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  • Horizontal MTM vs MMTMM Center

    Well I sold some items here on the PE classifieds, so have some playpal money in hand to move forward with my new music/HT project :D.

    Paul C has graciously offered to do the design work on a custom center channel. He has rightfully left the choice of MTM 2-way or MMTMM 2.5-way to me, but while researching the forums I found mostly conflicting info as to which might be "better" in my application. I ask for your input and advice.

    Drivers are XT25SC90-04 tweeter, and RS125-4 (MTM) or RS125-8 (MMTMM) woofers, box is sealed. Pics of CC location and proposed box attached. Seating distance ~2 meters, two people sitting side by side about 20-25 deg off axis for HT, no sub. On topic discussion appreciated (no horizontal MTM's are the end of the world talk please ).
    Attached Files

  • #2
    Re: Horizontal MTM vs MMTMM Center

    The MMTMM gives you more spl at lower crossover settings to a sub would the only real advantage over an MTM.
    Dave

    If you can read this, thank a teacher.
    If you are reading it in English thank a Veteran
    .

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    • #3
      Re: Horizontal MTM vs MMTMM Center

      The disadvantage to a sideways MTM is that the MTM has a naturally wide horizontal dispersion, and a shallow vertical dispersion. This desirable trait becomes a liability when laid on its side, although I have no doubt whatsoever that someone like Paul has the chops to deal with that issue.

      2.5 way MMTMM is better about this, still not optimum, though (But it is what I built, aesthetics mean something, they really do. There. I said it. Flame away.:p).


      If you have the drivers, build the MMTMM.

      That is my recommendation.


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

      ~Pink Floyd

      Comment


      • #4
        Re: Horizontal MTM vs MMTMM Center

        Originally posted by Mark65 View Post
        The disadvantage to a sideways MTM is that the MTM has a naturally wide horizontal dispersion, and a shallow vertical dispersion. This desirable trait becomes a liability when laid on its side, although I have no doubt whatsoever that someone like Paul has the chops to deal with that issue.

        2.5 way MMTMM is better about this, still not optimum, though (But it is what I built, aesthetics mean something, they really do. There. I said it. Flame away.:p).


        If you have the drivers, build the MMTMM.

        That is my recommendation.


        Mark
        Well since his midwoofers are small as is his tweeter he should be able to get very tight spacing which would reduce the off axis lobing considerable and at 20 to 25 degrees he shouldn't have any major issues. Plus there is always the option to allow a little rise around the crossover point where the off axis droop is mostly likely to occur.

        Plus if he makes his cab a little taller and pushes his midwoofers together and the tweeter slightly higher he can further improve off axis performance. Based on his pic it looks like his reasoning for a horizontal MMTMM is due to space considerations, always compromises.

        Plus if he is like me just sit in the center sweet spot and let all those family members who don't know and don't care to know set off axis.
        Attached Files
        Dave

        If you can read this, thank a teacher.
        If you are reading it in English thank a Veteran
        .

        Comment


        • #5
          Re: Horizontal MTM vs MMTMM Center

          Originally posted by dthomas View Post
          Well since his midwoofers are small as is his tweeter he should be able to get very tight spacing which would reduce the off axis lobing considerable and at 20 to 25 degrees he shouldn't have any major issues.
          Thanks for the input guys!

          The above statement is the EXACT reason I made the "on-topic" request, and tried to keep "MTM's on their sides are bad" discussion out of it. Properly designed and used (i.e. tight driver spacing, narrow off-axis requirement etc), the "compromises" created by bad engineering/poor usage/BS marketing are diminished imo.

          I am actually wondering if combing and or lobing are actually worsened by the MMTMM 2.5-way. Seems they are not (even bettered maybe). If that's the case I am with Mark65 on this, looks DO matter (after function anyway) and the MMTMM has it ALL over the MTM in that department !!!

          Comment


          • #6
            Re: Horizontal MTM vs MMTMM Center

            Just remembered, also wondering about any BSC differences/problems between MTM and MMTMM where my CC will be located on the TV stand.

            Comment


            • #7
              Re: Horizontal MTM vs MMTMM Center

              Originally posted by rvsixer View Post
              I am actually wondering if combing and or lobing are actually worsened by the MMTMM 2.5-way.
              Theoretically, the comb filtering will be about the same in MTM or 2.5-way MMTMM. Reason being, the inside woofers are the ones that have to play high to meet up with the tweeter. The outside woofers will cut off much lower, and shouldn't interfere with the tweeter.
              Isn't it about time we started answering rhetorical questions?

