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Budget 12" three~way Background: I had a need for a basic garage rock-n-roll speaker. We are having a large group of people at our place for a grooms dinner outside and we wanted some tunes. I didn't want to donate my "more delicate" bookshelf speakers or my ADS towers for the cause, so the garage project was born. The family CFO (aka wife) however placed a budget limit of around $100 for the whole thing. With that, the design goal was made...decent garage / outdoor sound and cost around $100. After first contemplating a nice 8" two~way, a friend and fellow speaker builder suggested a retro looking three way..."with as much cone area as possible". The power for the system will come from a circa 1985 Luxman L-430 100wpc integrated amp that is now in my closet. Process: So we went onto the task of picking out drivers. I had a pair of the Peerless 811546 1" textile dome tweeters that were currently serving as tweets in my Jeep. I thought that would be a good start, mostly because I already had them and they didn't cost an arm and a leg ($12 ea on sale at Madisound). Onto picking woofers... There really isn't too much out there in the 10 ~ 12" range that will perform well and be low enough in cost to fit this project design goal. To try and make the cost goal, we looked at MCM and Parts Express. The Dayton 4 ohm standard 12" was my first choice, but it was about $30. MCM had a number of 12" woofers and then I found the Mica cone series. They came in sizes 6.5" to 12" and cost from $7 to $20 (Internet specials). I had just found the woofer and the mid! The 12" woofer is 91 dB, 8 ohm, has 6.9 mm Xmax and handles 100 watts RMS. WinISD modeled the optimum box at a refrigerator sized box, but I wanted about a 3 cubic foot total size. I ended up with about 2.1 cube for the 12" vented and tuned to 33 Hz. The 6.5" mid was placed in a .5 cube sealed, heavily stuffed, sub-enclosure of the main box. You can probably see the lines on the finished box. Final box size ended up being 16" wide, 14" deep and 30" tall (outside dimensions). The sub-enclosure is 8" wide by 12 3/4" tall and the depth of the entire box (outside dimensions). The vent is 3" PVC and is 6" long. The Fb ends up being about 33 Hz Crossover: The HiVi clearance crossovers came on 4 separate boards. The published crossover points are 250/3300. However when we ran the numbers they came out like this...The frequencies and slopes are as follows: The only other mods to the stock HiVi crossovers besides the additional inductor were to change out the zobels for the woofer and mid to match the MCM drivers and the L-Pad for the tweeter (-3 dB). We also changed the tweeter boost circuit to add more shaping to the response of the Peerless tweeter. (Our 35 + year old ears needed a bit more information in the extreme hi end :~)
Results: The sound is very surprising considering the final cost was just over $120...including cabinets! The MCM 12" does a good job. We pounded it with a Hafler DH220 and the amp clipped before the woofers would bottom out, even when heavily EQed and on material with a ton of low frequency information. The mids aren't nasty at all. They are about 87 dB efficient so we were able to emphasize the low end by using the 91 dB efficient woofer. Because of the lower crossover frequency this ends up enhancing the low end without getting too boomy. (Not nearly as much equalization is needed to get the required effect for Boston or Billy Thorpe :~). Frequency Response as modeled by WinISD. Just to show something to compare it too, I modeled the Swan 305 12" woofer in the same size box, with the same Fb. The MCM mica 12" is in blue, the Swan 305 12" is in yellow. The MCM 12" F3 is about 44Hz and the Swan 305 12" F3 is about 38Hz.  SPL graph as modeled by WinISD. Again, the MCM mica 12" is in blue and the Swan 305 12" is in yellow.  Look before any finishes are applied.  |
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