3.5 Way or 4 Way Crossover. Is there such a thing?

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  • intelonetwo
    Member
    • Jan 2003
    • 48

    3.5 Way or 4 Way Crossover. Is there such a thing?

    I just ordered the drivers and built the cabinets for my next project, however I do not have a crossover design finalized. The speaker project looks very similar to the Tyler Acoustics Linbrook series speaker. However I am using a cabinet with 3 cu. ft. of volume on the bass module which holds 2 Peerless CSX 8" drivers each, for the MTM module I am using Peerless CSX 6.5" drivers and a Vifa PL27 tweeter.

    I am concerned about to much mid bass, so I am would like to explore the idea of a crossover that would have the two bottom woofers operate at different frequencies. Similar to the Von Schweikert VR-4 I. Which uses dual crossover frequencies. This is from the Von Schweikert website.
    Dual crossover frequencies: Both woofers operate down to 20Hz for sub-bass impact. However, to maximize the linearity of the response, separate crossover points are used at 60Hz and 125Hz, eliminating the mid-bass thickness which plagues other designs.
    . I would like to duplicate this design in my speaker. Is this difficult to implement? Thanks.




    MI-II-CENTS
    ______________
    The TailWind Generation I
  • ThomasW
    Moderator Emeritus
    • Aug 2000
    • 10934

    #2
    Proper XO design starts by taking accurate measurements of the drivers mounted in the boxes that are going to be used. Note that mfgr's published data isn't reliable for this purpose

    The measured data along with the T/S parameters is then imported into a XO design program.

    I'd suggest making a 3-way to start. Then if it's 'plagued with midbass thickness' (ROTFLMAO) play with other options.




    theAudioWorx
    Klone-Audio

    IB subwoofer FAQ page


    "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

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    • intelonetwo
      Member
      • Jan 2003
      • 48

      #3
      OIC. Thanks for the info.




      MI-II-CENTS
      ______________
      The TailWind Generation I

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      • JonMarsh
        Mad Max Moderator
        • Aug 2000
        • 15214

        #4
        Your inquiry and the commercial speaker on which it's based got me thinking a bit, not that I think I would want to do exactly that, but pondering what reasons one might have for doing it?

        What occurs to me is the whole issue of balance and boundary loading; i.e., the change in radiation resistance when going from a full space to half space or quarter space radiation. Now, ideally, one would like to set the distances to the wall so that these changes occur in the LF region where the cabinet + driver is starting to roll off, so that the room lift compensates for the roll off. Often speakers are placed closer to the ideal, and at non ideal ratio's; when this occurs, you can have both "thickness" at some midbass frequencies, and nulls at others! For a more in depth explanation than I care to write this afternoon, you could refer to the September issue of AudioXpress, which has the first part of a three part article on an 8" two way system; this part discusses this phenomena in some detail, along with typical graphs of the boundary load effect on the speaker response.

        Now, I can imagine that cutting in one of the woofers below 40 or 50 Hz would help lessent the effects of excessive reinforcement from boundary conditions in the 70-125 Hz region, as long as the midrange and all frequencies were tuned for that specific set of boundary conditions. Otherwise, it would be a rather incomplete fix to the problem.

        Now, another reason for doing this might be if you've got a very low Q sealed alignment, and you want to cut in the extra driver somewhere around where the first driver is 4-6 dB down. This could flatten and extend the low bass, prior to room lift, but then, when added to room lift, may run some risk of "overpowering" the low end. Of course, lots of folks don't mind that at all, in fact, even enjoy it. :W But technically, it is still a coloration. I like the Q of 0.5 critically damped alignment because it's critically damped with regards to transient response, and with correct placement, it's easy to get a nice compensation for the -6dB effect at Fb from the room lift, leaving one with deep, clean, unboomy bass. When I do poted systems, I tune for the same characteristic, a gradual slope down to Fb, so that the bottom end doesn't overpower things from the room lift.

        All in all, I'd suggest just thinking carefully about what you want to do with your system, where you want to place it, and what design tradeoffs will serve you best in the long run, considering all these issues (room lift, boundary effects if the room modes aren't staggered at golden means, etc.). Good luck with your project.

        Regards,

        Jon




        Earth First!
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        the AudioWorx
        Natalie P
        M8ta
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        Resistance is not futile, it is Volts divided by Amperes...
        Just ask Mr. Ohm....

