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Ndawg12

Subwoofer Port Ideas

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Ndawg12

So I scaled down to a 12" sub in order to build a ported box and install a heater. I now have a P3 DVC 500 watt Rockford sub. Its a little older as the newer ones are rated at 600 watts but I assume most of the specs remain the same. I think I can build the enclosure and get the suggested 1.8cf (plus port and sub displacement). The specs call for a 4" round port by 10" long. That's roughly 126ci. I would like to build a square or rectangular built-in port. What would the recommended port dimensions be?

School me up on ports.

I've also heard of problems with "chuffing" with ports like these, any thoughts on how to combat this?

TIA,

Nate

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bamabonners

From what I can remember from my stereo install days (long time ago), shape of port doesn't matter as much as long as it is flared on the ends. That should cut down on the chuffing.

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Earmark Marine

Flare the edges of the port at both ends with a large router radius. You'll be fine.

Disregard the port displacement. You can't just change dimensions in order to maintain the same port volume. You have to maintain the port length as a ratio of the port surface area in order to achieve a particular resistance. If you change one you have to change the other. That requires the application of a complex formula best left to a computer program.

So stick with the port length as is. And, change the shape of the port to round, square, triangle or rectangle as long as the surface area remains the same.

I'm trying to remember the conversion formula. Someone needs to verify this. I think it's the radius squared times pie in order to arrive at a square area. Then find the square root of the square area to come up two symmetrical dimensions for a square. From there a triangle or a rectangle is a breeze.

David

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jk13

Surface area is pi times radius squared like David said.

winisd beta is a good free download generic box builder, you can input your sub (or almost any sub really) and input your box size, tuned frequency, and round port diameter. Then you can change the round port to square and change dimensions as you want. The program will then give you proper port length for that frequency tune.

You may have to experiment a bit with tuned frequencies to get the round port close to the recommended length, then play with dimensions after.

Always flare your port. As a failsafe, that program also gives you a "vent mach" value (speed of air at port mouth). Keep it near a similar value to the original round port or lower and you should be golden.

Keep in mind if you enlarge your port surface area, it will need to be lengthened to get to the same frequency.

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Cdoogles

Since I'm also planning a ported box build this month, I thought I would add a second question to this topic. I'll be building a rectangular box with a rectangular or slotted port. I'm assuming "flaring" the port means rounding the squared edges of the port, which I did plan on doing. So, onto my question, a port isn't just a slot on the outside of the box, but has a side of the port that continues into the box several inches. How do I determine how far into the box the port extends or does it matter?

Thanks!

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Ndawg12

I would like to keep it simple, I've heard of the winisd program and it confused the heII out of me, maybe I'll look at it again.... But I'd like to keep the port length at 10" and I've fugured I need a surface area of 12.56" or 3.54" square. I don't have a problem with building a 3.54" square port but if I do that and my port is 10" deep, that only leaves me with 1.25" from the end of the port to the back wall (interior box depth is only 10.5" plus .75" for the front board). Is that enough? Or should I make it taller or wider so that there is more area at the entry of the port (hope that makes sense)?

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Ndawg12

Since I'm also planning a ported box build this month, I thought I would add a second question to this topic. I'll be building a rectangular box with a rectangular or slotted port. I'm assuming "flaring" the port means rounding the squared edges of the port, which I did plan on doing. So, onto my question, a port isn't just a slot on the outside of the box, but has a side of the port that continues into the box several inches. How do I determine how far into the box the port extends or does it matter?

Thanks!

The student becomes the teacher :biggrin: As David said earlier without using a very complicated calculation you need to use the original spec for port depth of your particular woofer. Look at the specs and look for "Dp" or similar.

You are correct, a port is not just a hole in the front wall, it needs a dimension of depth. I plan on drastically rounding the edges of the port wall. Sounds like that will suffice for the "chuffing" issue.

Edited by Ndawg12

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shawndoggy

as a simpleton, this box calculator really appeals to me though I make no representation as to the accuracy of its calculations: http://reaudio.com/box.php

Looking at the P3 specs (1.8 ft2, tuned at 40hz) and from what I can recall about what fit under the helm of my vride, I think this should work(?):

natesbox_zps40670377.jpg

Edited by shawndoggy

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Earmark Marine

I would like to keep it simple, I've heard of the winisd program and it confused the heII out of me, maybe I'll look at it again.... But I'd like to keep the port length at 10" and I've fugured I need a surface area of 12.56" or 3.54" square. I don't have a problem with building a 3.54" square port but if I do that and my port is 10" deep, that only leaves me with 1.25" from the end of the port to the back wall (interior box depth is only 10.5" plus .75" for the front board). Is that enough? Or should I make it taller or wider so that there is more area at the entry of the port (hope that makes sense)?

Even if the port terminated 3.5" from the back wall in a corner, you have effectively lengthened the port. 3.5" would be okay in a stand alone port. But absolutely no go on 1.25" of clearance.

Build your port in an 'L' shape to remedy the problem. Calculate the port length down the center of the port rather then against any interior port surface. If changing the port, whether stand alone or sharing one surface with the enclosure outside wall, make sure that you calculate any change in total port and wall displacement in your total enclosure displacement.

