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Build Thread: jkim's "Poor Mans": SB/Vifa TM

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  • Build Thread: jkim's "Poor Mans": SB/Vifa TM

    Finally decided on jkim's "Poor Man's High End Monitors" (yes, really, parts have been ordered :p). These are for my best friend's 40th birthday. Intended for music, to be run full range, unless he decides to add a sub.

    First things first: Big thanks to jkim for all his help on this, his work on generating this design, and all his contributions to the DIY community.

    More info on the Poor Mans here: http://techtalk.parts-express.com/sh...d.php?t=207805

    Volume is .8 cubic feet, vented (volume accounts for braces). Baffles are tipped back at a 5 degree angle. All 3/4" mdf, painted, color TBD (blue is very likely). Small PE spikes on the bottom. 5/8" roundovers on the vertical corners.

    Baffles and braces will be CNC'd, since they are too big to fit on the rotary table here at work, I hate plunge routers, I have a friend who will give me a great deal, and mdf dust is no fun... plus I'm lazy.

    Ports will be PVC pipe, exact port dimensions TBD. Walls will be lined with 1" rigid fiberglass. Region below lowest brace will be stuffed. Driver geometry in illustrations is approximated.

    Crossover will be mounted to the base, and accessible by unscrewing the base. Note the lugs attached to the side walls that will accept screws for attaching the base.

    Crossover design will be kept confidential until jkim decides if and when to publish the design himself. Crossover shown is obviously approximated, and does not represent any particular components or even a part count.

    Much more to follow of course... Any comments are greatly appreciated. Thanks!


    Vifa DQ25SC16-04 1" Titanium Dome Tweeter




    SB Acoustics SB17NRXC35-8 6" Woofer









    EDIT: Updated design... taller, rear panel now leans back 4 degrees (was vertical)

    Last edited by lunchmoney; 11-06-2009, 05:43 PM.

  • #2
    Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

    yikes... over 100 views and no comments? Tough crowd.

    I guess it ain't the most exciting build in the world, but... nuthin?

    I guess I won't bother next time, unless the build is something crazy.

    feel the love :rolleyes:

    Comment


    • #3
      Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

      Lunchmoney,

      It's Sunday man...never post on Sunday! Should look pretty sweet when all is said and done. I am just finishing up a cabinet for CurtC's Mavericks, that have the same overall look...just a tad bigger, and 7degree lay back, and it's a t-line, and it uses different drivers...but looks somewhat similar.

      Your braces - - - - watch out that you don't create lots of mini ports with those. They should have openings at least twice the size as your main port otherwise...funky things man.

      Good luck.

      Wayne

      Comment


      • #4
        Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

        OK, I'll bite...

        I LOVE that tweeter. It's in the Zaph ZMV5 and sounds wonderful there. I'm sure that it will sound good in this build too.

        For a two-way, your plan to use the bottom plate for the crossover will probably work fine. For a 3-way, it would probably be a bit small. I like the cleverness you employed in designing the bottom section.

        Going for paint again, or will you try for veneer this time?
        Bill Schneider
        -+-+-+-+-
        www.afterness.com/audio

        Comment


        • #5
          Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

          Originally posted by waynew View Post
          Your braces - - - - watch out that you don't create lots of mini ports with those. They should have openings at least twice the size as your main port otherwise...funky things man.

          Good luck.

          Wayne
          See? That's why I post this stuff. I need the feedback. Still a newb.

          Ok, I'll redesign those braces with way bigger holes.

          Thanks Wayne!

          Comment


          • #6
            Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

            Originally posted by williamrschneider View Post
            OK, I'll bite...

            I LOVE that tweeter. It's in the Zaph ZMV5 and sounds wonderful there. I'm sure that it will sound good in this build too.

            For a two-way, your plan to use the bottom plate for the crossover will probably work fine. For a 3-way, it would probably be a bit small. I like the cleverness you employed in designing the bottom section.

            Going for paint again, or will you try for veneer this time?
            Thanks william

            Gonna go with paint again. I've got a kick-a$$ paintbooth at my disposal, and the paint is free (mix colors from leftover stuff). Gotta keep the cost down.

