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Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

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  • Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

    Well, I've been planning my HT for a couple years now. Originally it was going to be a Tritrix setup all around with an RSS315HF sub. I purchased all the Tritrix kits to build everything, built a sealed center channel (bare MDF), ported RSS315 (bare MDF), and then procrastinated for the longest time. I changed my mind and decided to go with a Stentorian front sound stage (L/C/R) and Tritrix MTM surrounds. Around Christmas time I finally purchased parts to build the Stentorians and started making dust after the first of the year. It's been a LONG, SLOW process, but I wanted to take my time and make sure everything was just right. So, here's my first build thread for the L/R mains:

    I picked the Stentorians mainly because of the combination of small footprint and high sensitivity. Plus, I think anyone will admit the Stentorians just plain look cool . I added my own twist to the design by going with curved sides on the cabinets. I kept the baffle width, driver spacing, and volume per driver the same as Curts original design. Instead of using window braces between each pair of drivers, I opted to make them all solid. I wanted the cabinets to be as solid as possible and was afraid window braces would give during the clamping process of building up the curved sides.

    Because the cabinets are so skinny and deep and I wanted the sides to be perpendicular at the front edge, I used an elliptical curve instead of circular. Since I knew what the height of each section would be, I drew up some cross-sectional views of the elliptical curves and integrated to find the cross-sectional area I needed to acheive the proper volume. After I knew exactly what elliptical curve I wanted, I drew up some 2-D plans in AutoCAD and some 3-D models in Sketchup to make sure everything lined up the way I was hoping it would.







    After being satisfied with the way things were going to look, I printed off the 2-D pattern for the braces. I can only print letter or legal pages, but the pattern wouldn't fit on one page, so I put a 1" square grid on the pattern and printed it on two pages. I then used the grid to align the two pages. Using Loctite spray adhesive, I applied the pattern to a piece of 3/4" plywood. This is the light spray adhesive which allows repositioning, but also sticks well. I like to spray both surfaces with a fairly liberal amount and let them tack up before sticking them together. After applying the paper to the plywood, I use the bandsaw to rough cut it and the disc/belt sander to smooth out the edges and finish off my pattern piece.



    Next, I traced my pattern piece onto 3/4" MDF (14 times) and again used the bandsaw to rough cut each piece. With each piece rough cut, I screw the pattern piece to the MDF and use a flush trim bit to accurately produce 14 copies of each other.





    The "frame" for each cabinet consists of a front, a rear, 7 braces (one cut short that goes directly behind the tweeter), and one false back to go behind the MTM section. Everything is made from 3/4" MDF except for the "fronts". The fronts are made from 1/2" MDF. A 3/4" baffle will be glued to the front later, resulting in a 1-1/4" total thickness to mount all the drivers. The sides will then have 6 layers of 1/8" HDF.

    The elliptical curve is perpendicular to the front baffle, so 90 degree edges are standard on the front pieces. Using the 2-D CAD drawings, I determined the angle of the back pieces. These came in at 68 degrees. Here are the stack of braces, fronts and backs:



    I cut the 3/4" baffles (1/2" over-sized) and centered them on the 1/2" front pieces. I marked the center of each driver location and drilled the 1/8" holes for the circle jig through both boards at the same time.



    I then cut 1/4" dadoes in the front and back pieces for the braces to fit into. This greatly eased assembly so I didn't have to worry about the braces sliding all over the place during clamp-up.


  • #2
    Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

    After cutting the dadoes, I cut the driver relief holes in the front pieces using my "modified" Jasper jig.



    The modifications to my Jasper jig allow me cut circles while rotating the jig, but not rotating the router. I use a plate with a brass guide bushing and a 1/4" spiral cut bit. This guide bushing fits perfectly into the bronze bushing I installed onto my jig. This way, I can use my shop vac on my router and not have all my hoses and power cords getting tangled. This came in VERY handy since the Stentorians need 7 holes per cabinet!











    After dry-fitting the pieces together, I applied glue into the dadoes and clamped the cabinet frames together. I used bar clamps to hold the top/bottom pieces in place and ratchet straps to apply pressure to the front/back pieces. I also used a small framing square to make sure the frame pieces were all perpendicular and adjusted the bar clamps to an angle to compensate for any twist.







    After the glue dried, I had to do a little bit of cleaning up of the outside edges of the glue joints. I used a flat sanding block to make sure the joints were all smooth.

