xrk971 Posted April 9, 2015 Share Posted April 9, 2015 (edited) Here is the drawing that I got from Moray James with which I based my dimensions from for the model (shown annotated in color). I modeled it as 7 segments with starting and ending faces of the "waveguide" element shown in green. The distance (in red) units are in inches and refer to the cross-sectional areas and lengths. Near the throat, there is a 3d expansion and the height of the channel (nominally 30in) is shown in parenthesis and dark blue. Annotated sketch of model: Here are the driver parameters that Moray James provided me. Probably a University C15W dual VC driver as measured using DATS: * Piston Diameter = 330.2 mm* f(s)= 69.98 Hz* R(e)= 6.63 Ohms* Z(max)= 74.00 Ohms* Q(ms)= 3.708* Q(es)= 0.365* Q(ts)= 0.332* V(as)= 91.420 liters (3.228 cubic feet)* L(e)= 1.41 mH* n(0)= 8.19 %* SPL= 101.20 1W/1m* M(ms)= 58.27 grams* C(ms)= 0.09 mm/N* BL= 21.58 These simulations are for 2.83v of driver with mic at 1m away in 2pi space, with speaker sitting on floor and mic at exit mouth centerline height. Freq response: Cone displacement: Impedance: Here is prediction for modestly priced ($160) modern 15 inch pro audio driver, the PRV 15W1600 which has a 0.37 Qts, is 100dB sensitive, and provides 7.6mm of xmax. Instead of using the same geometry, if we simply extend the space from the throat to front of the horn and add a 11.5in stub (shown in light blue with yellow cross-hatch), we can extend bass response deeper at the expense of a little less max SPL and a more prominent dip at the first reflection null around 300Hz. For many sub woofer duties or bass horn duties, this is perfectly sufficient. Here is performance at max SPL with 96 volts drive. I am running -24db BW high pass filters as needed to optimize the xmax. Here, the HPF is set at 58.5Hz. Freq response - the new fb is about 67Hz and if one were to EQ this flat at 133dB, the -3dB extension is 57Hz which is really quite amazing for a $160 driver and minor mod: Cone displacement: Impedance: I have tried one other driver, a budget Dayton PA for $70 and it works quite well still. Given the excellent cone motion control of this design, it would be best to pick high thermal power rated drivers with high sensitivity. Although lower priced drivers with less thermal capability can be an excellent choice for the budget minded user who doesn't need 130dB is also fine. At 1 or 2 watts of drive is about all you will need for most home listening applications. Hope this was helpful. Regards, xrk971 You can see more of my work on diyAudio in the Foam Core thread here: http://www.diyaudio.com/forums/full-range/223313-foam-core-board-speaker-enclosures.html Current projects: http://www.diyaudio.com/forums/full-range/268524-xki-xs-ab-initio-karlson-6th-order-bandpass.html http://www.diyaudio.com/forums/full-range/271011-rockin-kazba-dipole-k-aperture-z-baffle-dipole.html http://www.diyaudio.com/forums/full-range/239338-mini-karlsonator-0-53x-dual-tc9fds.html http://www.diyaudio.com/forums/full-range/270614-subjective-blind-comparison-3in-5in-full-range-drivers.html Edited April 9, 2015 by xrk971 Quote Link to comment Share on other sites More sharing options...
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