In my previous post, I mentioned a discussion about this project on the diyAudio site. One comment referenced an analysis by Martin J. King (http://www.quarter-wave.com/), widely regarded to have the best transmission line modeling software available. He stated that Dr. King had found “Dalines” (what G. L. Augspurger calls “Pipe with Coupling Chamber” ?) inferior to designs. I did find this reference on diyAudio that supports his statement.
Without further ado, here is my model of the Tang Band W8Q-1071F in a RSTL line. Could there be something better? Maybe. Does this strike me as a configuration that will have deep bass? Yes. Am I worried about the dip at 100Hz? Not really – right now I expect I’ll have an active crossover at or below 100Hz, so I’m not at all concerned. Should I go full passive, I’ll have to review my stuffing plans.
Simulation of TangBand behavior in the RSTL line
I hadn’t been on this site for some time and just happened to check my stats the other day. I had the biggest peak ever! A little poking around and I found this post on diyAudio.com . Somebody out there actually thought this site was worthwhile. Yippee!
It has been a long time again since I’ve posted. Two reasons. One, through the generosity of a visitor, I’ve been digesting some much more detailed information about the original DIY version of the RSTL. When I get done with the translations and cleanup, I’ll post more about what I’ve learned here.
Today though I’ll tell you about a(nother) project that took WAY longer than it should have – creating the countersink template for the woofers. Oh why oh why can’t they be nice and round like most of the other drivers I’ve worked with over the years? Even the line array of ribbons I used in my last speaker were nothing compared to this guy.
I used “Easy Driver Flush-Mounting” in the June 2001 audioXpress as my guide. Suffice it to say Mr. Buike was facing far fewer issues with the Focal woofer in his example than I did with the Tang Band’s irregular shape. The basic idea is to use a flush-trimming bit with a bottom-mounted guide to create a template 1/2″ larger than the driver:
Using router table, trim bit and driver to make 1/2 inch “oversize” template
Note the taped-on plastic bag to keep dust out of the driver. Also note the trim bit protruding just to the left of the driver, so it can use the edge of the driver as a guide. I’m going to skip a WHOLE BUNCH of stuff that turned out to be hard here and jump to the next good part. When it is all done, you’re left with a template that is the right shape except it is 1/2″ bigger than the driver on all sides (the width of the trim bit):
Completed first “oversize” template
Finally, cut this template down by 3/8″ per side to leave a nice 1/8″ border around the driver:
Completed template, with driver for comparison
Notice I left a large border all the way around the cutout, both to leave room to clamp the template and to support the router. A lesson learned (over and over) the hard way.