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Dadio Super Twinsound (a suitcase boombox)

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  • Dadio Super Twinsound (a suitcase boombox)

    I wanted to share my nearly-finished build. I started planning this in the summer of 2015, put it on hold over the fall, and then picked it up again in the winter. So here it is, 9 months later.


    ENCLOSURE AND PROJECT OVERVIEW
    I found a forest green vintage suitcase in my in-laws attic and wanted to make a 2.1, 12V battery-powered system out of it. The original design (posted in a thread named "Golden Age") was going to have OSMTM for the L and R channels. A number of users on TechTalk (specifically 'fbov') pointed out that I had too many competing requirements here: relatively low-efficiency speakers, 12V power supply, giant woofer but not enough volume in the suitcase for everything.



    So I simplified the concept to a 2.0 design, higher efficiency drivers. First I had a neighbor help me frame the inside of the suitcase with 1/2" plywood, including a box in the middle to hold the electronics. The enclosure, for now, is sealed:


    Used a jigsaw to cut the speaker holes in the plywood





    DRIVER SELECTION
    I wanted to keep the cost of the drivers to <$50 total. I also knew I needed drivers with >90dB sensitivity. After a lot of research, I settled on:
    • Tweeter: Goldwood GT-510 1" (~$11 each, 8 Ohm, 90dB at 1W/1m but the graph suggests it's closer to 93dB)
    • Mid/Woofer: GRS 8FR-8 8" "Pioneer BOFU clone" (~$14 each, 8 Ohm, 91dB at 1W/1m)


    Even with a relatively modest 15W/ch class-D amp (which provide up to 8W per channel before the THD starts to climb), these could theoretically get close to 100dB.

    CROSSOVER DESIGN
    I posted a question about how to cross the BOFU and the GT-510 after fumbling around with some online calculators. Chris Roehmer was a savior and basically designed the crossovers for me, which is great because I had no clue what I was doing. In his words:
    "So we put a "Zobel" across the 8" terminals (an 8ohm resistor and a 10uF cap - an "npe" is fine here) which pulls its impedance at 20kHz down from 160ohms to 8ohms. That lets you get by w/a relatively small (1st order) coil. Use a 0.60mH #20.

    The tweeter needs to go 2nd order (a big reason why is that it does NOT have "ferrofluid" and hits 27ohms at Fs). You need a 3uF series cap and then a 0.40mH "shunt" coil (to gnd). Between that filter and the tweeter we need an "L-pad": SR = 4ohms, PR = 12ohms.

    This crosses around 3.5kHz. Shouldn't sound too bad. Looks like the worst "artifact" is about a +3dB "hump" around 800-1000 cycles which is inherent in the 8"FR's response."

    The finished crossovers, with literally the ugliest soldering job ever seen:



    AMPLIFIER WOES
    I originally picked the Lepai lp-2020a+ because of the price and built-in tone control. Ultimately, I gave up after getting 3 bad units in a row. I ripped a Dayton DTA-2 out of an older project, but not before I had already cut holes in the suitcase to mount the Lepai. Ugh...



    Luckily, PE had a nice 5" x 7" speaker terminal blank plate (Part#260-110) that covered the mistake nicely. I got a replacement knob for the DTA-2, two 12V LED illuminated rocker switches (one to turn on/off a USB charger and one for the Sure 12V APT-X Bluetooth Module). I found an automotive panel jack that had a nice waterproof cover and both a USB female plug and a 3.5mm aux input.


    POWER AND WIRING
    I used two 12V 7Ah SLA batteries, stashed at the bottom of the suitcase to keep the center of gravity low. They're wired in parallel for 14Ah of power. A built-in trickle charger keeps them tuned up. Some terminal barrier strips keep everything clean. There's a 10Amp fuse between the battery/charging circuit and the downstream electronics.




    I wired the trickle charger through a hole in the ventilation plate on the back. When you open the suitcase, the extra cable simply slides through a grommet to provide slack. Two drawer pulls screwed to the back allow me to wind up the cable when not in use.


    FINISHING TOUCHES
    What's a project without a name? My twin 6 year-olds wanted to name the speakers. One suggested the name "Dadio" (Daddy + Radio) and the other suggested "Super Twinsound". Porque no los dos?

    I designed some logos on Inkscape (free vector design software) and had them custom lasercut in silver acrylic on Ponoko.com. New users can get a $20 credit. Since my design was simple enough, it was within the $20 and all I had to pay was shipping. They are amazing. Very crisp and look/feel great. The Super Twinsound plaque includes a shout-out to my neighborhood, naturally.



