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  • Push Push sealed sub. Ideas?

    Push push with a middle slot. Works out well with my desire to hide the drivers from sight and still be able to place the sub close to a wall (trying to avoid rear firing). I already have the oak cabinet shell. It's drawn to scale below. I only need to add baffles and speakers. It has 4.2 Cu Ft of volume before adding braces/baffles/drivers. I'm aiming for something as unspeakerlike as possible, no drivers visible, false door with dummy hinges and pull handle on front (facing left in image below). Have mostly eliminated downfiring in order to open the prospects for driver choice.



    Side panel removed...


    Sealed. Bit of extra carpentry, but not too bad. Would be much easier on myself if I just placed the baffles in at right angles, but the diagonal placement would add significantly to rigidity and possibly even tame the resonant cavities. Driver cones directly opposite one another. That's not a passive radiator in there. I'm just too lazy to draw the motor assembly.



    A pair of SD315A-88 12 for 90 USD certainly is a nice price.

    http://www.parts-express.com/pe/show...number=295-488

    The 7mm xmax is less of a handicap in a sealed dual driver arrangement no?

    Other driver suggestions or comment on the cabinet idea?
    Last edited by frascati; 10-30-2011, 03:43 PM.

  • #2
    Re: Push Push sealed sub. Ideas?

    what a great drawing. wished i could do that. i thinks thats a great idea. but thats me.
    " 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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    • #3
      Re: Push Push sealed sub. Ideas?

      What advantage does subs facing each other give? Is this for HT or what?

      With wood skills to build that furniture, I'd recommend nicer drivers. I have the 10" version in my car. They are nice for the price, but if your going to go through all the work for that table, I think it deserves nicer drivers. That's just my opinion.

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      • #4
        Re: Push Push sealed sub. Ideas?

        You almost have a design that would benefit from having an arrangement that would eliminate a lot of cabinet vibration but not quite.

        Could you move the driver faces closer to each other (shrinking the "opening"), add/change the current "opening" to the internal enclosure while at the same time venting the output downward from the rear of the drivers (you would then have two down firing openings)? Hard to explain in words but I think it would decrease cabinet vibration considerably.

        I think it would be much more obvious if you could draw it.
        Thanks,
        Aaron

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        • #5
          Re: Push Push sealed sub. Ideas?

          Arlis, have you tried google sketchup? I use it for hobby stuff with no prior cad training and really enjoy it. And I'm the type who frustrates pretty easily. You can download it free here...
          http://sketchup.google.com/download/

          So many ways to approach this.


          If I follow you you're suggesting a variant to figure two but with the drivers mounted outside the sealed cavity and firing inward. The slots to the room would be behind the drivers.

          Mechanically there seems to be very little difference, I think, with regard to any cancellation of forces, between any of the push-push arrangements. As long as the drivers share the same rigid foundation and are working against one another (like a bmw boxer engine). The original drawing makes optimal use of volume available, but it could be built as you suggest just about as easily. The slot as I've drawn it is probably larger than necessary. I believe it only needs to be the sum of the driver's SD. I didn't bother calculating it for the rough drawing but it will probably end up narrower. I really don't know yet what internal volume I need for push push. Once I pick out a pair of drivers I'll need to download and start learning WinISD or similar.

          Anyone else able to weigh in on one way or the other?

          Comment


          • #6
            Re: Push Push sealed sub. Ideas?

            Yeah I think you're following me. It more or less becomes an issue as to which "rigid foundation" is more rigid. With some additional bracing to your original design I think you could come close to duplicating the goal of my iteration and possibly equaling it. I didn't consider some extra bracing to your design when I initially posted. It sounds like you are aware of the concepts I was trying to utilize so I'm sure a final design will be well thought out.
            Thanks,
            Aaron

            Comment


            • #7
              Re: Push Push sealed sub. Ideas?

              I could even go crazy and mount the drivers with eight lengths of threaded rod bolting them to their baffles and to each other. Overkill, but easy enough and why the heck not?

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              • #8
                Re: Push Push sealed sub. Ideas?

                Interesting idea, and bracing running across between the drivers is exactly what I had in mind.
                Thanks,
                Aaron

                Comment


                • #9
                  Re: Push Push sealed sub. Ideas?

                  The significant space between the two driver sub-enclosures may result in a cavity resonance.

                  Consider either reduce the volume of the cavity or consider remounting the drivers (cone-basket) rather than the (cone-cone) arrangement you rendered.

                  Comment


                  • #10
                    Re: Push Push sealed sub. Ideas?

                    The driver arrangement doesn't eliminate cab vibration, which is the product of how much internal pressure is created, not the positioning of the drivers. But having the baffles brace the top and two sides is very good materials utilization.

