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2 Ohm MTM Design opinions wanted

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  • 2 Ohm MTM Design opinions wanted

    Hi guys, Looking for opinions on this topic. With most modern class d amplifiers able to handed very low impedances these days. I have considered designing a 7" mtm with two 4 ohm woofer and a 4 ohm tweeter. I am having a hard time finding flaw with this concept if the amp will handle the load. The idea of using much smaller value inductors is very appealing when looking at build cost. Please shoot this idea full of holes. Lets use the dayton rs180p-4 and rst tweeter as examples of this construction.
    b3s/nd20 line arrays
    Markk's RS225rs28
    2-rs390's

  • #2
    What if you want to sell the speaker, or change amps ... an affordable tube amp ... might limit your choices later down the road.
    http://techtalk.parts-express.com/fo...khanspires-but
    http://techtalk.parts-express.com/fo...pico-neo-build
    http://techtalk.parts-express.com/fo...ensation-build

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    • #3

      Not saying 1ft³ is ideal just showing an example of the load the amp will see. 2ohm and below in some very power hungry regions. Of course the crossover will alter some of this.

      From experience, using a pair of Acurus 3x200 driving a pair of Carver Amazing OB/ribbon. Those amps are very robust and they get too hot to touch after extended listening sessions. Not to mention you can smell the dust burning off something .... I think it's the resistors in the speakers crossover ... maybe.

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      http://techtalk.parts-express.com/fo...khanspires-but
      http://techtalk.parts-express.com/fo...pico-neo-build
      http://techtalk.parts-express.com/fo...ensation-build

      Comment


      • #4
        Originally posted by Kornbread View Post
        What if you want to sell the speaker, or change amps ... an affordable tube amp ... might limit your choices later down the road.
        Yes, that's a big issue. You're amp choices will be highly limited. And the amp's output resistance may be more of affector in determining performance.

        What amp(s) did you have in mind?

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        • #5
          The inductors would be smaller but the cap values would be higher. If you have the amp why not? You can always reconfigure it with the woofers in series later. FWIW i ran DVC subs wired for 2 ohms on a cheap early 80s Technics receiver for years and it still works to this day. Not that i'd recommend it of course

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          • #6
            2ohm speakers will likely require inductors slightly smaller than 1mH which often means more expensive AirCore inductors, while 4ohm and 8ohm speaker LowPass XO's will generally use large enough inductor values that you can easily find SolidCore inductors which are typically cheaper and lower-resistance.

            I think the 2ohm capable amps are usually rated for much lower distortion when pushing 4ohm speakers instead.

            There might be a somewhat larger selection of 8ohm woofers compared to 4ohm woofers if you're looking at mids, unless you're looking at car audio or subwoofers.

            The tweeter will likely need to be slightly padded down by resistors to avoid being louder than the woofers, so the tweeter impedance often ends up higher either way....unless you'll be using PA woofers or something similarly efficient.

            I think you'll have an easier time finding a common 4ohm-stable amp with more than enough watts, but it might be difficult to find a good, 2ohm-stable amp that has everything you want/need.

            If you ever decide you want to use your new and awesome speaker creations for movies as well as music, you'll have a much easier time with 4ohm (or particularly 8ohm) speakers if you want to plug them into a surround reciever.

            Outside of car audio where higher voltage may end up limited, I don't think 2ohm speakers have any advantages....I could easily be wrong though.
            My first 2way build

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            • #7
              Bad idea. Just look at the data sheets for the amps. Distortion increases with power. Efficiency goes down with power. I am actually considering a 12 Ohm speaker system. (MMMT)
              Leave the 2 Ohm speakers for low end car stereos too cheap to build in a DC-DC converter.

              Your selection of 2 7-inch Daytons and their tweeter is a good first step. Just wire them in series and build an 8 Ohm nominal system. The tweeter will have to be padded anyway. If doing an MTM, look into a "D'Apolitto" alignment. Actually, I'd be surprised if that very combination has not been done and published. All MTM are not "D'Apolitto" If you really want, use the 8 Ohm version and built a 4 Ohm system. Reasonable if building as self powered. Not smart if external amp as you may have a amp stable into 4 Ohms, most AVRs are not. ( I don't care how many have gotten away with it. All it takes is just the wrong signal to introduce instability and POOF goes the amp. It is just plain stupid. They put the specifications on the AVR for a reason.)

              If inductor size is causing you a problem, you probably have picked too low a crossover point or a poor choice of Q. The paper cone Daytons can cross as high as 2500 which will inherently lower the midrange distortion by not pushing the tweeter. The RS aluminum cones are a lot harder to use. Boy do I know, but if tamed, very good. Outstanding if one considers their price.



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              • #8
                What people are saying about amps is true for the most part. But if you just have to do this, some class D amps from Hypex are happy with loads down to 1 ohm.
                Francis

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                • #9
                  Thanks for the thoughtful replies. I have purchased a few of the 3e audio tpa3255 stereo and mono modules that I plan on using for my mains. Amplifier technology seems to be evolving more than most other speaker/audio technologies and was surprised nobody has tried this yet. The Idea of buying the smallest value air core is appealing especially when we are talking about fancy inductors. That being said, with class ab amplifiers I have usually preferred higher impedance designs. I have always felt like I could here the mids and bass change as the dampening factor drops. Could be purely psychoacoustic.
                  b3s/nd20 line arrays
                  Markk's RS225rs28
                  2-rs390's

                  Comment


                  • #10
                    You're not buying a house, it's a speaker, do it, do a build thread, report on your results. Good luck.

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