by Chris Bobiak
Speakers in room. Enjoying the results.
<clik on most images for a larger picture>
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If ever a web page needed a personal dedication, this one goes to my long suffering,
much better half, Susan Donell B, for her never ending patience, and to Dr. D., for
guidance, humor, and spare parts. Math aficionados, proceed at your own risk, while there may be some soft core arithmetic later, -- This is a MATH FREE ZONE. Still here? OK let's go. Like many of the readers of this site, I've been playing around with audio gear for quite a few years. Long enough actually that the first console my parents let me muck about with was mono, with one of those 60's Garrard changers with the art deco 5 pound tone arm, and some kind of tubed electronics. Since getting a little more serious in the early 70's, I've seen a lot of gear (and dollars!) come and go, some that I'd never admit to now, others that could still get the mid-fi nod today. I've always liked to tinker with my toys, so there was some tweaking etc., assembly and mods to Hafler amps, the usual stuff. More recently blasting off the occasional enclosure for car audio subs. But aside from a couple of pair of RSC factory kits (remember Radio Speakers of Canada? -- whatever happened to them anyway?), building a home audio speaker was always a bit intimidating. The KEF kits of the 70's just never did it for me musically, but I think it was the math required for customized crossovers that scared me the most. Well technology sometimes progresses in a positive direction, and surfin' the net reintroduced me to the idea of rolling my own. The range and quality of drivers and information available to the newbie constructor is almost mind boggling, and if you spend enough time researching, you don 't even have to do any complicated math. (Do I hear an AMEN?) |
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| With all due respect to the quality of research, engineering, build quality, and
sonic performance of the manufacturers of the better audio gear, it's just so easy
today for a DIY'er to create a very musically satisfying loudspeaker for a relatively
modest cash outlay. This is particularly true if you can leave your old prejudices
and conventional wisdom at the door, and start with a blank sheet. Of course the
economics of (inter)national marketing a wide range of products, and the profit goal
of any healthy business contributes to the ultimate cost. But eventually most of
these products are rather cookie cutter as far as style is concerned. I think most
readers that would follow a page this far would agree that a loudspeaker is the easiest
component for most of us to build, and one that allows a high degree of personal
aesthetic expression, both sonically and visually. There were several inspirations for this project that should be mentioned. I readily admit to liberating ideas from these sources, as well as adding a few of my own. Lynn Olson's Ariel -- I think this started it all for me. Arguably not a true T-line, but I was captivated by the very well documented journey undertaken during the development of this design. I had considered it for my first project. The cabinet design, though certainly not an afternoon project, was not the most intimidating factor. Neither was the crossover -- it had already been worked out. There were numerous builders' sites full of enthusiasm, and with tons of useful and insightful information. Ultimately, though it's the cost for a first time project that deterred me. Scanspeak tweeters, that "non-minimalist" crossover, and intricate enclosure -- easily over $1,000 CDN. But it is still interesting, and maybe in a couple of years... |
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The main legacy of this source was the selection of the Vifa mid-bass driver (P13WH-00).
This has got to be one of the best values for the DIY 'er. OK, it won't rock the
house like a 12" Shiva in a 3 ft3 ported enclosure -- which I found
I can't use anyway. (Never underestimate the power of the room.) You can start with
a very basic low pass filter for this driver if using sub(s) or none at all. The
midrange is really good. (Search elsewhere for rhapsodic elucidations -- it just
sounds wonderful, natural, and effortless when used within its range and power limits) There have been numerous improvements to the enclosure, the design becoming more sophiticated along the way -- the most recent including sand filled chambers etc.Since the beginning, the Ariel has used 2 of these drivers, each in a separate "labyrinth / line", sand filled chambers etc. Call it a T-Line if you like. As this speaker was designed for low powered tube amps (SET particularly), the increased output using 2 drivers is significant. To simplify my first project, and as power was not as much a concern for me, I decided on one per side. |
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Another interesting site - Steve Deckert's High Performance Audio. Not really a speaker building site, but just a fun ride.
Drivers & Bits
[ Plans ]
The computerized milling machine Chris used to build the side panels
Every new design has its teething process, and as an official T-line virgin, I can say that getting the stuffing just right is the biggest pain. The mathematically talented can calculate models, or refer to charts or graphs, but eventually you will need to listen and adjust it in a real room. As I knew there would be some mucking about here, I built the box as a rough case with one side removable, to be finished later.
