Aura NS6-255 and Vifa BC25SC TM

[donradick]

Thanks to many patient gurus here who have helped me with many aspects of simulation and modeling. I found some cheap drivers, the Aura NS6-255-8A mid-woofer and the Vifa BC25SC06-04 tweeter. Since everyone seems to need to name their creations, I dub them AURBACS. Here is the first test box, about 14 liters, ported - Unibox predicted about a 63 Hz F3, which would make them good for HT surrounds. A crossover cobbled together from my junk box sounded pretty good, so the final design was a go.

[donradick]

I really liked the basic sound of the drivers, but frankly, the bass was a disappointment. Not sure whether I had messed up the box tuning, but Unibox predicted a F3 of 43 Hz with a slightly larger box. That sounded more like it!

[woodtradesman_audio]

Awesome.

I am glad to see this project finalized. Your work on this build is much appreciated.

[greywarden]

you can import the frd file to unibox in the "active filter" section or w/e and get a better idea as to the bass response.

[donradick]

The "final" box was constructed of 1/2 inch red oak faced plywood from Lowes. In retrospect, not a great choice, but I didn't want to drive 30 miles round trip to buy baltic birch. (Not to self, next time, make the drive!) Outside box dimensions are 16H x 11.5D x 9.5W, yielding a .84 ft ^3 inside volume. Since the box was a bit too big for 1/2 inch, I added several braces, and a lip of 3/4 inch ply to attach a removable 3/4 inch baffle. Port is 2 inch inside diameter PVC and 4 5/8 inch long. Unibox complained a bit about port air speed, but I knew that I was not going to play them very loud.

[donradick]

you can import the frd file to unibox in the "active filter" section or w/e and get a better idea as to the bass response.

Sorry, Grey, I have NO idea what you are talking about!

[donradick]

I'm sort of proud of this - the most clamps I've ever used.


I used corner clamps and brad nails to secure the basic box. Not real satisfied - the pieces still shifted a bit, and the wood filler is still visible after finishing.

[donradick]

Finished boxes came out all right - I'd decided that I wanted a black baffle with light sides and top. Used a 3/4 inch ply for the baffle, and (per LouC), hit it with sanding sealer, Krylon satin black, and Krylon satin clear. Sides were finished with a couple of coats of Deft satin.


Here you can see the imperfect match of the brad nails with generic wood filler.


My wife was SO kind, she said they were very beautiful, that she didn't know I could make something so perfect. (aaawww....)

UPDATED BAFFLE PLACEMENT INFORMATION:

One of these days, I should post a nice drawing. For now, this is what I built:
Overall baffle dimensions: 9 1/2 W X 16 H
NS6 woofer: centered left to right (4 3/4 inches), center of woofer is 9 inches from the bottom of the baffle.

Vifa BC25 tweeter: 14 inches from bottom of the baffle to center of the tweeter, tweeter center is offset left of right of baffle center by 1 1/4 inches (mirrored offset per pair). Or you can think of it as the edge of the tweeter is about 5/8 down from the top, and about 1 7/8 in from the respective left or right baffle edge.

Port is centered left to right on the pack, center of hole is about 4 5/8 down from the top of the box.

[donradick]

I learned a TON about simulation and modeling on this - thanks once again to Jeff Bagby, Wolf, and Paul Carmody. Here are the PCD screen shots with all the details. I went through many crossover revisions - finally settled on stock values as much as possible, and played with the resistors in the "legs" to get a decent frequency response and good phase matching. I found that as little as .1 ohm would really affect the null. I finally got a 50 dB null, and decided that was as good as it gets.

Null actually goes to 50 dB. I really don't notice the slight bobble around 1-4 K, and the bass does not sound like it drops - which is probably due to imperfect BSC modeling on my part.