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    • #3
      Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

      To glue up the curved sides, I needed a fixture to hold the cabinet and clamp evenly across the entire height. I used a piece of 1/4" OSB attached to several pieces of 2x4 ripped to 2x2 size (1.5" square). I used a few 2x scraps perpendicular to the side forms to hold them together. I used a few pipe and bar clamps to hold the jigs at the front edge of the cabinet, and then drove a screw into the bottom 2x pieces to keep the side jigs from sliding up when the clamping pressure was applied. Some hefty strap clamps were used to apply pressure directly over each brace. I used a couple scrap pieces of 1/8" hardboard under the front to make sure that my sides extended past the front edge and I flush trimmed them when complete. A couple scrap pieces (~1" in total thickness) were also set on top of the back to ensure the strap clamps did not apply any "downward" pressure to the clamping jig sides, causing them to bow outward and not apply any pressure to the middle of the sides.









      I used Titebond Extend glue to ensure I had everything assembled before the glue began to set. Standard Titebond and Titebond II only have a 5 minute open working time, but Titebond Extend has a 15 minute working time. It is also the recommended glue (per Titebond's website) for bent laminations. When applying the first layer, I only applied one side at a time to make sure I got the entire glue surface covered, and I could inspect my glue joints before putting the second side on. One problem I encountered is that I angled the edges of the backs just a bit too much. Since the curve is elliptical, it continues to get tighter and tighter as you go back. This meant that I needed TREMENDOUS clamping pressure at the back edge to get the side boards to completely clamp. I couldn't quite get them to wrap all the way around, but the inside edge of the back was sealed off and the inpected glue line showed that. So, I was left with a small gap between the sides and the back on the outside of the enclosure. I will just have to fill it when I get to the finishing stages.

      I also cut a short piece of scrap MDF and inserted it between the back and the secondary back behind the MTM section. With the clamping pressure at an angle on the back piece, I was afraid it would bend inward in this section. This small piece would be removed when I made the cutouts for the crossover cavity.



      After the first side glue lines were inspected, it all looked good. I spread glue and clamped the other side in place.



      I was very happy with the overall shape and the elliptical curves at this point. To apply each of the next layers, I poured glue across the next piece and then spread it evenly using a 1/16" triangular notched trowel. To keep from making a total mess and wasting a lot of glue, this took a decent amount of time. I was only able to do one piece on each side before I would have to clamp them in place. Titebond recommended clamping overnight for bent laminations, so I made sure to give it AT LEAST 8 hours of drying time before removing the clamps. After applying the last layer, I made sure to leave the clamps on for at least 24 hours.







      I knew these cabinets would be very solid and they were starting to get VERY heavy at this point. In hindsight, the curved laminations of HDF are significantly stiffer than an equivalent thickness of a piece of straight MDF and I probably could have gotten away with only 4 layers (~1/2"). However, at this point, limiting to 4 layers would have made my baffle width 1/2" narrower, so I went with 6 layers.

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      • #4
        Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

        My top and bottom edges were a good 1/2" to 3/4" over, so I first used a hand saw to trim them close. To trim the back edge, I screwed a scrap piece to the back of the cabinet. I made sure that the screws were going in to locations that I would later drill out or cut out so I wouldn't have to fill the holes during finishing (the design has a hole drilled into the back of each enclosure to act as an aperiodic vent, I had to drill two holes for the terminals, and the section behind the MTM gets cut out for the crossover). Once the scrap piece was attached, I used a 3/4" straight bit and a hand-held plunge router to remove the extra length of the sides. I trimmed them just a touch proud, and then sanded them flush with a sanding block.







        Since the sides are perpendicular at the front edge, I was able to use the flush trim bit around the top, bottom, and front.





        Here you can see the small gap between the sides and the very back edge that will be filled when I get around to applying the finish.



        I used my homemade sanding block to sand all surfaces flush. The sanding block uses 2 full sheets of paper and the sanding surface measures 9.5" x 18". This allows large surfaces to be sanded flat/flush. Because my 2.5 yr old son loves to watch the Cars movies, and we've seen them both at least 50 times now, I have affectionately called this the colossus sanding block. If you've seen Cars II lately, you'll understand . I started with 40 grit sandpaper to make quick work. A "build thread" for how I built this sanding block can be found here. It is a torsion box construction, so it's fairly lightweight for it's stiffness and size, but it has enough mass that all you really have to do is slide it back and forth without pressing down.





        More to come later...
        Last edited by 1100xxben; 04-08-2013, 12:19 AM.

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        • #5
          Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

          These look amazing, I am really impressed.

          I was wondering, however, what sealing each of the individual sections is going to do for the f3?

          Comment


          • #6
            Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

            Originally posted by NickJ View Post
            These look amazing, I am really impressed.

            I was wondering, however, what sealing each of the individual sections is going to do for the f3?
            That same exact thought came to my mind as well. I was also wondering what your plan is to route the driver wiring and mount the XOs?
            Bryan K.

