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  • 2.5 Topology?

    I am working with several other members right now, helping where I can, how I can. Still have my arrays to finish (postponed due to a move), coming soon. ALWAYS thinking of other things to build. Been trying to find more information on 2.5 Topologies. I have a couple of questions, don't beat me up to bad for my ignorance.

    1. Can you build a 2.5 speaker with woofers wired in series or parallel?
    2. If you can build them in series, would their be any advantages other than being an easier load for the amplifier? Size of inductor for second woofer or something like that?
    3. Would it be a 3db gain in series and a 6db gain in parallel? This has always confused me, don't know why.

    Thanks for the replies.
    Last edited by Kevin K.; 12-29-2016, 05:04 PM. Reason: Fixed a typo before AE found it. :)
    My "No-Name" CC Speaker
    Kerry's "Silverbacks"
    Ben's Synchaeta's for Mom
    The Archers
    Rick's "db" Desktop CBT Arrays
    The Gandalf's

  • #2
    Typically they are parallel with one woof getting a steeper roll-off than the other. In a way it is like each woofer "taps" off the filter at different spots.

    This esentally eliminates the need.for BSC. Having one woof do the mids also will reduce potential phase and modulation issues between drivers resulting in better fidelity.

    I have also found that reactence hurts more than gross impedence magnitude. Keep it above 3.5 and keep the phase between the 30's and you can drive it with anything. The T3's have been on my 8 ohm HT recieve for fronts for about a month and it barely warms up.

    ...But like any other topography, there are look-outs and give-ups for the gain. The Tenacious 3 was going to be a 3.5 way, but after measuring the Fs of the woofers in-cab would have created a peak in response aroid 150Hz,.and THAT is not a pretty sound. So it made more sense to do a dual woofer 3-way.

    I have another idea for a 3.5 way....its a secret though. ;)
    .

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    • #3
      Originally posted by mzisserson View Post
      In a way it is like each woofer "taps" off the filter at different spots.
      +1, I was going to say the woofers are not strictly connected in parallel (per Mike's statement) but the XO is a parallel topology.

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      • #4
        Kevin, take a look in PCD at the circuit layouts. This will give you a good idea how to design the circuit. The sensitivity with a 2.5 typically turns out to be the same as the 2-way with no BSC.

        Woofers with rising low frequency response don't work well as the 2 in 2.5. However with the ART array I'm considering a 2.5 to frequency taper the array.
        John H

        Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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        • #5
          I was wondering if this was the case because I was having a difficult time finding any examples for a Series 2.5 way. Just asking some general questions here guys, bear with me. So, if you take a couple of 8ohm woofers wired parallel, Re is usually down around 3 to 3.5 ohms. Does the additional inductor and/or the DCR from both inductors bring this back up a little and typically how much? I realize the resistance varies some throughout the frequencies.
          My "No-Name" CC Speaker
          Kerry's "Silverbacks"
          Ben's Synchaeta's for Mom
          The Archers
          Rick's "db" Desktop CBT Arrays
          The Gandalf's

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          • #6
            Originally posted by jhollander View Post
            Kevin, take a look in PCD at the circuit layouts. This will give you a good idea how to design the circuit. The sensitivity with a 2.5 typically turns out to be the same as the 2-way with no BSC.

            Woofers with rising low frequency response don't work well as the 2 in 2.5. However with the ART array I'm considering a 2.5 to frequency taper the array.
            Thanks John, I think you just answered my question that posted right after your post went up. I was wondering about the sensitivity. Would you consider the DSA135-8 a good candidate for a 2.5 way?
            My "No-Name" CC Speaker
            Kerry's "Silverbacks"
            Ben's Synchaeta's for Mom
            The Archers
            Rick's "db" Desktop CBT Arrays
            The Gandalf's

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            • #7
              I don't like to think of it as you don't have to adjust for BSC. I don't think that is really an accurate description of what is going on. Basically one of the woofers is playing with a rolloff in the range above BSC and one woofer is rolling off in the area below BSC. The summation makes something that sums to flat but you get no additional output over a standard 2-way because in both configurations you have two woofers in parallel (giving you 6db more output. It just makes for a different summation and can sometimes be a better or easier choice depending on what you are doing. It would probably be better to explain with a graph, but I don't have one handy right now.
              -Kerry

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              • #8
                Originally posted by Kevin K. View Post

