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Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

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  • Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

    I’m sure most of you guys have seen my thread seeking design input for a DIY build centering around the Kef R-series concentric. If not, here's the link. To save you the trouble of reading through it if you haven’t (though there is some good data in there if you wish to go with dual woofers), the short story is I have decided make this DIY build a fully active 3-way setup consisting of the following gear:
    • Kef R-Series concentric mid/tweeter
    • Scanspeak 26w/8867T 10” woofer.
    • Rane RPM26z for processing (crossover and EQ)
    • Crown DriveCore XLS1500 for tweeters (525w x2 @ 4ohm)
    • Crown XLS2000 for mids (650w x2 @ 4ohm)
    • Crown XLS2500 for woofers (775w x2 @ 4ohm)






    Total power overkill, I know, but I had a couple already and I see no downside to using them. Talk about headroom… sheesh!

    Initially, I had planned to use dual woofers per tower. This was intended to keep the driver within beaming at the crossover but also allow me the abillity to smooth the LF response with the 2nd woofer. As the testing and simulations went on, I realized that using a single 10” would behoove me in regards to vertical polar and strike a nice balance for where I intended to cross thanks to the mid’s lower frequency limits and the woofer’s higher frequency limits, combined with baffle step. Ultimately, I plan to have the crossover between the woofer and concentric mid in the neighborhood of 400-500hz. I may still be lacking in regards to the LF smoothness, but it's a tradeoff I'm willing to take.

    I’m really not a fast worker when it comes to wood. I’m not a fan of building anything because I can’t achieve the ‘measure twice, cut once’ aspect. With that said, this build really will be simple at least with respect to the cabinet. I wanted to go with curved cabs but I was worried I’d spend more time and money buying materials than I have at my leisure, it’d make more sense to start with a very KISS method and possibly revisit a more complex, but aesthetically pleasing tower design this summer when I have time.

    Each cabinet is 12x13x48. This size was chosen in order to achieve a baffle step between the woofer and mid at about 500hz. Again, I’m just assuming that doing so allows for a more natural driver response without the need to put any correction in to the system. Of course, the 10” woofer size really drives the necessary baffle width… I suppose it all just sort of fell together in this regard. The woofer height will be placed about 23” from the floor. This height was chosen as it helps me stay within some reasonable range of lobing limits in conjunction with being at a good frequency with respect to floor bounce. The concentric will be placed roughly 41” from the floor. This height was chosen because that’s approximately where my head will be. There’s nothing I can’t stand more than looking down on a speaker at a normal seated height. It totally kills my psyche, man. :D

    I did a klippel test on each woofer to obtain large and small signal parameters. Small signal specs indicate a sealed enclosure size of 0.75ft^3 to hit a Qtc of 0.707, though my measurements showed different. Ultimately, based on my measurements, I arrived at a sealed volume of about 1.75ft^3. This puts the Qtc at about 0.60. Namely, however, it gives me some play room and by adding or removing stuffing, I should be able to achieve a Qtc that I desire. The upper section, where the midrange concentric will be housed was not targeted for any particular Qtc. I did, however, model up the enclosure size I plan to use (simply by default of bracing location and cabinet size) and found the f3 to about 213hz. This is less than half of the desired crossover point, so I think Im OK here. I wanted the extra room in the enclosure to be able to stuff it with varying materials. A target Qtc isn’t important to me here. Though, managing the internal reflections is.



    On to the build...

    I went to a local lumber yard to look at their Birch offerings. $65/sheet for domestic. And it looked good. The problem was they wouldn’t cut the sheet in half for me to fit in my civic. And they closed soon which meant borrowing a truck wasn’t going to happen and I wanted to get started the next day and work on the project during the weekend. I went to the local Home Depot and found they sell 12x48” MDF shelving pieces for about $5/sheet. These were practically perfect for me. $75 later I drove back home with a stack of 13.

    All said and done, I didn’t get too far this weekend. I did manage to cut dados in the main structure pieces for both enclosures to support the 4 braces I plan to have. In my first time ever using a dado, I learned a couple things. So, if you look closely you’ll probably see some bad spots where those lessons were learned. ;)
    I also took a scrap piece of birch and cut some practice holes for the drivers so I’d know exactly what size the OD, ID, and depth was in order to flush mount them. Pictures are below.














    Sawdust sucks! Thank goodness for respirators.



    I’ll update this as I go. But that’s pretty much where I stand for now.


    - Erin
    Last edited by ErinH; 03-05-2014, 10:10 AM.
    ErinsAudioCorner.com

  • #2
    Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

    You sure got a lot of sawdust on your dalmation!