            Midwest Audio Club

            Speedster | Sub Attachť | The Wildeman | Sean's NLA Towers | CO‹GAR, COUGAR II and CO‹GAR JR | Triton | Lithium | J-Boom | Trym MLTL | Docere MLTL

            Comment


            • #7
              Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

              Originally posted by NickJ View Post
              These look amazing, I am really impressed.

              I was wondering, however, what sealing each of the individual sections is going to do for the f3?
              Thanks... they have been a LOT of work. Probably more than they should have been

              Each driver having its own space should have no effect on the f3. I designed the enclosure to have the same volume per driver. Curt even mentioned on his website that the braces could be solid.

              You can try this yourself in WinISD. Model one driver in a sealed enclosure, then model two in an enclosure of exactly twice the size and the response will be the same.

              Comment


              • #8
                Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

                Originally posted by bkeane1259 View Post
                That same exact thought came to my mind as well. I was also wondering what your plan is to route the driver wiring and mount the XOs?
                I'm getting there... It takes me a while to type all this up with a 2.5 yr old interrupting me . I forgot to post it earlier, but I have the wire routing planned and all the holes pre-drilled in the braces before assembly.

                Comment


                • #9
                  Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

                  Well the build looks outstanding so far!! I'd be interested in the sanding block plans. I glue sandpaper down on large scrap and run the box across it -- opposite of what you do. It's not nearly as effective and it wouldn't work with a large cabinet. That homemade sanding block of yours is sweet.
                  Bryan K.

                  Midwest Audio Club

                  Speedster | Sub Attachť | The Wildeman | Sean's NLA Towers | CO‹GAR, COUGAR II and CO‹GAR JR | Triton | Lithium | J-Boom | Trym MLTL | Docere MLTL

                  Comment


                  • #10
                    Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

                    That looks awesome. I'd really like to see the plans for your sanding block.

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                    • #11
                      Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

                      Looking great so far! I can't wait to see them done.

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                      • #12
                        Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

                        Super-smart move with the Jasper Jig. I wish mine did that.
                        Isn't it about time we started answering rhetorical questions?

                        Paul Carmody's DIY Audio Projects
                        Twitter: @undefinition1

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                        • #13
                          Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

                          Wow, awesome build! Looks awesome, and that sanding block would have saved my a$$ on the Deadhorses, they look awful up close... and from far away, haha.

                          रेतुर्न तो थे स्रोत
                          return to the source
                          leviathan system thread
                          deadhorse thread
                          shockwave build thread

                          instagram :: greywarden_13

                          in war, victory . . . in peace, vigilance . . . in death, sacrifice.

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                          • #14
                            Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

                            FYI, I posted a build thread for my sanding block. It can be found here.

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                            • #15
                              Re: Stentorian - Curved Cabinet Build Thread (VERY PIC HEAVY)

                              Continuing...

                              After trimming and sanding all edges flush, I laid a straight edge across the front of the cabinet and found that it was anything but straight/flat in either direction :(. This was actually the main reason for building my sanding block, and it definitely made quick work with 40 grit sandpaper! As you can see in these pictures, when holding the straight edge on one end of the cabinet and the middle, I've got about a 1/4" gap at the other end. The third pic shows a baffle laying on the cabinet and the ridiculous gap.







                              I started sanding in the middle and kept checking as I went. I would use the straight edge to find the high spots and mark them with a pencil. Then I would sand those areas. After several rounds of sanding, checking, sanding, checking, etc... I finally had a flat front that I felt I would be happy attaching the baffle to.





                              As a final check, I scribbled over the entire surface and sanded a few swipes back and forth. If any scribblings remain, they indicate low spots and more sanding needs to be done.





                              After trimming and sanding everything flush/smooth, I cut out the openings for the crossover cavities. I drilled holes in each corner of the opening and used a jig saw to cut them out.



                              I placed another 3/4" piece on the top and bottom. There were three reasons for this. One, this helps stiffen up the top and bottom since they aren't braced in any way. Two, since the top is going to be painted, this provides a smooth surface without any seams to have to treat. And three, this makes the enclosure the height that I wanted . I placed the cabinet on top of the MDF and traced each cabinet twice. I rough cut each piece over-sized on the bandsaw and then glued them in place. Since I don't have a large quantity of clamps that can reach the full height of the cabinets, I used 4 pipe clamps and some curved cauls to apply even pressure across the entire surface.



                              Once these pieces were dry, I used the flush trim bit again to smooth everything out. My plan is to use a piece of grill cloth and frame to cover the crossover opening. I made a pattern from 1/4" plywood to use my router and bushing guides to make a 1/4" x 1/4" recess in the opening. This will allow a speaker grill frame to drop right in.





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