Crossover circuits, and bi-wiring 3-way speakers

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  • csuzor
    Senior Member
    • Nov 2004
    • 413

    Crossover circuits, and bi-wiring 3-way speakers

    Can someone enlighten me on the differences between simple and more complex crossover circuits? What is meant by n-th order cross-overs?

    In addition, many (most?) 3-way and 2-way speakers have 2 sets of binding posts, not 3... Obviously, the specs state crossovers like 350Hz/4kHz for 3-way, and 4kHz for 2-way speakers... I can see that bi-wiring the 2-way makes sense, but what about the 3-way? Can I assum each set of binding posts addresses <4kHz and >4kHz (B&W)? Would it not make more sense to split the 3-way at <350Hz and >350Hz, which would more evenly spread the actual load from typical music?

    Finally, if a speaker manufacturer (like B&W) has carefully selected a crossover with n-th order circuitry, is it really of interest to split the signal prior to amplification using another type of crossover? OK, the amplification will be easier, no mixing of fequency signals/current... but bi-wiring doesn't bypass the speaker's internal crossover, so isn't there a risk of slight frequency or n-th order mismatch, resulting in some signal loss? And if the internal crossover is bypassed (quite complex for a 3-way speaker, right?), isn't there a risk that the selected cross-over of n-th order is not as good as the speaker manufacturer selected themselves?

    Thanks
    Christophe
  • NonSense
    Senior Member
    • Nov 2003
    • 138

    #2
    Christophe

    The n in the n-th order cross-over refers to the number of reactive components used to construct the cross-over filter network. For example, a first order high pass filter could be just a series capacitor connected to the HF driver unit.

    As you add inductors and capacitors to your network arrangement, you will be increasing the n the the nth order.

    With regards to two sets of binding posts. Most manufacturers only offer two, even if the speaker is a 3 way system. The intention is to isolate the low frequency driver or drivers from the other higher frequency drivers and crossover elements. One school of thought is that the larger, longer travelling, slower moving mass of the low frequency driver requires more driver current, and a direct connect will offer better control without interaction with the other speaker elements. (The two networks meet at the binding posts of the amplifier and not at the ends of long cables?) The large mass of the LF driver unit, may produce a back EMF due to the larger inertia of the voice coil. (HF drivers tend to have less mass and require less travel)

    Therfore the manufacturer offers the option of coupling this driver directly to the amplifier (to avoid local interaction?, allow different cables?) or to a seperate amplifier in a bi-amp arrangement.

    Some high end speakers do offer a seperate set of posts (3 or more) for each crossover arrangement.

    I can't say for sure but I expect that the midrange and HF drivers for B&W's to be on the same binding posts, with the LF seperated as you suggested at 350Hz.

    I don't have any first hand experience with active crossover networks and Bi- or Tri- amping, but with a good quality speaker with passive network, I would expect it would be very difficult to surpass the native performance. The network has been constructed to match the chosen drivers and specific enclosure. Carefully tuned (usually).

    My feeling is that the best results for active crossovers would be obtained when applied to speakers constructed for use with active crossovers. B&W has done this in the past. I have also seen applications in the past using low wattage tube amplifiers with active crossovers. The low wattage requires high efficiency, and the direct connect removes the losses associated with the passive network. However, the active network and speakers were a pair.

    Simply a different system architecture.
    Bruce

    Comment

    • csuzor
      Senior Member
      • Nov 2004
      • 413

      #3
      Thanks for the details. I don't know if B&W binding posts are split for tweeter Vs the rest of the drivers (4kHz crossed) or split for tweeter+mid-range and lower, can't find that info anywhere.
      It is usually recommended to do active bi-amping rather than passive, but that seems risky without knowing great details about the speaker's crossovers, whether bypassing the internal crossovers or not. I suspect the commercial B&W are designed for passive bi-amping or bi-cabling, that's all.

      Regarding n-th order crossovers, are they better for handling complex non-sinusoidal sound waves, which are composed of multiple frequencies? For example, a guitarist hitting their guitar with their hand (like LAGQ), creates complex sound signals, perhaps close to square waves, which can be decomposed into sinusoidal signals of much higher frequencies. Are complex crossovers better than simple crossovers at splitting this signal into each driver capable of rendering that frequency? Another way to put the question, when using simple crossovers, is each driver actually being asked to reproduce signals with frequencies which can span beyond it's normal limits?

      Does a simple or complex crossover help drivers integrate better? I have occasionally found that crossovers cause changes in the quality of sound because they abruptly switch frequencies between 1 driver or another... It seems a gradual transition would be smoother.

      Thanks

      Comment

      • NonSense
        Senior Member
        • Nov 2003
        • 138

        #4
        Regarding high order filter networks, as with anything there will be trade offs. Higher order networks, will allow for a greater (or sharper) roll off at the expense of additional signal loss and expense. Drivers will have a native frequency response (and SPL output) over which they operate. However, they may have a "sweet" spot which is ideal. By selecting a set of drivers and tuning the crossover, the designer is trying adjust the gain and response of each element to give a natural response over the entire range and smooth transitions for frequencies near the crossover points where a given frequency may be generated by multiple drivers.

        The more components in the crossover network, the more adjustment the designer will be able to make to the response curve. The better the quality of the components used, the better the result, at the expense of higher cost. I cannot recall the manufacturer, but their flagship speaker had a 200lb crossover network, with a single inductor weighing nearly 100lbs. These were not selling at a bargain price either. A smooth transition is the key, and I would expect the designer to only use what was necessary to achieve the best results with the buget at hand.

        To rate a particular design, the whole package must be considered. A speaker using a high order network with poor components and driver units will still sound inferior.
        Bruce

        Comment

        • csuzor
          Senior Member
          • Nov 2004
          • 413

          #5
          To confirm, the B&W 3-way speakers are crossed at the binding posts at 350Hz, this was easily verified on mine. The mid-range and tweeter share the binding posts. What fooled me is that the 2-way and 2.5-way speakers also have 2 sets of binding posts, and they are crossed at 4kHz. To bi-amp or bi-wire these would be totally different than for the 3-way speakers.

          Either B&W believe separate binding posts are not really necessary for tweeter and mid-range (but still provide them for 2-way speakers for marketing purposes), or 3 separate binding posts would be too much for 3-way speakers (from a marketing point of view).

          Regarding crossovers, B&W claims for their latest 800 series (similar to your thoughts):
          >>The thing to look for is its simplicity. Some speakers demand complex crossovers to compensate for the shortcomings in their drive units. The better the mechanical design, the simpler the electronic design can be. That’s why the 800 Series uses simple circuit design, with the crossover between the critical tweeter and midrange drivers being 1st-order – the simplest circuit possible. That simplicity, coupled with using components of the highest calibre, helps to retain the purity of the signal.<<

          I have seen some reviewers of these speakers claim that the sound is deteriorated because these 1st-order crossovers are inappropriate for the drivers on the B&W, and n-order crossovers would have been a better choice.

          It may be a theoretical topic, but I wanted to understand some of this.
          Thanks for the explanations.

          Comment

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