    Comment


    • #3
      Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

      Indeed! He could almost be a collie with all that sawdust on him! ;)
      ErinsAudioCorner.com

      Comment


      • #4
        Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

        That's some serious firepower! I have the xls1500 and love it I want another! We have the SAME EXACT work space setup, router, etc. 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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        • #5
          Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

          I love these amps, man. They're really just great. Excellent efficiency, small-ish footprint, and lightweight. Tons of power for the (used) price.

          As for the work space, I'm stoked to have this garage. We built a 3-car and I separated this single side from the double side where we park our cars. This is my play area. Best part is I can just move everything inside and not have to take down my saw horses or put things up to get the car back in. Woot!


          In other news, I recently purchased a pair of the JL Audio E112 subwoofers. Managed to pick up a used set for a good price and just went ahead and jumped on it. So, those will hold down the sub-60hz content.
          ErinsAudioCorner.com

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          • #6
            Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

            all that power, all that bosch gear... looking good.

            dalmation comment made me spit a lil beer. :D

            Comment


            • #7
              Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

              I agree, the dalmation comment was clever.

              Bosch gear... man, I used hand-me-downs for years. When I finally bought some new stuff, I was delighted to use something that could actually cut worth a flip.
              ErinsAudioCorner.com

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              • #8
                Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

                Moved to new thread.
                ErinsAudioCorner.com

                Comment


                • #9
                  Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

                  I've been going rather slow with this build. I've been doing this while my 3 year old plays in the driveway on her new bike, so I'll work a bit and then jump on mine to ride with her. Trying to balance this project with being a good Dad. Needless to say, I haven't gotten to where I'd like to be, but I have managed to make some decent progress. I got all the pieces cut for the tower and managed to glue them up, sans the front baffle.

                  So, here's the point at which I beat myself up... you ready? Let's go...

                  This was my first time cutting dados and I'd say I got about 75% of them right. The other 25% are about 1/8" too large or have crazy spots in them because the router wandered.
                  Reading up on dados before purchasing a bit for the router, I found out that typically 3/4" mdf is actually typically undersized and the dado bit for this kind of project is typically a hair smaller: 23/32". I ordered one up from Amazon. When I got the MDF pieces I realized they're actually oversized... say 0.80". Really?! Man! So, I wound up having to make multiple passes anyway, which effectively doubled the time I thought it would take. Lesson? Don't buy a bit until you get the wood... that, or just plan on doing multiple passes since not all wood is created equal.

                  I also made a TOTAL nooB mistake when cutting the dados for the top braces (3rd & 4th from the bottom in the picture below). I had taken some pre-measurements to make sure those two would give me the airspace needed for the woofer, and I also liked the idea of having a gap between the woofer and mid volumes. Thinking I could treat it with something later (made a post about it here). Anyway, at some point in the process, I cut the top brace about 2" too high; putting it's location just under where the midrange would mount. Didn't realize it until after I glued up the first cab. Speaking of realizing your mistake once you've already glued, I also realized I didn't cut the air holes for the woofer enclosure brace (2nd brace from the bottom) so I had to do the best I could with a hole saw and jigsaw. I got enough material cut out but it looks ugly. Luckily I caught that before I glued the 2nd tower up so I could cut that brace as needed before it was glued in to place. I'd like to say lesson learned, but I doubt it.

                  I really seem to have no ability to cut a perfect square but somehow they turned out OK. There are some gaps that are going to get some bondo-glass treatment for sure to cover them up and sturdy up the structure. Somehow or another when cutting the top/bottom pieces, my straight edge wasn't so straight so at one point the piece matches up perfect with the cab, but at the other end, it's off by nearly 1/4". Ugh. :rolleyes: But, as sad as it is, I'm actually REALLY looking forward to the bondo/Rage Gold sanding phase on these. That means I'm closer to the end and those spots should clean up. Anything is better than cutting more MDF. I had that stuff all in my beard. Glad I have a respirator because MDF boogers suck!

                  Maybe you guys can learn some lessons from my mistakes. But, judging by the caliber of builds here, I'm probably the only one making these mistakes and I also seem to be the only guy here who can't cut a square to save his life!

                  All said and done, however, I'm pretty happy with how things turned out. The small gaps I have can be remedied and I can take pride in knowing I did this all myself, as much as an aggravation and time consumer it was. I'm about 80% done with the construction. I'm going to double layer the baffle so I need to glue those pieces together. Before they are glued in, I'll line the enclosures with varying density material and route the wires where needed. Not a whole lot to see, but here's some pictures.



                  ErinsAudioCorner.com

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                  • #10
                    Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

                    You have clean white shutter blinds in your GARAGE. Bless you, son. Those would last like 20 seconds in my garage.
                    Bryan K.

