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Build Thread: SR71-inspired Center Channel

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  • Build Thread: SR71-inspired Center Channel

    So I'm building a center channel to compliment my SR71 mains (see zaphaudio.com for info on the SR71's), as the Tritrix MTM center I'm currently using with them just ain't cutting it. Nice though it is, it's not on par with the SR71's, and I'm looking forward to a center channel that matches the SR71's better.

    Since an SR71 Center Channel design does not exist, Zaph (John Krutke) has very kindly helped me to design a center channel that should match the SR71 mains well.

    This will use the same drivers as an SR71, and a similar crossover design...

    However, I will stop short of calling it an "SR71 Center Channel", because although Zaph did help in designing the crossover, and gave me some invaluable advice for designing it, this speaker will not have the benefit of actually having been listened to and tweaked by Zaph... in addition, the crossover he designed is an approximation, certain component values will be tweaked once the speaker is in place, by me... in other words, this speaker will not have earned the right to be called an "SR71", a high accolade to be sure.

    Edit: We have a name: The Blackbird Center Channel... inspired by the SR71 Blackbird jet

    SEAS ER18RNX Woofer




    SEAS 27TDFC Tweeter




    Here are some images of the design. All 3/4" mdf. Note that the flange of the tweeter will be trimmed in order to get the tweeter as close as possible to the woofer. 2" Precision Port facing out the back. Outer dimensions are 21.75" wide X 8.125" high X 10.75" deep. Internal volume is .5 cubic feet, not including the sealed off chamber for the crossover (to the left of the tweeter). There will eventually be a grill over it for baby-proofing reasons, by sheer coincidence the PE 1 cu ft MTM grill is a perfect fit. The small panel on the back will be for accessing the crossover. In general, aesthetics are of no concern, as it will be buried in an AV cabinet, all that will be seen is the PE grill. Usual over-the-top bracing scheme that I like to use. I'm a firm believer in a lot of bracing, after hearing how nice my SR71 cabinets sound, which used a similar bracing scheme.




    One of the challenges with this design is that the speaker will sit inside of an AV Cabinet, with a 46" TV directly above it... so it's almost as though it's flush wall-mounted, with an infinite baffle. Here's a pic that shows the AV cabinet, the upper shelf in the middle is where the speaker will sit. The TV will sit directly above it.




    Zaph very kindly did an approximate simulation for me, with a crossover design that is similar to an SR71 but with much lower BSC... I must emphasize approximate, since how the cabinet and TV will ultimately effect how the speaker sounds is difficult to predict. I will be trying different values for the woofer inductor and tweeter resistor to dial in the right amount of BSC. There will definitely be a lot of trial and error going on here. Mike Z will be prodded with coffee, beer, and doughnuts to assist.

    As you can see, Zaph's approximated simulation shows quite symmetrical horizontal lobing, despite the assymetrical driver layout. Not perfect, but very close. This is quite consistent with the nearly perfectly symmetrical vertical lobing that SR71's exhibit, which is what made the SR71 a good candidate for a matching horizontal center channel.

    This design obviously challenges the notion that center channels need to be symmetrical. At least that is the hope, we shall see.



    Parts have been ordered and sawdust will soon fly. More pix as the build commences.

    Thanks for any comments!

    EDIT: Here is the final crossover schematic



    EDIT: Here is a dimensioned drawing of the final design

    Last edited by lunchmoney; 02-01-2011, 06:44 PM.
    Form does not follow function
    Form is simultaneous to function

  • #2
    Re: Build Thread: SR71-inspired Center Channel

    The grille should cancel any psycho-acoustic effects from looking at the asymmetrical layout. And keep fingers out too.

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    • #3
      Re: Build Thread: SR71-inspired Center Channel

      if your avr is crossed low, i think youll notice a big difference. nice build. nice of john to help out.
      " 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/

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      • #4
        Re: Build Thread: SR71-inspired Center Channel

        Originally posted by [email protected] View Post
        if your avr is crossed low, i think youll notice a big difference. nice build. nice of john to help out.
        My Yamaha receiver crosses at 90 hz.

