Choosing a flanged port

[cjcc67]

Fellow DIYers
If you were to build Troels Jazzman ScanSpeak 3- and had a choice of two 70 mm ID flanged ports which would you choose and why:
1) 125mm outside diameter with a deeper flange/ throat made from plastic
2) 105 outside diameter shallower flange and throat plastic flanges cardboard tube.

Is there a likely to be any audible difference?

[breez]

The one with the both ends flanged/radiused. Reason: symmetrical ports have better distortion performance.

[cjcc67]

Thanks Breez
Thats a good point. I could use two of the plastic ones back to back could be used for symmetry. I was curious if the internal radius of the throat had any impact. I would guess a more gradual radius would create less turbulence. Whether that is of any consequence ???

[breez]

Yes, the radius can have an effect. If I remember correctly the radius at the end should be 0.2 times the (inner) diameter (or was it half of that?) of the port for good performance.

It's hard to see from the picture, but do any of the ports have a changing inner diameter? Different kinds of port profiles have a measurable effect on distortion, even at lower levels.

It's a lengthy read, but good stuff for DIYers: http://www.harman.com/EN-US/OurCompa...ions/11094.pdf Lot's of experimental data, good graphs and pictures. The information on the end radius is also found there.

Note in that paper, flanged port means a port with changing inner diameter and radius is what is usually referred to as flanged port around here. Some of the commercially available ports with huge radiuses start to get closer to the profiled ports, especially when the port is short in length.

[Brett]

Lots of port and flaring info here.
Porting at Subwoofer-Builder.com