CSS SDX10 Ported Build Thread

**Mike P.** · **02-11-09, 11:16 PM**

Owen, there is a problem. I assumed the 24.5 tuning with a 3 inch port was "designed". I have discovered that with 300 watts and a 20.4 HPF the port air speed will be 40 m/s.

That's well into port noise territory. By increasing the port length to 25 inches, including both flares, the tuning drops to 21.5 hz and the airspeed is 30 m/s, which won't be a problem. Since you don't have the room for a 25 inch port, you'll need to use an elbow and turn the port up. It's the only solution I can think of.

**Owen Bartley** · **02-12-09, 06:34 AM**

Ben: I had actually been considering that, and specifically remembering Thomas W's Klone. When test fitting some bits last night I even thought about a rear facing port that I could easily build up 3/4". I think it's still an option, but I would have to get fancy with the grille in that case. If I'll see a large improvement, I think I would do it.

Mike:

That will eat up a lot more interior volume too. I guess I could always go back to the original plan and leave the flares out. Would keeping just the front flare with a total length of 17" be what you calculated to 40 m/s? I'm sure I'll end up running into size constraints with a bend as well, because the amp protrudes into the back wall a little.

**Mike P.** · **02-12-09, 08:55 AM**

40 m/s is with the flares. Port noise at that speed will be worse without them, and the end of the port is too close to the sub wall. Your cabinet volume is 2695 cu. inches. An extra 8 inches of port would take up 57 cu. inches. You can try it as you stated, if noise is an issue you can always make some adjustments later.

**annunaki** · **02-12-09, 02:51 PM**

In my opinion, even 30m/s is too high of a vent velocity. I prefer to keep the vend velocity around 17m/s. At 30m/s there is a fair amount of port compression that is building, limiting overall output as well as clean output capability.

After seeing the final layout, I would have opted for a slot vent along the bottom of the enclosure.

Similar to this:

**Mike P.** · **02-12-09, 04:09 PM**

Port compression starts at 26 m/s from what I/ve read. You can get port noise at 30 m/s with test tones, but it's not an issue with program material in most cases. At this point his options are limited without doing a rebuild.

**annunaki** · **02-12-09, 06:16 PM**

Quote:

Mike P. wrote:

Port compression starts at 26 m/s from what I/ve read. You can get port noise at 30 m/s with test tones, but it's not an issue with program material in most cases. At this point his options are limited without doing a rebuild.

Mike,

I would assume that if the port hole has not been cut into the baffle, it is still an option. A folded slot internally may still be viable, though the displacement may be counterintuitive. I am surprised no one suggested it earlier.

**joorge** · **02-13-09, 02:01 AM**

I am dealing with a small ported box, too. I wanted to use those pretty flared ports, but just didn't have room to meet all the guidelines for port placement.

I finally decided on a folded, square port. All the fitting problems disappeared and construction was simple.

You may find that a 4 1/2" x 23-24" with a max speed of 17 m/s will work. That's just a guess. I'm sure it will turn out nice whatever you decide to do.

**Owen Bartley** · **02-13-09, 08:08 AM**

Thanks everyone, I hadn't considered a slot port, but at this point it could still be an option. I haven't cut the mounting hole for the flare, so it could work. I can always find another project to use the flares in, so no problem there.

George, would I really need it 4 1/2" ?? That seems huge! Can I reduce that to shoot for a tune in the low-mid 20's, with airspeed closer to 30 m/s? I'm with Mike, thinking that on program material I'll be fine, especially since this will be the smaller of 2 subs I'll be using for a while. It won't be cranked to the max.

When I get home tonight I'll post the actual dimensions I have to work with. I assume I can use 1/4" or 1/2" MDF or something thin so it eats up less volume?

**Bent** · **02-13-09, 09:05 AM**

Owen, I haven't run the numbers for your project in unibox, how short are you for clearance at the rear of the port?

I don't know for sure, but I'd think with a rear flare you could go a "bit" closer to the rear wall than with a straight but-end of a pipe.

**annunaki** · **02-13-09, 09:58 AM**

What is the internal width of the cabinet? .5" mdf would be allowable to help keep displacement down. I would try to brace the port though to help strengthen it. That, or build the port from some spare .5" 13 ply birch (from a cabinet maker?). It is stiffer & stronger than MDF.

**Bent** · **02-13-09, 11:42 AM**

Owen, is this a possibility?

**Owen Bartley** · **02-13-09, 01:14 PM**

Ben, that's what I was thinking about doing. I'd have to make the grille fill out the rest of the face, which could look kind of cool. Also it would keep the port out from behind the cloth which I like.

That would give me 20 1/2" of total room, which means about 18" of port length including both flares. I'm still an inch short of the length Mike calculated, but that might be acceptable.

**Bent** · **02-13-09, 01:23 PM**

You could prolly flush trim an entire new front cover - remove the flare base with a jig saw, which would ensure a symmetrical match-up and then cut the big piece out to make the grill.

or do it the way I sketchup'ed, and use the flare base as a cut-out template for something like a 1'2" thick piece for the grill

**joorge** · **02-13-09, 01:43 PM**

Owen,

I just took a stab at the numbers, but here's one way to do it accurately for your actual numbers. I use UniBox and just arbitrarily increase the size of the port until everything looks good. The port size is no longer limited to commercially available tube sizes.