                    Midwest Audio Club

                    Speedster | | The Wildeman | Sean's NLA Towers | , COUGAR II and | Triton | Lithium | J-Boom | Trym MLTL | Docere MLTL

                    Comment


                    • #11
                      Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

                      It's a new house. I don't cut any wood in the garage anyway. Have to open up the garage door and move it outside. ;)
                      ErinsAudioCorner.com

                      Comment


                      • #12
                        Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

                        We all make some mistakes when starting out. On my last build I wrote out a list of things to do for the build and still managed to make 2 left speakers instead of a left and a right
                        See my projects on Instagram and Facebook

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                        • #13
                          Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

                          Well, in that case, here are some pictures of the latest progress. $50 in all thread and hardware and I'm starting to brace the fire out of this enclosure.

                          These are only the vertical supports. I'm actually also considering adding two more main supports in the woofer cabinet and running a board between those two to act as a seat for the woofer and take any torsional load off the front baffle. Though, that may be completely unnecessary.

                          Anyway, here are a couple pictures. That middle brace got butchered. The other tower will look better. Thank goodness there'll be a baffle to cover up the screw ups. ;)

                          Click image for larger version

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                          ErinsAudioCorner.com

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                          • #14
                            Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

                            I went and bought more tie-rod. Though, I dropped the woofer support idea. I don't think it's necessary.




                            Some CLD on the midrange enclosure section to help add a touch of mass and bonding to the bare panels.



                            Insulation/foam/stuffing, with some side threaded rods added to the woofer section.




                            Close ups, showing some luxury liner pro (a 1/8" foam layer with MLV backing) for added mass loading to the midrange enclosure bottom and then the (3) cross-rods in the woofer section.






                            Some notes:
                            Man, this is taking much longer than I really intended. I intended to have these completed this weekend but my daughter came down a virus Friday, and Saturday was spent at a baseball game followed by a 4-hour stint putting together a basketball goal together. :rolleyes:

                            The woofer section is SOLID. I can tap on that section and I get nothing but a solid thud. I imagine once the front/rear rods go in I'll have a very stout construction. Much moreso than I would with additional shelf bracing. And the placement of the rods at the center of each plane are intended to stop transmission at the weakest points; the corners have natural corner bracing. Before the rods went in, you could hear a noticeable difference between the center section and ends by tapping on them. I think adding rods at the edges of the enclosure wouldn't be beneficial. Still, this is me going by gut. With nothing more than trying to use some simple methods and logic to define the needs. I wish I had access to some CFD programs to see if what I'm doing here is as useful as I'm thinking it is.

                            I'm not sold on adding rod to the midrange section. As it is, it's not *dead* like the woofer section when you do the knuckle-rap test, but if the goal is lower the Fo, then stiffening won't do that; mass loading will. So, that's why I've added the CLD and Foam/MLV layer to that section.

                            I believe I'm going to leave the gap between the woofer and midrange enclosure as is. Adding foam such as great stuff is going to be incredibly messy and will only serve to further couple these two sections which isn't necessarily what I want. (unless I used a WHOLE lot of the window & door version which is designed to remain flexible)
                            I wanted the gap to act as an additional buffer of desnsity between the two sections. The name of the game in sound attenuation is changing density. By leaving an air gap with some slight acousta-stuffing, I think this serves the purpose well. Sony actually does something similar it seems with their flagship AR-1 speakers. I was reading their "white paper" on the Sony SS AR1 speaker and they mention leaving an air gap between the woofer enclosure and mid enclosure in the cabinet. Start on page 6. Here's the excerpt:
                            What appears from the outside to be a single enclosure is actually divided inside by two thick birch partitions with an air cavity in between. Just as a double-pane window with air in between helps provide thermal insulation in winter, the partitions and air cavity create two well-insulated enclosures: one for the woofer and one for the midrange/tweeter. The mid/tweeter sub-enclosure is also vented with a bass reflex port that’s been carefully tuned and positioned.
                            Note: This "white paper" is much more like marketing. But, it's still an interesting idea.
                            ErinsAudioCorner.com

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                            • #15
                              Re: Erin's first DIY build: Active 3-way with Kef Concentric and Scan 26w.

                              Looking good so far Erin. Don't worry a bit about the "mess ups" as they are easy fixes and best of all- INSIDE the cabinets ;) We all have an "uh-oh" on builds, especially the first one.

                              A few questions...why the threaded rod? I'd think you should have very adequate bracing for the cabinets with MDF cross sections. Another thing you can use is standard wood dowels from home depot/Lowes. Cut to fit, tap and glue/resin them in place and they add very good bracing as well. They sell them in pretty beefy diameters as well.

                              Do you plan to do a single thickness front panel or laminate it with another piece to increase thickness/mass and strength of the panel you'll be mounting those beefy 10" drivers to? I probably went overkill with mine by doing a double layer of 3/4 mdf for 1.5" thick front baffle, but it was VERY solid and strong and you couldn't feel much of any vibration on the cabinets with dual Usher 8955a's.

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