My Tempest is here!(plus more questions)

Discussion in 'Archived Threads 2001-2004' started by Justin Ward, Nov 29, 2002.

  1. Justin Ward

    Justin Ward Supporting Actor

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    Well, I just received my order from CSS today. My Tempest and dual input cup both arrived safely. My first impression opening the box and picking up Tempest was "damn, this thing is huge!". It makes everything look micro in scale! Anyway, I am just about ready to order an RCA based 20hz high pass filter. My friend may be willing to lend me his 110 w x 2 Technics amp for the time being until I buy my own.
    This weekend I hope to start building the box. I do have a few questions left though. I will be cutting a hole for the dual input cup, but if at a later date can I simply make it bigger to fit a plate amp? I think as long as I put it on a side that is not touching a brace it will be ok.

    Also, how heavy will this thing be? I am designing the SBB4 and the Tempest alone is quite hefty!

    Thank you all,
    Justin Ward
     
  2. Justin Ward

    Justin Ward Supporting Actor

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    I'll throw another question in there too. I am tuning to 18.8hz using 2-4inch PVC pieces. The length will have to be around 22.5 inches according to LspCAD. I have two questions about the ports.

    The inside of the box is only about 24.5 inches, will the performance be affected if the ports come within a couple of inches of the top? Another question, would the design work with only one port? It seems like the single port could be quite small and achieve the same results as two ports.
     
  3. Justin Ward

    Justin Ward Supporting Actor

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    No one on the forum can lend me their expert opinion?
     
  4. Jeremy Stockwell

    Jeremy Stockwell Supporting Actor

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    Patience, Justin, it's a holiday weekend.

    Yes, I believe your ports will be affected by being only a couple of inches from the end of your enclosure. You may want to consider "bending" your ports using an "L" or "U" shaped connector.

    JKS
     
  5. Dave Milne

    Dave Milne Supporting Actor

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    Justin,
    The rule of thumb is to have at least one port diameter of clearance at the end. So Jeremy is right, you will want to put an L or U bend in them.

    As far as your other question...
    two 4" ports gives about 25 m/s vent velocity which is nice and low to prevent chuffing. A single 4" (10.0" length for the same tuning) will put you up at 50 m/s --higher than most experts would recommend. A compromise might be two 3" ports (12.2" length). This yields about 42 m/s --a little high, but probably acceptable. By the way Adire's plans for the SBB4 alignment call for two 3" vents.
     
  6. Justin Ward

    Justin Ward Supporting Actor

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    thanks, I suppose I will take a look out in the garage for some 3 inch PVC. But if I only have access to the 4 inch stuff, will the performance be affected by "bending" the port? I don't think I could use the L shaped one because it would probably hit a brace. But it is ok to use a "U" connector?
     
  7. Dave Milne

    Dave Milne Supporting Actor

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    Justin,
    U connectors are fine. You may need to do a bit of measuring and calculating to determine the effective length (the length through dead center). And don't forget to subtract the overlap where the U connector fits onto the pipe. Of course, it's a good idea to glue the fittings with PVC cement... you don't want the thing coming apart inside your box! Finally, you will need to include the volume displaced by all the ports and connectors in your box volume calculations.

    good luck

    Dave
     
  8. Justin Ward

    Justin Ward Supporting Actor

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    Thanks for all your help guys. I went and bought some 3 inch PVC today anyway since it is dirt cheap. Adire says that the net volume of the box is 194L, is this the total with ports? Would it hurt to make the pipes a little bit longer to tune it slightly lower? Or is it not a good idea to go changing things like that?
     
  9. Justin Ward

    Justin Ward Supporting Actor

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    Another question, does anyone know of a way i can arrange the cuts for the box so they all fit on a 4 x 8 sheet of MDF? I have tried many times and I get SO close!
     
  10. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    I didn't think the box can fit on a single sheet, even if you didn't cut the edges off the sheet to make the edges fresh/crisp. You mean the braces, side panels, and top/bottom right?

    The box will weight at least 100lbs according to the wood alone. Add the weight of the driver, polyfil, and amp -- it may add up to 150lbs. You figure one sheet of 3/4" MDF weighs approx 100lbs.

    What I usually do is cut the input terminal hole last with a jigsaw or hole saw. I guess you could off set it away from the center brace if you plan to mount a plate amp. If not, you may have to cut a portion of the brace away to allow clearance for the amp you plan to use.

    If you tune the box too low, you might lose some output. I think adires plans allow for a fairly smooth response for the different bass types so I'd stick to the proven plans if you don't know what to expect.

    Also, if you're using flared ports then the effective length will be a little different than non-flared.
     
  11. Dave Milne

    Dave Milne Supporting Actor

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    Justin,
    There are software programs that will optimize cutting of sheet materials. Try Sheet Layout. I belive they have a free "evaluation" version. There are a number of other freeware programs. I'm sure you could find some with some searching.
     
  12. Justin Ward

    Justin Ward Supporting Actor

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    Well I got lucky. I measured the plywood and it was an inch longer in both directions. Me and dad had no problems fitting on all the cuts(even leaving room for errors and the saw width). We put a few hours work into the box and we are almost done. We have all major cuts done, the only ones left are the circular cuts in the braces and the cuts for the driver and ports.
    Now, what is the best way to mount the PVC in the box. Would it be best to mount the pipe flush with the bottom of the box and apply some chaulking on the inside of the box where the port goes through?

    Also, once I wire up Tempest is it ok to use standard 16 gauge speaker wire? There also seem to be 2 clips for each terminal on each voice coil, does it matter which ones I use?

    Thanks again
     
  13. Chris Bates

    Chris Bates Stunt Coordinator

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    I would use a 2 part liquid epoxy to attach the port. It will expand slightly to fill any gaps and its pretty darn tough. I havent had one fall out yet. Also, it would be a good idea to round over the port opening using a router and a 1/4" roundover bit. This serves to cut down on port noise. If you dont have access to a router, you can use a wood rasp to shape it, and some sandpaper to clean it up.
     
  14. Justin Ward

    Justin Ward Supporting Actor

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    Me and dad put together the enclosure tonight(minus the top piece). It looks good, we used about 20 screws mostly because we had not clamps. We did have one small split but it was in a brace and it was minor. The enclosure is very sturdy. I hope to do the ports and small touches on the enclosure tomorrow.
     
  15. Justin Ward

    Justin Ward Supporting Actor

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    Well, the subis basically done. Tomorrow me and dad will stain the cabinet and hook it up.
    Thanks again to all who offered advice!
     
  16. Dan Hine

    Dan Hine Screenwriter

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    Glad to hear it Justin. I have no doubt you will be happy with your work. Any chance we'll get to see some pictures of your new Tempest?
     
  17. Justin Ward

    Justin Ward Supporting Actor

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    A friend is going to lend me their digital camera. I hope to take some pics soon and post them.
     
  18. Justin Ward

    Justin Ward Supporting Actor

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    I got a chance to test out my Tempest. I burned a 200-18hz wave to a cd. I couldn't test any music because I don't have any filters or crossovers yet. I hooked up the Tempest to my parents 220 watts Technics reciever.
    I was blown away! This design has tons of muscle in the 30hz -50hz range and also hits down to 20hz well. Once, the frequency dipped to 18hz I couldn't hear a thing from the sub but everything was shaking like crazy(and this was 4 feet away any wall so I'm sure it will sound even better once it is in my bedroom). I am extremely impressed already and judging by others projects it will sound even better once the woofer breaks in a little more.
     

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