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Need Port help for 3 Sundown E8's


aburger

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Hey All, I just have a quick question about which port would work for the box I'm planning to build. It's a small ported box for (3) Sundown E8v5, D2's. They'll be running at 1.3 Ohms off of a Crescendo S1v2 monoblock. This is for a single cab Dakota so space is at a premium (amps are going under the seats). I'm aiming for the box to have an internal volume around 2.25 ft^3 after bracing and port displacement, tuned to 32Hz (per Sundown's website).

My question is this...can I get away with a 3" diameter precision port with a length of 7", or should I go with a 4" precision port with a length of 12.5"? The lengths were calculated via the Precision Port length calculator (http://www.psp-inc.com/tools2.html). These subs aren't the strongest, so I'd like to go with the smaller port if possible. But this is my first time building a ported box, so I will gladly take any advise from the experts. 

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So I would reasonably expect around 1250 watts out of that amp into 1.3 ohms.  Based on that amount of power, a net volume of 2.25 cu ft, and a tuning frequency of 32 Hz you are going to need a LOT more port area than either a single 3" or 4" port will provide.  

If you really want to use aero ports you will need three 4" ports, roughly 40" long each.  I doubt you are going to be able to make that fit, so my suggestion would be a single slot port with 36 sq in of port area.  

This may sound like a lot of port area, but keep in mind Sundown's recommendation is for 8-12 sq in of port area per sub and that's assuming you are running RMS power of 300 watts per sub.  You are exceeding that power level by at least a 1/3 so 36 sq in of port area for the three is pretty much the minimum you will need to avoid nasty port noise and port compression.  

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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Well holy crap, hahaha! I wasn't expecting that! Thanks for the info, looks like I'll be rethinking my layout. Would it be possible to split it up and do two slot ports with 18 sq inches of port area each? That way I can put a port on either side of the box with the three subs in the middle.

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1 minute ago, aburger said:

Well holy crap, hahaha! I wasn't expecting that! Thanks for the info, looks like I'll be rethinking my layout. Would it be possible to split it up and do two slot ports with 18 sq inches of port area each? That way I can put a port on either side of the box with the three subs in the middle.

Yup, you can split it up and run one 18 sq in port down each side.  Keep in mind they will each have to be around 33" long to get your tuning frequency where you want.

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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Cool, thanks so much for the help! I probably should have mentioned the box dimensions because that will affect the length of the ports. The usable width is 38.5", height is only 7.5", but the depth can be up to 14". That being said, I'll have to bend the ports around the back of the box. Does it matter how long the bend can be? 

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Sorry, I'm so confused. Why do all the port calculators say I only need one or two aero ports. For instance, I used the calculator at http://www.decibelcar.com/apps/108-slotcalc.html and it says for an enclosure volume of 2.25, tuned to 32 Hz, I can use (2) 3" round ports with a length of 14.34" each. Are these calculators incorrect, or am I just reading this wrong? Sorry again for all the Noob questions.

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1 minute ago, aburger said:

Sorry, I'm so confused. Why do all the port calculators say I only need one or two aero ports. For instance, I used the calculator at http://www.decibelcar.com/apps/108-slotcalc.html and it says for an enclosure volume of 2.25, tuned to 32 Hz, I can use (2) 3" round ports with a length of 14.34" each. Are these calculators incorrect, or am I just reading this wrong? Sorry again for all the Noob questions.

So that tuning calculator you listed is correct, you could use two 3" round ports 14.34" long and that would tune your box to around 32 Hz.  The problem is while two 3" ports will give you the tuning you want, they aren't going to be enough port area and you will have issues because of that.  

If you look at the Minimum Usable Vent Diameter calculator at the top of the page and put in the info for your setup, it tells you you need about 35 sq in of port area.  Here is a screen shot:
image.png.5f0d37563c407e3d94de46ddc7c40920.png

I will warn you though, the formulas used to develop that particular port area calculator are based on work that was done over 30 years ago and it isn't always reliable with modern subs.  To properly determine how much port area you need you have to take input power into account as well.  In this case the calculator above was very close to what Sundown and I were recommending, but that isn't always the case.  I've developed my own port area calculator that does a better job IMHO.  You can see it here: https://goo.gl/STAv4p

"Nothing prevents people from knowing the truth more than the belief they already know it."
"Making bass is easy, making music is the hard part."

Builds:

U7qkMTL.jpg  LgPgE9w.jpg  Od2G3u1.jpg  xMyLoO1.jpg  9pAlXUK.jpg

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Thanks again! I actually downloaded your calculator the other day and totally forgot to look at it. I've been trying to figure out the best option for a while now and I keep confusing myself. I'll plug the specs into your calculator and read up more to see if I can understand this a little better.

 

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