                Thanks John, I think you just answered my question that posted right after your post went up. I was wondering about the sensitivity. Would you consider the DSA135-8 a good candidate for a 2.5 way?
                Kevin, I don't think that it is the choice of woofer that dictates whether something is a good choice for a 2.5-way over a 2-way. The main considerations I would have is how far away the second woofer is from the tweeter and first woofer and the range that you are crossing in.
                -Kerry

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                • #9
                  Originally posted by Navy Guy View Post
                  I don't like to think of it as you don't have to adjust for BSC. I don't think that is really an accurate description of what is going on. Basically one of the woofers is playing with a rolloff in the range above BSC and one woofer is rolling off in the area below BSC. The summation makes something that sums to flat but you get no additional output over a standard 2-way because in both configurations you have two woofers in parallel (giving you 6db more output. It just makes for a different summation and can sometimes be a better or easier choice depending on what you are doing. It would probably be better to explain with a graph, but I don't have one handy right now.
                  Symantics.

                  Kevin, add that to yor reasons for lack of activity, too.
                  .

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                  • #10
                    Originally posted by mzisserson View Post

                    Symantics.

                    Kevin, add that to yor reasons for lack of activity, too.
                    C'mon Mike. I don't think Kerry was meaning any disrespect with his statement. Just a different viewpoint. If there is one thing I think we can all agree on here, this is a very subjective hobby.

                    Thanks for all of the feedback guys, it helped. I will eventually dive into PCD and things will probably become more clear after that.
                    My "No-Name" CC Speaker
                    Kerry's "Silverbacks"
                    Ben's Synchaeta's for Mom
                    The Archers
                    Rick's "db" Desktop CBT Arrays
                    The Gandalf's

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                    • #11
                      I like a 2.5 when there's a clearly defined baffle step to fill in. As I recall it's a narrow baffle that highlights the baffle step. You could play around with the blender and do a few sims. However every time I've thought I'd do a 2.5 I come back to a 2.0 to pick up a bit of sensitivity and make a simpler (and cheaper) design.
                      John H

                      Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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                      • #12
                        It has been shown to be very tricky if not completely impractical to wire a 2.5-way in series. For the record, your efficiency would increase +3dB for either parallel or series connections, but your voltage sensitivity would be +3dB for parallel or -3dB for series, resulting in +6dB for parallel and +0dB for series.

                        I tend to agree with Kerry on the reasons to choose a 2.5-way over a 2-way TMM. In my experience, I can't really hear the difference between these 2 topologies, so I would say it's just another tool in the toolbox to get to the sonic results that you want.

                        Dan
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                        • #13
                          Originally posted by mzisserson View Post

                          Symantics.

                          Kevin, add that to yor reasons for lack of activity, too.
                          Come on, Mike... Really...

                          I'm not one to play semantics games to try an prove how smart I am. I know what you are saying and what you mean, but I just don't think it is the best way to describe it to someone who is trying to learn the theory of how it works. I think it could easily be confused when you say "it essentially eliminates the need for BSC" to mean that baffle step is not an issue in a 2.5 way, which could lead people without a strong background like yours to think that they would get 6db of gain on top of an infinite baffle response, which is not the case.
                          -Kerry

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                          • #14
                            Originally posted by jhollander View Post
                            I like a 2.5 when there's a clearly defined baffle step to fill in. As I recall it's a narrow baffle that highlights the baffle step. You could play around with the blender and do a few sims. However every time I've thought I'd do a 2.5 I come back to a 2.0 to pick up a bit of sensitivity and make a simpler (and cheaper) design.
                            Agreed. I've done the same thing many times as well. Most of the time when I sim an X.5-way, it just ends up being easier (and cheaper) to do a standard 2- or 3-way.
                            -Kerry

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                            • #15
                              I've done two different 2.5 ways, a mmtmm center channel and a tower-ish tmm. For the center, the goal was to maximize off axis response, for the tower the goal was keeping the center to center distance reasonable while using a pair of 6.5" woofers. I think the goal was met, to varying degrees, in that a sideways mtm will never be optimal, but a 2.5 way mmtmm ameliorates the issue somewhat; and the woofer to tweeter center to center is simplified and kept within the length of the wave at the xpt while still getting the benefit of a pair of woofers in parallel. Simplifying BSC is a good reason for a designing a 2.5 way, but it's far from the only one.



                              Mark
                              You go your way, I'll go mine. I don't care if we get there on time.

                              ~Pink Floyd

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