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Originally Posted by BogeyBass  Designing ports is not that difficult , but i understand your concerns.
Which is why i stopped caring about common slot ports.....since a slot port can share either 2 or 3 walls of the enclosure...i got sick and tired of calculating correction factors. |
It's really not that tough. But yeah, it's an extra step until you've gotten the hang of it.
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Going with a flared round ports makes things easier to calculate and in my opinion eliminates errors with tuning freqs and gets rid of the chuff and turbulence of slot ports.
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Properly sized shared-wall ports do not have any more turbulence or chuff than properly sized tube ports. They do however have an advantage for lower tunings in that they require less length to get to that low tuning, and thus one can often go with a larger frontal are for the porting than they can with tubes. This then actually translates into
less turbulence and chuffing. That's why shared-wall porting is often seen in enclosures meant for high output at sub frequencies.
A very narrow space between shelf and wall translates into a bad design though, so that's a thing to watch for.
Being able to get a low tuning in a relatively compact box with a low velocity (large) cross-section is why high output low-reaching direct radiator subwoofers so often go with shelf (or four triangle) shared-wall porting.
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hi fi speakers and highend studio monitors dont use slot ports...they use round ports. nothing really extremely wrong with slot ports...but if your going to take the time to build a cabinet, might as well go with the better method
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Pretty much a case of suiting the port to the box size and purpose. Nothing to do with a type of port being lower quality or higher quality. When you get into club PA and beyond there are a fair number of slot or shared-wall ports (the two are not mutually exclusive), and direct radiator subs for the reasons mentioned above are real big on shared-wall porting.
Finding tube ports in pro sound subs often points to higher tunings or especially spacious alignments - or even sometimes, bad designs that haven't allowed enough for velocity at full power.
Mains, on the other hand, often don't need to be tuned that low, and are designed with the assumption that they will be used only above 80 or 100 Hz and in conjunction with subwoofers when big broadband SPL is desired. Thus they often have tubes, slots, whatever the designer thinks fits best. It can get pretty crazy with composite-molded enclosures these days.
Port choice, just another item to examine when doing a box design, on which types of porting to consider, and where to place them. I think the JBL website has a good tech paper somewhere on their site on flares and the best approach to using them to improve porting.