        The mains are also high-passed, I noticed a big difference in mid bass when swapping the Tritrix mains for the SR71 mains.
        Form does not follow function
        Form is simultaneous to function

        Comment


        • #5
          Re: Build Thread: SR71-inspired Center Channel

          Originally posted by djg View Post
          The grille should cancel any psycho-acoustic effects from looking at the asymmetrical layout. And keep fingers out too.
          Ha!

          Yeah, I can't help wondering how many center channels out there have less than optimal performance because of a pointless requirement that they be visually symmetrical.

          If all goes well, this should perform better than many MTM center channels, despite the asymmetrical layout.
          Form does not follow function
          Form is simultaneous to function

          Comment


          • #6
            Re: Build Thread: SR71-inspired Center Channel

            Top, bottom, and sides glued up...




            Cutting out the braces...

            Form does not follow function
            Form is simultaneous to function

            Comment


            • #7
              Re: Build Thread: SR71-inspired Center Channel

              Looking good! How do I know??? I was there! Amazing to have such a shop at your fingertips. It was also a lot of fun to hang with another builder... and build!
              .

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              • #8
                Re: Build Thread: SR71-inspired Center Channel

                Braces and crossover compartment divider glued in...




                Here I used the milling machine to face off the edges of the walls and braces... did this on both sides... this ensures an absolutely flat surface to glue the front and back onto...




                Back panel and the back of the precision port clamped up. Used 5 minute epoxy for the port...

                Form does not follow function
                Form is simultaneous to function

                Comment


                • #9
                  Re: Build Thread: SR71-inspired Center Channel

                  Wall lining installed... 2" fiberglass knauf board on the back panel, .5" PE Sonic Barrier on the top, bottom, and sides... hiking boots by Lowa :rolleyes:




                  Inside end of the precision port installed, solvent-bonded with MEK...




                  Crossover compartment door...




                  Crossover ready for voicing... 4 of the components aren't installed yet, I'll be trying different values when the time comes. The loose wires trailing off of the board are for connecting components via test leads. That's a Matrix board from Madisound (the green square, not the Radio shack board behind it), first time I've tried one. I'm a fan, will use these from now on. Made layout and soldering a lot easier. $7 well spent...

                  Form does not follow function
                  Form is simultaneous to function

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                  • #10
                    Re: Build Thread: SR71-inspired Center Channel

                    Lookin good! How does that sonic barrier stuff work? I've contemplated buying it a few times, just can't bring myself to spending that much, not that I've actually got anything else to use or used anyhting else, yet...

                    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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                    • #11
                      Form does not follow function
                      Form is simultaneous to function

                      Comment


                      • #12
                        Re: Build Thread: SR71-inspired Center Channel

                        Great build as usual Lunch. You had better not be soldering on that pretty white oak table. :D
                        I am thinking of using the same (or square) speaker terminal in my build. Looks good in your picture.
                        Mark
                        My TriTrix Build
                        My Core 2 Way Build
                        My RSS315HF-4 Subwoofer Build

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                        • #13
                          Re: Build Thread: SR71-inspired Center Channel

                          Another great build thread. Keep up the great work.

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                          • #14
                            Re: Build Thread: SR71-inspired Center Channel

                            Originally posted by MrkCrwly View Post
                            Great build as usual Lunch. You had better not be soldering on that pretty white oak table. :D
                            I am thinking of using the same (or square) speaker terminal in my build. Looks good in your picture.
                            Those Binding post plates are really nice, I have a pair of the black ones currently, they're heavy too. Quality

                            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.

                            Comment


                            • #15
                              Re: Build Thread: SR71-inspired Center Channel

                              A milling machine!?!? Are you farking kidding me? That's gotta be the ultimate build tool.
                              Isn't it about time we started answering rhetorical questions?

                              Paul Carmody's DIY Audio Projects
                              Twitter: @undefinition1

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