Woofer crossover and low pass


Tweeter crossover and high pass


Filter transfer functions


System Impedance

[donradick]

Crossover bill of materials (Parts Express) for a pair:


The final BOM should have:
Qty 2 1.20 mH 18 guage
Qty 2 .20 mH 20 gauge

A crossover schematic:


And a pic of the finished crossover:


(I paralleled a 1.0 and 1.2 to get .57 for R12)

[donradick]

Subjective eval -
Very good bass, clear and balanced mids, clear highs, with dynamite imaging both side to side and back to front. Well exceeded expectations for $100 a pair. I tried playing with the tweeter level several times, and never wanted more, but I felt highs were a bit recessed when I cut them down a bit.

I'd post measurements, but I'm having trouble getting reasonable results from my hardware at this time. The sims correlate well with what I am hearing.

[woodtradesman_audio]

Nice work Don. its good to see that a build like this can be had for Just under a hundred bucks.

I like it so much that I'll be building me a pair in natural 5/8" baltic birch in the near future.

By the way my Karma Indignias are done. I'll post pics pretty soon.

[XtremeRevolution]

Nice design. I can finally see everything!

I actually ended up getting the parts I needed for nearly the same price from erse audio even having to run 6uf and 1.5uf caps in parallel for the 7.5uf component. The crossover parts ended up costing $47 per speaker including shipping and I used their Pulse-X caps. I ordered enough parts for 3 pairs of these.

My brother-in-law is building these as his first set of speakers. Prior to this, he's never used a table saw, a router, a dremel a soldering iron, or even seen a crossover diagram.

Boxes for this design are 19L, 8" wide x 16" tall x 14" deep. Should be a 5.75" port length for a 43hz F3 as you mentioned in our emails.

I'll get some pictures up of how we're doing as soon as I get a chance.

[50 watt head]

Wow, Don, that's a nice design. The finish on your cabs looks great, and I like the contrast of the black baffle. Well done!

[greywarden]

Wow the GRS from Johnny and this one are $4 different on the BoM! Sounds like a "sound-off" to me!

I noticed that in the test box, the tweeter was centered, and in the final it's offset, is that going to affect the FR any?

[donradick]

Wow the GRS from Johnny and this one are $4 different on the BoM! Sounds like a "sound-off" to me!

I noticed that in the test box, the tweeter was centered, and in the final it's offset, is that going to affect the FR any?

The test box was definitely "quick and dirty" - once I got into playing with Jeff Bagby's Baffle Difraction sim, it was obvious that the tweeter would be a bit smoother if offset. Couple of things in this regard - first, I "forgot" to mirror image the baffles - both tweeters are offset to the left (lol). Second, I'd originally planned for the woofer to be lower on the baffle, but glued in one of the braces in the wrong position, so the woofer ended up centered top to bottom - not the best pos for ripple.

I'd almost like to ship them to Dayton for the Midwest Audio Fest, but my wife would chew me out every day they would be gone - she likes them that much.

[donradick]

Thanks everyone for your interest and support. It's a real pleasure to be able to give back to the community!

[XtremeRevolution]

The test box was definitely "quick and dirty" - once I got into playing with Jeff Bagby's Baffle Difraction sim, it was obvious that the tweeter would be a bit smoother if offset. Couple of things in this regard - first, I "forgot" to mirror image the baffles - both tweeters are offset to the left (lol). Second, I'd originally planned for the woofer to be lower on the baffle, but glued in one of the braces in the wrong position, so the woofer ended up centered top to bottom - not the best pos for ripple.

I'd almost like to ship them to Dayton for the Midwest Audio Fest, but my wife would chew me out every day they would be gone - she likes them that much.

Well then, that just makes me want to push my brother in law to build his faster. I know for a fact the drivers get extremely loud with some free air testing I did. Keep in mind the kid is only 17 so having him build stuff like this is a huge learning experience.

Thanks everyone for your interest and support. It's a real pleasure to be able to give back to the community!

Its a real pleasure getting a design like this to work on.

[2leftthumbs]

I "forgot" to mirror image the baffles

been there done that

[2leftthumbs]

but Unibox predicted a F3 of 43 Hz with a slightly larger box.

When I plugged in the numbers I got from the wt3 instead of the factory #s I got an f3 in the mid 50's. Truth is probably somewhere in between.