new box for alpine type r

Equipment:
1 Alpine Type-R 1542D (15" dual 4Ohm coils)
1 Alpine MRP-M1000D (1000Wrms @ 2Ohms)
1 Honda Civic hatchback

Now:
The current box is about 2.5 cu ft and tuned at about 40Hz
I'm content with the current sound, I just know that there's more in my equipment than I'm getting. When playing the Low lows, you can feel a "breeze" of air coming from the sub, but you cant hear (feel) it as much as expected. And with the current 3" diameter port, I have terrible port noise at these low frequencies.

Goal:
More Low frequency SPL. No port noise.

Alpine says 2.25 net internal with 22.5" port area, But I was thinking closer to 3cu ft net with 44" of port area....

I know most box builders don't like to deviate anymore than 10% from manufacturers specs, but for my particular goal, does this seem ok??

(sorry for the long post, Just trying to get it all in there)

EDIT:
New design will be Slot Vent (If that changes anything at all. lol)

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UNLABELED Custom Car Club President

What frequency are you planning to tune to? Going that large is okay to do with that sub. They tend to perform better in a larger enclosure and especially for what you are looking for.

Well Im thinking of tuning at 30.... Think I should go lower?
I Really want the Lows but dont want to loose All of the output

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UNLABELED Custom Car Club President

Another Question....
Wut are the advantages of puttin 45's in the corners of the port?

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UNLABELED Custom Car Club President

Your 40Hz tune now is why you are lacking low end and your 3 inch port is only 7 square inches of port are, which is why you have nasty port noise. Simply lowering the tune will put you more where you want to be. 30-32Hz should be good and around 30 square inches of port area if your going 3cu.ft.. Doing 45s on a port fold simply helps to channel the air better. Making it less turbulent and alowing it to flow more efficiently.

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I've had good luck dividing the port up in two and adding additional length to it. That way the sub can sit in the center of the box and each port can fire to each side of the sub. I think it fills the sound more evenly and it looks a lot better to see the sub centered. Here's a old sketch of the basic idea


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This is what I do for FUN!

This is Wut Ive got so far..
it should be right at 3 cu ft after bracing total port length of 35 inches (port 2.5 x 18.8 x 35)

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UNLABELED Custom Car Club President

Ianarian, I like your symmetrical design, but i simply dont have enough space to get 3 cu ft net volume in that box in my little hatchback.
Maybe Ill try somethin like that after i convince myself that my back seats are un needed

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UNLABELED Custom Car Club President

WAY to much port area. for 3 cubic foot net you only need 30 square inches of port area. You have 47 there. Also are you figuring your Net right? Total GROSS internal volume minus port, driver displacement and bracing. Im getting 32.2Hz tune if you have correct Net of 3 cu.ft though. If that is a gross of 3 cube your tune will be much higher. Post your measurements and i can double check them, but i can tell you now you don't need that much port area.

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28 x 16.75 x 20 (external with double baffle on front)
port length one = 13.5
port length two = 12.75

What is the disadvantage of having too much port area?

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UNLABELED Custom Car Club President

Women Have Legs- width x height x length
Width? 28" x Height? 16.75" x Length/Depth? 20" (external with double baffle on front)
(port W?-2.5 x H?-18.8 x L?-35)
So looking at the picture, is the 18.8 the top-bottom measurement? Its indicating the outside height is only 16 3/4, so that 18.8 cant be correct on the height of the port. Perhaps were thinking its(just as it sits in the pic) -2.5" wide -15" Height -??length?? hmmm 24 linear inches of your 2.5x15=37.5 <----the area of your port is that number. Each sub size pretty much has a general area, (slot or round) that you can reference to. The slot/port length is the keys to the instrument that allow a fellow to make some tuning adjustments if so inclined. Except when a fellows car is a little short on room. Dam, with 4 1/2 ft3 we could end the possibility it could be any better. Not to mention I was gonna bid 1" MDF. Have you tried the 15 sealed?

