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  • LithMTM

    Background:

    The Lithium design is a really small monitor that sounds a lot bigger than it has any right to, and even though it is not the lowest cost design around, it is still pretty reasonable. Once it was out for a while, interest developed for an MTM version. I have never done an MTM before - generally speaking, whenever I have contemplated doing an MTM, I have always wound up going a different direction (either bigger, more expensive single woofer or dedicated midrange and tweeter). In this case, I can see a clear case for the MTM. The Dayton ND-105 is impressive to be sure, but it is a 4" woofer trying to operate down into the 40's. Having a pair of these gives the displacement of a high excursion 6" woofer while retaining the attractive dispersion characteristics of a 4" midwoofer.

    Cabinet Design:

    The original Lithium shared cabinet dimensions with Paul Carmody's Overnight Sensations design, so the MTM has the same dimensions as the OS MTM's (which is the same as the Nano Neo cabinet). The cabinet is 15" tall by 6" wide by 10.5" tall and made using 3/4" MDF. DIYSoundGroup.com sells the OS MTM cabinet for less than $25/each, so that is a good option if you don't want to cut your own or want that CNC precision fit. I discarded the front baffle and made by own with different cutouts to accommodate the drivers (Dayton ND105-4 and Vifa BC25SC06-04). The 1.5" by 4" flared port sold at Parts Express tunes this cabinet to 50 Hz (a few Hz higher than the Lithium, but in the same ballpark). I located the port behind one of the woofers (the cabinet's brace interfered with the preferred location behind the tweeter and I would rather keep the rigidity that the brace provides.) The interior is lined with R-8 Ultratouch Denim fiber insulation affixed to the cabinet by 3M 77 spray adhesive.

    Crossover Design:

    The Lithium crossover did a good job beating the ND-105 high frequency output into submission, so I wanted to retain similar performance for the MTM version. I also wanted to keep a similar crossover point and slopes for both drivers. Like the Lithium, I used a 4th order electrical low pass on the ND-105 with a resistor on the first shunt leg. Likewise, I have retained a second order electrical high pass on the Vifa Tweeter with a shaping resistor on the shunt leg and a two resistor L-pad.

    Initial Impressions:

    Like the Lithium, the LithMTM is clean and resolving. The MTM version does sound more dynamic and, predictably, can deliver more SPL without strain. With the woofers aligned vertically, tonal balance is optimal with the tweeter at or near ear level. Part of the point of an MTM is to minimize floor/ceiling reflections - so none of this is a real surprise. Unfortunately, this also means that if you use the LithMTM horizontally as a center channel, there are limits to how far off axis you can be and still get good sound quality. We're not cheating any laws of Physics here.
    Attached Files
    Keep an open mind, but don't let your brain fall out.

    Argon | Helium | Lithium | LithMTM | Hafnium
    Mercury | Matrix | Shrubbery

  • #2
    Re: LithMTM

    On axis measurements were taken at tweeter height and the center of the baffle horizontally. The on-axis plot shows a crossover point of 2.4 kHz and sensitivity of approximately 81 dB / 2.83V. As a gated measurement, the frequency response isn't accurate below about 300 Hz. Above that, the response is +/- 2dB up to 20 kHz and +/-1 dB up to 4 kHz. Between 4 and 8 kHz, there is a glitch in the tweeter response. I have seen this before with the BC25SC06-04, but usually only when I am measuring the raw driver response at high levels.

    Off-axis measurements were taken at 15, 30, 45, and 60 degrees horizontally. They are shown in addition to the on axis FR (red line). The off axis remains smooth through the crossover region. The tweeter response depression from 4-8 kHz smooths out off-axis. Above 8 kHz, the tweeter with its shallow waveguide becomes significantly more directional.

    The impedance measurement shows the 50 Hz port tuning frequency. The impedance stays above 7 ohms throughout the audible range, so this should be an easy load for any amplifier.
    Attached Files
    Last edited by scottsehlin; 11-26-2013, 10:25 PM.
    Keep an open mind, but don't let your brain fall out.

    Argon | Helium | Lithium | LithMTM | Hafnium
    Mercury | Matrix | Shrubbery

    Comment


    • #3
      Re: LithMTM

      For the baffle layout, I show a diameter of 4.75" for the woofers, This is the outer diameter at the largest point of the ND-105 flange. When building these, use the center points indicated on the layout drawing, but cut holes that are 3.75" diameter. The woofer holes should be chamfered toward the interior of the cabinet (mine are) - as airflow will be pretty restricted otherwise.
      Keep an open mind, but don't let your brain fall out.

