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Totally Flat MK II

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  • 4thtry
    replied
    Here are a few XSim modeled squigglies:

    1) XSim model using on-axis FRD's and on-axis mod delays (sitting position)
    2) XSim model using +15V FRD's and +15V mod delays (standing position)
    3) XSim model using 45H FRD's and 45H mod delays
    4) XSim on-axis model showing reverse nulls

    Crossovers are about 390Hz and 1.7kHz. This is the post-InDIYana revised crossover, which reduces the woofer relative to the mid and tweeter by about 1dB. This was done by adjusting the L-pads on the tweeter and midrange drivers only. No change was made to the woofer circuit.

    That is all I have time for today. I will stop back later with a few finished pics.

    Leave a comment:


  • 4thtry
    replied
    Woofer mounts: I glued 4 small hardwood blocks below the woofer mounting holes to reduce the chance of stripping as I tightened the screws.

    Banana plugs: I picked up a pair of PE 091-3608 right angle stacking banana plugs to make the tweeter connection. This model has expanding plugs with an insulated polycarbonite shell to prevent shorting.

    Voice coils: I brought the voice coils out the back separately, giving each one its own banana jack. This gives me maximum design flexibility to swap crossovers or flip driver phase as I test and debug the system. Hopefully, I will not accidentally connect the woofer cable to the tweeter by mistake.

    Next up: A few squigglies

    Leave a comment:


  • 4thtry
    replied
    Forgot the graph showing how the corner stuffing reduced the peaks:

    Leave a comment:


  • 4thtry
    replied
    Corner stuffing: Also, before gluing on the side panel, I installed the woofer and a temporary edge gasket so that I could run NF port measurements and examine the 1st and 2nd box/port resonant peaks. Then, by trial & error, I arranged and re-arranged some extra stuffing material into and out of the corners, in an effort to reduce the 1st and 2nd box/port resonant peaks. As you can see in the graph, I was fairly successful. The peaks at 300 & 700Hz were significantly reduced and I only lost about 1dB at the main port resonance (FB).

    The extra corner stuffing is held in place with some old, unused shoulder strap material, cut to length and stapled in place. Note that the area between the woofer and slot port is left completely open.

    Next up: Woofer mounts, banana plugs, and voice coils

    Leave a comment:


  • 4thtry
    replied
    Box lining, bracing & wiring: Before gluing on the side panel, I lined the cabinet internally with 1/4" thick denim sound control strips. The strips come out of the box as a very long 12" wide sheet, held together with tabs, making it easy to pull them apart as needed to glue them in place. I also glued 4 side to side braces in place to dampen the big side panels. I installed the voice coil wires along the top & bottom edges with gaffers tape.

    Next up: Corner stuffing

    Leave a comment:


  • 4thtry
    replied
    Triangular midrange enclosure: For the sealed, internal midrange enclosure, I decided to go with a triangular shape. This should help to spread out internal resonances compared to a rectangular shape.

    Next up: Box lining, bracing, and wiring

    Leave a comment:


  • 4thtry
    replied
    Slot port flare: I put 3" and 4" radius curves on the inlet end and exhaust ends of the slot port to create an asymmetrical flared port type effect. I used a smaller 3" radius on the inlet end based on information in the Loudspeaker Design Cookbook. (LDC version 7, page 73) For some unknown reason, a shallower radius inside the cabinet lowers distortion and port compression.

    Next up: Midrange enclosure

    Leave a comment:


  • 4thtry
    replied
    Baffle roundovers: I used strap type clamps to glue 1.25 x 1.25" radius quarter round pine molding to the edges of the baffle board. I found this material in 8 foot lengths at my local big box lumber yard. After cutting them to length, I glued several thin strips of 3/16" HDF onto the molding to form a mounting lip, which helped to keep everything firmly in place during the final glue up.

    Next up: Slot port flares

    Leave a comment:


  • 4thtry
    started a topic Totally Flat MK II

    Totally Flat MK II

    Greetings all,

    This will be my >$200 entry this year at MWAF. I brought the partially complete speakers to InDIYana and they were well received. Thanks for all the positive feedback. Someone asked me if these were the "Totally Flat" speakers that I had built last year. They look similar, but are completely different; new box, new drivers, new crossover.

    Based on feedback, I will be revising the crossover to reduce the woofer level by about 1dB. It may have been the room, but the woofer seemed just a little too overpowering, masking the detail just a tad in the mid and high frequency areas.

    Driver selection:

    Tweeter: Peerless DA25TX00-08 (8 ohms) (see pic). This is the poor man's high end tweeter, with sound quality comparable to some of the very best tweeters available, regardless of price.

    Midrange: Tang Band W3-1797S 3" aluminum sandwich full range (4 ohms) (see pic). This driver has the midrange clarity and detail of a good planar type driver, such as the B & G Neo-8 or Neo-10. TB also makes a 4" version of this driver, but I decided to go with the 3" because it has 20% less cone mass. Power handling will be a little less than the 4" version, but it should be able to hit my goal of roughly 95dB in the listening chair with both speakers playing.

    Woofer: Tang Band W6-1139SIF (4 ohms) (see pic): I wanted to keep baffle and cabinet size to a minimum, yet have a system that could dig deep with authority. This subwoofer can go right down to 25Hz in a very small box (3/4 cubic foot or so). The trade off is efficiency, which should be OK as long as I use an amplifier with sufficient power that can handle the load.

    Impedance: The mid and sub are both 4 ohms, which causes the overall system Z to dip to about 3.5 ohms at 600Hz. Phase angle, however, is zero at this point. The amplifier output stage will get very warm but this should not be a major problem.

    Efficiency: Probably somewhere in the 83dB/1W/1M area, which is quite low. Again, a big power amp that can handle a 4 ohm load will be necessary.

    Progress: I am currently working on re-painting and re-finishing the box. I'm also replacing the particle board xover box with a much improved hardwood unit. And I just put in my parts order for a couple crossover revisions.

    Next up: A few historical construction posts. I started building these about 4 months ago and am now approaching the finish line. In the next few weeks, I'll finalize & post the completed xover, cabinet, and FR measurements. Comments and questions are always welcome.
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