            Comment


            • #7
              Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

              I like the box shape, the top and front make a 90 degree angle so you only have one angle to contend with so it would be fairly easy to build. I like that look a lot. Man, the frame on that woofer looks thick and beefy, is it a cast unit or plastic?

              TomZ
              Zarbo Audio Projects Youtube Channel: https://www.youtube.com/channel/UCEZ...aFQSTl6NdOwgxQ * 320-641 Amp Review Youtube: https://youtu.be/ugjfcI5p6m0 *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
              *Part 2 *Gluing multiple curved laminations of HDF

              Comment


              • #8
                Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

                Originally posted by tomzarbo View Post
                Man, the frame on that woofer looks thick and beefy, is it a cast unit or plastic?

                TomZ
                Cast

                Comment


                • #9
                  Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

                  Originally posted by waynew View Post

                  Your braces - - - - watch out that you don't create lots of mini ports with those. They should have openings at least twice the size as your main port otherwise...funky things man.

                  Good luck.

                  Wayne
                  Wayne, are saying that each hole in the braces needs to be that big? Or the area of the holes combined? If you mean combined, then I guess I'm all set. If you mean each individual hole, I'll need to change the plan.

                  Comment


                  • #10
                    Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

                    Originally posted by lunchmoney View Post
                    Wayne, are saying that each hole in the braces needs to be that big? Or the area of the holes combined? If you mean combined, then I guess I'm all set. If you mean each individual hole, I'll need to change the plan.
                    You basically want to minimize the amount of brace, and have the holes as big as possible, while still providing some side and cross bracing to the box walls. Ideally you want nothing in there to interfere with the airflow, and infinite strength, which of course is mutually exclusive.

                    Back to the real world, if your holes are smaller, you create different smaller boxes connected with really short ports. So making them rather large gets that effect below the noticeable level. I'd be thinking 1" thick members and the rest cutout, for that size box.

                    Another thing, make the braces like the shape of a window, rather than an X, so the wood in the middle will go from center side to center side, rather than from corner to corner as you have it now. That will make it a much stiffer support to the centers of the box sides. (wood in compression/tension rather than bending lengthwise)

                    Comment


                    • #11
                      Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

                      I built the sealed version and they are very good, especially for the price.

                      Comment


                      • #12
                        Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

                        Okay, here is is with redesigned braces... (oops, port not shown)



                        My first thought was "doesn't look as strong" since there's nothing going across... and I'm sure it isn't, but I'll bet it's more than strong enough... it sure worked for the Romans...

                        Comment


                        • #13
                          Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

                          A semi-circle and a circle aren't the same thing.
                          "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

                          http://www.diy-ny.com/

                          Comment


                          • #14
                            Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

                            Originally posted by Face View Post
                            A semi-circle and a circle aren't the same thing.
                            They do, however, follow the very same basic principles of structure.

                            The previous solution (the original x-braces I had in there) only had 1" wide elements... and I suppose they were too restrictive in terms of airflow...

                            So I think this is a good solution for adding rigidity while still maintaining good airflow.
                            Last edited by lunchmoney; 08-24-2009, 08:32 AM.

                            Comment


                            • #15
                              Re: Build Thread: jkim's "Poor Mans": SB/Vifa TM

                              Gosh, I post so infrequently now.
                              And for some reason only in your threads.
                              Maybe because you post such pretty pictures. ;)

                              As touched upon by others, the panel vibrations, however slight of course, are going to originate and be worst at the point of least constraint- in the middle. That is where the greatest deflection is going to be, and like a speaker cone with more xmax or driven to greater displacement, achieve greater output in the form of cabinet coloration. Therefor, I would place your brace attachment points nearer to the center of the panel, instead of the corners which are already much stronger inherently. If I remember correctly, like you did on your SR-71s.

                              For a brace to act as a port and impart some transfer function upon the sound might require that the length in question be longer to support such a resonance. This was pointed out to me when I brought up the same concern here some time ago. However, I believe Roman experienced detriment when he tried to connect two chambers in a system by a narrow passageway behind his midrange enclosure and reported how he redesigned the whole thing because the bass response was not acting predictably. I personally suspect this was because the passageway was long and did support a resonance. At the same time, if window braces didn't work, we would have seen it by now from the more studious measurement people- I would think.

                              Cheers.

                              Greg

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