Need advice on first DIY sub project (possibly isobarik)

Discussion in 'Archived Threads 2001-2004' started by Dustin B, Mar 12, 2001.

  1. Dustin B

    Dustin B Producer

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    This will be my first DIY sub project if I decide to do it (a thread on diy over on AVS from Bob Sorel lead me over to this forum, Thanks Bob). I'm a University student and have access to a table saw, router and any other tool I am likely to need to complete this project at my dad's place (and his jack of all trades experience in using them, as he grew up on a farm). This will be fairly long, but I'm not sure whether I want to do it or not. So I'm just gonna through out everything I'm thinking about and see what feed back this forum can provide me with, hopefully making the decision easier rather than harder.
    First off I'll put out that I'm in Canada and therefore have access to Paradigm stuff pretty cheap. I currently have a Paradigm PDR10 (payed about $230 USD for it) that is feed everything below 80hz. For it's price I like the way it sounds, and am reasonably pleased with its output. However, with some DVDs and some tracks from Enya or Lenny Kravitz the sub feels strained (and I feel I'm missing something, but for a PDR10, I guess I can't complain). So keep in mind that I'm not looking for that much more than a PDR10 can put out. I just want to beable to produce sound down to 20hz with some authority (but not knock you over from 6 feet away authority). Anyways, before I came across the possibility of building my own sub I was planning on getting a Paradigm PW2200. In the end it would have cost me between $900 and $950 CDN including taxes (aprrox $600 to $630 USD) depending on the deal I got at my local dealer. So that's the budget constraint I'd like to stick to for my DIY project.
    I want my cake, and I want to come as close as possible to eating it too [​IMG] I would like to make a 50/50 compromise between music and hometheater capability. I don't need 20hz at 120 db, I just want full bass that has some impact to under 20hz. I don't have room for a huge box or sonosub either, the biggest I could live with would be about 2' x 2' x 2'. Although I would like at least the width to be less than that by 4 to 6 inches.
    I'll also give a quick description of my room. The room forms a rectangle that is just under 17' long and is 12' wide. Listening position and equipment are on opposite sides of the 17' length. From the listening positions perspective there is an opening to the right of the equipment. Not a door, but an opening that makes this an L shaped room. The opening starts flush with the wall the equipment is against. The opening is 9' wide and the area it opens to extends just over 8' before getting to a wall. That wall has a door sized opening that leads into the kitchen. There is also a door sized opening to the immediate right of the listening position (small entry way with a closet). The ceilings are 8'. The whole room is carpeted with thick underlay, there are 3 peices of plush furniture, the walls are sheatrock as is the ceiling, but the ceiling has a stucko finish. I have very limited sub placement options, well really to keep the space liveable and keep the mains in good postion it would have to be starting from the 9' opening along 12' wall, right speaker, sub (would need to be really close to the wall, so if it gets a port or two I'd want them on the front or top), tv, component rack, left speaker.
    From the little bit of reading I've done so far, I thought it would be easiest to just get the non box stuff from Adire Audio (driver, amp, and port flares if I go with a ported box). I could go for ported or sealed Shiva with a 250 watt plate amp. I could go for the same thing but with a Tempest. I might be able to take a Tempest with the 700 watt amp (but that would mean all cabinet material purchases take me over budget). Are their other drivers and amps I should be looking at?
    From Bob's suggestion on AVS though I was also thinking about an isobarik design. I could go with 2 Shiva's and a 250 watt amp. Could do 2 Tempests with the 250 watt. Going with the 700 watt for either would take me over budget though. But if the gains would really be worth it, I could probably come up with the money for the more powerful amp. However, I'd like to avoid the clam configuration for an isobarik sub. The second driver sticking out the front of the sub would be too ugly for me to be happy. So that leaves both drivers facing the same way (smaller amount of sealed air, but different coil environments) or the drivers facing opposite directions with the backs of the drivers almost touching (larger amount of sealed air, but same coil environments). Any comments or things I should know about these isobarik configurations?
    So, what would you guys recommend, and how do you think it would compare to a Paradigm PW2200? Bob seemed to think that an isobarik Shiva with a 250 watt amp would completely destroy a PW2200. Do you think he's right? Do you have an option that would blow away a PW2200? Is anyone here willing to help me through the design and building process (more so the design, once I know what it's supposed to look like, I shouldn't have a problem building it)?
    Thanks in advance for any help or info you provide.
     
