Still baffling

To fix the destructive interference issue, I building a new baffle. It will also be almost twice as thick, partly to reduce resonance, and partly as a way of loosing all the ugly screws on the front but still allowing access to the inside. The star of the piece is the new circle cutting jig.

(It fits only some Craftsman routers - the plunge router has a larger base, but it does fit the fixed base model). Depending on which way you put in the center locating pin slider thing, you can cute really small circles (<2 inches in diameter) to fairly large ones.

The router jig enabled me to rebate the drivers which I hadn't done on the first baffle. Although I don't understand the physics, there is a strong school of thought that the tweeter in particular needs to be flush with the baffle.  Presumably something to do with diffraction from the sharp edges?

This shows the double layers and the neat rebate the router cuts. The lower section of the baffle will be screwed in close intervals to the cabinet, and the upper section will be attached to the lower plate with the driver mounting  bolts and possibly four screw, one at each corner. 

The AC 250F1's are now in so I want to get this (Phase IV) completed before building he new cabinets.Once the new baffle is built I will likely line the cabinet with SAE-13 or SAE-15 1/4" felt. I didn't do this first time round since I wasn't sure I wanted to blow $80on felt if the sound really sucked. (I also wanted to test the reflective diffusing properties of the cabinet design without any absorbing material). 

Phase V

Current plans are forming around the AC-250F1, an AC-130F1 or MkII, probably the latter (I like the idea of using carbon fiber somewhere) and Hiquphon OW1. The two driver idea will have to wait. Some testing of the implications of the phase change created with any second order or higher filters suggest using only first order. I am assuming the trade-off is with harmonic distortion when significant signal gets to the drivers outside of their ideal operating range. This remains, as they say, an empirical question.  What bothered me was the real mess second order filters seem to make of a square wave.

Above is the simulated result of passing a square wave though the second order crossover designed around the AC-250, AC130 and OW1. Speaker Workshop generates the phase shift data in the total frequency simulation. Using these, I simulated a square wave from odd harmonics, and then applied the phase shifts from the Speaker Workshop output which I had dumped to a file. This (above) was the result and it looks terrible - nothing like a square wave.

This, by way of comparison, is the simulated for the first order crossover I designed for the same drivers. While obviously not square, it seems much better than the signal passed by the second order network.

If the rendition of detail has a lot to do with the accurate reproduction of transients, then the first order network should do much better at this than the second order.

My current plan is to build the speakers (when the wretched drivers get here in March or April) and two pairs of cross overs, one first order, the other second order, and see how they sound.