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  • Variable Volume Test Enclosure...

    Variable Volume Test Box:

    Before I had good modeling software available to me I dreamed of making something like this in a large format to see what a particular driver/enclosure volume combo sounded like, but BassBox, WinISD as well as experience have made that unnecessary as I’m familiar with what 30 to 90 Hz bass sounds like by now, and I trust software to more or less give me accurate results.

    With smaller drivers, I’m far less sure of what I’m looking for as far as a particular drivers’ low-end cutoff is concerned. That’s why I designed this test box. It allows for a variable interior volume between 0.25 Liters (15.44 cu. in) and 4.55 Liters (278 cu. in) as well as any volume in between. Adding in a block of wood of a known volume should be easy enough for the few situations where the frame/magnet size of a driver creates too large of a volume otherwise. The brass toggle latch clamps the two outer runners to the stationary inner runner, holding the piston in place.


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    The idea is to create 1/4” MDF test baffles and mount the driver(s)/passive radiator(s)/vent(s) of choice, clamp the baffle on with spring clamps, and then either test out a modeled design, or just have fun and see what various enclosure volumes sound like. I plan to use this in conjunction with Omnimic and the DATS for design verification and just to learn from.

    I think it will be interesting to see on the fly what a larger/smaller enclosure volume actually sounds like. Want to re-tune a passive radiator? Just unclamp the baffle, spin off the wing nut and add another washer… probably a minute to do. Although I’m familiar with the low end of an ND65 driver, I designed this to be able to mount three of that frame size, one driver and two PR’s.

    I’m going to give it a few coats of polyurethane just to keep things protected a bit. I also plan to add an arrow attached to the sliding plywood runner that will index with running numbers on the box which will have the enclosure volume listed in liters, and cubic inches.

    I also need to create a seal between the inside of the box and the moving piston. There is a bit less than a 1/16” gap all around. I’m thinking felt may work well enough, but I’ll have to test that out for sure. Whatever I use, I plan to cut some foam to insert between the two piston plates which will push out some on whatever material I use to do the sealing, acting like a piston ring of sorts. I will glue on a piece of thin rubber gasket material or craft foam to the front to seal the baffle off.

    I’ll drill a hole in the front/side near the bottom for leads to go to the speakers terminated in small insulated alligator clips to connect to the speaker.

    That’s about it. Not rocket science for sure, but it was fun sketching and building this, and I think I will have fun playing with it. I’m sure I will learn something about box tuning, and what bass frequencies in the 90 to 200 Hz range sounds like.

    TomZ


    *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
    *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

    *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

  • #2
    I love the concept!

    Extra points for ingenuity.

    Reminds me of my automatic cat feeder . . .

    Comment


    • #3
      Hey Tom, what about the closed cell foam that comes in layers for tool boxes and such. It's the foam that you can cut shapes into for individual items. If you cut it just so you may not need any other gasket on you piston. Just a thought.

      Comment


      • #4
        Originally posted by Steve Lee View Post
        I love the concept!

        Extra points for ingenuity.

        Reminds me of my automatic cat feeder . . .
        Whoa, wait a minute ... did you make that or buy it?


        Love the idea Tom, I'd thought about doing this to educate my ears but never got around to figuring out how. I have thought about some sort of adapter plate that could accept various port diameters though.

        Comment


        • #5
          With say 1/2 thick foam rubber between two plates, tightening the plates together would squeeze the rubber to make an air tight seal. Loosen the plates then you could move it. Like a plumbers test plug. https://www.lowes.com/pd/Oatey-PVC-T...itting/3880609
          John H

          Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

          Comment


          • #6
            Excellent idea John!!!!

            Comment


            • #7
              You need a vent that you can open when sliding the piston so you don't suck the speaker cone in or blow it out, obviously does't apply when using a port.

              Comment


              • #8
                If you put a check valve in it you can use it as an aquarium air pump below 30 HZ while breaking-in new speakers . . .

                Comment


                • #9
                  dlneubec did a variable port on one of his speaker projects. I don't remember the details be that might be fun to add to your adjustable box.
                  John H

                  Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                  Comment


                  • #10
                    That is really awesome Tom! John your idea of an expansion plug type seal is spot on.

                    Comment


                    • #11
                      Neat solution there, I like it.

                      I tried making a variable volume enclosure some years ago - basically a bucket with an interchangeable baffle that you fill with water, with the driver under test screwed to the top of the baffle. Water's basically in-compressible, so adding or removing it from the bucket was enough to effectively change the volume of the enclosure. And floating a circular panel on top of the water was enough to reduce any ripple caused by test signals.