  2. Mark Hayenga

    Mark Hayenga Supporting Actor

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    Hi Dustin,
    I have some experience with both the Tempest and the Shiva, and for your application I think a single Tempest in 6-8 cubic feet tuned to 18-20Hz would be ideal. A single flared 4" port would be required at a minimum, with two offering moderately better performance. I wouldn't worry about venting any more than that though.
    Given that you have sufficient volume for a single Tempest, I wouldn't recommend an isobaric sub. Too costly for not enough gain in my opinion, especially since a 2x2x2 box would certainly have enough space for a single Tempest.
    Also, the AVA250 amp is also surprisingly good for a plate amp. I wish it had a steeper lowpass filter, but that's my only nit to pick with it.
    ------------------
    Mark Hayenga
    www.hayenga.com
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    "Saru mo ki kara ochiru"
     
  3. Blake Middleton

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    Dustin:
    I am building the Shiva sub enclosure from Adire. I am building the largest vented box they have designed and it is only 22.5" square. I will hopefully be finishing it in a week or so, so I will let you know how it sounds. I am waiting on the parts and amp right now. If you have any questions about it let me know or ask Dan Wiggins of Adire. He is very helpful.
    Blake
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  4. Dustin B

    Dustin B Producer

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    I just did some more precise measuring. Depth is my most fexible unit. I can go over 24" if I have to, but I'd like to be less than that. Height is pretty fixed. From the floor to the top of the finished box I can't be more than 25". Width at 24" is really stretching it, I'd like width to be 20" or less. The wider it gets the less room I'll have between the sub and a doorway that leads to the bedrooms for my left speaker.
    I'll be looking for your report Blake. And I'm hopeful Mr. Wiggins will join in on this thread. From what I've seen with my search on this forum for "isobarik", he is definitely a member of this forum worth listening to.
     
  5. Jack Gilvey

    Jack Gilvey Producer

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  6. Blake Middleton

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    Dustin:
    Well, with those restrictions you probably cannot build the same size cabinet that I am. Try this link; it shows 3 different vented boxes you can build for the 12" Shiva. http://www.adireaudio.com/Files/Vent...plications.PDF I hope you find it helpful. I certainly did.
    Blake
     
  7. Craig LeBlanc

    Craig LeBlanc Stunt Coordinator

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    I started my 142.5L EBS Shiva sub a week ago...check out some of the pics:
    http://dopey.hil.unb.ca/craig/
    Once it's completely done, I will also do up a frequency response graph and show what one of these puppies can do.
     
  8. Blake Middleton

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    Hey Craig, that looks familiar! Are you going to use the AVA250 amp or an outboard amp? Also did you glue and screw, or did you just use glue? I think I am going to use screws just to make sure everything stays nice and tight. It looks great!
    Blake
     
  9. Kevin Kloet

    Kevin Kloet Agent

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    Just make sure your final box shape is not (or does not too closely resemble a cube).... that is the worst possible shape for a box in terms of acoustical performance.
     
  10. Mark Hayenga

    Mark Hayenga Supporting Actor

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  11. Bob Sorel

    Bob Sorel Stunt Coordinator

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    Guys, my recommendation of an isobarik Shiva/Tempest was simply due to Dustin's original request to have the enclosure as small as possible. I certainly agree with everyone here that a larger, ported single Tempest would be the most cost effective, best way to go, and I mentioned that to Dustin in the other thread. That is also why I suggested that he post here [​IMG]
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    STOP DVI/HDCP/5C/DFAST!
     
  12. Craig LeBlanc

    Craig LeBlanc Stunt Coordinator

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  13. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Dustin, you might consider a sonosub to keep you within budget. Here's my Tempest 6.2 ft^3 sonosub with attached enclosure for the Adire AVA250 plate amp. Sorry for the low res pictures, I don't have a clue about photo posting. http://www.geocities.com/hankbond1/My_page.html
     
  14. Dustin B

    Dustin B Producer

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    I've done some more reading. Including going through the application notes on the Shiva and Tempest. The more I read the more I'm beginning to aggree with Bob. The dimensions in both papers for the performance I want result in boxes bigger than I want. I've already considered the sonosub Frank, but I don't think that's how I want to go, thanks for the suggestion though (although if I do build this, I will likely also be building a sonosub for my parents).
    So I think an isobaric design would allow me to come the closest to eating my cake too (acceptable price increase that allows a box size and frequency performance level that will make me happy). Buying 2 Shivas, and two Tempests would not be a problem on my budget as long as they are paired with the AVA250. If I try and up the amp power, that's when I go above budget.
    2 Shivas and AVA250 = $420 USD = $630 CDN
    2 Tempest and AVA250 = $460 USD = $700 CDN
    So that would leave me $270 to $200 left for cabinet construction and finishing materials (but shh, I think with my dad helping me build it, he'll just pay for the materials when we go buy them, especially if we are building him a sonosub too [he's got a lot more space]).
    So now that I think I've decided on an isobarik with either Shivas or Tempests and a AVA250, it comes down to a few concerns I have left that I would like your opinions on. Is a 250 watt amp enough to give an isobarik shiva good performance (this is more volume wise on what I already know will be a great frequency range)? Can a 250 watt amp drive an isobarik Tempest with good performance (volume wise again)? With 250 watt amps, will the Tempest perform better than the Shiva? Will the difference be siginificant enough to justify the larger box and higher cost of the Tempest? And again, what should I expect from either in comparison to a Paradigm PW2200?
    I know I'm asking questions that are difficult to answer without first hand experience, but I'll take opinions. Though I'll be really grateful to someone with first hand experience who can give definitive answers to the above questions.
     
