Last Tuesday I received another delightful package from The Ringmaster, forum member and expert metalsmith, TOOLFORLIFEFAN. This time, the SRS hot rodding enhancement items were steel brackets for SDA tweeters. It's great being a member of an audio club with such talented membership. This report discusses the installation of steel tweeter brackets to my SDA SRS 1.2TL's, SDA SRS's and SDA CRS+'s.
Discussions of the installation of steel rings for my SDA SRS 1.2TL's, SDA SRS's and SDA CRS+'s can be found here:
Link: Steel Retaining Rings for SDA Drivers and Passive Radiators
Link: Driver and Passive Radiator Rings for the SDA CRS+
Figure 1. I don't know if the extra drilling template was included on purpose, but it was convenient when setting up drilling for
SDA's that had two or more tweeters per cabinet.
CRS+ (1989 Version) Tweeter Bracket Installation
Prior to the tweeter bracket installation, all three pairs of CRS+'s had received "TL" modified crossovers with Mill MRA-12 resistors and premium polypropylene film capacitors, RD0198 tweeters, improved grille cloth, Mortite speaker seals, Dynamat Xtreme driver basket insulation, improved heavy duty binding posts and steel retaining rings for the drivers and passive radiators.
Figure 2. A quick partial disassembly, and drilling, and I was on the way to better sound.
Disassembly, drilling, cleanup and reassembly took 12 minutes per CRS+ cabinet. Transporting one pair of CRS+'s to and from work, packing and unpacking them, digging two pairs of CRS+'s out of storage, unpacking, repacking and placing them back in storage took 3.5 years.;)
I did not completely disassemble the CRS+'s. I only needed to remove the tweeter, both drivers and the polyfill batting. I could have just removed the tweeter, drilled the holes, and popped the brackets in place...if I didn't mind having sawdust in my cabinets. However, that would have been very disrespectful toward the CRS+'s.
Figure 3. Completed. Goodbye wood screws and cracking particle board forever.
Figure 4. This pair of SDA CRS+'s is going back to office system duty at work.
Figure 5. A bracketed pair of teak CRS+'s were compared to their unbracketed twins (in the right corner).
Three pairs of SDA CRS+ speakers received brackets: a black oak pair and two teak pairs. The black oak pair was done first and compared to an unbracketed teak pair. Next, the left speaker of one of the teak pairs was bracketed and compared to the unbracketed right speaker. Finally, a bracketed teak pair was compared to an unbracketed teak pair.
All I was expecting from the bracket installation was a better mechanical connection of the tweeter to the baffle. The first thing I noticed when listening to the newly modified black oak CRS+'s was an improvement in bass weight, bass definition and and bass clarity.
On the "For You Always" track of Everette Harp's "Better Days" CD, there is an electric bass growl at 00:12 that was clearly defined on the bracketed oak CRS+'s but slightly blurred on the unbracketed teak CRS+'s. The synthesizer cloud stretching across the sound stage had a lighter, more airy sound with the bracketed CRS+'s. The bracketed CRS+'s also sounded apparently louder.
When the left speaker of one of the teak CRS+'s was bracketed and compared to the unbracketed right speaker, the left speaker sounded louder and the drum sounds shifted slightly to the left.
Comparing the fully bracketed teak pair to its unbracketed identical twin teak pair demonstrated the same differences as heard during the comparison of the bracketed oak pair to the unbracketed teak pair.
Figure 6. One of the secrets to the superior, clean bass response of SDA's is the 100% asbestos fiber fill material. Scientific
subjective listening tests confirmed that no other fill material sounds as good as pure asbestos.
Just kidding about the asbestos.:)
SDA SRS 1.2TL Tweeter Bracket Installation
The installation of the SDA SRS 1.2TL tweeter brackets took 4.5 hours, exclusive of the time it took to go to Home Depot to get some Dremel reinforced cutoff wheels to trim the brackets. The ends of all brackets required trimming and the straps of the brackets for tweeter #2 required trimming.
Figure 7. The Monoliths wonder how many more times they will have to strip naked for
the furtherance of Such Good Sound.
Figure 8. The bracket ends bumped against the bracing. The contact points were marked and 1/8th" of metal was sliced off.
Figure 9. I opted for larger and stronger reinforced cutting wheels for this project.
I usually use a heavy duty Dremel cut-off wheel (part #420) for metal cutting. However, I was only able to cut 3 brackets per wheel. The reinforced Dremel cut-off wheel (part #426) allowed faster cutting and I was able to cut 8 brackets per wheel. The total cutting wheel cost was higher with the reinforced cut-off wheels ($1.50/wheel vs. $0.30/wheel), but I was able to complete the job much faster due to the reinforced wheels faster cut time and not having to stop and change wheels after every third bracket. Plus, the reinforced wheels were more resistant to overheating and shattering.
Figure 10. Cutting jig for brackets with a bracket on the left popped in place.
I made a cutting jig out of a 12" x 12" piece of melamine covered MDF. I drilled two holes in the board which corresponded to the size and location of the bracket's thread shafts. I cut the first bracket, verified that it cleared all of the internal braces, then used it as a template to mark the other 15 1.2TL tweeter brackets. Please remember to wear safety glasses when cutting.
Figure 11. The left bracket for tweeter #2 of the right speaker with ends trimmed. Still a little more cutting to be done due to some
ring/bracket overlap at tweeter #2.
Tweeter #2 is directly between the second (from top) set of horizontal drivers. This resulted in an overlap of the tweeter brackets and the driver rings (figure 11). I don't think it is absolutely necessary to cut out the overlapping portion of the tweeter brackets, but I wanted mine to fit flush. I marked the ring contact points on the brackets and used the driver ring template to draw a cutting guideline (figure 12). The trimmed brackets are shown in figure 13 and one of the installed brackets is shown in figure 14.
Figure 12. The contact points between the #2 tweeter brackets and their adjacent driver rings was marked. The driver ring drilling
template was used to draw a curve guide line for the cut out.
Figure 13. Trimmed brackets for tweeter #2 of both speakers.
Figure 14. Left side trimmed #2 tweeter bracket installed.
Figure 15. Complete set of end-trimmed tweeter brackets for SDA SRS 1.2TL's.
Figure 16. Drilling holes for two bracket sets at a time was convenient. If I were doing another set of SRS's I would order a second
pair of tweeter drilling templates so that I could do all four at one time.
The listening evaluation for this tweak provided the same benefits noted with the CRS+, plus the added benefit of my accidental room treatment discovery discussed here. I installed brackets in the right speaker first and did left/right comparisons. I immediately felt more bass vibrations coming through the right armrest of my seat and heard more enhanced bass growls from organs and electric bass guitars. I also noticed a big difference in the clarity and weight of synthesizer sounds, particularly when such sounds were mixed to envelop the entire sound stage.