Tempest sub almost ready!!! Need help with port length, please! :)

Discussion in 'Home Theater Projects' started by Javier_Huerta, Nov 1, 2003.

  1. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Well, my Adire Alignment Tempest is built! All I'm missing now is installing the whole works into it.

    I had it built by a professional carpenter; there was something he did that modified the overall size of the cabinet, though. He used 1" MDF, and followed the Adire instructions.

    So, the box, without ports, has a 207L volume.

    I have tried to use LSPCad to help me with the port length (I'll be using the 3" flared ports), but so far, I haven't had much luck. And Unibox & WinISD are giving me different answers...

    Can anyone help me calculate the final length of the port so that the box is tuned at 15.4 Hz?

    Thanks a lot!!!

    Javier.
     
  2. Jack Gilvey

    Jack Gilvey Producer

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    With dual 3" ports, I get anywhere from 19.5" to 21.8" for 15.4Hz in 207L. You'll typically add 1" to account for the flares. The best thing to do is install the ports with screws and weatherstripping so it's not permanent(yet). Start with the ports at 22" or so, see what that gets you, and shorten if needed.
    The range of lengths given is only going to amount to 1-1.5 Hz variation at most, so it's unlikely any performance gain/loss could be noticed. I'd just shoot for a value right in the middle.
     
  3. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Thanks for your post, Jack!

    I'm getting values in the 10.5 - 12.5" range using LSPCad. Adire's own plans say it should be 11" for 214L. Now I'm confused... [​IMG]

    According to LSPCad, using the same length as the 214L box will give me 15.7 Hz. So I think I might start with this...
     
  4. Javier_Huerta

    Javier_Huerta Supporting Actor

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    EDIT:

    Jack, I'm using dual 3" flared ports, as per Adire's instructions. I'm building the Adire Alignment box, as described on their white paper. The funny thing is, they tell you the "center tube" should each measure 11". This does not make sense to me at all, since I'd think it should be at least 60% larger.

    I'd assume the flares add a lot more than 1" to the overall measurement. Closer to 5, or 6", in order to make sense. But no matter how hard I've tried, I haven't been able to find info on the subject. Maybe I'll just measure the entire thing, flare to flare, add 1", and work from there.

    End of Edit.

    When playing around with stuffing, I now get results between 13-14" to 21", depending on whether I'm using LSPCad, WinISD, or Unibox! Wow.

    After reading about many people who simply followed Adire's plans and ended up with great subs, I decided to do so myself. Since I only lost 7 liters' worth of volume, I'll add half an inch (11.5") to the centre tube, and start from there.

    Now, the logistics of moving the thing around is my next problem... no matter what people tell you, the shock of seeing an Adire Alignment box for the first time is undescribable... and the weight of the thing makes you think every commercial sub looks like a joke!

    Pics, of course, tonight. [​IMG]
     
  5. Jack Gilvey

    Jack Gilvey Producer

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    Much confusion. [​IMG]

    Adire lists the length of center tube to use with their port kit, the flares do add another 5-6". What I meant by adding an inch for flares is that the programs typically don't account for flared vs. non-flared.

     
  6. Patrick Sun

    Patrick Sun Moderator
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    Rule of thumb: When using flared ports, add 1" to the final calculated length for the port to arrive at the final END-TO-END flared port length when using a flared port kit.

    For example. If you needed 17" of port length (straight port), then you'd need 18" of END-TO-END length for a flared port. You'd have to cut the center section of the flared port to arrive at the 18" END-TO-END length. Measure the linear length of the flared section, multiply by 2, and subtract from 18 to get the length of the center section for this particular example.
     
  7. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Jack and Patrick, thanks a lot! I'm taking out the Dremel now. A 6L volume drop apparently needs 1.5 cms. to make up for it. So I'll just take the 11", add 1.5 cms., cut, glue, and pray. [​IMG]

    I'm almost done...
     
  8. Javier_Huerta

    Javier_Huerta Supporting Actor

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    It turned out just fine! [​IMG]

    I finished building the sub yesterday afternoon.

    I ran into some very unexpected problems. I hope this is normal for a first DIY sub...

    I installed the sealant around the flared ports, and screwed them in. Big surprise - the edges of one of them were raised. I repositioned the tubes, but the problem never went away. I ended up using lots of sealant around both tubes.

    Then, when I was installing the driver, two locking t-nuts came off the baffle! What was even worse - they became locked to the allen screws. There was no way for me to remove them - the caulk didn't allow me to raise the driver up, and when I managed to do so, I could not separate the t-nuts from the screws! [​IMG]

    So I just glued those two screws so that they wouldn't rattle, added lots of sealant, and screwed down the driver as hard as I could. It was so tight, in fact, the caulk began coming out of between the driver and baffle.

    I cut off the excess caulk, and put the sub in position...

    Listening impressions could make up for a whole new thread. I'm pretty sure the driver and ports are well sealed now... so I think the sound wasn't affected by both screws not grabbing the MDF.

    Words like "impressive", "effortless", "deep", "superb" and "huge" come to mind. This sub is not for the weak of heart - it's a huge, gentle beast!!!

    I need to upload pics of the sub, and of my DIY steel speaker stands... but first, I need to find a place to host them.

    Until then... thanks a lot for all your patience! After 1 year of planning this out, I finally finished my first sub - and I have noone but ALL OF YOU to give thanks to! It would have been impossible without all of your help... I'm very, very grateful for it!

    EDIT: I did notice not much air is coming out of both ports at any time. Is this normal?
     
  9. Jack Gilvey

    Jack Gilvey Producer

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    Glad it worked out. [​IMG] Why all the sealant/caulk, though?
    In the future, dry fit everything first (you would have seen the raised port edge, not that it matters) then use weather-stripping on the ports and driver. As it stands, you won't be able to remove the ports or the driver.

     
  10. Javier_Huerta

    Javier_Huerta Supporting Actor

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    Jack, I guess I used so much sealing caulk so as to be on the safe side. I wonder whether I'll be able to remove the driver later on, though... I hope so [​IMG]

    Building the thing was a nice experience. I can't do any woodwork (I'm asthmatic, and the doctor is strongly opposed to it) but I told the carpenter exactly what to do.

    I (we) made some mistakes, too. Today, I heard a sharp noise inside the cabinet while running some test sweeps. Apparently, something inside it came loose. There's a buzzing noise near 60-70 Hz. The noise is only obvious when listening at *very* high levels, though.

    I guess I should have used countersunk screws and some other glue... still, I tried all the music I could find, and no strange noises can be heard. I guess I was lucky this time.

    I guess (hope!) this is normal the first time around, though. At first I was a bit sad about it, but now I'm planning a second subwoofer. Since (I think) size had a lot to do with my problems, my next project will be an Isobaric sub!

    Jack, thanks a lot for your help throughout this year... I now have an amazing sub. And it's very probable it will *not* be the last one!
     

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