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  1. #1

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    Need help building a sub box

    I've been reading up on this crap for a while now, and can't figure out how I'm going to make this work.

    I picked up a 15" sub from Slick a while back, a Hifonics Olympus OLM1615. This is a 15" sub, 1600W RMS.

    Specs are here:

    http://www.maxxsonics.net/manuals/hi...r%20Manual.pdf

    The biggest box that I can fit in the trunk of my regal is 38" width x 32" depth x 17" height. I'm planning on having this sub facing upward. Those dimensions have an inner volume of 2.15' cubed.

    The specs recommend a 2.75' cubed box, which is obviously much larger than what I can fit in my trunk.

    What I'm trying to figure out is how I can make this work. My biggest issue is figuring out how to tune the ports. I've been using this calculator:

    http://www.carstereo.com/help/Articles.cfm?id=31

    Its useful, but I'm getting asinine numbers when getting a port length. To tune the box to 40hz, I'm getting a port length of 57.77", which I don't see happening if I my max dimension for this box is 38".

    Can anyone help me out here? I know a larger box would be ideal, but I'd like to try to make this work. It should give me better performance than my current Alpine R12.

  2. #2

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    Re: Need help building a sub box

    Yeah, that's too little of airspace. Your best bet, make a fiberglass box to maximize trunk space. I can walk you through that, and I can also walk you through measuring the internal volume so you can tune your port accordingly.

    You really don't want to build a mdf enclosure that has a bunch of offshoots. The standard rectangular enclosure is optimum, mainly due to the resonant frequency of the wood. However, once you step out of that, and into the fiberglass, then your safe to have funky shapes and designs.
    Chris D.-
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  3. #3

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    Re: Need help building a sub box

    IIRC, the box I had was like 2.9-3.2 cu ft with like a 39-41 hz tune. It's been a while though.
    Chris D.-
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  4. #4

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    Re: Need help building a sub box

    Hmm, I'm a bit scared to run into fiberglass. Seems time consuming and I've never done it before. Then again, I do have a bit of time to work with. I've pretty much accepted the fact that I won't have any more trunk space after this is all done.

    Would it be at all possible to run it with the amount of space I have right now? I know a bigger box would be ideal, but would it work at all?

    I also patched a couple of tears in the sub's foam surrounds using electric tape and silicone sealant. It holds very well, but obviously doesn't look amazing. I'm not too concerned with how the end product will look, so long as it gives me significantly more bass than my current Alpine R12 with a ported off-the-shelf box.

  5. #5

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    Re: Need help building a sub box

    I would advise against going with the smaller box. The output will be greatly reduced.

    Some people would disagree, but I would also not face the sub in an upward position.

    You're not using your backseat, correct? You could probably get an 8 cu ft enclosure to fit right there.

    I guess the question is, just how xtreme (pun intended) do you want to get?
    Chris D.-
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  6. #6

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    Re: Need help building a sub box

    Quote Originally Posted by xtremerevolution

    The biggest box that I can fit in the trunk of my regal is 38" width x 32" depth x 17" height. I'm planning on having this sub facing upward. Those dimensions have an inner volume of 2.15' cubed.

    The specs recommend a 2.75' cubed box, which is obviously much larger than what I can fit in my trunk.


    http://www.carstereo.com/help/Articles.cfm?id=31
    You have plenty of room for that space. 38" = 3.17 ft 32" = 2.67 ft and 17" = 1.4167 ft. If you were to build this size box, you would have 11.963 cubic feet of volume. I am not sure how you arrived at 2.15 ft. Now, keep in mind you will want to allow for the amount of volume the sub itself will take up of the box.

    I agree with slick. You don't want this facing up.

  7. #7

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    Re: Need help building a sub box

    You should have plenty of room in there. I had a almost 5 cubic foot box for 1 15" in my Lumina and i had plenty of room to spare.
    August
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  8. #8

    Re: Need help building a sub box

    What are you doing? Tuning and building boxes? Just turn it up louder.... ha ha!
    <br />Once proud owner of the once infamous &quot;Christine&quot;

  9. #9

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    Re: Need help building a sub box

    Quote Originally Posted by boulevard
    What are you doing? Tuning and building boxes? Just turn it up louder.... ha ha!
    Don't be surprised when someone's single 15" tuned box goes louder than your dual 12" off-the-shelf box. If you want the most out of your subs, you have to do it right.


    Quote Originally Posted by Leadfoot
    Quote Originally Posted by xtremerevolution

    The biggest box that I can fit in the trunk of my regal is 38" width x 32" depth x 17" height. I'm planning on having this sub facing upward. Those dimensions have an inner volume of 2.15' cubed.

    The specs recommend a 2.75' cubed box, which is obviously much larger than what I can fit in my trunk.


    http://www.carstereo.com/help/Articles.cfm?id=31
    You have plenty of room for that space. 38" = 3.17 ft 32" = 2.67 ft and 17" = 1.4167 ft. If you were to build this size box, you would have 11.963 cubic feet of volume. I am not sure how you arrived at 2.15 ft. Now, keep in mind you will want to allow for the amount of volume the sub itself will take up of the box.

