1 plus 1, Output, varied output sound level

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Jim Lesniak2004-02-23 22:21

Mr.Andy Szabo, I recently purchased a used pair of Acoustat 1+1\'s. They sound great but one of the speakers will vary in output sound level. I removed the socks because they were dirty and in doing so discovered a problem with both the upper and lower panels on this speaker. The diaphram conductive coating on both has cracked and is peeling right where the bias wire is bonded on. It looks to me that when the cracks progress far enough the connection the whole panel will be lost.

The area affected is only at the bias wire pad area and only affects about 1 square inch. Interestingly the rest of the panel seems intact. These panels do have the yellow/red striped bias wire indicating the more up to date coatings. Is there any way to repair this damage? Is there any conductive coating material that would fill and bridge these crack gaps?

Thank you in advance for your advice. Jim Lesniak


Andy Szabo2004-02-23 22:21

This is a rare problem indeed, and perhaps the first time I have ever heard of such a failure. When Acoustat began use of the new ”high resistance” coating (indicated by the yellow/red bias wire), the older ”low resistance” coating was still used for the small area next to the wire connection. There was some concern that too much heat might be dissipated in that small area if the high resistance coating was used. Later on, that concern was found to be unwarranted, and the high resistance coating was used everywhere. I suspect you have panels from those early days that used the two different coating formulations.

The only reason I mention this is to help explain why the coating is failing on that small area only. There is nothing inherently wrong with the low resistance coating that would make it fail. Instead, I think this is a case of bad workmanship, in that the coating was improperly applied in that small area.

So much for the explanation of why: how does one fix this problem? Since Acoustat panels are so reliable, no one has any experience in fixing such a problem. When Acoustat was active, the rare bad panel was merely replaced under the lifetime warranty.

My first advice: enjoy the speakers while they are still working, and don\'t try to fix them until there is a performance problem (but perhaps you are already at that point). The panel should be okay as long as there is a complete conductive path. Attempting to repair the panels will be a touchy operation at best, and there is always the possibility of permanently destroying them.

I have located a conductive material that may be okay for this application. Beware that I have never attempted such a repair, and that this method is untested. MG Chemicals #840-20G, called ”Nickel Print” is a nickel bearing acrylic paint. It is a very low resistance, so it would not be suitable for coating the main area of the panel, but should be okay (electrically) for the small bias lead-in. My one concern is how well this material will adhere to the Mylar. The original coatings were solvent based, and would bond on a molecular level to the diaphragm. The Nickel Print, being acrylic, will merely adhere to the surface: how well is unknown.

The paint is available from Allied Electronics, www.alliedelec.com; their part number is 661-0385. A ¾ ounce bottle is about 8 dollars. This material should be applied only on the small area that serves as the bias lead-in.

I do have some concern about applying a new coating directly on top of the failed area. If the original coating is not adhering well to the Mylar (i.e. flaking off), a new layer might also fail if not properly bonded to the diaphragm. This is like any re-painting operation: the old, flaky paint must be removed before a new coat is applied. If however, the original coating is well bonded, but merely cracked, then it may be okay to apply the repair directly on top of the original.

Good Luck, and let us know how this works out!

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