Armacell Armaflex pipe insulation tape was compared to original SDA foam seals and Mortite seals in three pairs of SDA CRS+ loudspeakers. Armaflex was compared to Mortite in SDA SRS 1.2TL's and SDA SRS's. Armaflex is composed of 1/8th inch thick by 2" wide elastomeric synthetic foam rubber. All SDA loudspeakers tested have tweeters, drivers and passive radiators secured with steel rings.
Figure 1. Mortite, original SDA foam seals and Armaflex pipe insulation tape.
Figure 2. Original SDA foam rubber gaskets that were replaced with Mortite. I usually keep original parts...just in case.
Results varied among the three types of SDA's. In the CRS+'s, there was no audible or tactile difference between speakers equipped with Armaflex or Mortite. Both Mortite and Armaflex outperformed the original seals in the areas of overall clarity, detail, bass articulation and tactile sensation. There was no change in spatial information.
Others have found the original seals/steel ring combination to sound superior to the Mortite/steel ring combination. Those reports can be read at these links:
Mortite, Rings and Gaskets
Jesse's Right About Mortite
Based on results from the CRS+ trials, original seals were not evaluated in the SRS's and 1.2TL's. In the SRS's, Armaflex provided more overall clarity, detail, bass articulation and tactile sensation. There was no change in spatial information.
In the 1.2TL's, Armaflex provided more overall clarity, detail, bass articulation, image weight and tactile sensation. There were improvements in spatial information ranging from subtle to substantial, depending on the recording.
I used a 1/2" wide chisel to scrape Mortite off the driver and passive radiator rims. For most of the tweeters, I could simply peel off the Mortite. I occasionally had to use a small flat blade screwdriver on some tweeters. If you decide to remove Mortite from your driver rims, take care not to hold the drivers by the magnet. You don't want to risk shifting the magnet assembly. I held my drivers by the basket spokes.
Figure 3. Mortite came off easily with a nice sharp chisel.
Figure 4. Mortited parts ready for stripping and application of Armaflex strips.
Marks 1/2" apart were made on the Amaflex's backing at regular intervals. Ink and pencil marks did not easily adhere to Armaflex's yellow wax paper backing, therefore a fine point ink pen was used to punch holes and then the pen and straight edge (24" drafting T-square and 48" carpenter's level) were used to scribe cutting guide lines. The tweeters' silk domes were protected while face down by placing the tweeters on a roll of electrical tape.
Figure 5. Completed Armaflex installation on CRS+ drivers, passive radiator and tweeter.
Audio Evaluations - Methodology
Listening evaluations were done with familiar, well-recorded CD's and SACD's. Detailed listening notes were taken and the placement and quality of sound images were marked on a chart. Measurements for frequency response, harmonic distortion and bass decay were taken with Dayton Audio OmniMic software running on a laptop computer. The OmniMic microphone was placed at the listening position at ear height. The home's central air conditioning units were turned off during listening and measurement sessions.
The color coded lines on the harmonic distortion plots represent the following:
Black - frequency response.
Dark blue - sum of 2nd-5th harmonics.
Red - 2nd harmonic.
Purple - 3rd harmonic.
Green - 4th harmonic.
Light blue - 5th harmonic.
You may find it easier to discern differences in the plots if you save them to your computer and flip through them. Reasonable targets for frequency response in residential music rooms are +/- 10 dB from 10 to 200 Hz and +/- 5 dB from 200 to 20 kHz.
Audio Evaluations - SDA CRS+
Figure 6. Two identical pairs of CRS+'s were evaluated in the home theater system.
The teak finished CRS+'s evaluated in the home theater system have been extensively modified as described here:
CRS+ (1989 Version) PCB, Xover and SDA Inductor Upgrade
Driver and Passive Radiator Rings for the CRS+
Figure 7. The SRS's were moved out of the room and each CRS+ was set up on a pair of Metal Technology TMT-30 30" stands.
One pair of CRS+'s was marked with blue tape and designated the "control" pair. It had Mortite seals throughout the trials. The other pair was "variable" and had its seals changed from Mortite to original foam to Armaflex.
I could discern no audible or tactile differences between the Mortited control CRS+ and the Mortited variable CRS+, although there were minor differences in the frequency response and harmonic distortion plots.
Figure 8. Frequency response of control teak CRS+ pair with Mortite.
Figure 9. Frequency response of variable teak CRS+ pair with Mortite.
Figure 10. Harmonic distortion of control teak CRS+ pair with Mortite.
Figure 11. Harmonic distortion of variable teak CRS+ pair with Mortite.
Figures 12 through 15 show the frequency response and harmonic distortion plots for the variable teak CRS+'s with the original foam seals and with Armaflex seals. Installing the original seals resulted in diminished clarity and detail and blurred bass. For example, on Jakiem Joyner's "Stay with me tonight" track ("babySOUL" CD) The distinct locations, as well as the note articulations, of the electric bass and kick drum became blurred. The congas on the left became muted and their reverberant envelope was significantly diminished. The string overtones and decay of acoustic guitar notes at the center right were muted. The echoes of acoustic guitar notes coming from the left and right speaker were muted. Tactile sensation and image placement remained the same as with Mortite.
Replacing the original seals with Armaflex restored the "life" to the sound. I could discern no audible or tactile difference between the control CRS+'s with Mortite and the variable CRS+'s with Armaflex.
Figure 12. Frequency response of variable teak CRS+ pair with original foam seals.
Figure 13. Frequency response of variable teak CRS+ pair with Armaflex seals.
Figure 14. Harmonic distortion of variable teak CRS+ pair with original seals.
Figure 15. Harmonic distortion of variable teak CRS+ pair with Armaflex seals.
Audio Evaluations - SDA SRS (Signature Reference System)
The SRS's in my home theater system have bee extensively modified as described here:
Further Improvements to the SRS...
Figure 16. SRS's in home theater system.
In the SRS's, the Armaflex seals provided more overall clarity, detail, bass articulation and tactile sensation. There was no change in spatial information.
Figure 17. Frequency response of SRS's with Mortite seals.
Figure 18. Frequency response of SRS's with Armaflex seals.
Figure 19. Harmonic distortion of SRS's with Mortite seals.
Figure 20. Harmonic distortion of SRS's with Armaflex seals.