Once ya get the number that works best, determine the area of that size opening (UniBox provides it). Take the square root of the area and you have the length of one side of the square port.

The advise I received was to use the port length as calculated in your program. Some advise a small correction factor, but I am going with the advise provided here.

You measure the length of the port to the center of the 90* turn in both directions. As to the volume used by this method, it doesn't change much from using a round tube. Only 2 sides of the square tube count towards the volume calculation. You also gain back the volume used for the round tube braces.

Edited to add: There is no need for bracing if you start in a bottom corner. It will be the strongest part of the box. I am stopping the port just over 1 diameter from the rear panel and starting up toward the top.

**Owen Bartley** · **02-15-09, 10:13 PM**

Quick update... I had time to do a little planning and a little work tonight. I decided to go ahead and add the extra 3/4" panel to the front corner and mount the port to it, as Ben suggested. This just ended up being the best compromise for me.

Lining up the new panel and transferring the lines to cut

The two pieces

I think I got a little carried away with the smoothing, and my pieces don't match EXACTLY, but by the time the fabric is overtop, I'm sure it will be fine. Tomorrow if all goes well I'll get the grille piece finished, and maybe even get the box braced and assembled.

**ISLAND1000** · **02-15-09, 11:07 PM**

Hey Owen,
You guys are getting just a little too slick for your own good. That's a mighty fine answer to a tough question. What're you going to name that front panel . . . . I mean what technical jargon are you going to use in the "Audiophile" discussion group to describe your product?

**Owen Bartley** · **02-15-09, 11:57 PM**

Heh... well it was called a "front baffle port spacer" HERE, so let's just stick with that. I'm happy with the way things are going so far, and I can't wait to start assembling.

I had another thought when mocking up the enclosure this afternoon. Would stuffing with some polyfill give me an effective increase in volume? I was planning to use some foam on the front and rear walls to help deaden reflections, but didn't think about stuffing until today.

**ISLAND1000** · **02-16-09, 01:06 AM**

Theoretically, stuffing the box, including foam and/or polyfill, will increase the "apparent" box size as much as 10-15%. To get the maximum apparent size increase will require several pounds of fill. The box will be filled but not necessarily having to squeeze the stuffing in.

**Mike P.** · **02-16-09, 03:43 AM**

Rule of thumb is one pound poly fill per cubic foot of box space. Along with making the box appear 10% or so bigger, it also has the effect of making the port appear longer so the tuning point will drop. The downside of poly fill in a ported cabinet is port output is reduced.

**Owen Bartley** · **02-16-09, 09:36 AM**

Thanks Mike. I couldn't remember what the drill was in a ported enclosure. I will definitely be stuffing this project, and it sounds like with the effective increase in volume and port length I'll be back to (or slightly ahead of) the numbers I designed for.

**Mike P.** · **02-16-09, 10:06 AM**

I'm definitely waiting to hear your impressions when the sub is done. Your port air speed and proximity to the cabinet wall is going to make or break some port "theories". Nothing better then real world results.

**Owen Bartley** · **02-16-09, 10:29 PM**

Yeah, I'm starting to get a little nervous about that port now... but it's too late to change it anymore! I didn't quite get fully assembled today, but only the back and top are still to be glued on. I can get those taken care of tomorrow night, and then when I'm back home on Saturday, I should be able to at least get a coat of primer on, possibly after a quick test.

Progress since last update:

Cutting out the grille corners with a hole saw

Holes drilled for the plastic mounting cups to attach the grille

Edges rounded over for a nice smooth look, and so the cloth won't tear

A quick mock-up to make sure everything fits

A look inside at my staggered side wall braces

The braces were attached with glue, and screws, done with the pocket hole jig. The same was used on the front and back walls, to really anchor everything together.

Clamping the front baffle (it got screws shortly after the test fit)

I guess I forgot to take a pic of the rest of the clamping, but after a little tinkering, we got the front, sides, and bottom all attached. There were a few minor problems along the way, mostly because I've never built such a tightly packed box before, but overall things are still looking good. Hopefully more tomorrow.

**Bent** · **02-16-09, 11:11 PM**

It's funny, but this thread about the little 10"er has my interest held like nothing before.
It's looking really good so far.
I can't see the little deviations from "optimum" design altering the final result too much, I doubt the slightly crowded port flare will be audible either. Consider it this way, your attention to detail is at least double what any commercial manufacturer might use - so you can expect similar results.

Have you considered finishing options?

**ISLAND1000** · **02-17-09, 12:04 AM**

A, "Pocket hole jig" ? . . . . . alright everybody that owns and uses their pocket hole jig to assemble their sub enclosure raise your hand!! No, not you Owen, I mean everybody else . . . . . anybody???
Wow! Owen . . . . I guess you're kinda unique.

**Owen Bartley** · **02-17-09, 06:56 AM**

LOL... thanks guys.

I'm still not sure about the finish, but I think I'm leaning towards a satin or semi-gloss black, with a couple of clear coats (also satin). The front baffle I'd like to do something fun with, and I'll probably apply fabric of some kind, which will only be visible when the grille is off.

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