Can you do a straight port with a 2" bend?

[Umbra]

I do realize that would no longer be a straight port, but I couldn't come up with a better title.

I made this thread in the Enclosure Design subforum about a month ago and didn't get any feedback. Since I'm asking for opinions I suppose it's worth posting in GD.

My brother does pro audio - mostly sound reinforcement, which is taking the sound from live performers and having it fill the venue.

He needs a sub (or two, but one for now). Rather than buy a $700 passive prebuilt with a $150 driver in it he wants to buy a serious driver and build a box for it with my help.

This is the sub he's purchased, a B&C 18SW115:

B&C Speakers

As per their 5.3 cuft and 35Hz tuning recommendations, here's my Torres design:



I haven't worked out bracing yet, so I'll tweak the numbers a bit. The height and width match grilles he's purchased, so I don't have play there. My concern is with the port length. In car audio the box is often shallow, so L slot ports are common to get needed length. My problem here is the depth is such that I could do either a straight port without a bend (ending a few inches from the back) or make it L shaped and add a bend at the back of the port (albeit a very short one - just a couple inches or so).

I know if the port ends too close to the wall it raises the tuning. I've heard you want at least the diameter of the port worth of clearance, but I don't know how that works for a rectangle. I don't know if adding a small bend alleviates that problem or if it creates new ones.

Any insight, concerns, or comments you'd like to make would be greatly appreciated. Three weeks ago this was in the planning stages, but now that he has the driver in hand I'm sure as soon as the weather here stops being ****** he'll want to build.

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[Jeffdachef 5,000+ posts]

i dont really think you need that much port area with a sub with low excursion. Port too close to the rear wall lowers tuning not raise because thickness of the port will start acting like port length.

I'd look into getting a proper horn loaded port design instead of a regular ported if you want concert level performance.

 

[Umbra]

i dont really think you need that much port area with a sub with low excursion. Port too close to the rear wall lowers tuning not raise because thickness of the port will start acting like port length.
I'd look into getting a proper horn loaded port design instead of a regular ported if you want concert level performance.

I thought the port area was just enough to prevent noise and seemed like a reasonable amount. If I'm way off, let me know.

You're right, it does lower tuning and it makes perfect sense if you think about it. I had a brain fart.

I hadn't considered a horn enclosure until you mentioned it. From my very brief research it sounds like they don't work well with low tunings and lots of power. I can't comment on the validity of those statements, but we went with a slot port because that's the design companies like JBL and Yamaha use, so there must be a reason. He wanted to build something comparable.

He dragged me out into the cold and we built something. It's not finished, but it's close. It reminds me of a front loading washing machine.

The holes on the sides are for handles and the holes in the back are for connectors.

The port doesn't have a division/brace down the middle; I just stuck that in there for assembly and drying. I could secure it, but I feel like that will reduce the port area and probably mess up the tuning. I was thinking of replacing it with a bolt or threaded rod for support. Thoughts?

I meant to put a 45 piece in the corner of the port, but forgot as the sun was setting. I can still glue one in there. Maybe also in the corner opposite it. Here's a crappy sketch to illustrate:

My main concern is still with the port length. I ultimately went with a 23" long port in a 23" deep box. I said "**** it", I'll figure it out as I go. The way I put it together I figured if I ended the port 3.5" inches from the back wall it'll act longer, as if it's trying to turn. If I drew a line down the middle of the port and had it turn 90° til it left the port space, then measured it it would 23" long. I'm 99% sure this logic is flawed in retrospect, but it made sense when I was numb from the cold. Is it close, though? Can I add a bit off length to correct this?

And bracing, should I add a board or a threaded rod somewhere in the middle?

I've long given up on having it perfect, but tuning and volume wise, I think it's within 5%. After taking about it for a month we're close.

When it's warmer, maybe next month, I'll make another box for my sa-18.

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