                      The only problem is that it couldn't be tipped sideways . I think your solution is safer
                      Brian Steele
                      www.diysubwoofers.org

                      Comment


                      • #12
                        Thanks for the great ideas guys, and the humor!

                        Brian, that's genius! I never would have thought to do that. Make a chart to convert inches to volume and that's an instant way to change volume. Requires no sealing either!

                        Well, my original plan was to use dense foam in between the two piston plates, and then cover it with something, I imagined felt would work... like this:

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                        John's idea would probably seal the best, but I'd have to re-do the piston as it's glued together, there are screws in there that I can't get to now... and then I'd have to create a way to tighten/loosen the plates either from the back, or take the baffle off to do it from the front. I'd like to just be able to slide it on the fly if possible.

                        I do see the need to possibly create a check-valve type of thing if I really wanted to slide the piston as the enclosure was in use. I thought I'd just take a clamp off and pull the baffle away a bit while I move the piston. I'll have to think on that a bit. Maybe I do nothing and see how it works, then add something if I think I'll need it... good thought though. I imagine a piston moving with a square inch surface like 20 times that of the driver may suck that little cone right out through the basket vent openings! No, I'm not going to do that to a driver! Well, yes, actually I will if I can find a blown one that will seal up good!

                        Thanks for the ideas guys. I'm glad that some of you see how this could be useful and didn't all just call me nuts.

                        Oh, Steve, we're on our second cat feeder, our cat Benson figured out how to 'break into' the first one. That one moved a top disc with an opening that 'revealed' sectioned-off pie-shaped openings of food.

                        We were away on vacation and my Dad called me and said "I think Benson figured out how to hack the automatic cat feeder."

                        Impossible I said, why do you think that?

                        Dad - "Well, he's laying on his back, his stomach is puffed out, and the feeder is empty and in stuck in between sections." It was supposed to last for I think 5 days and when he called it was day TWO! The new one spins a rotating paddle-wheel type of thing that lets food out as long as it spins from a top mounted hopper. It's pretty much Benson-proof.

                        TomZ
                        *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                        *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                        *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                        Comment


                        • #13
                          You may learn something about what air leaks are like as well as the desired outcome!

                          Comment


                          • #14
                            I think I figured out how to seal the piston:

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                            That's basic packing foam that you get with some items as packing material that you see in between the two piston plates. The material covering the entire piston is a lambs-wool looking fabric that I purchased cheap at Wallyworld to glue on the inside of speaker cabinets to reduce echo and resonance slightly in side. It's light, so a quick spray of adhesive and it sticks well. Thought it would work for this as the little 'textured parts' of the fabric compress easy enough to not create unnecessary friction while moving the piston.

                            This seems to provide a good seal that was very difficult to compress even with the box just face down on the table not sealed. I clamped the baffle with a driver and PR and it behaved similar to a cabinet, so I think I'm good there. I went with two leads in case I ever want to connect two drivers and use one PR as I could see happening in the future. That would give a good approximation of the bass response of two different signals in the same enclosure as opposed to just wiring two drivers in series.

                            Anyway, I'm not sure if I want to reduce the width of the gasket material, or use the plywood clamping ring to secure the baffle. This is PE's 1/8" by 1/2" wide gasket tape. It takes a bit of effort to compress it. I have thinner gasket tape, but I thought I'd try this first as I thought it would flex more and seal better to the 1/4" MDF panels I plan to use as test baffles. Testing will answer this question I suppose.

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                            TomZ
                            *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                            *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                            *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                            Comment


                            • #15
                              Here's a shot of a test baffle loaded with one ND65 PR and one of the tiny Dayton 1.5" drivers.

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ID:	1435578 I did have to use a rounded rasp to make some breathing room for both of these, it took a minute or so to do so, but even in 1/4" material, it was still air-constricted in my opinion. Those are #4 x 3/4" screws I think. I even have #2 screws that I sometimes use with mini drivers like this.

                              Seems like the Aura Whisper and Cougar drivers are forward-thinking options for stuff like this!

                              And a shot of the 3/4" Baltic Birch clamping ring that I may end up using, recycled from some kids toy at school that broke! Speaker opening cut-outs as a weighted base for room to get the clamps on. I may end up getting a few strap hinges for the bottom and just a clamp for the top. I don't want to sink too much cash into this as it's just a test box but if it makes life really easy... Oh, I really didn't spend any money on this at all actually, using parts and scraps for the most part.

                              More to come...

                              TomZ

                              *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                              *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                              *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                              Comment

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