2 plus 2, Panels, rattling

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Ronald Hicks2004-02-23 22:21

The upper left panel on one of my 2+2\'s is making a \'rattling\' noise on low bass notes. I\'ve isolated to this particular panel after thinking it was some window panes rattling in the room. When playing a test disck at a low level, this is the only one out of the eight total that\'s making this sound. Since the panels have a history of being \'indestructable\', is it possible the mylar has become loose? It almost sounds like the diaphragm is hitting the stators, but this is the only element doing this.

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Andy Szabo2004-02-23 22:21

There\'s not much that can go wrong with an Acoustat panel. Sometimes, however, the Mylar can loose its tension, and exhibit the rattling sound you describe. This can be fixed.

Disconnect power from the speaker and allow it to discharge. You\'ll need to remove the grille cloth, so see my Technical Bulletin Grille Cloth Removal: Cleaning and Replacement. Once you have access to the inside of the frame assembly, check all the panel mounting screws for tightness. That\'s not likely the cause of your problem, but it\'s a good idea to check while the speaker is open.

The Mylar is a heat-shrinkable material, so a re-application of heat is required to re-tension the diaphragm. It is not necessary to remove the panel from the frame assembly. For a heat source, use a high-powered hair drier, or (with care, on a low setting) an industrial heat gun. Hold the heat source a few inches away from the panel\'s grid and keep it constantly moving. Slowly blow the hot air over the entire surface of the diaphragm. The idea is to evenly heat the entire surface until the Mylar re-shrinks. DO NOT hold the heat source on one point: excessive heat can actually burn a hole in the diaphragm, which is not repairable. This caution is especially important if you are using an industrial heat gun.

How do you know when you have successfully re-tensioned the Mylar? It is unlikely you\'ll be able to tell by appearance or touch. Wait until the panel has completely cooled, re-apply power to charge the speaker, and wait several hours for it to stabilize. Then play a signal known to cause the problem, and see if the rattle has been eliminated. Repeat the process as required, making sure the speaker has been completely discharged prior to each re-heating.

This is a relatively simple process, but, as mentioned above, it can also result in disaster. So, it is better to apply the heat gently, and slowly work up to a heat level where the Mylar re-shrinks. This may take several attempts.

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