Rectangular ports

[mikeoddone]

I know it´s an already talked theme here but, I am still getting different answers about it, so:

Is there a big difference in the Port End Correction factor related to Port Shape?
Rounded ports 0,732 and Rectangular ports 2,227??? What´s the best ratio related to heightXwidth?
I want to build a 3way system with a rectangular port at the bottom of the box....

I am getting really different thoughts from people that are into building speakers...
Just founded this image online but don´t know how fiable it is...

 

[profiguy]

It depends on the starting length of the port and the distance from the LF driver too.

 

[GM]

'Best' is 1:1.273 according to the pioneers, pgs 248/236, column 'J'.

Example: 8" dia. vent:

circ = pi * 8" = 25.133"

short side = 25.133/4 = 6.283"

area (Av) = (8^2 * pi)/4 = 50.265"^2

long side = 50.265"^2/6.283" = 8"

ratio = 8"/6.283" = 1:1.273

Yes, though best to use the late bjorno's rev. one.

 

[WhiteDragon]

Rounded ports 0,732 and Rectangular ports 2,227

2.227 if it shares 3 walls
the walls make it behave as if longer
so correction factor makes it shorter.

For a port sharing no walls.
The typical .732

And often in simulators like WinIsd
they add correction up to .850 to .732
which is considered flared.
And only assumes non shared walls.

In real world if port sharing no
walls. But is still rather close to a
wall or great distance from the
speaker such as a tower.

You could add a little extra correction
even without flares. having no "flares"
you could still add a bit up to .850 / .9
if it is close to walls or distance from
speaker.

Square or triangle shape in general
considered less efficient as well.
So less port output.

 

[stv]

A port being located at the bottom (or any wall) of the box will output more respective enclosure resonances (because of pressure maximum at the enclosure walls).
I did some Measurements in my port resonance thread:
https://www.diyaudio.com/community/...-port-resonance-absorbers.388264/post-7487914

 

[IamJF]

The surface of the floor will make the port "virtually longer". You can realise 2 different tunings with turning the woofer upside down - port is free in the air.
Some PA systems use that effect to make port resonance a little lower when stacking woofers. But most of the time you want a stable tuning ... so keep it down there.

When the port is long enough there will be no pressure maximum in the enclosure and the resonance behaviour will change (actually it should be an half open pipe - Lambda/4, 3/4 etc).

But I don't build reflex cabinets any more, I don't have detailed investigations about it.