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Help with TB 704D /Vifa DQ25SC16-04

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  • Help with TB 704D /Vifa DQ25SC16-04

    I had previously bought a few pairs of the TB704D last year and I'm looking into finishing at least one pair to try a new combination I haven't seen yet. I'm thinking about mating the TB 704 with the Vifa DQ25SC16-04, because it is relatively inexpebsive (and got high marks on Zaph's website). Anyone out there willing to put these two drivers in a simulation tool? I also had previously bought the 2nd order parts for the TB used on the Noobsters (1.5 mh and a 5.6 ufd cap) but not sure if they will mate well with the little vifa tweet? Anyone with spare time?

    thanks

  • #2
    Re: Help with TB 704D /Vifa DQ25SC16-04

    The Vifa DQ25SC is not suitable for a LR 2nd order design with its xover frequency at 3.5 kHz or lower, due to its rolloff starting early.

    I once modeled a crossover for MTM with W5-704D and DQ25SC for a person I came to know at diyAudio. Here's what I did:




    Baffle can be 8" to 9" wide. If you want to go vented, here's an example of build:

    http://techtalk.parts-express.com/sh...d.php?t=208702

    For a sealed design (to be used with a subwoofer), the PE .75 cu ft MTM cabinet is perfect.

    The tweeter can be centered or offset up to 1.25". In case it's centered, a bit of off-axis listening with slight or no toe-in will be optimal. The only fine-tuning option I provide is the tweeter output level by adjusting the R9 value (default: 1.75 ohm, two 3.5 ohm resistors in parallel). You may want to experiment with values from 1.5 to 2 ohm. At least I'd compare 1.75 ohm and 2 ohm settings.

    -jAy

    Comment


    • #3
      Re: Help with TB 704D /Vifa DQ25SC16-04

      Originally posted by jkim View Post
      The Vifa DQ25SC is not suitable for a LR 2nd order design with its xover frequency at 3.5 kHz or lower, due to its rolloff starting early.

      I once modeled a crossover for MTM with W5-704D and DQ25SC for a person I came to know at diyAudio. Here's what I did:




      Baffle can be 8" to 9" wide. If you want to go vented, here's an example of build:

      http://techtalk.parts-express.com/sh...d.php?t=208702

      For a sealed design (to be used with a subwoofer), the PE .75 cu ft MTM cabinet is perfect.

      The tweeter can be centered or offset up to 1.25". In case it's centered, a bit of off-axis listening with slight or no toe-in will be optimal. The only fine-tuning option I provide is the tweeter output level by adjusting the R9 value (default: 1.75 ohm, two 3.5 ohm resistors in parallel). You may want to experiment with values from 1.5 to 2 ohm. At least I'd compare 1.75 ohm and 2 ohm settings.

      -jAy

      jay, would a P-core suffice (.14 DCR) for the 1.2mh in lieu of the air cores?

      Comment


      • #4
        Re: Help with TB 704D /Vifa DQ25SC16-04

        Originally posted by Wushuliu View Post
        jay, would a P-core suffice (.14 DCR) for the 1.2mh in lieu of the air cores?
        It will work just fine.

        Comment


        • #5
          Re: Help with TB 704D /Vifa DQ25SC16-04

          Originally posted by jkim View Post
          It will work just fine.
          thanks jay. I've attached some pics of the build. Just about done, just some cosmetic touching up needed once I'm happy with everything. I am currently using 18ga 1.5mh inductors unwound to 1.2 (per the online calculator), and ~1.96 ohm (paralleled resistors) for R9.

          I decided to give this design a go because of:

          1. My previously mentioned bass/room boundary issues
          2. Desire for increased efficiency and lower impedance, which
          provides greater flexibility for diy amp designs.
          3. I wanted to buy and learn to use a plunge router & jig
          4. I had all the components except the woofers, so it was pretty cheap.

          I have never owned tower/mtm/tmm, etc. speakers before so it's hard for me to judge the sound. Also my room issues compromises the low end to a degree, so I know I'm not getting the most accurate response -but it's *much* better than the Poor Man's and sub setup I had in that regard. No more gap in the midbass. I did demo several $2k and up at a local hi-fi shop a few weeks ago. I would say the midrange and up of this mtm sounds just as good to my ears. I love being able to attenuate the tweeter as most retail designs are too hot for me.

          Thanks again, jay. Hope the job search is going well.


          ainsley
          Attached Files

          Comment


          • #6
            Re: Help with TB 704D /Vifa DQ25SC16-04

            They look great! Using 18 gauge air cores for the 1.2 mH coils is just fine, too. Don't bother to buy new coils. You used the Jantzen 18 gauge, didn't you? Do you remember how many turns you take out from the 1.5 mH? I can double check it for you.

            -jAy

            Comment


            • #7
              Re: Help with TB 704D /Vifa DQ25SC16-04

              Yes, they're a step up from the first build:p. The plunge router was far easier (and more fun) to use than I expected.

              I believe I unwound by 20 turns. Yes, 18ga Jantzen (not the steel laminate in the photo).

              Comment


              • #8
                Re: Help with TB 704D /Vifa DQ25SC16-04

                Yes, it is close to my calculated 22 turns.

                Comment

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