ingenieur Forum Resident

    It looks like the speakers crossover (the one that is jumpered, it has 2 since it is a 3 way) is at 3000 Hz.

    But imo a line level xover is not necessary. The speaker xover is designed for it, hence the option to do it.

    The amp connected to the speakers hi range will not produce power at the low end, and vice versa. The line level will try to.

    The hi amp will start to roll off below 3000 Hz.
    I can't find the slope but will be something like 12 or 24 dB per octave, assume 12 dB/oct.

    Assume the amp is making 100 W from 20-20 kHz for reference.
    At 1500 Hz it would be down 12 dBW (down to ~6 W from 100 W) because at THAT frequency the impedance would be much higher attenuating/choking power down.
    Last edited: Jan 2, 2021
  9. yanquiuxo

    yanquiuxo Well-Known Member Thread Starter

    this is a great response - thank you. I appreciate the pros and cons and recommendation!
  10. fireprix

    fireprix Forum Resident

    Greenville, PA
    I agree as I do the same thing with my JBL L7s. However and please correct me if I’m wrong, the amps that will be driving the HF, above 3000 HZ will be very underutilized since the high frequency drivers require much less power to operate at the same SPL than would the low frequency drivers.
  11. yanquiuxo

    yanquiuxo Well-Known Member Thread Starter

    there are companies that make crossovers for line level signal, one was suggested above. Your presumption above is exactly the reason why I am wanting to try it!
  12. yanquiuxo

    yanquiuxo Well-Known Member Thread Starter

    I’ve read this a few times and am trying to understand it, although I am not very technical! Do you think there is a risk of damaging the speakers by running the external crossover at 3k Hz into a powerful amp (~150w-200w) and that amp effectively powering a single tweeter? Would the speaker’s internal crossover be a sort of protection from any potential damage? The only reason I am hesitant to try to the external crossover is potential damage to the speakers
  13. Ingenieur

    Ingenieur Forum Resident

    That is correct. It takes more power down low than up high for the same apparent loudness. We hear on a Lou Ed's curve so to speak.
    Lies need to be louder, hence more power, to be perceived as the same loudness as highs.
    Equal-loudness contour - Wikipedia
    Last edited: Jan 2, 2021
  14. Ingenieur

    Ingenieur Forum Resident

    Most have gain controls like the one I posted.
    Then you equalize volume between hi and lo, messy.
    If you use identical amps driven by the same signal (pre-out) and let the speaker crossovers do their thing no issues.
    yanquiuxo likes this.
  15. edwyun

    edwyun Well-Known Member

    You dont use active crossovers if you use the passive crossovers inside your speakers. Doing so wont harm anything but doubt you will like the sound, as the signal would be subject to two sets of crossover transfer functions (unless your speakers with 2 sets of binding posts allow you to bypass the passive crossovers - most do not). Just because you have 2 sets of binding posts and you use them does not mean you are bypassing the passive crossovers.
    yanquiuxo and monte4 like this.
  16. Curds

    Curds New Member

    Vancouver, Canada
    I have a somewhat similar question.
    I have a Classe 100 Power Amp running a pair of Magnepan MG 1.7i speakers. and use a Sunfire True Subwoofer.
    I use an ARC SP9 as my pre-amp, splitting the signal from the pre-amp to the power amp & sub woofer. But this means the power amp is getting a full range of frequency. It may be better to spare it the low end so it has more headroom?
    I have a M&K passive crossover I used previously when I had a pair of (massive) non-powered M&K bass speakers running off a separate Classe PA.
    My question to the forum is: should I put my passive crossover back into the circuit in place of the splitter I'm now using?
  17. Curds

    Curds New Member

    Vancouver, Canada
    I answered my own question by taking it out and trying it - sounds a little better to my ears. The mid & upper range have quite a bit more clarity, probably because the power amp is not being burdened by the lower frequencies?
    Anyway, so far I'm happy, and glad I found I use for the crossover that's been on the shelf for many years
  18. harby

    harby Forum Resident

    Portland, OR, USA
    This is a quite different question.

    But yes, a high-pass electronic crossover on your main speakers that mirrors the subwoofer's for best sound and least distortion is always preferable. This is often not easy for those that have integrated receivers.

    The Sunfire subwoofer can be inserted between your preamp and amplifier. It has high-pass RCA outputs, but this passive (non-electronic) crossover is limiting at a fixed 70Hz 6dB per octave.

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