Steel Retaining Rings For SDA Drivers And Passive Radiators
Introduction
This article discusses the procedure used to install stainless steel driver and passive radiator retaining rings on my SDA SRS 1.2TL speakers and the initial listening evaluations after installation.
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Figure 1. A package from the ringmaster: driver and passive radiator retaining rings for five sets of SDA's.
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Figure 2. Real, big-deal, steel rings and drilling templates...laser cut to exact specifications. I feel sorry for SDA owners who are not Club
Polk members. Such Good Perks.
Tools
1. 9/64" hex bit for the stock and new 8-32 socket head cap screws used on the 6-1/2" drivers and crossover plate.
2. 5/32" hex bit for the stock retaining nuts for the socket head cap screws.
3. 3/32" hex bit for the new buttonhead hex socket screws used on the passive radiators.
4. #1 Phillips screwdriver for the stock passive radiator wood screws.
5. Four 2" C-clamps. Two were used to hold the drilling template for the drivers and four were used to hold the drilling template for the passive radiators.
6. Flashlight for inspecting cabinet interior prior to and after vacuuming and for peering into drilled holes in cases of slight misalignment.
7. Cordless drill with a leveling indicator light to help maintain a straight, level cut.
8. Cordless power screwdriver.
9. Manual socket screwdriver.
10. 9/32" drill bit. This size drill bit is the same size as the diameter of the retaining ring screw posts. This means that I had to use the drill bit to route out the holes a little after drilling. If I had used a larger drill bit, I would incurred the risk of damaging the template holes.
11. Tyson DC-14 animal vacuum cleaner with circular brush attachment.
12. Staple gun for securing polyfill damping material to cabinet side.
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Figure 3. All set to go in one more time.
Installation Procedure
The right speaker was done first and then compared to the left. Each speaker took 2-1/2 hours to complete. It was well worth the time, effort and cost.
I did not use hot glue to further secure the rings to the inside of the cabinet. The rings fit snug and I did not think glue was necessary. Plus, if I ever needed to remove the rings, glue would have made removal difficult.
1. Speaker cables were disconnected. Turning off the amplifier works just as well.
2. Drivers, passive radiator, crossover plate/circuit board, internal wiring, polyfill batting was removed. The binding post wiring was covered in plastic wrap and the end of the binding post wiring harness connector was covered with tape.
3A. I started drilling at the bottom of the cabinet and worked my way up. That way, I did not have a big pile of sawdust accumulating below me as I worked my way down. I could have put something in place to catch the sawdust, but it was much easier to just vacuum the cabinet after the drilling was done.
3B. The passive radiator template was aligned so that the existing screw holes were in the center of each template holes and secured with four 2" C-clamps. It just so happened that the passive radiator screw holes on both speakers perfectly lined up in the centers of the template holes. This was not usually the case with the driver screw holes in both speakers.
3C. The wood (MDF) is relatively soft, therefore a lot of drilling speed and pressure was not required. You want to maintain a slow, steady, straight and level cut through the wood so that the holes will be true with the retaining ring posts. The leveling indicator light on the drill was a big help in keeping my cuts straight.
3D. After the holes were drilled, they were slightly enlarged by passing the drill bit over the inside only one time.
3E. The holes and area around the holes were brushed and vacuumed.
4A. The passive radiator retaining ring has two opposing slots cut out in order to make bending for insertion easier. The ring was easily bent back into flat shape once it was inside the cabinet.
4B. The passive radiator ring posts were a snug fit, but were perfectly aligned with the cabinet holes and easily popped into place.
5A. Next I moved up to the lower driver holes. The 6-1/2" driver template was carefully aligned with the existing four holes, secured with two C-clamps, then holes drilled with the same slow, steady procedure stated in step 3C.
5B. The template was removed and the holes were slightly enlarged by passing the drill bit over the inside only one time. Driver rings were inserted through the crossover plate opening.
In only a few cases did the existing holes perfectly align in the center of the template holes. Usually, three ring posts would be perfectly aligned with three holes. I used a flashlight to peer into the misaligned hole to see where I needed to make a cutting adjustment. The adjustment was always minor, after which the ring could be pressed into place. In a few cases, the center of the existing holes matched perfectly with the template and no adjustment was necessary after the initial hole enlargement.
5C. After each driver's holes were drilled and enlarged, the holes and area around the holes were brushed and vacuumed.
6. After all rings were installed, the cabinet interior and exterior was vacuumed three times with the circular brush attachment.
7. The column of polyfill batting behind the right speaker's stereo drivers had slid down six inches. The column of polyfill batting behind the left speaker's dimensional drivers had slid down six inches. The other two polyfill columns were still in place after 20 years. During reassembly, all polyfill columns were secured to their adjoining speaker side with one 3/8" staple.
8A. The right speaker was reassembled a listening evaluation was done. After the listening evaluation, the left speaker's rings were eagerly installed.:)
8B. The socket head cap screws (SHCS) can be used to secure the passive radiator. However, the head diameter of the buttonhead hex screw (BHS) is almost the same as the head diameter of the stock Phillips wood screw. The SCHS head diameter is approximately 75% of the diameter of the stock Phillips screw. I used the BHS's to secure the passive radiators to their rings.
8C. WARNING: Since you will be securing the driver and passive radiator baskets to metal, and you are now relieved of the concern for stripping out the wood threads, you must be mindful that you must still use care when tightening the screws...especially if you are using Mortite driver seals. Remember that the driver and passive radiator baskets are made of relatively soft metal. Over tightening could cause the metal screw heads to punch through the basket rim holes. I tightened just past the point where the turning resistance significantly increased.
I used a power screwdriver to remove all screws but only used it to reinstall strews halfway down. The rest of the way was hand tightened with a regular socket screwdriver. I hand tightened a couple of turns per screw in a sequential, diagonally-opposing pattern to minimize stress on the basket rim and to assure a level seating on the cabinet face.
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Figure 4. Such good drilling. I wish I could say the same of British Petroleum.
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Figure 5. The gleaming ridge behind the passive radiator opening is the newly installed retaining ring. How many of you have toothpicks
stuffed in your passive radiator screw holes due to stripped threads in the wood?
Cabinets Standing Up Or Lying Down?
I understand that some may prefer to perform this modification while the speaker cabinets are lying flat. Before doing so, I ask that you consider the following:
For me, laying the speakers on the floor and then having to kneel over them while trying to hold the drill steady would have been very awkward since I was concerned with making a straight cut. If someone prefers to lay the cabinets flat, I would advise laying them on a surface that puts them at waist height.
Keeping the cabinets upright allowed me to keep my body upright and it allowed me to keep my wrists straight and to keep the drill bit perpendicular to, and close to, the the center of my upper body. This facilitated better control over the drill. Most people tend to have better hand/eye coordination when looking ahead than when looking down.
I started drilling while sitting on the floor, then kneeling, then standing.
