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Thread: HELP please Airspace calculations for irregular sub box

  1. #1
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    Question HELP please Airspace calculations for irregular sub box

    Hi, guys, I need some help figuring out how to best calculate the airspace in an irregular shape. I am building 2 custom enclosures from fiberglass in the trunk of my 97 prelude. they will go in the rear corners closest to where you open the trunk up. I have 2 12"Kicker l5's and i know they both they each have a kicker recommended min .66 cubic feet and max recomended 1.0cf but it is a weird contoured shape. If anyone can help me figure how it is best to calculate odd figures like that it would be greatly appreciated.

    Yes i know a standard shape would be l*w*h usually in inches and divide by 1728 for cubic feet. No so easy when dealing with indentations and such.
    I am sure they taught this in school and it was probably chalked up to one of the useless things i thought i would never use and never committed it to memory.

    I googled the hell out of it and found no good solutions for irregular shapes.
    Searched the forums turned up nothing as well
    Thank you,

  2. #2
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    i think most use water to fill up their fiberglass boxes, then dump the water into buckets and figure volume from that. or im sure packing peanuts will get you close too.

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    Quote Originally Posted by trader007 View Post
    i think most use water to fill up their fiberglass boxes, then dump the water into buckets and figure volume from that. or im sure packing peanuts will get you close too.
    ergo the problem i need to know how deep to make it. unless my though process is way off essentially these steps,

    i will probably just pull my trunk liner out as it is molded not just carpet and hang it up. lay down plastic and do the hard part of laying the chop mat then resin for a layer or two. beginning what would be the back of the finished enclosure but then i am looking at how to gauge how deep to frame the top then onto that. i could fudge it but from experience the amount of the air really makes all the difference. so my point is i would not have a finished product to fill with water.

    is there something here i am missing?

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    My suggestion would be to lay a minimal amount of glass to hold something for meaurement, and start with the biggest possible volume you can use. It is easier to fill in than it is to build another box. Use the volume testing method. I like the small peanuts, but I too have heard of people using some form of liquid.

    Either you need a professional photograph to CAD design software $$$, or build a couple of layers and bring it in on the inside from there.

  5. #5
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    Quote Originally Posted by coastaldamage View Post
    My suggestion would be to lay a minimal amount of glass to hold something for meaurement, and start with the biggest possible volume you can use. It is easier to fill in than it is to build another box. Use the volume testing method. I like the small peanuts, but I too have heard of people using some form of liquid.

    Either you need a professional photograph to CAD design software $$$, or build a couple of layers and bring it in on the inside from there.
    Yea, i guess that will be how i have to do it. Make a skeleton a little big to test and trim to taste. Thanks guys for your thoughts and help

  6. #6
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    Easy!!!

    Yes...the water thing works but I prefer a slightly different material that works very closely to the same. Use SAND...it will not pour right out of any little imperfections. If you don't have a "solid" shape or area to pour it into, use duct tape and cardboard (from a LARGE pizza box) to "close in" the area you want to measure. fill the area with sand and then use your shop vac (CLEAN FIRST, of course) to suck it all out. then, pour the contents of the shop vac container into gallon jugs. 1 U.S. Gallon = .134 cubic feet...do the math. if your "enclosure" is too large, move the piece of cardboard that means the least to your "final look" in just a little to shrink the enclosure and start over.

  7. #7
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    The sand is a good idea for greater accuracy. I normally use foam packing peanuts, just because I always seem to have them around and there's no clean up. It's probably not the most accurate, but enough for sub enclosures. It's good for when you don't know the sub's displacement as well. You can put the sub in the enclosure with it filled with peanuts and just remove the amount you need, just don't let the sub compress the peanuts to keep it as accurate as possible. An enclosure doesn't have to be exactly to spec. You can always add dampening material to increase the size or additional bracing to decrease the size of a finished enclosure.

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    Quote Originally Posted by black_mamba View Post
    The sand is a good idea for greater accuracy. I normally use foam packing peanuts, just because I always seem to have them around and there's no clean up. It's probably not the most accurate, but enough for sub enclosures. It's good for when you don't know the sub's displacement as well. You can put the sub in the enclosure with it filled with peanuts and just remove the amount you need, just don't let the sub compress the peanuts to keep it as accurate as possible. An enclosure doesn't have to be exactly to spec. You can always add dampening material to increase the size or additional bracing to decrease the size of a finished enclosure.
    actually...I disagree, the closer you are to perfect the better the sub will react and likewise sound. I prefer to design the enclosure LONG before I build it. I would much rather spend hours in a chair with a computer and music and air conditioning/heat while designing a box as opposed to hours rebuilding the same thing over and over. I have been building enclosures professionally for the last 12 years and, for me, it is MUCH less frustrating to create the "optimal" enclosure at a desk and make absolutely sure that the ending product is exactly what the design program called for. I have had customers purchase EXPENSIVE subs and then put them in a "basic" box because they felt the need to complain about my price to build a box...all I could tell them is "it's your decision, but, I wouldn't". I have also had customers come to me first and I have always told them the truth..."it's the BOX that matters and makes or brakes the sub, not the other way around".

  9. #9
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    I absolutely agree about the box being more that half the sound quality. The greatest subs in the world will sound like garbage if the box does not meet the required specs and thats why i hate using universal sub boxes. Right now i have the kicker l5's and at least they are in the box from kicker made to work with them however it is ported. I looked closer at my car and i do not have those indents on both sides so i think i have decided to move the custom enclosure to somewhere else and it will be a normal rectangle so should not be a problem, and it will be a lot smaller because it will not be ported. thank you all for your responses and you help.
    Quote Originally Posted by Darkhorse972 View Post
    actually...I disagree, the closer you are to perfect the better the sub will react and likewise sound. I prefer to design the enclosure LONG before I build it. I would much rather spend hours in a chair with a computer and music and air conditioning/heat while designing a box as opposed to hours rebuilding the same thing over and over. I have been building enclosures professionally for the last 12 years and, for me, it is MUCH less frustrating to create the "optimal" enclosure at a desk and make absolutely sure that the ending product is exactly what the design program called for. I have had customers purchase EXPENSIVE subs and then put them in a "basic" box because they felt the need to complain about my price to build a box...all I could tell them is "it's your decision, but, I wouldn't". I have also had customers come to me first and I have always told them the truth..."it's the BOX that matters and makes or brakes the sub, not the other way around".

  10. #10
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    Dang, guys! I didn't mean for it to sound like box size accuracy wasn't important. I also agree it should be as accurate as possible. I just meant to say that using peanuts was accurate enough. When I use peanuts, I use smallish sized peanuts and will measure several times to make sure the variance between measures is small enough. I also spend several hours on the computer playing with different setups before building the box.

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