Design my boxes for me please.

Discussion in 'Home Theater Projects' started by DanielGM, Mar 25, 2004.

  1. DanielGM

    DanielGM Stunt Coordinator

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    Hey guys,
    I've got all the parts together for what I think will make an excellent (pair of) sub(s), now I just need a cabinet design.

    Goal: pair of subs for 2 channel music, I've got a seperate HT, I don't listen to organ music, so extension to and beyond 20 hz is not needed, and I would like to maximize the flat extension to 30 hz and get the highest SQ possible.

    I am thinking of two sealed enclosures, tall and narrow for use as speaker stands ( I am aware of the issues of dual non co-located subs) the other option is something that was suggested to me before, a 4 sqft. sealed enclosure with the drivers mounted opposite-firing ( one into the cab, one out). I liked that design but I figured I would see what everyone else thought before I went with something. I'll post a picture to explain exactly what I am talking about.

    [​IMG]

    The parts:
    2 Eclipse 12" 88120DVC drivers
    Fs:29Hz
    Qts:0.34
    DCR:3.0 /coil
    Vas:2.68cuft
    Xmax:
    (one way) 1.17"

    I understand that xmax value may be overstated, so if someone knows the real world value let me know.

    Citation 5.1 4 channel amp, capable of 4 x 175 into 4 ohms (one channel/coil) or 2x300 into 8 bridged (one channel for each sub)

    signal will likely come from a paradigm x-30 crossover that has yet to be purchased

    I have modeled a few enclosures in winISD, but it's difficult to determine the optimal enclosure volume, and as fun as some of you may insist it is, I would rather not build 3 boxes before I get the sound I want.

    So that's your mission should you choose to accept it! If a few of you could plug those t/s' into your respective modeling programs and suggest a few alignments I would really appreciate it.

    Thanks!
     
  2. Mike SJ

    Mike SJ Supporting Actor

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    My setup has 2 10"s in a 4 cu ft box and I couldnt be happier. I was thnking about going with 2 sealed, one below each mani, but I had a spare 4 cu ft box laying around so I made it my sub. It sounds wonderful.


    This one in one out could possibly work, but it will look awful and I havent seen mny subs designed that way suggesting to me that its not aan efficient solution.

    I would say if you had both 12"s in a 5 cu ft box, youd be very happy
     
  3. Dan Hine

    Dan Hine Screenwriter

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    Most of M&K's subwoofers are designed this way and they have a great reputation among commercially available subwoofers. I've seen enough DIY versions like this as well to think it would be a viable alternative.

    Also, I'm sure you know this, but saying "two 10's" or "two 12's in a 5cubic ft. box" doesn't really mean anything. Just because it is a 12" doesn't mean it will have more output than a 10" nor does it mean that a 5ft^3 box would be a good cabinet for it/them. There is more to it than that. I just like to clarify that for those lurking along at home (or work!). [​IMG]

    Speaking of work...Daniel, I gotta run. But I'll try to look at those subs and give you my take on them. I'm no expert but the subs I've build have sounded pretty good. [​IMG]

    - Dan Hine
     
  4. Mike SJ

    Mike SJ Supporting Actor

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    I wasnt trying to compare his 2 12"s over my 2 10"s or anything of the sort. I was mearly comparing the push-pull option to the dual sealed option. And of the M&K subs I have seen, they do not have the back of the driver facing out for all to see. When I said awful, I only meant astheticaly.
     
  5. Dave Poehlman

    Dave Poehlman Producer

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    Couldn't the same effect be achieved by wiring one driver out of phase with the other and mount them normally?
     
  6. Andrew Pierce

    Andrew Pierce Stunt Coordinator

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    It would be the same as mounting them normally and running out of phase, except the slight added space you get.

    I don't think you want to do that though, because they're going to mostly cancel each other out if they're running out of phase side by side.

    Maybe someone was describing an isobaric configuration, where the drivers are mounted face to face. Only in that arrangement they aren't fighting each other, they're assisting each other.
     
  7. Chris Popovich

    Chris Popovich Stunt Coordinator

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    It's not the same as just wiring one out of phase. If you just wired one out of phase and they were firing the same direction, you'd get little to no useable output (huge cancellation).

