I thought this mod on one pair of my "baby SDA's" would be as easy as a day at the beach, but it turned out to be more like a long day at work. It was worth it.:) This pair of 1989 version CRS+'s is clad in the elegant black oak veneer with satin finish. The following modifications were previously performed:
1. Crossover upgrade with Mills MRA-12 resistors, Clarity Cap and AudioCap polypropylene capacitors, "4.1TL" modification which allowed the use of the RD-0198 (SL3000 replacement) tweeter.
2. Mortite seals for tweeters, drivers and passive radiators.
3. Custom heavy gauge SDA interconnect cable.
4. Replacement of SL2000 tweeters with RD-0198 tweeters.
5. Vampire binding posts.
6. Foam rubber damping material on the driver and passive radiator baskets.
My experience installing rings in my SDA SRS 1.2TL's is discussed here. My experience installing rings in my SDA SRS's is discussed here.
Based on my previous experiences, I expected this modification to take about two hours. It actually took a little over five hours due to some unforeseen difficulties. This time included a half hour to install Dynamat Extreme vibration damping material on the driver and passive radiator baskets.
Figure 1. CRS+ cabinets prepped for surgery.
Figure 2. Foam rubber insulation on the metal baskets was replaced with Dynamat Extreme.
Installation of the driver rings was easy and went as expected. I was surprised by the brittleness of the cabinet material. Figures 3 and 4 show the severe cracking that occurred during the drilling of two of the driver ring holes. Most of the other drilled holes exhibited much less severe, or no, cracking. The grade of MDF used for the CRS+ cabinet material is a lot different from that used in the SRS series SDA's.
Figure 3. Cracked driver hole on right CRS+.
Figure 4. Cracked driver hole on left CRS+.
Two of the driver cutouts were close to cabinet corners that had about 10.8 pounds of glue on them. Some of that glue needed to be cut and pried off to clear space for the rings (figure 5). I used a very sharp box cutter to slice through the glue and a large flat screwdriver to pry it off.
Figure 5. Gobs and gobs of glue in the corners, some of which had to be cut away to provide space for this ring.
Figure 6 shows the amount of glue that had to be removed near one cabinet corner, the toothpicks that were formerly used to "fix" five stripped driver screw holes and some of the cracked off MDF material that resulted from drilling. Considering the brittleness of the cabinet material, it is easy to see why the screw holes were so prone to stripping. Fortunately, the rings make that concern a thing of the past.:)
Figure 6. Top to bottom: glue that needed to be removed, "toothpick fixes" that were used to secure stripped driver screw holes, cracked
off cabinet material due to drilling.
When I started to install the ring for one of the passive radiators, I discovered that the drilling template was too big to fit inside the passive radiator cabinet cutout. I measured the cabinet cutout diameter as 10-10/64", the passive radiator rim diameter as 10-6/64", the ring diameter as 10-15/64" and the drilling template diameter as 10-15/64". The drilling template diameter should have been about the same as the passive radiator rim diameter, but it (and the ring diameter) exceeded it by a little over 1/16th" all around (figure 7). The larger ring diameter was not an issue since the ring holes lined up with the passive radiator rim holes and the ring was going inside the cabinet.
When I taped the over-sized template over the passive radiator cutout, I saw that four of the template holes lined up perfectly with the four screw holes in the cabinet cutout. The template's internal diameter also matched the internal diameter of the cabinet cutout. Therefore, the only thing wrong was the template's external diameter.
Larry (forum member TOOLFORLIFEFAN) said that he had two versions of 10" rings and templates and he had sent me the wrong ones. He is cutting me a new template and rings this weekend and I should have them next week. However, I wanted to get these speakers back in service, so I decided to grind off the excess steel. I had two options:
1. Do the grinding myself (hours).
2. Take the template to the machine shop at work and have it ground in about five minutes.
Actually, option 2 was less efficient and more time consuming because, by the time I spent an hour (round-trip) going to/from my work location, then tracked down someone in the machine shop to do the grinding, then answered 689 questions about why I needed this done and what I was going to use it for, then listened to them explain how much other work was ahead of me, probably four or five days would have expired and the replacement rings and template from Larry would already be here.
Figure 7. Passive radiator laid on top of its steel ring.
I used a compass to draw a circle 1/16" from the edge of the template, then a Dremel with grinding stone attachment #8193 was used to grind off the excess steel. It took two and one-half hours (four 30 minute sessions) with rest breaks in between grinding sessions to allow the Dremel and my hands to rest.
Figure 8. Setting up to draw a ring around the template for a grinding guide.
Figure 9. Me grind you long time. Of course I didn't do the real grinding in the dark. I dimmed the lights so the sparks would show up
better for this picture.
The grinding was tedious, but it was a labor of love. I fully expected that the end result would be Such Good Sound that all my toil and tedium would be quickly forgotten the moment I fired up my "new" CRS+'s.:)
Figure 10. The adjusted template worked as required. I numbered sections of the template so that I always knew where I was as I was
Figure 11. The famous, "temperamental" CRS+ passive radiator grille gets sized up for drilling.
How many of you CRS owners have passive radiators where one, or more, or all of the screws are going in at an angle instead of straight in? This is due to the fact that care was often not used to perfectly align the holes in the metal passive radiator grille with the holes in the passive radiator basket rim. This misalignment often caused the passive radiator/grille screws to be deflected and go into the wood cabinet at an angle. I laid the passive grille on top of the passive ring and placed dots of red paint where the new holes were to be drilled. The grille was secured to a 12" x 12" piece of scrap wood with two of the original wood screws to hold it for drilling. The rim edges of the CRS grilles were often cut out of round. This could cause problems if the grille holes were not reinstalled with the original orientation to match the corresponding cabinet holes. I marked the "top" of the ring and the "top" of the grille so that they both would maintain proper orientation at installation.
Figure 12. Finished CRS+ passive radiator and grille installation, with an optimal eight button head hex screws instead of the standard
four wood screws.
Figure 13. Finished driver installation with four 8/32 socket head cap screws (just like the SRS's use) rather than four wood screws.