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Old 15th March 2015, 07:52 AM   #1
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Default Another MJK Open Baffle

I started out with the plan to make on open baffle speaker at roughly the same cost as my last rear folded horn project (NZ$1000) aka the "Monoliths". So I had to keep the costs of drivers down, as the crossover was low (and expensive). Being a subscriber of MJKs worksheets I started with the woofer and sniffed out a couple of Eminence alpha 15a's locally second hand avoiding the terrible postage cost to NZ. Looking to match a wide ranger the Alpairs and big Tang Bands looked attractive but were expensive and would require padding down kind of a contradiction so I looked at the Tang Band 1320.

The TB1320 ticked a few boxes, a big(ger) paper cone, 88dB/W and cheap(ish). Some complimentary reviews online too but and obstructed rear soundpath. It modeled well with the Eminence alpha (see graphs) so I dived into the Parts Express website and picked up the crossover components as well, the 18mH low pass inductor ended up being iron filled, thinking that well away from the critical spectrrum it would do little harm (and is fine so far).

The model is for a narrow 7" vertical baffle, with a classic H frame 17' square and 8" deep (either side). The baffles are made of Formply a structural grade, void free, 17.5mm phenolic coated plywood made locally from fast growing Monterey pine similar to Birch and intended for concrete shutters :- ). I like the look of it too.

As it was I've had to add some old supertweeters (Fostex 17H) as the Tang Bands perform poorly above 10K I've attached the MJK modelling, my most recent measurements via REW.

Plenty of work to do yet, constrained layer damp the H frames with Fibrous reinforced cement board (the best material with plywood in my experience), reduce narrow baffle to a square and play some more with the crossover. Current problems room influence below 100Hz despite dipoles (weirdly lower by 200Hz than problems with the back loaded horn) and the bump in the TB between 500 and 2K or too little above. The sound is simply amazing open, in the room, realistic, startling..whatever the measurements might show.
Attached Images
File Type: png OB modelling1.png (6.4 KB, 204 views)
File Type: png OB modelling2.png (4.6 KB, 200 views)
File Type: png OB modelling3.png (5.2 KB, 198 views)
File Type: jpg cube squared ob basic inital.jpg (68.6 KB, 202 views)
File Type: jpg OB speaker 1.jpg (120.3 KB, 205 views)

Last edited by Steve Duffy; 15th March 2015 at 08:55 AM. Reason: lost paragraphing in cut and paste hard to read
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Old 15th March 2015, 10:17 AM   #2
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Typo re room resonant hump, it goes about 20Hz lower than with the rear folded horns but it's upper limit is the same, I seem to have excited the modes differently with the OB.
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Old 15th March 2015, 06:20 PM   #3
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Default Picture with super tweeters balanced (and velcro'd)

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Attached Images
File Type: jpg OB Square Cube.jpg (339.2 KB, 97 views)
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