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Message: <blockquote data-quote="Art Welter" data-source="post: 24483" data-attributes="member: 52">Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter SystemsHelge,That box is too small to take advantage of the LF capability of the B&C 21SW115 inch speaker.The BC18SW115 puts out more LF  in a “too small” box than the 21SW115.The dual Lab 12 has almost identical low frequency output in a smaller box with the same Fb as the  BC18SW115.I did not save all the interim tunings, but have included the ones I did, all using the same drive levels.The four ohm B&C is receiving a few less “watts” than the nominal 3 ohm dual Lab 12.The BC18SW115-4, given twice the power, will get about 3 dB louder than the Lab 2x12.But it takes a bigger box to do it.The exterior dimensions of the box I used to test the  BC18SW115-4 are 36 x 24 x 17 inch, 8.5 cubic feet compared to 7.76 for the 2x12. In all but the 38 Fb test, the magnet was outside the box, effectively adding about .56 of a cubic foot. That said, bigger is better (until Xmax is exceeded before Pmax) but the boxes are very close in volume.The BC18SW115-4 with the 37 Hz tuning almost exactly overlays the Lab 12, were it not for the lower upper filter on the Lab 12 , they would look more identical.It is plain to see that the 28 Fb box trades around 4 dB of 40 Hz output for  being “flat” to 30, while in actuality puts out the same level at 30 Hz as the 35 Fb tuning.Not a good trade, unless most of your sub output needs to be that low, which is why I chose an Fb of 36 for the Lab 12 design, and I’d do the same for the BC18SW115.The BC18SW115 in the test box are pictured next to a box exactly double the size of the 2x12.That box, the Keystone sub, is about 6 dB more efficient than the bass reflex designs using either the Lab 12 or the BC18SW115-4 with the same low corner.I have  one pair of the dual Lab 12s for sale, anyone interested can PM me.Art Welter</blockquote>

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