Pretty

I just had to get a peak at what it was going to look like loaded up. Nice! Note also my wonderful assistant, whose support both in the shop and out is instrumental to the success of this project. 🙂

Image of external view of the speaker

Gloria demonstrating the prototype with the drivers mounted

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Progress

I’ve made progress the last two weeks – finishing all the front cuts except for the midrange port. I’ve also made progress on the inner baffling (see also An Elephant in the Room).

Speaker cabinet picture

Latest front of view of prototype

 

Rear-view of cabinet

Rear view display installed internal baffles so far

 

An Elephant in the Room

Until now I’ve ignored one of the biggest cabinet problems – the Tang Band woofers are much deeper than TDL/Elac drivers used in the RSTL. How much deeper? Deep enough that I have to cut holes in the vertical dividers between the woofer and midrange sections to allow the woofer magnets room. Of course the woofer and midrange sections should not be open to one another, so I’ll need to build some sort of “cup” to cover over the hole from the midrange side. I didn’t design the hole size via a CAD system, but rather determined it empirically by cutting, trying to seat the woofer and repeat until it fit. I’m confident now I can make it work, but it certainly doesn’t appear in the original plans!

Photo of speaker internals

Hole cut in divider between woofer and midrange chambers to accommodate the depth of the woofers

Resurrected

The good news is that I got a chance over the holiday weekend to cut and bevel (but not route) a new woofer panel and to cut and route (except for the TL terminus) the center section. With a number of “L” brackets, pieces are now held  in place nice and tight. While it looks like a step backward from 2 months ago, overall it is actually progress. Really. 🙂

The new prototype shell, 3/4 view

 

New prototype shell, front view

Broken!

The astute reader will notice I haven’t posted for the better part of two months. There are a few reasons for this. The first is that I’ve started a new job that takes much more of my time than my old job (60+ hours vs. 40 hours). I love my job at @Pay, but it seriously cuts back on my free time. Secondly, I suffered a series of setbacks in the form of broken pieces (and hence spirits). Both the woofer panels and M-T-ST-T-M panel get quite thin where the driver countersink diameter is the widest. If such a piece falls over flat against a cement garage floor, it can split right in two, taking hours of cutting, routing and so on with it.

The top half of what was the prototype M-T-ST-T-M section of the cabinet

I cut the panel shown slightly too narrow, exasperating the problem. A similar fate befell (ha!) a woofer section, it also breaking in two when it happened to fall over. Once supported by the rest of the cabinet structure, this won’t be a problem, but as free-standing structures they are fragile! I am going to reduce the depth of the countersink on the woofers to increase the strength of the panels.

Why can’t it be Round?

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:

Image of Routing first template

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):

Image of completed first template

Completed first “oversize” template

Finally, cut this template down by 3/8″ per side to leave a nice 1/8″ border around the driver:

Image of completed template

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.