              Paul Carmody's DIY Audio Projects
              Twitter: @undefinition1

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              • #8
                Re: Horizontal MTM vs MMTMM Center

                Paul thanks for chiming in, check your email....

                Comment


                • #9
                  Re: Horizontal MTM vs MMTMM Center

                  My only add is to look at tweeter distortion characteristics when determining how low you can push the XO frequency. Lower is better for lobing, but not for distortion, and my ears are much more sensitive to non-linear distortion than the linear distortion that result from lobing.

                  Remember, it's a system; all parts affect the outcome....

                  Have fun,
                  Frank

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                  • #10
                    Re: Horizontal MTM vs MMTMM Center

                    Originally posted by fbov View Post
                    My only add is to look at tweeter distortion characteristics when determining how low you can push the XO frequency. Lower is better for lobing, but not for distortion, and my ears are much more sensitive to non-linear distortion than the linear distortion that result from lobing.

                    Remember, it's a system; all parts affect the outcome....

                    Have fun,
                    Frank
                    Intersting points on distortion. I did some snooping around and found this regarding the XT25C90, distortion, and xo points:
                    http://techtalk.parts-express.com/sh...8&postcount=10

                    It will be interesting how this all comes together!

                    Comment


                    • #11
                      Re: Horizontal MTM vs MMTMM Center

                      That was my concern; only a few tweeters are clean enough on their low end to sound good when crossed over low enough to completely avoid wave interference between the dual mids.

                      At the same time, there is no "cliff" in response but rather a point of diminishing returns when trying to optimize sound field uniformity. You have two good options:
                      1) trade off a little off-axis uniformity (a linear distortion at extreme off-axis seats) and cross over high enough to avoid the non-linear distiontion (which affects all seats, all the time).
                      2) use a better ($$$) tweeter that has a lower Fs and a better distortion profile between there and where you'd like to cross.

                      That's the beauty of DIY - you make the call!

                      Have fun,
                      Frank

                      Comment


                      • #12
                        Re: Horizontal MTM vs MMTMM Center

                        Originally posted by rvsixer View Post
                        Intersting points on distortion. I did some snooping around and found this regarding the XT25C90, distortion, and xo points:
                        http://techtalk.parts-express.com/sh...8&postcount=10

                        It will be interesting how this all comes together!
                        http://www.madisoundspeakerstore.com...-dome-tweeter/

                        This would be a great tweeter for your project. Small faceplate and the ability to go down to 1500Hz.
                        Dave

                        If you can read this, thank a teacher.
                        If you are reading it in English thank a Veteran
                        .

                        Comment


                        • #13
                          Re: Horizontal MTM vs MMTMM Center

                          Originally posted by fbov View Post
                          That was my concern; only a few tweeters are clean enough on their low end to sound good when crossed over low enough to completely avoid wave interference between the dual mids.
                          We'll have to see what Paul comes up with with the given drivers.

                          That said, if it looks like there might be too much compromise involved:
                          1) No drivers have been purchased yet.
                          2) I do have alternate locations (top of TV, top portion of TV stand) where I can fit a taller center speaker.
                          3) Due to the above, it may open up use of the left/right mains matched XT25G30. Also the truncated frame version of the RS125-8 (http://www.parts-express.com/pe/show...number=295-340) could mitigate things.

                          Let's see what develops, if a doable design comes out of it I am ready to go.

                          Comment


                          • #14
                            Re: Horizontal MTM vs MMTMM Center

                            Originally posted by dthomas View Post
                            http://www.madisoundspeakerstore.com...-dome-tweeter/

                            This would be a great tweeter for your project. Small faceplate and the ability to go down to 1500Hz.
                            Yes that tweeter gets some good reviews!

                            I am trying to keep the drivers in the same "family" as the mains (XT25G30 & RS125). I just saw Vifa has the very small XT25SC40, but haven't found a place that sells it as of yet....

                            Comment


                            • #15
                              Re: Horizontal MTM vs MMTMM Center

                              I know what you're going through. I have an assignment to build a center channel for someone right now. You try and explain the issues of using a horizontal MTM and they just don't get it. And they don't have the space for a vertical speaker. So, what do ya do.

                              I'll be using that tweeter dthomas pointed out. I have a few here already and I've tested the crap out of it. It's fantastic. I would stongly encourage using it for this application. Trying to stay in the same family of drivers isn't going to do all that much. The CC is already going to be different because of the driver arrangement and xo topology.

                              How about a 2.5 way MTM? I've considered this. Depends on the surroundings though. The person I'm dealing with has it on a media stand thingy, with the TV right above it. So I'm leaning towards partial BSC.

                              Good luck.
                              https://www.youtube.com/channel/UCm2...oSKdB448TTVEnQ

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