, 12-28-2010 at 02:47 PM (5415 Views)
Deullati build, Dayton Audio DA115-8 / Seas 25TAFC/D MTM, 10 liter vented cabinet
Design goals: I wanted to build a speaker to use the pair of Seas 25TAFC/D tweeters that I have had lying around for a year or more. I wanted them to do justice to the tweeters, dig fairly deep, and stay relatively small, without breaking the bank in regards to driver and crossover cost. This seemed daunting at first glance, but wound up being relatively simple to accomplish.
As mentioned, I needed relatively high quality drivers at a relatively low cost. I wanted the design to be repeatable, if it worked (I know, the tweeter is no longer available, more on that later.), I wanted it to go fairly low, I NEEDED it to go in a small box (WAF, you know!), and I wanted it to look nice. Given those constraints, Dayton drivers just naturally came to mind. I’ve built a few projects using Dayton drivers: Shawn A’s Triska sub, Wolf and Shawn’s Deuterium, the BR-1 kit, and a center channel speaker of my own design. I’ve also heard a couple of iterations of the TriTrix, and helped with the Design and construction of a Sub using the RSS265HO driver. I like them all. I like the sound of the Dayton classic drivers that I’ve used, but I really wanted to step up a bit from them, and the thought of an all aluminum system was appealing. I naturally gravitated to the RS series woofers, but honestly, they’ve been done an awful lot, and besides, they’re black anodized, which wouldn’t quite fit with the aesthetic, even if the cone material was the one I wanted. That left the DA series. I modeled a couple of boxes using a single DA175, a single DA135, and a pair of 135’s. I liked the thought of the MTM, but the vented box was just too big, and the sealed alignment didn’t go quite low enough for me. I shelved it for awhile, and only revisited it when I spotted the new DA115 in the 2010 PE catalog. The only questions I had were would it work in a small box, and would it go reasonably low? Some quick modeling in WinISD answered both in the affirmative! I’m not quite bright enough to use WinISD Pro just yet, but I was able to fiddle some with the box that was recommended and wind up with a ported 10 liter box, with a 2” I.D. x 6.5” vent, that tunes the box to approximately 55 Hz. This gives a modeled F3 around 50 Hz, more than acceptable extension, especially when paired with a sub, as they will be in my room. I think we have a winner!
With the tweeter being unobtanium, I needed to choose an alternative that would make the design buildable for anyone who might choose to so, so after some research and soliciting of advice, I chose the Seas 27TBFC/G (H1212), to keep the same flavor going, if you will.
As noted above, I used a 10 liter ported cabinet tuned to 55Hz. I used exterior dimensions of 7”Wx16”Hx11”D using ¾” MDF for all panels, screwed and glued. This yielded a box a bit bigger than the spec’d 10 liters, to account for driver and port volume (although I will admit to the actual amount being nothing more than a guess, net volume may well be a touch larger or smaller than spec.). I used a pair of 1” dowels side to side in each box for bracing. It’s not a big box, but I’m sure more bracing would help, and it certainly wouldn’t hurt. I placed the woofers on the vertical centerline, offset to the top, with the tweeter offset half an inch from center, to help with diffraction, and rounded all sides with a 1/2” radius roundover bit . I made the port out of 2” PVC pipe, epoxied to the rear baffle behind the tweeter, and rounded over with the same bit. I finished with Rustoleum Hammered Bronze spray paint, and a couple of coats of gloss clear.
I’ve heard horror stories about the breakup associated with metal cones, and I kept that in mind while I was modeling, but the breakup in this particular driver occurs pretty high up (a double peak from around 8kHz to about 10kHz), and follows a nice natural rolloff that starts at about 2.5kHz and ends at about 5k. This made it pretty easy to get an LR4 slope at 2kHz using a simple 2nd order electrical filter topology. I used about 4dB BSC, which, when coupled with the 6dB gain from two drivers in parallel, gave the system a sensitivity right at about 85dB. I used a third order electrical filter on the tweeter, padded about 6dB to match. Voicing consisted of listening to them for a couple of weeks, trying to pinpoint any weaknesses, but I just couldn’t. Listeners with more sensitive ears than mine might find the top end a little hot, but that will be easily tamed with a little more padding on the tweeter. The 27TBFC/G uses the same topology, obviously with some value changes, and the addition of a lifting cap on the series resistor of the L-pad, to bring up the falling response of the tweeter above 15k. That addition can (and should, I’d say) be seasoned (or even omitted) to taste, as well. I haven’t built that version, much less voiced it, so that would be up to the builder at this point. I hope to try it soon, as the H1212 is a physical drop-in, and I am curious. If/when I do I’ll be sure to update!
I’m just amazed at the sound of these little guys. They have way more bass than a 4” woofer should be able to produce, and the clarity is really nice. I kept expecting them to get fatiguing, but that has just never happened. They have very nice, balanced overall sound, and they will get uncomfortably loud without obvious distortion (although they do start to complain when pushed too hard, no getting around Mr. Hoffman!). It’s hard to call a design that uses $45 tweeters a “budget” design, but at a little over 200 bucks a pair for drivers and crossover parts, they won’t really break the bank, either.
Edit: The alternate tweeter is now the Vifa BC25SG15-04 silk dome. I had wondered some at the use of a fairly high dollar tweeter in this design, and when that same thought was expressed to me by Soundslike, I realized that, in this case, "budget" is a bit more important than "aluminum". Also, having heard basically that same tweeter in LouC's LECBOS design, I concluded that the Vifa isn't really giving anything critical up to the Seas, aside from price. I have no doubt at all that the Seas is the better unit, but for this design price point, just not really appropriate.
Here is the XO diagram for the Vifa version, forgive my poor drawing skills...
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