Is Option 1 better than Option 2? If so, how much?
I'm in the process of wrapping up the ports, etc inside the subwoofer cabinet I'm working on in this thread:
Nearfield Bass Cabinet
I've got two square 6"x6" ports in the main volume of the cabinet for one UM18-22 @ around 11.3 cubic feet. The box should be tuned around 16-17Hz so both ports are 50" long and they both have two 90 degree bends.
As you can see below, the ports exit the cab at the bottom corners of the cabinet, they each run along one end of the cabinet, then turn up and run along the back of the cabinet, then turn in and run along the top of the cabinet a short ways before opening up into the cab interior.
My question is about airflow at the 90 degree bends. Most slot ports I see have panels fit at right angles on the outside of the corner and on the inside corner. Some, maybe most, have a roundover on the inside edge of the turn. But most are only 1" to 4" tall and don't bother with any smoothing or filling of the outside corner. I would guess that in most cases it isn't necessary and wouldn't really add anything to the function of the port and specifically the bend in the port. I know air is fluid and has a boundary layer and in most places where there are gaps, holes, troughs or recesses, the air in the recess will sit pretty still and the moving air will flow right over it. I have seen pics of turns like this where the air in the outside edge of the corner has some turbulence, but may not really flow and just acts as a boundary for the air moving around the bend.
Some builds do have a small panel at port turns at 45 degrees to help the air turn in the 90 degree bends.
On my port though, there seems to be a pretty significant recess in the outer corner of the 90deg bend where the air can sit and maybe turbulence could be a problem. Due to the shape and size of my port, I was wondering what would be best.
So my question is, between these two options:
1. With curved piece filling in the outside corner/recess of the turn
2. Without anything in the outside of the corner, just two straight pieces attached at a right angle.
(there is a small 3/4" roundover on the inside the corner)
Is Option 1 better than Option 2 for airflow?
How much better is Option 1 than Option 2? (If it is)
Are there any specific or proven advantages of the one or the other?
I don't want to put in a 45 degree panel; due to the design and build so far, that isn't an option. I'll either go with Option 1, with a curved piece of plastic or wood to help the air turn and flow at the bends. Or I'll go with Option 2, leaving it as is, trusting the fluid character of air to fill the recess and create boundaries for smooth air flow. I've seen many builds which don't address this as an issue, so I'm tempted to leave it as is and not worry about it. But if I can put something in place to improve the design in a noticeable or significant way, I'm happy to do that.
(just wanted to tag a few people who had great comments in previous port and flow threads:
@diy speaker guy
like this one The Perfect Port?
that thread and the Harman paper are part of the reason I put in the flanges on the inside ends of my ports)