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This is what I do for FUN!

Port length from front to back = 13.5
Port length from left to right = 12.75

(All measurements are with the top On the box)

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UNLABELED Custom Car Club President

The way I have figured that will tune you to around 34.5Hz. A tad high for the results your looking for. Im getting 3.20cu.ft. net without figuring bracing or port wall. So you are right on the money once bracing and port wall are figured, but im only coming up with 29.5 port length. For a folded port you measure length in the center of the port. Taking into account bracing and port wall to get you to your 3.0 cu.ft, port 2.5 x 18.5 X 29.50= Fb of 34.5Hz

Me personally I would do it at 30 square inches of port area for 3 cube. Its more than enough to eliminate port noise. Your last enclosure was using a 3in round port. Thats only 7 sq.in. of port area and the reason you had MASSIVE port noise. You essentially had a leaky sealed enclosure

As for you earlier question, about port area. You want enough port area to be around 20m/ sec in your open civic. 30 square should more than do that eliminating port noise. Going to a too large port area can result in a very fast roll off and a peaky out put. Notice how comp vehicles have really huge port areas? Although there can be a gain in output it make it much more narrow frequency response. Thats why they call them burp boxes. Not ideal for daily listening.

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Thanks A lot for helpin me out J.Reed.
So I changed the port opening to 1.75" = 32.4 sq in port area
port length one = 14.25
port length two = 6.75
(measured 22.5 total down the center on the port)
This should be real close to 30Hz after Lots of bracing

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UNLABELED Custom Car Club President

blackcivichatch wrote:

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Thanks A lot for helpin me out J.Reed.
So I changed the port opening to 1.75" = 32.4 sq in port area
port length one = 14.25
port length two = 6.75
(measured 22.5 total down the center on the port)
This should be real close to 30Hz after Lots of bracing

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Yep bracing is your friend. Just remeber as you take away from your net it will raise tune a bit, so it important to account for everything as well as you can. Might take a few back and forth trips to the calculator, but the end result will be worth it. If i might make one more slight suggestion. See if you cant widen the port a bit more. 2.5 was good, you could shorten the height a bit to get it where you need it. So it important to account for everything as well as you can. may take a few back and forth to the calculator but the end result will be worth it.

If you need or want a double check feel free to post it up.

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I kinda wanted to keep the port the full height of the box for cosmetic purposes.
But if you think there will be much of a difference, I can work somethin out.

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UNLABELED Custom Car Club President

blackcivichatch wrote:

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I kinda wanted to keep the port the full height of the box for cosmetic purposes.
But if you think there will be much of a difference, I can work somethin out.

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port area wise it is fine. I just think that 1.75 is a bit tight and could end you with a bit of port noise because of the narrow gap.

You could do 2" x 17" that would mean just adding a strip of 3/4 to the top and bottom keeping it uniform. Not much of a change though. Thats only 1/4" more open for 34 sq.in. It could be fine by simply rounding over the edges of the port too.

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I did plan to round the edges pretty good.
(just dont know how to show that on sketchup yet lol)
And the 2 x 17 seems feasible.
Give me a few min to make the changes.

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UNLABELED Custom Car Club President

blackcivichatch wrote:

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I did plan to round the edges pretty good.
(just dont know how to show that on sketchup yet lol)
And the 2 x 17 seems feasible.
Give me a few min to make the changes.

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Well your better at sketch up then me lol. I just use photoshop and 2D it.

Looking at your design I thought it would retain your look pretty well.

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Ok. 2 x 17 x 26 long
Net of 3.3 to 3.4 after Bracing.
should be 29.5 to 30 hz

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UNLABELED Custom Car Club President

I think that your last suggestion actually helped the design.

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UNLABELED Custom Car Club President

looks good.

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Hopefully it'll sound as good as it looks. lol..
.....Now i just need to find a truck, Not sure if the Sheet of MDF will fit in my hatchback.

Thanks again for the help

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UNLABELED Custom Car Club President