  15. Craig LeBlanc

    Craig LeBlanc Stunt Coordinator

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    I'm not sure about using an isobaric chamber, but just by looking at the freq response graph in the vented box pdf, the 142.5L box should compete very well with the Paradigm pw-2200... or at least up to 80Hz. Once mine is ready to go, I can actually do comparisons between my Shiva and a friend's PW-2200 and let you know. The main difference between the paradigm and the shiva would be it's handling of frequencies about 80hz, the 142L box drops off pretty hard around 70Hz or so. I don't think you would really need more power than the ava250 to run it well. Maybe your best bet for figuring out how to design your box would be to get lspcad and do some modelling with it.
    As for the cost of the wood... it's pretty damn cheap for a sheet of 3/4" MDF... I paid $27.99 CAN for a sheet. You'll end up paying more for the glue/silicone/finish than for the wood.
    Another thing to maybe think about, run each voice coil in the opposite direction and add a resistor to create an electromagnetic brake? You would need more power, but power is relatively cheap if you don't need the crossover from one of the sub amps. That would tighten up the bass response for music and still give you the bass extension we all want for HT applications. (I'm still thinking about using this method)
     
  16. Bob Sorel

    Bob Sorel Stunt Coordinator

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    How about this idea? Build a cube with internal dimensions of 19"X19"X19", put an Audiomobile Mass 2012 driver in it, and port it with dual 4" flared ports? Isn't that the box that TerryC recently built and tested? If memory serves, shouldn't it be about equal to an isobarik Tempest in size and performance? Just another idea.
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  17. Dustin B

    Dustin B Producer

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    Ok, I don't know what I'm doing. I downloaded WinISD and started playing with it [​IMG]
    The Pe value, is that the Pmax value listed on Adire's site (I currently have it set to 650 for the Shiva)?
    What about "Z" and "dia"? No idea for Z. Is dia just the diameter of the cone (12" for the Shiva), or is there a more precise measurement to be used. I just left both blank for now, so they are both at 0.
    Anyways, playing with values I came up with an isobaric shiva that was 3.6 cubic foot box tuned to 16hz with two 3" ports. It says 38.33" for the ports, my assumption is that is total between the two ports, so each port should be just over 19". This results in the gain displaying just over -3db at 20hz.
    The PW2200 is rated at -3db at 18hz, or am I misinterpreting the values?
    Am I doing something wrong? Does this seem reasonable?
    What about the Q of the box I keep reading about, where and how do I figure that out for this box?
     
  18. Dustin B

    Dustin B Producer

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    I'm getting confused with this WinISD program. The port number changes are confusing me (ie I don't have the knowledge to know why they change that way). I select one three inch port and I get the shortest port length (but the mach number is always in the red). When I select two three inch ports the length number more than doubles (but the mach number goes way down). Then with one 4 inch port, the length is longer than the 3inch, and the mach number goes down a lot. Then with 2 four inch ports the length goes way up, but the mach number goes way down. That just seems backwards to me.
    While I'm at it, I put some more configurations through and came up with a 96L box with isobarik Shivas tuned to 18hz. If I add another 30L to the box to allow for the volume taken up by the two connected drivers (cylinder with the coils facing each other approximately 30cm long and 18cm in diameter, don't know if this would be big enough or not) that would result in a box with outer dimensions of approximately 24"x23"x21" (depth, height, width). Which is a chunk larger than a PW2200. I'm just having problems getting numbers to add up.
    Well I guess the real add up problem is 2 Shiva's and a AVA250 will be between $650 and $700 by the time I get them to Saskatchewan and then spending another $100-$150 on box constructions and finish adds up to between $750 and $850 CDN. I can buy a PW2200 for right around $900.
    Also considering these numbers I grabbed from another post on this forum:
    Here is some data from Tom Nousaine (respected sub expert/reviewer):
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    All figures are for a corner loaded subwoofer, 2 meter mic distance,10% distortion limit,and the SPLs have been averaged from the maximum output at 1/3 spacing at 25/31/40/50/63hz.
    Paradigm PW2200 - 107.4dB / 20hz~91dB(106.25)
    HSU RESEARCH VTF-2 - 107.1 / 20hz~93dB(106)
    ---------------------------
    This is a quote from the guy who posted those numbers:
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    I think the first number is avg. output and the second part is the low-end extension. The number in parentheses is a "corrected" value because the amount of output at 63Hz can skew the avg. upward. As you can see, in terms of output, the $500 Hsu is right there with the Paradigm (actually a smidge higher). I'm pretty sure a single 25-31PC (powered version) can beat the VTF-2....
    --------------
    Can I get sufficiently better performance in a package close enough to the PW2200's size with a DIY sub that is worth the time it would take to build it?
     
  19. Craig LeBlanc

    Craig LeBlanc Stunt Coordinator

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    Dustin,
    Maybe you should email or call someone at Adire and see what they have to say. I'm not sure you really need to have 2 drivers to get the performance you are looking for. And the building materials won't cost more than $70 CAN for a single sub, unless you need more than 1 sheet of MDF.
     

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