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The Bulli Barn: A Vented STW-350F Enclosure

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  • The Bulli Barn: A Vented STW-350F Enclosure

    It has begun...

    See this thread: http://techtalk.parts-express.com/fo...ial-alignments

    I will update as I go along, but I decided that the Peerless STW-350F checked all the boxes for my next subwoofer build, so I spent waaaay to much time sim'ing it up in WinISD to decide on the "perfect" enclosure for it. Much to my simultaneous chagrin and delight, the driver models exceptionally in anything from 1.7 cuFt sealed to 3.5 cuFt vented to an 8 cuFt LLT alignment. As much as I would like to start off with the 8 cuFt enclosure, I decided to pursue more of what the driver was designed for - a relatively small enclosure with exceptional performance.

    After much deliberation, I chose to go with Option #D - 3.5 cuFt tuned flat to 20hz. I chose to start here for several reasons. First, It's smaller than what I would expect to get this type of performance from a 15" driver. Second, it met the minimum requirements for me - sub-20hz F3, high power handling, estimated 115db capability down to 20 hz, and a decent footprint. Third, I wanted a design that I could cut out of a single sheet of MDF; except for a few extra braces that I decided I needed to add halfway through the build, one sheet will do.

    I decided on a folded slot port design. To get enough port area, the port had to be somewhat obnoxiously long. Initially, I tried folding a single, wide port up and around the back of the driver but the math didn't play nice, and it made it difficult to use the rear basket mounting points. So I tried two square-ish ports on either side of the driver in the bottom corners of the box; I tried folding them up and around but ran in to the same problems. So I took the required box volume minus the port, and made it into a cube. I then folded as much as of the port underneath it, using the previously determined dimensions. The remainder of the port stubs up vertically behind the driver instead of terminating just below the basket. I did this intentionally to try and equalize flow and pressure from the entire driver. I am also hoping that folding the port a couple of times will mitigate any mechanical noise from the driver - just as can be done with HVAC ducting to temper furnace noise in a home.

    I'll let the pictures do the talking...


    Basic layout. All panels and bracing are dado'd except for a few smaller pieces that were added later.
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    Baffle and Brace
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    Test Fit: NEED MORE BRACING!!!
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    Pulled back apart. Added some bracing
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    Bracing and Vent
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  • #2
    Continued...

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    I used a couple of clamps to keep it all together....
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    View from the back
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    Awaiting the driver...

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    Comment


    • #3
      Nice work so far!!

      Do you have any concern that your vent area will not be sufficient under dynamic peaks? With so much headroom and Xmech on that woofer I would have modeled at a minimum of 3/4 full power to <17m/s.

      I am sensitive to the vent noise and it bothers me though so I may be a tad OCD there.

      Separately, any reason you did not consider dual 18” PRs as an option?

      Regardless it will likely turn out awesome. Just some questions I had.

      Comment


      • #4
        Thanks.

        Vent area vs length is always a concern; see the above-mentioned post for more details on the enclosure such as vent air velocity, cone excursion, etc. WinISD says it should be sufficient in this application. ~26 m/s at 18hz at full power.

        As for a pair of 18” PRs, I wish it were just that easy. Also see the above mentioned post. I could not find a robust enough 18” PR to use; nor could I find a 15” PR for that matter. Simple answer is they couldn’t handle enough weight to tune low enough. The manly CSS APR12 would work in triplicate or a quartet for a Bash 500 or 1000 watt amp, respectively. That requires over 1000 grams on each passive! The SLAPS M12 would also work. The trade off is steeper rolloff on the bottom end and, of course, the added cost. Initially, I wanted to use PR’s for this build but decided on this route. I can always build another box if I change my mind

        Comment


        • #5
          Nice roundover work on all those braces. Looking really really good for the inside of the box!

          Comment


          • #6
            Originally posted by scottvalentin View Post
            Nice roundover work on all those braces. Looking really really good for the inside of the box!
            Thanks!

            Got the driver temporarily mounted last night and spent an hour listening to it. My initial impressions:


            * * <---- (eyes)
            ^ <-----(nose)










            ______ <-----(floor)













            \__/ <-----(Jaw)


            Seriously. WOW. Not only does it sound amazing, but it makes prodigious amounts of bass. And the power this thing can handle is unreal. I accidentally turned it up past 11 and for the first time ever, I hit the red light on my Crown XLS1500 and hit the limiter. The sub just laughed at me... Time to try out the XLS2000. Actually, I need to get the rest of the system up and running. I just gutted it completely and started over with a new receiver and hopefully soon to be worked on MTM LCRs, plus some new surrounds. I had to piece together some drivers with a poorly executed crossover from years ago in some shabby cabinets just to listen to the sub. So ignore the mess and the lack of other firepower. No matter - this sub is insane. Worth every penny so far.

