Voxel - a mini-sub+

[Wolf]

Otherwise, I am a bit confused on the port itself... I found this build thread that used a totally different port, with supposedly good results:
http://techtalk.parts-express.com/fo...234#post975234

I don't understand how this guy used a 3' I.D. x 4.5" long port and got the right tuning out of the box. Am I missing something?

You're not missing anything. That project builder mistakenly thought port tuning was a function of volume in the port, and made the port larger diameter and shorter to get the same volume of port spec. Larger port diameter = longer vent, so you are thinking correctly.

Later,
Wolf

[Millstonemike]

No, 1/4" of breathing room for that port would not be enough. I believe the general rule of thumb is at least the internal port diameter away from the wall. It could be a down firing port and still use an elbow. You could also look at using standard PVC and possibly even using two or more elbows. Good luck!

+1. PVC elbows are an easy solutions. Just be careful the "nominal" PVC diameter is rarely the actual diameter. For reference a 1.5" PVC pipe has an actual internal diameter of 1.61". That will require a slightly longer port for the same tuning.

[KEtheredge87]

Thanks Mike, Wolf, and Kevin. There will certainly be some caliper measurements to make sure the diameter of all the port parts are up to spec. Assuming I used PVC pipe instead of the port tubes, how critical is the internal flare? I ordered all the Parts Express stuff tonight, so I'll have two port tubes on hand to tinker with soon. I could always frankenstein a port flare from one of those tubes on to bare PVC if I'm careful.

Also, I intended to post some more design updates after Kevin suggested two elbows as a possibility, but my SketchUp kung-fu isn't feeling all that strong tonight. I hate working with the revolved features like the port flare in sketchup. ProE is so much easier for that. Maybe I'll get more gumption after the parts show up and I get to tinker hands-on.

[Kevin K.]

Assuming I used PVC pipe instead of the port tubes, how critical is the internal flare? .

I would address you by first name but don't have a clue what that would be based on your membership name.

Flares are not essential but can be beneficial if you are running a port diameter that's closer to being to small as compared to being to big. It's all about the vent velocity, to much of it and you will hear "chuffing". I haven't modeled Paul's Voxel in Bass Box so can't give you a recommendation on the flare, perhaps Paul or someone else will chime in with that answer.

Either way, you are modifying this design enough that verifying the tuning would be a good idea. I would suggest picking up the DAT's hardware. If you're planning on building more speakers in the future and want to attempt some of your own designs, this is really a good tool to have, lots of uses. You may also find that your driver's T/S parameters are a little different from the one that Paul measured for his original design. Sometimes the drivers vary from one run to the next and this might require a small change in the volume of the enclosure to accomplish the same tuning. Here is the link: http://www.parts-express.com/dayton-...ystem--390-806

[KEtheredge87]

I would address you by first name but don't have a clue what that would be based on your membership name.

I like the way you said that... very professional! My name is Keith. I thought about the whole name vs. screen name deal when I was signing up for the forum, but it was easier to remember the same email / screen name for everything. I added it to the signature line, so hopefully that's a bit clearer from now on.

Thanks for suggesting the DATS package. I'm intrigued and will probably buy it just for the fun if nothing else... what's an engineer without his fancy tools after all? Assuming I get the software and measure a difference in the parameters over what I expect, the next steps would be something like BassBox or winISD? I don't have experience with those tools outside of their names, but since I'm going through the trouble of tweaking the design this heavily I may as well provide the total service package and make some results!

[Millstonemike]

... what's an engineer without his fancy tools after all?

Huh, I did my entire boombox build, modified digital amp with electronic LP XO and passive HP XOs with only a $5 DMM from HF. A lot of guess work / intuition along the way.

Got me thinking about pulling the trigger on laptop based $100 Oscilloscope for the next project.

Forgot to add a tip: 1.5" PVC can be embedded in MDF using a 1 7/8" hole saw. After sawing the hole, removing (e.g., hand sanding) a slight amount of material from the inside diameter of the hole may be warranted depending on the brand of hole saw. Then, camber an edge of the PVC pipe and it will press fit it into the hole, no gluing required. The press fit may require some effort. After that, you can use a smaller router round-over bit for the external flare (or fashion via hand sanding). The press fit has held up for the entire beach season with the unit being lugged around every day. This is pic after the season, no cracks or seams appeared. The 1 7/8" hole saw is a rarer size - got my from amazon for less than $10.

[Kevin K.]

Couple of suggestions Keith. Once you move forward with the purchase of DAT's, start a new thread for your build. Title it "Down-firing Voxel with SA70" or something like that. We have managed to derail Paul's original thread somewhat and it would be better IMHO if you created your own for this build. You will probably have more questions for your build and the answers to those questions would be directed towards your version of the Voxel. Assuming you purchase DAT's, download WinISD and play around with it. Lot's of guys use it around here and you can't beat the price, FREE! I believe there are a couple of more freeware versions to pick from also.

[KEtheredge87]

We have managed to derail Paul's original thread somewhat

Quite right... Sorry Paul! For what it's worth, your Swope HT designs are still my pride and joy in the living room!

I'll start a new thread soon.

[barrymossel]

If I would implement a rectangular port, should that be like 0,4 inch?

[Chris Roemer]

If you keep your x-sectional area the same (as a 1-1/2" round vent), then the same port length will give you the same tuning.
If you had a slot mouth of 0.4" x 5", I THINK you'd need to go a tad longer (for the identical tuning).

[barrymossel]

I have been playing around a bit with WinISD and I think I have the right dimensions now... Although based on the T/S parameters by the manufacturer...

[Drjay]

I just completed a Voxel with a 70 W PE plate amp using Kevin K's construction diagram and it sounds great. A very nice match for my Overnight Sensations. Thanks, Paul C. and Kevin K.

[Millstonemike]

I just completed a Voxel with a 70 W PE plate amp using Kevin K's construction diagram and it sounds great. A very nice match for my Overnight Sensations. Thanks, Paul C. and Kevin K.

We don;t believe you. Show us a pic

[Drjay]

Well, if I can get them to upload, here is the proof of build. I am not too pleased with the cosmetics. Every joint shows, despite white glue impregnation and many coats of shellac but it stays under the desk and sounds great.

[Kevin K.]

Well, if I can get them to upload, here is the proof of build. I am not too pleased with the cosmetics. Every joint shows, despite white glue impregnation and many coats of shellac but it stays under the desk and sounds great.

Nice!

Yea, the joints and seams are a pain and difficult to hide. There are a couple of threads here on the forum with different approach's to eliminate the problem. Fiberglass resin has worked really well for me. I use an industrial version but here is a link for something that could be purchased at a Home Depot.
http://www.homedepot.com/p/3M-Bondo-...0122/202077790
It may take a couple of coats and is usually ready to sand within a couple of hours. Can also be accelerated with a hair dryer if its cooler weather. I know it's "to little, to late" for this build but you may build something else in the future and want to give it a try.