My Iron Driver 2018 Entry

Ron_E

Here's a PDF of my ID 2018 build.  It took first place out of the two entries that made it to the contest. My build featured a sealed 2 way combined with a 4th order BP sub.  There's no crossover between the sub and the 2 way and the 2 way features an unusual crossover that features 42db/oct slopes.

Ron

Ron_E

I don't see my attachment so here's a link to Google Drive.

https://drive.google.com/open?id=13rVaY5qNFCtwkroHP6zbyo3SbfDc9wXJ

Ron

4thtry

Congrats on your win.   Nice project, I like that nice, wide curved surface created by the curf cuts.  Also like the 4th order BP subwoofer.  Are the interior walls of the BP sub cabinet lined with damping material of any kind? 

rjj45

Ron - very creative design, and great writeup.  I am seriously digging that large radius - do you have any thoughts about what might work well to fill the kerfs?  How much did you leave uncut on the face side?

Wolf

I have seen that filter topology before, but only on the tweeter. It doesn't do what I thought it did as it turns out. I thought it gave a lift to the top octave on the tweeter, bypassing the xover and attenuation, but I can see that it would do as you depicted. I may have to try that myself. 
And yes, what did you use on the kerfs, the PDF does not say conclusively.

Ron_E

I found that the BP walls needed to be lined. Without lining the upper slope of the BP had a shelf in it and you need to do everything you can to reduce the highs out of the port output. I used UltraSonic Acoustic panels for the most part to line the front and rear chambers and offset the port away from woofer.

I used wood filler and hot melt glue on the kerfs - no do-over after you've done it. Google says fiberglass resin or epoxy make good fill for kerfs. I used Baltic birch plywood and the birch layer is very thin and the kerfs need to run perpendicular to the grain. In order to do that the remaining wood was thin enough to shine light through. If you look at the pictures you can see some wood filler touch up on the curves and one curve had a sharp ridge in it that I easily sanded through the kerf removing. I wasn't too concerned because the Formica hides a lot of imperfections. There are a lot of YouTube videos on kerfing.

My friend Alan Hulsebus sketched the crossover on the back of a place mate over lunch in 1996. His sketch shows a sharp notch filter that drops -50db and rebounds to -30db. It didn't indicate what the initial roll off rate is and SoundEasy would only let me set a -42db target for its optimizer. Alan indicated that you need optimizer software to design the crossover. Alan recently sent me 4 PDF's of similar filters. I'll try to put them up on Google Drive. A friend of mine plotted the response of my crossover using resistive loads shown below.

Ron

Ron_E

I put two PDFs of infinite slope crossover patents on Google drive.

https://drive.google.com/open?id=1koJujIgLarEvQch69H7gDnZNykjPlqjb

Ron

Ron_E

Missing from my write up is an impedance curve. The impedance does drop briefly to 2 ohms.

Ron

Wolf

I know Joseph Audio used 'infinite slope' filters before, using transformers relatively unconventionally as the 1st and 3rd sections of the lowpass, with the tied leads on the inner connection to the cap and ground. I have thought more than once on how those are supposed to work, but not really able to process it since the coils would inherently couple through the transformer's cored connection.

jhollander

Very similar to the NTM filter