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Old 15th June 2012, 09:45 PM   #1
CCU is offline CCU  Denmark
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Default How do i calculate triangular ports?

Hi

I'm building some PA speakers and i wanted to make the refleks ports triangular so i can place the on the front around the speaker unit.

But i can't find any calculator or formulas to calculate the size of the ports (that provide the same answer...)

Can you guys help me?

Thanks a bunch!
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Old 15th June 2012, 10:15 PM   #2
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As a first approximation I would probably calculate based on a square/rectangular port of the same area, as a triangle would have turbulence closer to a square than a round port, as they both have sharp corners.

A triangle has half the area of a square port of the same width and height, so I would just enter the width of the triangle base as the rectangle width and half the height of the triangle as the rectangle height.

Bear in mind that calculation of ports is only a rough approximation anyway - even if you use a smooth round tube or a rectangle it will never be exactly what is calculated because there are other variables at play that are only estimated in the calculation, such as proximity of the internal end of the port to other cabinet walls, the size of the baffle the port is located on and how close it is to the edge of the baffle etc. (Most programs assume the port is flush mounted in an infinite baffle)

Always allow room for an extra 30% length beyond that calculated and expect to trim the length down based on measurement...
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Last edited by DBMandrake; 15th June 2012 at 10:19 PM.
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Old 15th June 2012, 10:19 PM   #3
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Just a wild guess here but the true value of a triangular port would probably be closer to the diameter of the circular tube that would fit inside the triangle
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Old 16th June 2012, 12:31 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

Most sims include the necessary end corrections and rectangular ports.
So simply halving the shortest dimension should work, i.e triangle area
is half base time height, make the base the longest dimension and
plug in a port base x half height into a simulator, should be near.

rgds, sreten.
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Old 16th June 2012, 12:33 AM   #5
tvrgeek is offline tvrgeek  United States
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I too would guess closer to the round. You'll have to prototype and measure, then report back. I can see the attraction of putting ports in the corners.
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Old 16th June 2012, 12:44 AM   #6
sreten is offline sreten  United Kingdom
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Hi,

It depends on the end corrections built into simulators.

You can guarantee the end corrections are wrong for slot ports
formed with a cabinet edge or triangular ports across corners.

rgds, sreten.
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Old 16th June 2012, 12:49 AM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Moondog55 View Post
Just a wild guess here but the true value of a triangular port would probably
be closer to the diameter of the circular tube that would fit inside the triangle.
Hi,

Clearly totally wrong for a say 2" high 5" wide triangle.

rgds, sreten.
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Old 16th June 2012, 01:31 AM   #8
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Quote:
Originally Posted by sreten View Post
Hi,

Clearly totally wrong for a say 2" high 5" wide triangle.

rgds, sreten.
OK point taken, although most of the designs I have seen are of equilateral triangles, as these fit the corners of most boxes more easily
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Old 16th June 2012, 01:40 AM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Moondog55 View Post
OK point taken, although most of the designs I have seen are of equilateral
triangles, as these fit the corners of most boxes more easily
Hi,

They are not equilateral (60 degrees each vertex), they are half squares.
Equilateral does have the least difference between its area and a circle
that fits inside, but the same for half a square is clearly much worse.

rgds, sreten.
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Old 16th June 2012, 03:02 AM   #10
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Quote:
Originally Posted by sreten View Post
Hi,

They are not equilateral (60 degrees each vertex), they are half squares.
Equilateral does have the least difference between its area and a circle
that fits inside, but the same for half a square is clearly much worse.

rgds, sreten.
This is why I failed geometry LOL
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