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The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

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  • The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    The Boxers are a 2-way stand-mount/bookshelf design utilizing a subwoofer driver with a very clean midrange and a waveguide-loaded soft dome tweeter. They debuted at InDIYana 2015 and will be entered into the MWAF Dayton category this summer. As I just registered for the competition, I thought I'd just copy and paste the info here in the project gallery. Thus the format you see below.

    DESIGN GOAL

    My goal with this speaker was to create what I would consider a true full-range speaker in a package that can actually fit on a bookshelf. Most bookshelf or stand-mount speakers utilize a 6.5" or smaller driver, and while some of them can dig pretty deep, they all end up being output limited pretty quickly. I wanted something that was smallish, could dig deep and could handle just about anything I could throw at it.

    DRIVER SELECTION

    There are many subwoofer drivers that can get low in a small enclosure, but most of them would require a midrange driver to take over by about 500Hz. This would require a separate chamber, taking away valuable air space in this compact design. The Dayton RSS210HO-4 is clean up past 1000Hz, allowing me to cross to a robust tweeter like the Dayton RS28F-4. The waveguide loading allows a low crossover point while still keeping up with the woofer in the output department. The particular waveguide used is a 3d printed model that is 8.5" in diameter and 2" deep with a 1.625" opening that is a perfect mate for the Dayton RS28 series of tweeters.

    ENCLOSURE DESIGN

    The enclosure is a simple sealed enclosure that is just large enough to hold the woofer and the waveguide, but just small enough to fit on a standard bookshelf laying down. The dimensions are 20" H x 11" W x 7.5" D with 3/4" thick walls for a gross internal volume of just over 17 L. The limited space inside was lined with fiberglass and filled loosely with polyfill. This gives the system a measured Qtc of 0.68 for a nice shallow rolloff (F3 = 45Hz and F10 = 30Hz).

    ENCLOSURE ASSEMBLY

    I used pre-finished 1 x 8 poplar from the big box store, which is actually 3/4" x 7.25". I made the top, bottom and sides from this material and joined them with mitered corners. I then glued 3/4" x 3/4" MDF strips just inside the front and rear perimeters of the poplar carcass to give the baffle and back panel a shelf to be adhered to. The front baffle and the back panel are both painted 3/4" MDF with a slight bevel around the perimeter for visual appeal and set into the poplar frame on the MDF rails so that the panel protrudes from the poplar about 1/8". Both panels are braced near the center using triangular gussets. Poplar doesn't take stain very well, so I just coated it with a few coats of shellac which really brought out the grain and colors of the wood.

    CROSSOVER DESIGN

    In order to get rid of some of the nasty upper frequency artifacts the subwoofer driver suffers from, it needed a 4th order electrical circuit with a tank on the leading inductor. This is pretty aggressive attenuation, but it puts the garbage about 40-50dB below the tweeter level and created a nice smooth rolloff near 1000Hz. The tweeter crossover was a breeze due to the waveguide loading and the flat impedance due to the massive attenuation necessary to match up with the woofer's low sensitivity. A simple 2nd order electrical circuit with some attenuation was all that was necessary to bring the frequency response and phase in line. Overall, the xo frequency ended up being about 1200Hz with 4Ω or higher impedance across its frequency response (except as noted below). This crossover point is low enough to mitigate the potential problems caused by a largish C-T-C distance of just under 9".

    I did add a couple other features to this crossover beyond what is described above:

    1) The waveguide generates an 8-9 dB suckout at about 13kHZ, but only on axis (15 off axis it smoothes right out). Some listening tests led me to add a small capacitor across the series attenuation resistor in the tweeter circuit to raise the top octave a bit. This brings the system impedance down to 2 ohms above 20kHz, which should be fine for most amp/content combinations. I felt it a worthwhile compromise.

    2) Since this speaker can legitimately be put on a bookshelf, I decided to add a switch to raise the tweeter level by 3 or 6 dB to counteract excessive bass reinforcement from this sub-optimal placement. The switch is a DPDT center-off type where the three positions engage or disengage series and shunt attenuation resistor combinations to produce the different levels. It should be noted that this crossover was designed for stand mounting and the switch just makes some other placement options more attractive.

    CONCLUSION

    These speakers offer a unique set of compromises that present a unique listening experience. I don't usually hear a presentation this large from speakers so small, but I think the waveguide dispersion pattern, the 8" midrange and the ability to play deep bass very loud offer such benefits. You don't get anything for free, so these speakers are quite inefficient and need a lot of power to get moving. The good news is, with a legitimate subwoofer as the bottom of this 2-way, they can handle a lot more power than other speakers this size.

    Dan
    Attached Files
    Last edited by DanP; 05-19-2015, 04:10 PM.
    _____________________________
    Tall Boys
    NRNP Computer Sub
    The Boxers
    The Hurricanes
    The Baronettes
    Conneccentric
    UX3

  • #2
    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

    A couple more pics of the impedance and completed crossover.

    Dan
    Attached Files
    _____________________________
    Tall Boys
    NRNP Computer Sub
    The Boxers
    The Hurricanes
    The Baronettes
    Conneccentric
    UX3

    Comment


    • #3
      Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

      Love the concept. I bet w/ a little power behind them they really rock! I like the cardboard/zip tie crossover layout, that's my favorite method.

      Comment


      • #4
        Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

        Very nice and useful project. This design covers quite a wide variety of applications. Hard to do with many designs of today.
        BSME
        Kannapolis NC

        Comment


        • #5
          Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

          Very nice. Liked it at InDIYana.

