2 plus 2, Various, resonant problem

Read more on the Acoustat 2 plus 2 in our home audio section

Aaron2004-02-23 22:21

Hello Andy, I have read almost this entire section on Acoustat. Wonderful information! I do have a question that I believe wasn\'t asked. I recently had a ”flopping” sound coming from one of my panels on my 2+2\'s. These are MK-121B Medallion with the 5 wire panels. Reading about the heat treatment I decided to give it a try. When I pulled the sock down I found that it was one of the dampening pads had fallen down and was creating the sound. So I said what the heck and heat treated any way. My mistake, one of my upper right panels now has a horrible resonant vibration coming from the entire mid section of the panel!(Maybe I got it too hot?) These speakers are so near and dear to me that I feel like just jumping off a cliff(humor).

Is there anything I can do to fix the ”vibrating” panel? There is a guy who has some spare panels but they only have 3 wires. Is there any draw back to these panels? Are they compatible? What should I do . .?! Thank you very much for your time. Aaron

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Andy Szabo2004-02-23 22:21

I\'ll assume that you have already reattached the felt pad(s) on the rear of the panel. If not, they are important for resonance control, and should be repaired. Using a spray contact adhesive, apply a generous amount to the felt\'s surface (not the panel!), allow the glue to get tacky, and then reattach at its original location.

Unless you actually melted a hole in the Mylar, you probably did not do any permanent damage to the panel with your ”heat treatment”. You may not have heated the Mylar evenly, or you may have dirt in the panel. First, use a vacuum cleaner to thoroughly clean the louver structure of any foreign material. Do this on both front and back. Also check the panel mounting screws for tightness: the nylon bushings can rattle if the screws are not tight. Then, using a high-powered hair drier, or, with care, an industrial heat gun, slowly heat the Mylar by constantly moving the hot air source. Do not allow the heat to dwell in any one area. Do this from the front of the panel, so the felt does not block the hot air. The idea is to get the entire diaphragm hot at the same time. Be patient: this may take a few tries.

If you cannot repair the panel, it is possible to use a three-wire panel as a substitute for a five-wire panel. The only difference is that the stator wires are connected at one end only on the three-wire version. It is unlikely that you\'ll detect the difference, and it is certainly better than no panel at all.

And stay back from the edge of that cliff: we\'ll get your speakers going again!

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