                    It's not push-pull. To be push-pull one of the drivers must be reverse mounted, with its connection polarity reversed. The supposed benefit of that is reduced THD, but with the downward facing output here that's already addressed via acoustical filtering, so push-pull might not add anything more.

                    All in all it's a good looking box, but two of the sides are unbraced. I'd add a 1x1 brace connecting the middles of the baffles to the middles of those panels.
                    www.billfitzmaurice.com
                    www.billfitzmaurice.info/forum

                    Comment


                    • #11
                      Re: Push Push sealed sub. Ideas?

                      a 4 cubic foot piece of furniture is gonna be a big boy. If you give up as much in the between chamber as pictured the DVCs prob will be overdamped down low.....

                      Have you thought about using he RS HOs? Theyre happier in a smaller box, handle more power, and almost twice the extension. Judging by the amount of carpentry your putting into it, I assume you'll be keeping it a while and the way its setup keep in mind accessing drivers later on if needed.

                      If you decrease the between chamber to about 3-4" between drivers maybe make solid top removable in case you need to access drivers(rear mounted)....... They fail, sometimes no matter what you do.

                      Doesn't this classify as dual opposed? Shouldn't opposed masses of drivers cancel out some vibrations?

                      Comment


                      • #12
                        Re: Push Push sealed sub. Ideas?

                        Originally posted by nottaway View Post

                        Doesn't this classify as dual opposed? Shouldn't opposed masses of drivers cancel out some vibrations?
                        As shown it's a manifold with sealed rear chamber. The manifold does add some loading and low passing, so response won't quite match what a simple box program will reveal. HornResp or AkAbak will do so.
                        Opposed masses of drivers don't cancel vibrations. But drivers mounted facing outward on opposed panels do cancel out the tendency for the cab to dance at high volume.
                        www.billfitzmaurice.com
                        www.billfitzmaurice.info/forum

                        Comment


                        • #13
                          Re: Push Push sealed sub. Ideas?

                          Consider either reduce the volume of the cavity or consider remounting the drivers (cone-basket) rather than the (cone-cone) arrangement you rendered.
                          What you're suggesting would be push-pull? Unless one of the drivers was reversed wired?


                          It's not push-pull. To be push-pull one of the drivers must be reverse mounted, with its connection polarity reversed. The supposed benefit of that is reduced THD, but with the downward facing output here that's already addressed via acoustical filtering, so push-pull might not add anything more.
                          Bill Just to clarify, are you responding to me or to Zobsky? I'm describing "push-push".. i think. Am I wrong? Both drivers share the same sealed cavity, connected across the top of the box. Both face each other and are wired with same polarity. Both are anchored to the same mass (especially if bolted with threaded rod face to face). Why wouldn't (if it's even slightly possible to address in lay terms) a mechanical implulse applied via both cones pretty much absolutely be cancelled? It seems not at all dissimilar to my BMW boxer engine. Or, in basest lay terms, rapping on either side of your head (in my case, a mostly sealed cavity) with your knuckles. When the 'impulses' are precisely timed, the movement/vibration/resonance of your skull is cancelled.

                          Judging by the amount of carpentry your putting into it, I assume you'll be keeping it a while
                          Actually there's surprisingly little carpentry involved here. I already have the cabinet.

                          It's a second-hand store antique for ten bucks.
                          Under the green paint was solid 3/4 oak.

                          That's a 12 inch driver and a little random orbital sander on the top for a bit of scale. It's not really very large at all. Only 17 inches wide, but 21 inches deep. Comes out to roughly 4.2 cuft. I've got it entirely disassembled and sanded down to the clear grain. All the tongue and groove and dowels are intact (fortunately the glue was quite old and brittle) so it'll go back together in about fifteen minutes. The only carpentry involved will be measuring, cutting, and installing those baffles. The front door will be sealed in place with the hinges reinstalled and a handle added just below the keyhole. It should end up disguised as nothing more than a tall(ish) end table.
                          Last edited by frascati; 11-01-2011, 01:31 PM.

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                          • #14
                            Re: Push Push sealed sub. Ideas?

                            Is my confusion stemming from the possibility that in all of these descriptions, definitively, "push" or "pull" describes the action of the cone relative to that woofers basket and motor assembly and not necessarily relative to the box itself?

                            Hope this is kosher.. quoting from another forum.

                            Originally posted by Djim
                            Linearity and non-linearity’s in the magnetic field:

                            Every voice coil is moving in a magnetic field. However this magnet field is not linear. Often when the cone moves forwards it faces a more or less linear magnetic field. When the cone moves backwards it faces a non linear magnetic field.


