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MTMWW versus TMWW advantages , disadvantages ?

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  • MTMWW versus TMWW advantages , disadvantages ?

    i recently saw a design using drivers i have considered . it was in MTMWW configuration , what difference would there be if you were to use one 4ohm mid same brand and everything in a TMWW configuration ? the one 4 ohm would have the same sensitivity as the two 8 ohms !? amp load should be the same !? in the TMWW configuration it would also open up choices for tweeter !?
    donc

  • #2
    If you have a design, it's best to build it as designed.

    I think you're asking if you can build an MTMWW as a TMWW by replacing the two 8-ohm M-M driver in parallel with a single, 4-ohm driver of similar construction? You're thinking that a single driver that matched the electrical characteristics of a pair of drivers would be a drop-in replacement. You're missing some things.

    MTMs have a 6 dB sensitivity advantage over TMs using the same mid-woofer. 3dB comes from drivers in parallel pulling twice the wattage. 3dB comes from doubling cone area. You didn't consider cone area, so your TMWW will have a 3dB hole in the midrange.

    MTMs also have a radiation pattern that places nulls above and below the listener ear level, with a very uniform left-right loudness off-axis. No idea what the pattern would be for your TMWW, given it's driven by the crossover phase relationships. It's not likely to be good by accident.

    So... build it as designed!

    HAve fun,
    Frank

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    • #3
      Originally posted by donwc View Post
      i recently saw a design using drivers i have considered . it was in MTMWW configuration , what difference would there be if you were to use one 4ohm mid same brand and everything in a TMWW configuration ? the one 4 ohm would have the same sensitivity as the two 8 ohms !? amp load should be the same !? in the TMWW configuration it would also open up choices for tweeter !?
      To expand on what fbov has said. There are relatively few purpose designed midranges for 3 ways around these days with most being midwoofers with a lower sensitivity that can also be used in 2 ways. The classical TMWW configuration tends to require a high sensitivity midrange and so using two midwoofers has become a common way to get the sensitivity required to keep up with woofers. The MTMWW configuration is rare at the top of the range for commercial speakers which are mostly TMWW. If two midrange/midwoofers are used they are more likely to be in an array WMTMW or WWMTMWW.

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      • #4
        Originally posted by donwc View Post
        i recently saw a design using drivers i have considered . it was in MTMWW configuration , what difference would there be if you were to use one 4ohm mid same brand and everything in a TMWW configuration
        The vertical pattern control of the MTM would be lost.

        www.billfitzmaurice.com
        www.billfitzmaurice.info/forum

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        • #5
          Originally posted by andy19191 View Post
          Is the narrow but symmetrical pattern good, bad or just different?
          I think it's good. It aids clarity by minimizing floor and ceiling reflections. But if you like reflections, it's bad.
          Francis

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          • #6
            I think it's good. It minimizes floor and ceiling reflections, which aids clarity. If you like the reflections though, it's bad.

            Note: I was answering andy19191. For some reason the post ended up here.
            Francis

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            • #7
              Originally posted by billfitzmaurice View Post
              The vertical pattern control of the MTM would be lost.
              Is the narrow but symmetrical pattern good, bad or just different?

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              • #8
                The radiation pattern of an MTM was brought to light, what about lobing (is that the correct term?) when the two Mids are spaced more than 1/4 their crossover frequency? Might that be one benefit of a TMWW?
                http://techtalk.parts-express.com/fo...khanspires-but
                http://techtalk.parts-express.com/fo...pico-neo-build
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                • #9
                  Originally posted by fpitas View Post
                  I think it's good. It minimizes floor and ceiling reflections, which aids clarity. If you like the reflections though, it's bad.
                  Is that supported by the measurements here? If it were true why is it rare among pro studio speakers? How much does the frequency response of the reflections matter?

                  BTW I have not studied the physics in detail and it is on the to do list as part of the current project. It is an interesting topic.

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                  • #10
                    Originally posted by andy19191 View Post

                    Is that supported by the measurements here? If it were true why is it rare among pro studio speakers? How much does the frequency response of the reflections matter?

                    BTW I have not studied the physics in detail and it is on the to do list as part of the current project. It is an interesting topic.
                    Can't answer your question about rarity, although studio speakers have the advantage of treated floors and ceilings. Much less advantage to MTM. That's assuming you don't mean near-field monitors, where MTM is clearly not appropriate. I do remember that Jeff Bagby designed MTM speakers for studio use.

                    http://techtalk.parts-express.com/fo...180-mtm-design
                    Francis

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                    • #11
                      Originally posted by andy19191 View Post
                      Is the narrow but symmetrical pattern good, bad or just different?
                      The horizontal pattern of am MTM is the same as a TM. The vertical pattern of the midranges in an MTM is more than halved. In most cases that's a good thing, as it greatly reduces early reflections of the mids off the floor and ceiling.
                      what about lobing
                      Lobing with an MTM occurs close to the speaker, say less than six feet or so. That's why MTMs aren't used as recording studio nearfield monitors, which typically are four feet or less from the listening position. Also, with that short of a listening distance early reflections are not a concern. At normal listening distances the wave fronts from the two midranges have combined as one, so there is no lobing there.
                      www.billfitzmaurice.com
                      www.billfitzmaurice.info/forum

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                      • #12
                        The destructive interference between the two mids in the MTM only happens over a small range that would affect floor bounce. And then the constructive interference outside that range would also appear in the floor bounce.
                        The polar response is different between MTM and TM with the TM offering a more uniform vertical field compared to the MTM (less response change between seated and standing).
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