    WHAT'S LEFT
    All I'm missing now is the BT module, which is on back order. Since it takes 12V, I plan to use a 3PDT 12V relay to automatically switch between the BT and Aux inputs. In other words, the Aux input (L,R,Ground) will be wired to the three normally closed "NC" poles. The BT inputs will be wired to the "NO" poles. And the output poles will go to the DTA-2. Applying 12V of power to the BT module (that other switch on the front panel, with a blue LED of course) will flip the relay and switch inputs.

    FINAL DESIGN AND LISTENING IMPRESSIONS
    This thing far exceeds my expectations. Easily better than those $300+ BT speakers you can buy, and completely bespoke. I spent about $200 on parts and materials. With the exception of the plywood, the trickle charger and USB/Aux input jack, everything is from PE. Huge thanks to TechTalk contributors Chris Roehmer, Frank "fbov", and countless others who helped me see this through. I listen to it with a touch of smiley-face EQ using a 7" Android tablet as the source, but it sounds really good even without. It gets LOUD. I haven't really tested the batteries, but this really should last all day long at a block party or similar event.

    (click the image or the link below for a video clip with a sound sample and a better view of the finished boombox)

    The finished Dadio Super Twinsound

  • #2
    Re: Dadio Super Twinsound (a suitcase boombox)

    Hey, that's a really cool project.
    You picked a good woofer to use, sensitivity is the key with portable stuff like this. Many I've seen tend to use pro-sound stuff because of the higher output per watt thing.

    Shame about the non-working Lepai 2020's. I don't understand that, I've purchased 8-10 since PE started carrying them, and they've all been stellar performers. I've had a few with scratchy potentiometers, but on mine, it ended up being a slight misalignment between the shaft of the knob and the front panel rubbing, not the actual pot. There have been a few others though who have gotten bad units as well, guess I've been lucky.

    Like the logo too. Nice!

    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

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    • #3
      Re: Dadio Super Twinsound (a suitcase boombox)

      Very cool.

      C Roemer

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      • #4
        Update: The bluetooth integration is now finished and works perfectly, using the Sure BT 4.0 AptX receiver board (runs on 12V). The front control panel has a few things going on:

        1) Power/volume for the DTA-2 amp with a blue LED indicator
        2) LED rocker switch for the USB charger (got a combined USB and Aux input automotive/motorcycle panel mount jack off of Amazon)
        3) LED rocker switch for the BT module

        Because the BT module works on 12V, I was able to use a 3PDT relay to automatically switch between the BT and the Aux inputs. Turning on the rocker switch sends power to the BT module, which is in series with the relay. This trips the electromagnet on the relay, flipping from the "normal closed" to the "normal open" contacts. It's a very effective and clean way to automatically switch inputs and power the BT module. The relay I used was PE Part # 075-314, along with the matching relay socket to make the wiring easier.

        I put a few fistfuls of polyfil on each side. At some point in the future, I might consider porting the woofers but for now I'm very pleased with how punchy and clean it sounds.

        Comment


        • #5
          That is so very cool. Great job, especially those great-looking logos! Can you imagine trying to go thru airport security with that in hand?

          GeeDeeEmm

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          • #6
            Very nice work!
            I've seen some guys sell these for $$$ each. just sayin'

            I think I hear a difference - wow, it's amazing!" Ethan Winer: audio myths
            "As God is my witness I'll never be without a good pair of speakers!" Scarlett O'Hara

            High value, high quality RS150/TB28-537SH bookshelf - TARGAS NLA!
            SB13/Vifa BC25SC06 MTM DCR Galeons-SB13-MTM
            My Voxel min sub Yet-another-Voxel-build

            Tangband W6-sub

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            • #7
              gdmoore28 - thank you! The logo is one of my favorite details. This thing stretches the definition of "portable". It's about 40lb and would not go over well with the TSA.
              donradick - thanks! I've seen very similar ones on the web selling for ~$700-$1000, including one made from this exact suitcase (small world!)

              If I ever build a "Dadio V2", I think I'm going to focus on choosing lighter batteries, slightly smaller suitcase, perhaps one that doesn't need plywood reinforcement.

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              • #8
                That's a fantastic build. Perhaps a hard side luggage set with some damping and reinforcement would lighten the load a bit.

                I've always been interested in a 2.1 setup ever since I saw this Cambridge thing in a Stereophile magazine back in 80 something. The case as the sub with a pair of satellites inside for transport.

                Electronics engineer, woofer enthusiast, and musician.
                Wogg Music
                Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

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