DARPA Jr - The 2015 InDIYana Winning Micro 3-way Design

[tyger23]

All;

This is an old design and has been posted before, but somewhere along the line when PE did an upgrade to their forums (around 2017), my original thread was lost due to an uncommon character in the title. Well, after literally years searching for a way to find the old text of the post, I finally found it. So, 5 years later, here it is again. Thanks for humoring this old geezer.

ORIGINAL POST:

OK, I know this is extremely late in posting, but I did want to get this out and share it with the community. I've been working on the writeup for this design since I left Fort Wayne, and I feel like I've been on a plane ever since.

I finally got the writeup finished. Typically, I would copy-and-paste the writeup into the forum format, but this writeup is rather involved and picture heavy. In order to save space on the PE servers and to facilitate easier printing for anyone who wants to actually read about this design, I've posted the complete writeup here:

DARPA Jr Design Writeup

Here's a few quick excerpts that will hopefully stimulate more conversation about this design. I welcome any and all feedback from those who were able to hear them!!

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For quite some time, I’ve had the idea for the DARPA project running around in my head. What’s DARPA? No, it’s not the Defense Agency thing. DARPA in this case stands for Dayton Audio Reference Paper and Aluminum. It refers to the fact that I use a paper midrange and an aluminum woofer from the Dayton Reference series, although the fact that the drivers look like stealth fighters helps with the pun on the Defense Agency. My intention behind the DARPA design has been to replace my stalwart Definitive Technology towers and center, which have for over 15 years occupied my main TV listening space (and still do). The original DARPA was supposed to be an RS225 with RS100P mid and RS52A tweeter, and I still plan to execute this project in time. However, when Ben announced the micro-3 way project for InDIYana 2015, I thought that might be an excellent excuse to concoct a smaller version of my DARPA concept. This would help me prove out the overall concept and see how the drivers played together. Thus, DARPA Jr. was born.

Overall Design Concept and Impressions:

DARPA Jr uses an RS180-8 woofer, RS100P-8 mid, and ND25FA tweeter for an all-Dayton design. It’s in a 0.5 cu ft. slanted baffle cabinet with a sealed mid-chamber.

I’m not one to brag on my own designs, but I’m very proud of this one. I knew from the moment I got the crossover correct that it was pretty special, and it would be worth traveling to InDIYana to compete with it. It’s not a bass-intensive design, as can be inferred from the smallish cabinet. There were other designs at InDIYana with more bass. However, the accuracy and smoothness of the frequency response on this design is really incredible. I voiced the DARPA Jr against my Continuum’s, and I feel they do a pretty darned good job up against the Continuum’s or most anything in the ~$320/pair designs (drivers and crossovers included in that price).

Crossover Design and Response Graphs:






Pic showing the MidWoofer Chamber:



Final Design awaiting Judgement at InDIYana:

[bungelow_ed]

Interesting design. Do you have more details to share? I'd like to know more about the cabinet and alignment. Thanks for sharing.

[tyger23]

Click on the link to the write-up for more details. The mid and tweet are time aligned. The woofer was close.

​​​​​​Here is the link again for reference:

https://drive.google.com/file/d/0B_PLKXLFi__DbnNhQ3R4N3FZZW8/view?usp=sharing

[ceiol]

great write-up and I really like the design. the reverse nulls are deep!

The slanted enclosures are beyond my current woodworking skills, so I'll have to wait until you and Erich come out with a kit!

[Kevin K.]

Nice design! How did you go about determining the angle required on the front baffle to time align the tweeter and mid? My idea on how to do it would involve mounting the drivers in the baffle only and taking measurements while incrementally changing the angle of the baffle until time alignment was reached. Just curious how you went about it, thanks.

[tyger23]

Kevin - That is exactly how I did it. I knew the baffle design I wanted, and I had the "mid enclosure" in the sealed chamber, so I built the baffle with just the mid and tweet active (woofer was installed but not active). I propped it up using a vice and took some measurements. Then I laid it back a few degrees and re-took the measurements. Then, math to figure out what the angle should be and validated the angle using measurements again.

So, it was very iterative and manual.

ceiol - I actually did work with Erich on a possible kit many years back. The measurements you see in the writeup were actually done for him. Discussions on that kind-of died away and I've been out of the DIY game for several years now. I'm sure Erich could possibly make the cabinets should he be commissioned to.

[bungelow_ed]

Click on the link to the write-up for more details. The mid and tweet are time aligned. The woofer was close.

​​​​​​Here is the link again for reference:

https://drive.google.com/file/d/0B_P...ew?usp=sharing

Thanks for your patience, I can be somewhat myopic when reading interesting subject matter. And Darpa Jr. is are very interesting. I'm just heading out for a week long vacation during which your write-up will be on my reading list. Could start cabinets next week. Thanks for sharing these again.

[Jakes_dad]

I was thinking of building these as a pair of small towers, maybe the same size and tuning as Paul Carmody's Amigas.

I intend on keeping the same baffle width and angle,

Do you see any issues with this Idea?

[tyger23]

If you keep the same baffle width, angle of the baffle, and speaker placement relative to the top of the speaker, then the crossover should be OK. You'll likely need to adjust the woofer's porting to account for the increased cabinet volume. You should be able to actually lower the tuning some and get more bass out of it with a larger cabinet.

[Jakes_dad]

Thank you for the reply.

That's what I thought, but I just wanted to confirm.

I am still playing around with cabinet designs, but this is the top contender so far. I just don't know if I can pull it off.