    With the inverted driver, it is inverted AND wired out of phase so the net result is that the cones are moving the same direction relative to each other. In an isobarik setup it's supposed to reduce certain types of distortion, but I'm not sure if that would still work in your favor when it isn't mounted in an isobarik alignment.


    Chris
     
  8. Dan Hine

    Dan Hine Screenwriter

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    Mike,

    I don't mean to come off as rude or anything but...




    There are plenty of subs designed that way. M&K was just the first one that popped into my head. And it's a perfectly viable solution. Don't get me wrong...you're more than welcome to be here but some people who lurk this forum really don't have a clue (hell I only have half a clue) and statements like the one you made could keep them in the dark, thinking that a 12" fits X-sized boxes and that the size of the driver is all that is important. Know what I mean?

    - Dan
     
  9. Dan Hine

    Dan Hine Screenwriter

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    Daniel,

    After modeling your drivers they seem pretty good...fs is a little high for HT but since this is music only sans organ music I don't think you'll have any problems. Since you have only two drivers and are considering using them as speaker stands then the in/out configuration is really a moot point. The 4ft^3 sealed option, regardless of how you position the drivers, rolls off a bit to quickly. You are almost -10db in the mid 30's. If you build two cabinets, I like how a 3.25ft^3 bass reflex sub tuned to 28hz looks. It has a nice rolloff that should give you strong bass to the low 30's (in fact, it's pretty flat till right at 30hz). And the cabinet size would work pretty well for speaker stands.

    If you decide to go with the single sealed design it would be fairly easy to try both drivers facing the same direction and as you described above. It would be worth trying out both ways to make your own conclusions. Either way sounds like a fun project though...I miss having room for projects.

    - Dan Hine
     
  10. DanielGM

    DanielGM Stunt Coordinator

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    thanks for the replies so far everyone.

    I am not worried about the aesthetics of the driver, it's an aluminum cone car audio marketed sub and so it looks excellent from the back. wires would be routed back through the box via binding posts on the front baffle, so no problem there either.

    push-pull arrangements and isobaric arrangements actually accomplish opposite goals. Both are reputed to improve sq, but the isobaric is supposed to half the box size for a given freq. response, at the expensive of efficiency, while push-pull alignments double the box size but are essentially as efficient as two seperate enclosures. M&K uses push-pull designs.

    a decent page of summary I am sure many of you have seen before:
    http://www.danmarx.org/audioinnovation/theories.html

    The problem is that both alignments are around 8-10 dB down at 30 hz, depending on box size and according to winisd pro.

    Dan,
    I appreciate your input, at this point I am trying to avoid a vented design because of the degraded transient response. Unfortunately, with an EBP of 78 these drivers aren't really ideally suited for a closed application...

    I would still love some more input so please chime in everyone. At this point I would like to take advantage of the characteristics of either a closed alignment, isobaric closed alignment, or push-pull closed alignment. It seems like I may need some EQ to get a flat response down to 30 hz. As I don't have gobs and gobs of power, an isobaric alignment AND EQ would be asking a lot of my amplifier I think, so perhaps two seperate closed enclosures or a single push pull with some added EQ. Let me know what you think !
     
  11. DanielGM

    DanielGM Stunt Coordinator

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    Hey guys, looks like I finally acquired myself some tools so it would be great to knock down a good alignment and start building this weekend.

    If some more of you with experience could check out these numbers in your modelling programs and let me know what you think I would appreciate it.

    Been reading up and it seems like the rule of thumb is 1 lb/ft. of polyfill for enclosures above 3 ft3, and that should give me a ~30% boost in perceived enclosure volume, maybe good for another 2 dB of output at 30 Hz.

    Thanks for any help you can give me, it's much appreciated.
     
  12. Rory Buszka

    Rory Buszka Supporting Actor

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    The M&K's slot loading acts as an acoustic low-pass with the added effect of adding mass to the drivers (the mass is not actually physically added but the mass-loading comes from the compression chamber.) This serves to lower the resonance frequency of the driver some. VMPS uses that trick to be able to use passive radiators that have lighter weight diaphragms, and the compression chamber adds the mass.
     

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