The shell, internal baffles and bracing are 19mm MDF. Selected use of Baltic birch or Apple ply would probably improve some aspects of the sound, however the price factor is significant*.
I used shorter, #6 screws the first few times the box was taken apart, finishing off with 2" #8 Lo-roots. Okay, cringe if you like, but as I knew the joints would have to come apart numerous times, I made the planed the baffles on the "free" side approx. (1 mm) under the dado size. Forcing the parts to a very tight fit several times to adjust the damping risks some damage to the material. Alright, I'll be honest, this happened with the first set of gables -- all of the inside diagonal corner braces broke on one of the boxes.
The premium grade MDF and the dadoes were each exactly 3/4". That makes for a wonderfully deadly tight joint, which would hold more that adequately with decent glue, no screws required. Just don't try and take it apart more that once. There is a lot of surface area involved in these internal dadoes. (Approx 1500mm lineal x 5mm deep = 7500 mm2) That's a lot of friction.
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*Note: on Materials |
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| 19mm (3/4") MDF = about $20 per 4'x8' (32 ft2) vs Baltic birch @
$45 for 5'x5' (25 ft2). My math calculates this as $.625 vs $1.80
per ft2. Apple ply is generally an architectural grade of material, with
at least one face of select grade finish veneer (ie Maple). It can be very gorgeous
when finished well, and easily cost over $100 per sheet. Note that true 13ply Baltic birch comes in 5'x5' ft sheets, which can give poor cut yield. Enclosure costs rise dramatically when 1 more sheet is required for a single gable. Working in a commercial millwork shop has numerous advantages, access to all the right power toys, and ample "offcuts" (read "free") of MDF and finishing plywood to be recycled. Just scale the cabinet carefully, prepare a detailed cut-list, and wait by the scrap bins. (Lumber prices can fluctuate, all prices quoted are circa May 2000, and CDN$. As always, YMMV) Note; when purchasing your material, -- there is a significant variation in quality of MDF. Some of the "utility or shop" grade board doesn't hold a screw on edge worth a damn -- whether you predrill and use Lo-Root screws or not, the board will split. There goes the holding power of your fasteners. Whether you intend to simply fill screw holes and paint the finished product or skin with plastic laminate or veneers, use only premium grade MDF (ie paint grade Ranger brand or similar) This material may not necessarily be available at your local Home Depot, etc, try wholesale commercial distributors. They are also more likely to stock different sizes. (MDF is widely available through these sources in sheet sizes up to 5x10' and up to 1 1/4" thick. That's 5.2 bd. ft = 230lbs! ) |
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Chris reveals the secret method used to hold the
finish wood in place. |
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Speakers in room. The sub is a ported Shiva which completely over-powered the room and has since found another home.
Note: stuffing in an early stage -- finished speaker has less
I definitely overstuffed at the beginning, with very low bass output, and excessive midrange from too low an overlap between the tweeter and the Vifa. Remember this driver goes smoooooth well past 3K, no peak, then just rolls off nicely - how cool is that for a first time project? This subjective observation was confirmed by technical measurement by Dr. D and his amazing Technicolor PowerBook
The end result was to line the outside shell (gables, front and back panels) with " Deadliner", line both side of the upper cavity and one side of the line, including the folds, with 1" Rockwool.
Further listening confirmed the crossover needed further work. Using readily available (not the best quality) parts to finalize the voicing of the system, we settled on 0.5 mH coil to slope down the high end on the mid bass, and 1.8mF cap in series with the tweeter (with a separate impedance compensating C/R leg). The circuit is mounted on the outboard pod at the rear of the speaker, with rubber bevel washers to further isolate the point to point wired circuit board.
This configuration sounded quite fine, thank you very much, and the Solen Hepa-Litz coil and Fast caps further enhanced performance.
The system is bi-wired, using Nordost flatline (copper) cable internally. Sounds great, but a little tricky to get used to working with. When budget permits, the system will be bi-amped, whether passively or actively isn't certain at this point. The existing network is just about as simple as you can get, and seems to work fine, so let's not fix it?
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A Toast to the Music |
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