          One question though, why is the response showing a 10db dip at around 15khz? Is this due to the waveguide or crossover? The RS28F should be flatter than that on its own, though it does roll off over the high frequencies.

          do you have the raw measurements of the RS28F - FRD/ZMA. I do have the RS28F on hand, and i will print out the waveguide.

          Comment


          • #6
            Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

            Originally posted by ani_101 View Post
            Very nice. Liked it at InDIYana.

            One question though, why is the response showing a 10db dip at around 15khz? Is this due to the waveguide or crossover? The RS28F should be flatter than that on its own, though it does roll off over the high frequencies.

            do you have the raw measurements of the RS28F - FRD/ZMA. I do have the RS28F on hand, and i will print out the waveguide.
            The dip is a product of the waveguide and only occurs directly on axis. It goes away quite quickly off axis. I'll post some off axis measurements here this weekend showing the smoothing off axis and the characteristic waveguide dispersion. I do already have the raw RS28F data that I can send to you.

            Dan
            _____________________________
            Tall Boys
            NRNP Computer Sub
            The Boxers
            The Hurricanes
            The Baronettes
            Conneccentric
            UX3

            Comment


            • #7
              Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

              Any changes made since InDIYana? They sure did need juice too! Power HUNGRY!

              Just curious,
              Wolf
              "Wolf, you shall now be known as "King of the Zip ties." -Pete00t
              "Wolf and speakers equivalent to Picasso and 'Blue'" -dantheman
              "He is a true ambassador for this forum and speaker DIY in general." -Ed Froste
              "We're all in this together, so keep your stick on the ice!" - Red Green aka Steve Smith

              *InDIYana event website*

              Photobucket pages:
              http://photobucket.com/Wolf-Speakers_and_more

              My blog/writeups/thoughts here at PE:
              http://techtalk.parts-express.com/blog.php?u=4102

              Comment


              • #8
                Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

                Originally posted by Wolf View Post
                Any changes made since InDIYana? They sure did need juice too! Power HUNGRY!

                Just curious,
                Wolf
                No changes yet, but I printed some ribs that I'll glue to the back of the waveguide and got some Dynamat to stick to them after the ribs. I did some more voicing, but ended up with the same xo that was at InDIYana - I think I just need to take care of that WG resonance you noticed and she'll be ready for MWAF.

                Dan
                _____________________________
                Tall Boys
                NRNP Computer Sub
                The Boxers
                The Hurricanes
                The Baronettes
                Conneccentric
                UX3

                Comment


                • #9
                  Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

                  Originally posted by DanP View Post
                  No changes yet, but I printed some ribs that I'll glue to the back of the waveguide and got some Dynamat to stick to them after the ribs. I did some more voicing, but ended up with the same xo that was at InDIYana - I think I just need to take care of that WG resonance you noticed and she'll be ready for MWAF.

                  Dan
                  Ooooo Can you send across the ribs and the raw measurements?

                  Is the waveguide resonating due to the Woofer pressurization? Would it help if the waveguide has its own chamber like a mid, sealed from the woofer?

                  Comment


                  • #10
                    Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

                    Really cool design! Hopefully I'll get a chance to hear it someday.
                    -Kerry

                    www.pursuitofperfectsound.com

                    Comment


                    • #11
                      Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

                      Originally posted by ani_101 View Post
                      Ooooo Can you send across the ribs and the raw measurements?

                      Is the waveguide resonating due to the Woofer pressurization? Would it help if the waveguide has its own chamber like a mid, sealed from the woofer?
                      Yes I can send those over to you.

                      The waveguide is resonating for the same reason that the rest of the walls resonate, but it is thinner than the rest of the walls and has a mass (the tweeter) attached to the center of it, so I think that the resonance is in a bad frequency range.

                      It would definitely help to seal the WG off from the woofer, but I wanted to use all the airspace I could. The resonance was just barely audible, so I think the ribs will push the frequency into a lower energy range and the Dynamat will help damp what little resonance does get excited.

                      Dan
                      _____________________________
                      Tall Boys
                      NRNP Computer Sub
                      The Boxers
                      The Hurricanes
                      The Baronettes
                      Conneccentric
                      UX3

                      Comment


                      • #12
                        Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

                        I would be tempted to spray the backs of the wg with bedliner or brush on Duratex.
                        " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

                        Quote Originally Posted by hongrn. Oct 2014
                        Do you realize that being an American is like winning the biggest jackpot ever??

                        http://www.midwestaudioclub.com/spot...owell-simpson/
                        http://s413.photobucket.com/albums/pp216/arlis/

                        Comment


                        • #13
                          Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

                          I really like this design a lot. Really looks nice!
                          Projects:

                          transcenD: http://techtalk.parts-express.com/fo...5035-transcend
                          Summits: http://techtalk.parts-express.com/sh...75-The-Summits
                          References: http://techtalk.parts-express.com/sh...-My-References
                          Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

                          Comment


                          • #14
                            Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

                            I'm curious about the WG cross section, is this something you can provide? Thanks

                            Comment


                            • #15
                              Re: The Boxers - a subwoofer and waveguide loaded tweeter based 2-way

                              Originally posted by [email protected] View Post
                              I would be tempted to spray the backs of the wg with bedliner or brush on Duratex.
                              Would this do more than just stiffen and/or add mass? I'm hoping the Dynamat will convert some of the kinetic energy of the WG motion into heat to effectively damp the resonance.

                              TN - I've attached a picture of the WG cross-section. It is effectively a 4" radius that transitions smoothly to a 57 degree throat entrance.

                              Dan
                              Attached Files
                              _____________________________
                              Tall Boys
                              NRNP Computer Sub
                              The Boxers
                              The Hurricanes
                              The Baronettes
                              Conneccentric
                              UX3

                              Comment

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