David

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Ndawg12

look out, one of my mspaint files are on the way.... :biggrin:

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Earmark Marine

Since I'm also planning a ported box build this month, I thought I would add a second question to this topic. I'll be building a rectangular box with a rectangular or slotted port. I'm assuming "flaring" the port means rounding the squared edges of the port, which I did plan on doing. So, onto my question, a port isn't just a slot on the outside of the box, but has a side of the port that continues into the box several inches. How do I determine how far into the box the port extends or does it matter?

Thanks!

You may be starting from the wrong perspective. A bass-reflex (ported) is a finely tuned resonant chamber. It is based on a precise relationship between the enclosure main chamber volume, port resistance and driver parameters. You cannot add a port to an existing sealed enclosure displacement. You can not change any singular element without changing the others. It's a 'from scratch' and interdependent relationship. In other words, don't put a ukulele string on a double bass body.

David

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martinarcher

You may be starting from the wrong perspective. A bass-reflex (ported) is a finely tuned resonant chamber. It is based on a precise relationship between the enclosure main chamber volume, port resistance and driver parameters. You cannot add a port to an existing sealed enclosure displacement. You can not change any singular element without changing the others. It's a 'from scratch' and interdependent relationship. In other words, don't put a ukulele string on a double bass body.

David

Lots of truth there. I've built bass reflex boxes and you need to do your homework in order to be happy with the outcome. Lets just say my take #2 turned out great and I don't like to talk about take #1. :lol:

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Ndawg12

Even if the port terminated 3.5" from the back wall in a corner, you have effectively lengthened the port. 3.5" would be okay in a stand alone port. But absolutely no go on 1.25" of clearance.

Build your port in an 'L' shape to remedy the problem. Calculate the port length down the center of the port rather then against any interior port surface. If changing the port, whether stand alone or sharing one surface with the enclosure outside wall, make sure that you calculate any change in total port and wall displacement in your total enclosure displacement.

David

Ok, so lets start here with this awesome sketch :biggrin: If my port shares the outside wall and is now 16.5" tall, will that work?

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martinarcher

No sketch, but I would sure think that would be cool......waiting for mspaint awesomeness..... :whistle:

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Ndawg12

No sketch, but I would sure think that would be cool......waiting for mspaint awesomeness..... :whistle:

Ever send an email thats all about an attachment that you forget to attach.... :biggrin: check my post again.

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Ndawg12

This is the dimensions from the ported box made for that speaker it fits perfect in my 06 V-Ride. not sure if it would fit with the heater or not.

http://www.rockfordfosgate.com/products/product_details.aspx?itemid=120451

Thanks BT, based on the outside dimensions your box is bigger (2.63cf) than I thought it would be. With sub and port displacement I need to be around 2.1cf from what I've seen. I can not got 15" deep, I'm surprised you could, I will run over top of the ventline, steering cable, heater hoses, and other wires that enter the floor back there. My max depth without severely down cutting driver footroom is 12". BTW my box will probably not be a straight rectangle because of the lines entering the floor and the heater.

Edited by Ndawg12

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martinarcher

That port design is fine if I'm reading your drawing right. You are right though, the sub specs are very important to the end result of a ported enclosure.

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Bradley Thornton

I could have went about 5 in wide and the hight is good so you may could go wider and not so deep.

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Ndawg12

as a simpleton, this box calculator really appeals to me though I make no representation as to the accuracy of its calculations: http://reaudio.com/box.php

Looking at the P3 specs (1.8 ft2, tuned at 40hz) and from what I can recall about what fit under the helm of my vride, I think this should work(?):

natesbox_zps40670377.jpg

I almost built a box to the complete opposite specs (ported vs sealed) based the owners manual online from their website. Their product is amazing, I can't wait to see what Bradley does with that monster, but I would double check some of their posted into.

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jk13

That port design is fine if I'm reading your drawing right.

Correct, other than it will lower the tuning frequency a bit compared to a 4" x 10" round port, which wouldn't matter much.

This computer won't enlarge that drawing for me so I can't quite read it all.

In a 1.8 cu.ft. box:

Rough equivalent to 4" round by 10" long if I'm reading that drawing correct is .75" x 16.5" (your dimensions right?) by 6.08" long.

Opening that up to 1" x 16.5" puts you right at 10". According to winisd, at least.

As long as your rear port entry opening (you labeled 1.25" I think) is greater than your port width (0.75") you should be good, if that was the question.

Edited by jk13

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shawndoggy

I had this box:

Screenshot2010-12-18at31543PM_zps4f46f15

plus heater and kick panel it looked like this:

P1060575.JPG

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shawndoggy

Correct, other than it will lower the tuning frequency a bit compared to a 4" x 10" round port, which wouldn't matter much.

This computer won't enlarge that drawing for me so I can't quite read it all.

In a 1.8 cu.ft. box:

Rough equivalent to 4" round by 10" long if I'm reading that drawing correct is .75" x 16.5" (your dimensions right?) by 6.08" long.

Opening that up to 1" x 16.5" puts you right at 10". According to winisd, at least.

As long as your rear port entry opening (you labeled 1.25" I think) is greater than your port width (0.75") you should be good, if that was the question.

Isn't a .75 port width REALLY narrow? Like if you are going to get noise a really narrow port would be the way to do it?

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Ndawg12

I had this box:

Screenshot2010-12-18at31543PM_zps4f46f15

plus heater and kick panel it looked like this:

P1060575.JPG

I'm really trying to stay back about 2.5-3" from where the bottom of your front panel "kick plate" is.

Edited by Ndawg12

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