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4th May 2017, 07:37 AM  #1 
diyAudio Member
Join Date: Oct 2016
Location: In Flanders Fields Gender: Female

[urgent] Slot ported version of The Tango
Hey everyone,
I'm sorry if it comes across as a bit selfish or alike, but I'm in a rush for school. In two days I have to order my parts and give my teacher the plans, and I haven't gotten any luck with the time stretching designer I hired before. I'm looking to replace the round port design by a slot port on bagby's design of The Tangos. I need them to perform equally well as the round ported ones but I don't know how to do it. I'd appreciate it if someone could help me out, and save my GIP. Thanks in advance, Anna 
4th May 2017, 08:12 AM  #2 
diyAudio Member
Join Date: Jan 2009
Location: Belgrade

Calculate surface of the circle using inner diameter of port tube. Use the same surface for slot port. Pipe depth remains the same regardless of port shape.
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Not for fainthearted Last edited by Zvu; 4th May 2017 at 08:21 AM. 
4th May 2017, 01:51 PM  #3 
diyAudio Member
Join Date: Oct 2016
Location: In Flanders Fields Gender: Female

I don't know and never understood how to do that. I don't have time to spend tedious hours learning it.

4th May 2017, 01:59 PM  #4 
diyAudio Member
Join Date: Aug 2006

What port diameter is specified?

4th May 2017, 02:13 PM  #5 
diyAudio Member
Join Date: Oct 2016
Location: In Flanders Fields Gender: Female

I will elaborate at home, but the specifications say 2" port that's 7inches and 3/4 including the 3/4 inch MDF in the back.
I'm not able to figure out myself how to add a tuning port without messing up internal volume because that one needs to stay exactly the same. Thanks for the help. 
4th May 2017, 02:50 PM  #6 
diyAudio Member
Join Date: Feb 2008
Location: Sheffield

Then you need a slot port with the same crosssectional area as the 2" diameter round port, it needs to be 7.75" long, and once you've done that, you can play with the cabinet depth a little to get the volume the same as the original.
Hint: the volume of air inside the port is the same for the round or slot port, so the volume you've used is the difference between the volume of the wood for the slot port, and the volume of whatever material the round port was made of. Maths lesson: The crosssectional area of a cylinder is just the area of the circle. Circles are unique in that a single number can be used to find a lot of different things. That number is the radius, the distance from the middle of the circle to the edge. The radius is also half of the diameter. If in doubt, draw it out  that'll make it pretty obvious. Now, there are some simple equations we can use to find out various things about this circle once we know it's radius. Lets say I've got one of those plastic ports that have a flare at one end, and I want to find out the length of a strip of foam I need to go around it. Going all the way around is called the circumference, and it's simple to find. C = 2*(pi)*r Where.. C = circumference (pi) = 3.141592654 (a unique number that perfectly describes the ratio of a circle's circumference and diameter) r = radius. Since the diameter, d, is equal to 2*r, we can also write C = (pi)*d So far, all of our units are a distance, and they're consistent. A circle with a radius of 0.5cm will have a circumference of 3.14159...cm. A circle with a radius of 0.5m will have a circumference of 3.14159...m. The area of a circle is a little more tricky, since we're starting out with the radius, which is measured as a distance, and we're getting out an area, which is measured as distance^2 (squared) A=(pi)*r^2, or A=(pi)*r*r. Those two equations mean the same thing,. Raising something to the power of 2 means you multiply it by itself. A power of 3 means you multiply it again. You'll learn more about that later in your academic career. In your case, the port is 2" diameter. That means the radius is 1", or 2.54cm since you really ought to be working in Metric, and don't let the Americans tell you otherwise. So, r=2.54cm. Put that into the area equation and see what you get. Chris Last edited by chris661; 4th May 2017 at 03:04 PM. 
4th May 2017, 02:54 PM  #7 
diyAudio Member
Join Date: Oct 2016
Location: In Flanders Fields Gender: Female

Hmm thanks that makes alot of Sense. So. If the round one is by corners 2*2 then the slot port can be anything multiplied that multiplies to the same as 2*2 like 1*4 or .5*8? Correct me if I'm wrong.

4th May 2017, 03:05 PM  #8  
diyAudio Member
Join Date: Feb 2008
Location: Sheffield

Quote:
Chris 

4th May 2017, 03:41 PM  #9  
diyAudio Member
Join Date: Oct 2016
Location: In Flanders Fields Gender: Female

Quote:
And afterwards would you mind checking what I tried? Thanks. Oh and hey, I'm making the box from the imperial plans and i'll do the port in the imperial plans too. Then I'll just rework it to metric. 

4th May 2017, 03:42 PM  #10 
diyAudio Moderator

The lack of basic math skill is shocking, what are they teaching in school these days?!

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