DXT-MAX - Small active monitors

[silverD]

This project pulls inspiration from several designs that utilize the SEAS DXT tweeter which is known to have excellent directivity. I chose to pair the DXT with the new Epique E150HE-44 in the Denovo knock-down 0.23 ft^3 cabinets. After a short break in, the woofers model similarly to the published specs in the small cabinet with a f3 near 40Hz. Porting these speakers was going to be a difficult task, so I looked to a passive radiator. Finding a PR with enough Sd that also fit the cabinet dimensions wasn't trivial, but I took a cue from another recent design that utilized a large Xmax driver in Denovo knock-down cabinet and chose the SB15SFCR-00. It essentially uses the full rear baffle. Instead of using the knock-down baffles, I glued up 2 pieces of 18mm baltic birch. Inspired by the trapezoidal chamfers of the Heissmann Acoustics DXT-MON, I built a taper jig to provide the ~7 degree angle I needed when I cut the 30 degree chamfers. CADing the baffle helped determine the needed angles, but was necessary as I utilized a friend's new CNC to cut the driver rebates once the chamfers were complete. Since the woofer is so inefficient, I felt this would provide me with an opportunity to dabble with active crossovers and utilize some recently assembled class D amplifiers. I'm using the ADAU1701 DSP which is programmed via the SigmaStudio app w/GUI. Armed with an OmniMic, I should have something to tinker with over the winter months. I'm just now gluing the baffles on and plan to get a few coats of shellac on the cabinets before testing. I have 2 layers of butyl sound deadener applied to the sides, tops, and bottoms which will be followed up by a layer of Sonic Barrier and Acousta-Stuf. I was thinking a crossover at 2KHz and level matching would be my starting point, but am open to suggestions. I will have a 25uF cap in series with the DXTs.
Thanks for looking, I now present the DXT-MAX.....or Epique Fail

[silverD]

[silverD]

[silverD]

[Kevin K.]

Cool looking project! I hadn't run the sims to confirm but was guessing the racetrack PR from SB might be a good match with the new Epique drivers. Jeff Bagby and Rick Craig used the same PR on a couple of their designs in the same fashion. Looking forward to seeing how the DSP works out for you using the ADAU1701 and Sigma, I'm currently working on a small set of desktops and was planning to DSP with the same stuff. Good luck!

[tomzarbo]

Nice looking design Nate! I was waiting for someone here to do a design with the new Epique subs.

Quick question... I modeled that driver with that same PR and although it did model fine, it just seemed that the PR wasn't moving much at all. I think I saw like 2-3 mm at the most. I modeled at a reasonable wattage since it would be used as a woofer in a two-way instead of a true subwoofer setup... but it seemed like the PR was REALLY loafing even at near driver Xmax. Wondering what you came up with and if your design has your PR loafing along as well. Not that there's anything wrong with that.

TomZ

[djg]

Very nice work. A friend with a CNC is a friend indeed.

Looking at that Epique sub magnet, are you going to put in T nuts or other inserts, or just long wood screws to mount the sub?

Pricey little suckers. How will you use these? And, show us your amps?

[Steve Lee]

Watching this one for sure - good looking set-up.

[silverD]

[silverD]

Thanks for the comments everyone
Kevin, this is my first time using the ADAU1701, but it seems you get a lot for your money. This is the 3E Audio version with 2 channel SE input and 4 channel balanced outputs. As I understand, I can use digital I2S input to avoid the ADC. It also supports I2C output so one could add more output channels via other DACs.
Tom, I'd have to pull up the WinISD model on other computer, but I think at 70W/100dB both the woofer and PR (with 30g mass added) are under xmax with a HPF at 20Hz.
David, I plan on using PE screws. There have been times where a T/hurricane nut has cross-threaded and backed out of the wood making for a difficult time. These will be used near-field without sub at a desk where I can also have the ease of reprogramming the DSP. The DSP is pictured above in the case I made for it. The amp above I picked up as an unassembled kit off the bay. It came with the 200ASC and 200AC modules, Ghent case, and all the needed wires and hardware. It will be used for the woofers. The tweeters will be powered by a 3E Audio TPA3255 I recently updated to have balanced input. The DSP will receive SE input from a SMSL Sanskrit 10th MKII connected to a pi.

[djg]

So, when you say active, you don't mean amps in the speaker cabs, just electronic crossovers?

[silverD]

Yep, electronic crossovers. Only the 25uF cap in the cabinet and two sets of binding posts.

[silverD]

I was able to make some more progress. Sanded the cabinets and applied a couple of coats of dewaxed shellac. The baffles will be left as is, but I plan on painting the rest of the cabs. Any suggestions?
Pounded in the binding posts, added foam, wired and mounted the drivers, put in some fill, and added 40g to the PR and mounted it.

[silverD]

One done.....at least for now.




Impedance sweep on the woofer:

Impedance sweep on the tweeter:

[Steve Lee]

Gosh, they look so good!

I just cannot get past the low sensitivity and $$$ but that is the trade-off for not having 1+ cu ft of cabinet volume, I guess.

Amps are cheap these days so I am really interested in your findings and subjective thoughts concerning how they sound and how they are employed.

[djg]

Are you leaving the baffles natural?

How much patience do you have for paint prep? Butt seam MDF cabs show the seams if you don't do a ton of prep. Easy way is some textured paint after modest prep. Do you have a spray gun or are you rattlecan limited?

These should outwoof your Speedsters.

[Wolf]

Use epoxy to seal the end grain of the mdf. It's very effective for this process.
Wolf