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The basic design concept for this project is a small 3 way mini-tower using some of the best vintage drivers from the 1990's.
Can 30 year old drivers sound as good as some of the best modern drivers? Or will they sound tired and worn out? This project will be my attempt to find out.
Tweeters: Matched pair of Morel MDT-33 one inch domes (1990). Picked them up used at MWAF at few years ago as a backup set for my existing pair. Spec sheet Fs is 700Hz on these, but I am measuring 883 and 943Hz on one pair and 1400Hz and 1450Hz on my slightly older pair. This is probably due to the ferrofluid drying out. So, my plan will be to clean out what remains of the old ferrofluid & replace it with new stuff. I'll start off with 100uL and adjust as necessary to reach 700Hz.
Midrange: Pair of vintage Vifa D75MX-21 three inch domes (guesstimating 1995 or so based on my old Madisound catalogs). Picked these up off the free table at Meniscus a while back (thanks, Dan!). See my "D75 chamber sizing" thread for more info. https://diy.midwestaudio.club/discussion/comment/18004#Comment_18004
Woofers: Pair of vintage Audio Concepts JC-12 twelve inch woofers (1991). Original TS parameters were roughly Fs 16Hz, Qts .30, Vas 10-15 cu ft., SPL 89dB 1W/1M and Xmax 12mm. The VAS spec measured way too high for a reasonably sized box, so when the foam surrounds rotted out, I cut the original 9.5" diameter paper cones down to 7 inches and then installed PE 10" re-foaming kits. I glued a masonite ring adapter onto the basket to make this work. Average DATS V2 T/S parameters after the mod were: Fs 20Hz, Qts .355, Vas 3.8 cu ft, SPL 86dB 1W/1M. In WinISD, this produces a very good alignment in a 2 cu ft box tuned to 24Hz.
Box: The box shape is going to be a downsized rendition of dcibel's Northern Pikes speakers (or a truncated version of Nick's Pointy speakers). While a little more difficult to build, the non-parallel walls should help to spread out box resonance spikes and excessive diffraction ripple. Type of lumber used will be based on what is available at reasonable prices . I am hoping to do something in a solid wood (poplar, cherry, mahogany, etc.) that looks nice. The box will have a removable back panel for port tuning, re-stuffing, and xover tweaking.
Stands: The speaker will be designed to be placed on top of a 13" high stand. I tried to design it as a floor stander, but didn't like the shape or woofer placement. Also, the cabinet was not deep enough to accommodate an 8" long straight port tube. But with a 13" stand, the cab is deep enough for an 8" port and the woofer will still be about 20" above the floor. This will give me a small amount of floor boundary reinforcement, which, when combined with roughly 3dB of BSC should produce a flat response from 1kHz down to 80Hz when placed well out into the room. The WinISD alignment should fill in the rest, with an F3/6/10 of 28/24/20.
Xover: Based on HD & FR measurements, the mid should be able to handle the 600Hz-4500Hz band. Wolf suggested 600Hz-2500Hz as the sweet spot, so I will be targeting this as my starting point in the design. Using dcibel's "Ideal centre to centre distance" thread recommendation of 1.0 to 1.4X wavelength, I set the center to center distance between tweeter and mid at 5.6 inches, which should be ideal for an xover in the 2500 to 3500Hz range. And to avoid on or off axis peaking at high frequencies, I staggered the tweeter to side and top edge distances by 1.62X (see drawing).
So, off to the big box lumber yard to see what I can find. Will post construction pics as I go along. Bill