      Argon | Helium | Lithium | LithMTM | Hafnium
      Mercury | Matrix | Shrubbery

      Comment


      • #4
        Re: LithMTM

        Scott, could these be a candidate for an MLTL alignment :rolleyes:


        BobC

        Comment


        • #5
          Re: LithMTM

          Wish I could have been there Friday night to hear these. If they sound anything like the original Lithium's this is a killer design Scott. It's also nice there is a flat pack (sans the baffle) available.
          Craig

          Comment


          • #6
            Re: LithMTM

            Originally posted by upsman View Post
            Scott, could these be a candidate for an MLTL alignment :rolleyes:


            BobC
            I'm sure they could. I suspect they would get bigger. To get more specific, we would need someone with some MLTL expertise to weigh in...
            Keep an open mind, but don't let your brain fall out.

            Argon | Helium | Lithium | LithMTM | Hafnium
            Mercury | Matrix | Shrubbery

            Comment


            • #7
              Re: LithMTM

              Originally posted by scottsehlin View Post
              I'm sure they could. I suspect they would get bigger. To get more specific, we would need someone with some MLTL expertise to weigh in...
              Paging Doctor Kittinger. Doctor Kittinger to the conversation, please.

              Comment


              • #8
                Re: LithMTM

                Scott, that 1.6mh inductor, can I go with a 1.5mh? I can't find one at PE. Also the 13ohm resistor.

                Thanks!
                Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

                Comment


                • #9
                  Re: LithMTM

                  Meniscus will custom wind/unwind inductors to your spec for no extra fee.

                  By the way, these are a great sounding slim MTM.



                  Originally posted by joeybutts View Post
                  Scott, that 1.6mh inductor, can I go with a 1.5mh? I can't find one at PE. Also the 13ohm resistor.

                  Thanks!
                  I was so much older then, I'm younger than that now.
                  OS MTMs http://techtalk.parts-express.com/sh...d.php?t=220388
                  Swope TM http://techtalk.parts-express.com/sh...d.php?t=221818
                  Econowave and Audio Nirvana AN10 fullrange http://techtalk.parts-express.com/sh...d.php?t=216841
                  Imperial Russian Stouts http://techtalk.parts-express.com/sh...=1#post1840444
                  LECBOS. http://techtalk.parts-express.com/sh...ghlight=lecbos

                  Comment


                  • #10
                    Re: LithMTM

                    Very nice Scott. Will you bring these to Grinnell?
                    A 6 and 7 ohm in series will work just fine.
                    " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

                    Quote Originally Posted by hongrn. Oct 2014
                    Do you realize that being an American is like winning the biggest jackpot ever??

                    http://www.midwestaudioclub.com/spot...owell-simpson/
                    http://s413.photobucket.com/albums/pp216/arlis/

                    Comment


                    • #11
                      Re: LithMTM

                      Thanks fellas. I was hoping to keep all the parts at PE if I could..... But if I should get one from Meniscus I will bite the bullet.

                      Thanks for the help gang!
                      Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

                      Comment


                      • #12
                        Re: LithMTM

                        Meniscus also has the 13 ohm resistor. Double score!

                        Thanks again guys! Another project to get done! :D Then on to one that has been on the backburner a LONG time.
                        Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

                        Comment


                        • #13
                          Re: LithMTM

                          For the woofer inductors, I used an 18 ga. steel laminate core as the preferred tradeoff between size, cost, and dcr. I had some 1.6's in my parts bin - I suspect they came from Madisound (but a long time ago). I wouldn't worry about using 1.5 mH - it's within tolerance.

                          The resistors will have some impact and I just noticed that PE doesn't have those. I bought an assortment of resistors in that range as part of a larger order from Erse, so that is where mine came from. Meniscus is a good source, so don't hesitate to go with them. As previously mentioned, they will do custom inductor values as well.

                          I will bring mine to Grinnell this year.
                          Keep an open mind, but don't let your brain fall out.

                          Argon | Helium | Lithium | LithMTM | Hafnium
                          Mercury | Matrix | Shrubbery

                          Comment


                          • #14
                            Re: LithMTM

                            Scott! One last question (I hope!). What is the offset of the tweeter? Thanks!
                            Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

                            Comment


                            • #15
                              Re: LithMTM

                              I think it is 1" offset from the center line. I know that is very close, but will verify tonight.
                              Keep an open mind, but don't let your brain fall out.

                              Argon | Helium | Lithium | LithMTM | Hafnium
                              Mercury | Matrix | Shrubbery

                              Comment

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