            Hoping to get some sort of measurements this weekend.


            A couple of notes to self:

            - I should have made the access panel in the back larger. I was going to originally make it the size of a Bash 500 cutout (just in case) but had a 6" hole size kicking around the shop that looked perfect for the job. It worked great and was easy to reuse the cutout as well as the cutout from the basket brace to plug the hole. Unfortunately, it makes for a little bit of chore to mount the driver to the brace.

            - Use two people to mount the driver the first time. I clocked the brace bolts but hadn't drilled the baffle yet so I had fun getting the first couple of bolts started with one hand using the undersized access panel while wrestling the driver and box with the other. Once I was able to get a few bolts on the brace, I was able to mount the driver to the front baffle.

            - 1" wood screws are INSUFFICENT for this beast. I planned on using t-nuts for the front baffle mount anyways but left the 1/4-20 machine screws at the shop so temporaries it with wood screws. They don't provide enough clamping force to keep air from blowing past the driver seal at high excursion.


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            Comment


            • #7
              I'm nobody, but joeybutts approves! Love sick bracing and love bass even more. Nicely done. Did I miss the finish plans or too late?
              Builds - C-Killa - Speedsters - LithMTM - Talking Sticks - Pocket Rockets - Khanspires - Dayton RS Center - RS225/28A - Kairos - Adelphos - SEOS TD12X - Dayton 8 - Needles - 871S - eD6c - Overnight Sensations - Tritrix (ported) - Lineup F4 - Stentorians - The Cheapies - Tub Thumpers - Barbells - Tuba HT - Numerous subwoofers - probably missing a few...... :p

              Comment


              • #8
                Glad you approve, Joey!

                Watched part of Tron: Legacy with my gremlins today. Their choice. It was every bit as good as I was expecting. Lots of palpable infrasonic and subsonic fun :D Really showed off the inadequacies of the temporary TM speakers I'm currently using, too.

                I also ran an impedance sweep with DATS. Box tuning turned out to be almost exactly where predicted - 17.5 hz. Also to note, the box isn't completely sealed up yet; the access panel has yet to be gasket and really bolted in (still wood screws like the driver on the front baffle) and the Neutrik connector is leaking. The enclosure is also completely devoid of stuffing at this point. I'm sure I will throw a couple pillows in there at some point.

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                Now, for a finish... Hmmm... I've been thinking a fair bit about that. Lots of crazy ideas floating around the noggin but I think I've got something close. Unfortunately for you, I'm not going to say. Except for this: part of the box will be painted - probably BenMor Graphite or NightFall (letting the kids help decide...), there will definitely be some hardwood, some man-made materials, and it might involve a couple hundred thousand volts...

                Comment


                • #9
                  wow beautiful construction. did you CNC any of that or is that all done on standard equipment? Regardless it's impressive.

                  Comment


                  • #10
                    Button Thanks! No CNC here, unfortunately. One day, I'm sure I will have one but these were all made with traditional tools, which I don't see as a disadvantage.

                    Comment


                    • #11
                      Took some measurements using Dayton's new DSP-LF. Initially, I used the phone's built-in mic but could see that it was tapering off below about 35 hz and had non-existent response below about 25 hz. So I pulled the Dayton iMM-6 off the shelf and plugged it on. I've barely used this mic for whatever reason but figured I'd give it a whirl. It fared better and was much more accurate down low. Here are some graphs of what I measured.

                      GREEN: Measurement with mic centered on cone, about 3 inches away.
                      RED: Measurement with mic at port level, same distance
                      Note: the DSP-LF automatically level matches and shifts the graph on the fly, so values are not absolute, meaning the curve is what is important. So, for example, if you shift the red line up 3 or 4 db you can see the woofer and port signals diverge. Summing them gives a nice flat response to 20hz (and below. Unfortunately, the DSP-LF doesn't measure below 20 hz. Kinda disappointed by that)

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                      BLACK LINE: Here is how the DSP-LF tries to tune the sub using the "Boomy" setting
                      NOTE: The Red and Blue line (next graphic) are measured in-room at main seating position.
                      NOTE2: Ignore the THD measurement; not sure how it is gathering that info but it has something to do with the gain settings on the amp and DSP-LF, plus the microphone. Either way, I'm 99.9% sure they are inaccurate.

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                      BLUE LINE: Here is howthe DSP-LF tries to tune the sub using the "Linear" setting . Well, better, at least. The 70 hz dip is easy to EQ out using the app.


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                      I wish I could edit the target response (dashed line). Maybe I can, I just can't figure out how to with the limited amount of time that I've spent using it. For now, the DSP-LF has been disconnected and I'm running it straight from the AVR until I can get the DSP unit figured out. I think I will be comparing it to the miniDSP unit as well.

                      Either way, so far, VERY happy with the Bulli Barn

                      Comment

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