By John E. Johnson, Jr.
Tekna Sonic Vibration Absorbers; Model C-10; operating range 50 Hz - 2 kHz; size 1 3/4"H x 7"W x 4 3/4"D; weight 1.25 pounds; $53 each; Model C-12; operating range 15 Hz - 500 Hz; size 1 3/4"H x 7"W x 4 3/4"D; weight 2.2 pounds; $78 each; Tekna Sonic, Inc., 442 Houser Street, Suite E, Cotati, California 94931; Phone 707-794-1512.
Coloration of sound produced by the vibration of speaker enclosures is not an easy problem to deal with. Most manufacturers use a combination of things to combat it, such as cross bracing and various types of damping material (fiber glass, foam, lead). In spite of this, there is often some residual vibration of the enclosure when sound is being reproduced through the drivers. The Tekna Sonic Vibration Absorbers are designed to reduce the effects of residual cabinet vibrations. They manufacture several models, and we were supplied with the Model C-10 for regular speaker use, and the Model C-12 for subwoofers.
The C-10 and C-12 look very similar. They consist of a black plastic face that adheres by use of a thin magnetic sheet which is first attached to the speaker enclosure (peel and stick surface). The absorber is positioned against the magnetic sheet, twisted a bit, and then you feel it click into place. Plastic fins hang down from the main body of the unit (see photo), which are supposed to dissipate cabinet vibrations.
We tested the C-10 with a pair of Velodyne DF-661 mini-monitors, and the C-12 with an M&K V-90 subwoofer. The C-10 test was performed single blind, using a 60 second segment from a CD which had vocals and instruments. The absorber was attached on the rear of the enclosure, just above the port. The music was first played for the referee with and without the C-10s attached (1 absorber on each speaker), stating which was which. Then the test was performed (the same 60 second music segment), utilizing five segments with and five segments without the absorbers, in random order, with 30 seconds in between each test, with the referee blindfolded throughout all tests and blocked from hearing what we were doing in between each test. The referee was asked to say whether the absorbers were on or off the speakers according to how they sounded. Of the ten tests, the referee judged three correctly (one with the absorbers, and two without). These results indicate that there was not a significant difference with or without the absorbers, as judged by the referee.
The next test was not performed single blind. We used two C-12s on the M&K V-90 subwoofer. We felt along the cabinet for areas that had the most vibration when playing music, and placed both C-12s on the one V-90. We then played music that had strong bass notes and alternately put the two C-12s on, and took them off, while the music was playing. Neither of two referees could hear any difference between the two configurations (C-12s on or off the enclosure) with twenty tests (ten on, ten off). We could feel the absorbers vibrating when we placed a hand against them.
The final test we performed was to place a C-10 on a rug and tap the uppermost fin. We placed a microphone close to the fins and recorded the sound. It produced a distinct tone that lasted for more than 400 milliseconds.
Now it seems to us that when such a force is applied to this device, it should not produce a tone at all, but should absorb the force immediately, like a shock absorber on an automobile. Such was not the case here.
In summary, we found no significant improvement in sound quality when the Tekna Sonic Vibration Absorbers were used on some of our reference speakers (mini-monitors and subwoofer), and therefore, we cannot recommend them. In all fairness, they may produce a more audible difference when used with inexpensive speakers that have a lot of cabinet resonance. However, it seems more prudent to spend that money on better speakers to begin with. If you already have some low priced speakers that have a great deal of resonance, and you don't want to part with them, you can try the Tekna Sonics for yourself. We hope your luck will be better than ours.
John E. Johnson, Jr.
© Copyright 1995, 1996, 1997 Secrets of Home Theater & High Fidelity
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