        Comment

        • intelonetwo
          Member
          • Jan 2003
          • 48

          #5
          Jon,
          In reading your post I am left thinking about what you stated in regard to cutting in the lower frequency driver at a lower frequency:
          Now, I can imagine that cutting in one of the woofers below 40 or 50 Hz would help lessent the effects of excessive reinforcement from boundary conditions in the 70-125 Hz region, as long as the midrange and all frequencies were tuned for that specific set of boundary conditions. Otherwise, it would be a rather incomplete fix to the problem.
          If excessive reinforcement from boundary conditions is to be lessened, but only by tuning for that set of boundary conditions, how do commercial designs that tout this feature get away with it if each person room is different. For example the Von Schweikert VR-4 in all its iterations from 1-3 SE, they all feature a woofer section which is cacaded so to speak. Is it because many rooms have similar problem areas with regard to bass. for instance from 70-150 hz many rooms have "boom" problems?

          Would an electronics/digital crossover help mediate this problem, by offerring the user a selectiable crossover frequency? And if so which one do you recommend of the two listed;
          dbx Driverack PA or
          Behringer UltraDrive Pro 24/96




          MI-II-CENTS
          ______________
          The TailWind Generation I

          Comment

          • JonMarsh
            Mad Max Moderator
            • Aug 2000
            • 15214

            #6
            It's not so much that all rooms have boom problems... (let's not be judgemental about our rooms, huh?


            What it is, is the change from full space to half space to quarter space radiation. This increases the effective output level, in a wavelength dependent way. Now, there are ways to make that work to your advantage, but they don't involve what I would call "conventional" speaker placement. (i.e., 1-2 feet from walls.)

            Let's look at a first placment example. The woofer is effectively 1M off the floor, it's a little over a meter from the nearest side wall, and a bit over two feet from the back wall.




            Hmmm, looks a little "thick in the midbass" between 40 and 80 Hz, doesn't it? But this is pretty typical speaker placement. And note that the "anechoic" woofer/cabinet response is quite ideal, without any peaking (magenta curve), before it's added to the room curve resulting from placement.

            Well, you could compensate that (make it go deeper, help the mid bass to low bass balance) by cutting in another woofer below 40 Hz, to lift the low bass level. However, it would really fix the other problems, especially not the dip resulting from this placement in the 100 Hz region.

            Let's look at another placement example with a single woofer.




            This placement is improved, doesn't have as big a dip at 100 Hz, but still has a "fat" midbass, and placement induced problems in the upper bass/lower mids.

            What would happen if we placed the speaker so that the woofer to boundary distances were at golden mean ratio's, and the LF room lift was chosen to coincide with the speaker roll off?





            This last graph is the M8 two way response with "correct" room placement. In this position, which uses golden mean ratios for the distances (to distribute the room modes as evenly as possible, hence, minimizing their amplitude) the distances to the boundaries are greater, so that the room lift kicks in with a complementary function to the speaker roll out in the bottem end, effectively extending the bottom end as perceived in the room, while minimizing ripples in the upper bass and lower midrange. Same speaker, same room, just a different placement of the speaker in the room. You can find more on this topic at the Cardas site, in their discussion on speaker placement. George has a set of guidlines based on ratios of room width and length; this minimizes the ripples, but may not be correct for the specific speaker roll off.

            These are boundary analysis calculations I do with a MathCAD document I wrote back in the 80's to analyze the influence of the three closest boundaries on the net speaker LF response; this is based on Roy Allison's work on boundary influences, from the 70's. This reflects how I setup the M8s in my own rooms.




            Now, there are other issues which arise from the room modal response; these are usually best addressed by dimensioning the room correctly (golden mean ratios at least) and through choice of the listener position, not the speaker position. RPG Acoustics Room Optimizer is software which can be helpful for predicting the modal response and optimum listener position.

            Of course, another route to take is to go dipole- than over half the room interaction problem goes away!




            Best regards,

            Jon




            Earth First!
            _______________________________
            We'll screw up the other planets later....
            the AudioWorx
            Natalie P
            M8ta
            Modula Neo DCC
            Modula MT XE
            Modula Xtreme
            Isiris
            Wavecor Ardent

            SMJ
            Minerva Monitor
            Calliope
            Ardent D

            In Development...
            Isiris Mk II updates- in final test stage!
            Obi-Wan
            Saint-Saëns Symphonique/AKA SMJ-40
            Modula PWB
            Calliope CC Supreme
            Natalie P Ultra
            Natalie P Supreme
            Janus BP1 Sub


            Resistance is not futile, it is Volts divided by Amperes...
            Just ask Mr. Ohm....

            Comment

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