    I agree with slick. You don't want this facing up.
    Looking back at it, I can't have it facing upward either way, so it would have to fire toward the front.


    I must have been having a bad night, since I went to an engineering high school (california academy of math and science), and an engineering university (Illinois Institute of Tech), and forgot how to convert cubic inches to cubic feet.

    Online calculator > me

    http://www.metric-conversions.org/vo...cubic-feet.htm

    Apparently I can get nearly 12 cubic feet of area.

    Now that we have that settled, I'd like to go a little bigger than 2.75.

    The spec sheet recommends 3 cubic feet for "Optimal Sound Quality - Flat Response" and 3.25 cubic feet for "SPL Very Boomie - Loud".

    the latter recommends a 15.5" port height, which would fit quite perfectly with the height of the box.



    Quote Originally Posted by slick
    I would advise against going with the smaller box. The output will be greatly reduced.

    Some people would disagree, but I would also not face the sub in an upward position.

    You're not using your backseat, correct? You could probably get an 8 cu ft enclosure to fit right there.

    I guess the question is, just how xtreme (pun intended) do you want to get?
    Now that I've figured out how big I can go, I'd like to go pretty big. My new limitations are 34" width (between trunk hinges), 17" height, and 29" depth.

    I've been playing with this calculator for a while, but I'm not sure if this takes into account the size of the sub you're using when designing the port.

    http://www.reaudio.com/speaker_box/LPort_Box_Calc.html

    Can anyone give me some help in figuring out some good dimensions for this box? Would this calculator suffice? I'd like to tune to around 35hz.

  10. #10

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    Re: Need help building a sub box

    So I've been playing with some numbers, and here's what I have:

    Width: 34"
    Height: 17"
    Depth: 20"

    Port width: 3.5"
    Port length: 15.75"

    This would have me tuned to 33hz.

    The convenient part about this calculator is that it tells you the exact size of the every piece of MDF you need to cut.

    This would have me sitting at 4.7 cubic feet.

  11. #11

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    Re: Need help building a sub box

    Here's one thing I'm not understanding.

    I figured out two boxes here.

    34x17x20, port width 3, port length 15.75, 31hz tune, 4.8 cubic feet.

    34x17x22, port width 3.5, port length 17.75, 30.6hz tune, 5.2 cubic feet.

    I'm going to guess that the difference in the tunes for both of these boxes will be minimal. However, one box is larger than the other. Since they're both tuned to nearly the same frequency, would the larger box be louder? How exactly does this work? How big can you get before you get too big?

    I've heard that the sub will sound fine as far as being too "boomy" with a low frequency tuned port so long as you don't go lower than the free air resonance (fs) of the driver, which in this case is 30.85hz.

  12. #12

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    Re: Need help building a sub box

    I didn't look at the link, but judging from your last post, it takes into account the internal vs. external dimensions of the box.

    Is the 34x17x20 the internal or external dimensions?

    I wish I still had the programs I used to have. I was able to graph out the frequency and gain maps based upon enclosure volume, port size, wattage, sensitivity, and a ton of other stuff. It's on my home computer, which is still broke.

    I guess it all depends on how detailed that you want to get when designing this enclosure. For simplification, I would say no, don't worry about the volume that the speaker will take up in the box.

    However, if you are worried about it, and really want to optimize it, you may need to download one of the several programs off of the internet. Insert data, do box design and port sizing, etc...

    http://www.bcae1.com has lots of good information.

    http://www.bcae1.com/spboxnew2.htm
    http://www.bcae1.com/spboxad1.htm
    http://www.bcae1.com/spboxad2.htm
    http://www.bcae1.com/spboxad3.htm
    Chris D.-
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  13. #13

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    Re: Need help building a sub box

    Larger the tuning Hz generally means the louder, or boomier you'll be. However, you sacrifice SQ.

    Most off the shelf boxes are in the 31-34 hz range, depending on manufacturer, and what speaker is installed into the box.

    General rule of thumb: 36 hz or higher, you're starting to get into the SPL side of things. Some people that do competitions do in the low to mid 40's range. However, you start to lose the low side of the frequency chart if you are listening to music that has a lot of lower frequency notes.

    32 or lower, your getting into the SQ side of things. Generally, not near as loud or boomy, but more of what you can feel. Also, you will be able to play those low hz notes, which some people really do strive for (music sounds a bit more real).
    Chris D.-
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  14. #14

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    Re: Need help building a sub box

    As for box size, stick to something that fits in your trunk, and along the lines of manufacturer specs. Getting into the big boxes, you're going to need big power, and even a ton more airspace inside the cabin.
    Chris D.-
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  15. #15

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    Re: Need help building a sub box

    Quote Originally Posted by slick
    As for box size, stick to something that fits in your trunk, and along the lines of manufacturer specs. Getting into the big boxes, you're going to need big power, and even a ton more airspace inside the cabin.
    In that case, both of those boxes I mentioned are far significantly larger than the manufacturer specs. The manufacturer recommends 3.25 cubic feet for SPL. I do have a Directed 1500d mono amp I picked up from someone here, so I shouldn't have too much trouble powering that sub, but I don't want to make my life more difficult. Is there any advantage at all to using a bigger box?

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