Cookie wonders why I would waste a beautiful spring day taking apart my speakers...again.
This is my favorite kind of mod: cheap and easy with a big payoff. Adding a few strips of Blackhole 5 to the driver/tweeter area of my speaker cabinets provided a bigger improvement than the expensive and very time-consuming rewire (with AudioQuest GO-4 speaker wire). Blackhole 5 is a five-layer foam and stiff polymer material that provides cabinet damping, isolation, and absorption. A 27" x 24" sheet cost $84.90 from Soniccraft (inclusive of $14.95 shipping) and was enough to do both speakers. Blackhole 5 is not recommended in the passive radiator area because it will interfere with the transmission of vibrational energy (fluid coupling) from the drivers to the passive radiator.
Figure 1. Blackhole 5 top side.
Figure 2. Blackhole 5 back side, sectioned off for cutting.
The following pieces were cut from the 27" x 24" sheet:
1. Four 3" x 27" strips, to go behind the stereo and dimensional drivers.
2. Four 1.5" x 27" strips, to go on the cabinet sides.
3. Eight 3" x 6.75" blocks, to go behind the tweeters.
The interior volume of a SDA SRS 1.2TL cabinet is 6.77 cubic feet. The total volume of the Blackhole 5 pieces was 0.26 cubic feet, or 3.8% of the interior volume. However, Blackhole 5 is claimed to only displace 0.25" of air, in which case the effective total volume of the Blackhole 5 pieces was 0.05 cubic feet, or 7 tenths of 1 percent of the total speaker interior volume.
Figure 3. I used common kitchen cutting tools.
Figure 4. My cuts weren't the neatest, but they didn't have to be.
I used a box cutter with a sharp new blade to score through the stiff polymer layer, cutting along guidelines in red. Next, I made a starting cut through the foam with ordinary, but sharpened, scissors. Finally, I used a sharp meat cleaver to saw through the foam along the guidelines. It took 20 minutes to complete cutting.
Figure 5. Blackhole 5 installed in right speaker.
Figure 6. Blackhole 5 block behind tweeter.
Figure 7. Blackhole strip on cabinet side.
Figure 8. Polyfill was reinstalled after Blackhole installation.
The cabinet walls were wiped with a dry cloth prior to installing the Blackhole 5. A small, quiet voice tried to get me to disassemble my speakers and reseal the cabinets with an appropriate construction grade sealant, but I ignored it. I'm getting a 3 second fall on the passive radiator pressure test...so I'm good.
The 3" x 27" strips were horizontally centered behind the drivers and were vertically centered by starting them 2.5 inches from the top of the cabinet. The 1.5" x 27" strips were horizontally centered on the side walls and started 2.5" from the top of the cabinet. Installation took 55 minutes per speaker. I only removed the drivers, polyfill, and the crossover. I would have removed the driver wires, but I have the stiff, solid core wire bent in a certain way for strain relief for the relatively soft driver connection tabs, and I did not want to have to go through the tedious process of realigning them again.
I was very pleased to find that the pressure sensitive adhesive was STRONG!
The right speaker was done first. Percussion instruments, like shakers, were much clearer than on the left. The articulation of words with clicks and sharp transients (e.g. unique, breeze, whisper, ocean, etc.) was much clearer and detailed on the right. The sound stage weight shifted to the right and there was more tactile sensation on the right. There was more speed, definition and articulation in the bass. This was evident in both stereo and mono modes with just the right speaker treated. I have been reading about this modification for years, but I was still quite pleasantly surprised at the level of improvement. The right speaker was generating Such Good Sound that I was very enthusiastic about treating the left speaker.
After both speakers were treated, There wasn't any improvement in spatial properties, but there was a significant improvement in detail overall, particularly at the sides and rear of the sound stage. Since the passive radiator was getting more clean coupling to the drivers, bass output, articulation, detail and speed was increased.
Thanks to Polkmaster1, drumminman, and Toolfan66 for their pioneering work with this modification.
When I put these speakers up for sale next April, I hope the next owner appreciates all the hard work that went into updating and optimizing their performance.