Loren Jones wrote on Mon, 01 November 2010 08:27 |
Quote: | I like the design can you post that too.
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I would love to post the design, however it isn't mine to post. I can put you in touch with the LABster who designed them if you would like to get the design from him. He may have some slight modifications that he has made since my Fb came out a little lower than the design called for. I don't know about that.
Perhaps he can chime in here if he cares to regarding his comments on the design or other thoughts.
Take care, Loren Jones
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Since it appears I have been "outed" on this design, I will offer a few thoughts:
0. I, in NO WAY, put Loren up to this. I didn't even see the thread until today, apparently a day old. I am glad Loren is enjoying his new baby. I should say Loren and I have never met, and that I am incredibly impressed with the cabinetry of the finished item!
1. This design came out of a previous LAB thread where I disagreed at length with Art Welter about the principles behind high performance vented box design.
2. In that thread I mentioned the RCF 21" because I realized that it was a very affordable driver for what it offers. I became aware of this driver as a result of unrelated conversations with fellow LABster Jeff Knorr. There are better 21s (e.g. B&C 21SW115), but I'd never seen a driver with better specifications for the money at retail.
3. Loren took a risk on building this design. I say took a risk because this came straight from a model. Even with the more advanced lumped parameter model, the port tuning is rarely absolutely correct. There was no guarantee the tuning frequency would be correct for this tapered port geometry. Loren went into the project with eyes wide open about the potential of the box Fb to be wrong.
4. I presented Evan with a modified version of the design to further test the accuracy of the tuning behavior of the model. To the best of my knowledge he has not built the modified enclosure yet. The modified design could end up only useful for firewood, model accuracy depending.
5. There are many more detailed measurements that need to be made of this cabinet before I would consider releasing a public design. Measuring a speaker system with SMAART for system tuning at a gig is much different than the detailed measurements one should take of a professionally designed loudspeaker.
6. Any sort of plans would also include a completed collection of measurements far in excess of what one normally gets from datasheets. Those measurements would provide unambiguous performance behavior, good/bad/ugly.
7. Should all those measurements ever get taken (by me or a vetted 3rd party), then I would figure out what to do with the design. More than likely I would sell it, not so much to generate revenue, but to discourage "non-serious" builders from approaching the project. I am not interested in becoming "tech support" for a vented box design
8. The box design requires 2 bands of in-band parametric eq and a highpass, so any builder would need access to DSP processing. Also, the box really needs an amplifier capable of 180+ V_peak (360+ V_p_p) to get everything the driver is capable of. For those with small amps, there are probably better ways to go.
9. At the end of the day, people should be realistic that this is still a vented box. While I feel confident that this box exhibits real extension to 35Hz, and output on par with a high-quality dual 18" (what a dual 18 will
really produce output-wise, not what the datasheet says). Those expecting to move mountains and cause earthquakes have read too many manufacturers spec sheets.
10. While the coupling efficiency of a 21" cone is superior to an 18" cone, one should not expect the efficiency of a single motor structure on a 21" cone to match that of two driven 18" motor structures for a given v_input. I
don't expect the "1w" at 1 meter specs to be as high as a dual 18 or tapped horn, even if maximum outputs would be comparable to the dual 18".
11. This new class of super-woofers stretches what we can do with vented boxes. My modified port geometry seeks to address some of the limitations that now come into play with drivers that have so much Vd. The goal was to reduce the limitations on box peformance that result as a consequence of turbulent effects in the port while still producing a design with acceptable ease of construction.
-Phil