                            Picture: Loudspeaker diagram

                            These non-linearity’s happen because of the use of (Ferro) metals that bends the magnetic field. These metals (Pole Piece and Top Plate) are used to create the ‘gap’. The function of the gap is to canalise the magnetic field to its maximum strength. In this gap the voice coil moves forwards and backwards.


                            Picture: Modelled magnetic field

                            Non-linearity’s result in even harmonics (ears -> human and animal -> don’t like them). Some (old) people call it artificial distortion. In the picture the model shows clearly how the (Ferro) metal ‘bends’ the magnetic field around the voice coil. The waves you see represent the magnetic field off the same value.

                            Push-Pull:

                            Now, if you flip one driver (Push-Pull) and exchange the poles, both will move in similar direction (in-phase). The only difference is one cone moves forward and the cone of the flipped driver will move backwards.

                            That means that one driver moves into the non-linear area while the other driver moves in the linear area and visa versa. That’s how the distortion, produced by the non-linearity, is minimised.


                            Picture: Push-Pull

                            Push-Pull effect versus bandwidth:

                            The closer and symmetric the drivers are positioned the more effective the PP effect becomes and the wider the bandwidth of the push-pull effect becomes.

                            Push-Pull-Slot-Loaded:

                            The effects of the push-pull become maximised because both drivers load the same air molecules that are captured within the Slot (= Plenum). Because of this captured air the slot will make the system into a 6th order system.


                            Picture: PPSL

                            Also the pressure inside the Slot (= Plenum) will become much higher (forwards cone movement) and lower -> more negative (backwards cone movement) than when the drivers would load directly to the air in traditional push-pull setups. This pressure will suppress (damping) certain Partial Movements that result in even harmonics of the cone.

                            In a PPSL the two different drivers are no longer seen as independent systems like in a traditional Push-Pull setup. Instead they will be seen by the system as one. The advantage of that is improved phase & impulse figures.

                            Partial Movement:


                            Partial Movement is caused by the resonances of the materials and structure of the cone. (Additional note for TB46 ;) : this is caused by the “eigenfrequenz” of the cone). If you want to see models of Partial Movement from a cone use this LINK

                            Now lets hope I didn't make to many mistakes :D
                            PLease help me associate this with my own box. The terms push-push and push-pull are getting a little unwieldy here.

                            With my drivers facing one another and in phase I'm getting none of the benefit described above wherein one woofer's coil is driven into it's most linear area while the other woofer's coil is driven into it's least linear area. Correct?

                            So If I turn one driver around, with the magnet structure in the slot, and reverse the poles on it, I will utilize that advantage. What's confusing me is that now I've simply reconstructed a push-push situation with the drivers cones, both loading the slot at the same time, but have made use of the distortion cancelling methods described merely by reversing the cones. No? Why is it referred to above as push-pull?

                            Refer to the fourth/last image in the quote above. If a signal is delivered to the top woofer, moving its cone downward, the simultaneous signal delivered to the bottom woofer will move its cone upward... correct? So with regard to the shared cavity (either one... plenum slot or box) aren't we describing push/push?

                            Also the pressure inside the Slot (= Plenum) will become much higher (forwards cone movement) and lower -> more negative (backwards cone movement) than when the drivers would load directly to the air in traditional push-pull setups. This pressure will suppress (damping) certain Partial Movements that result in even harmonics of the cone.
                            That quote seems to confirm that both drivers are "pushing" into the slot on the same signal impulse.

                            Is my confusion stemming from the possibility that in all of these descriptions "push" or "pull" describes the action of the cone relative to that woofers basket and motor assembly and not necessarily relative to the box itself?

                            And while we're at it, isn't a woofer's cone far more structurally rigid in the forward phase than in the backward phase? Think umbrella. Can sustain far more pressure without distorting against the concave side than the convex. Is this ever considered when designing these push-pull arrangements? I realize that could sound counterintuitive. The shape of an eggshell or a beer can bottom are cases where the opposite is true. But a woofer cone, with it's relatively flexible membrane and rubber surround seems to me more structurally akin to an umbrella or a parachute. Much better suited to pressure against the concave side than against the convex.

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                            • #15
                              Re: Push Push sealed sub. Ideas?

                              Originally posted by frascati View Post


                              PLease help me associate this with my own box. The terms push-push and push-pull are getting a little unwieldy here.
                              If both drivers face the same direction with respect to the air outside of the cab it's push-push. If they face different directions it's push-pull, and one must be wired reverse polarity so that they don't cancel each other.
                              www.billfitzmaurice.com
                              www.billfitzmaurice.info/forum

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