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In Reply to: May be a dumb question, but here it goes............ posted by benglert on July 19, 2004 at 20:44:20:
I asked about Dynamat Extreme and the benefits of the aluminum layer. Not rollers and points!Thanks!
Follow Ups:
The original Dynamat, and similar products, are simply gooey, heavy sheets that stick to the car metal and offer limited damping while adding a lot of mass. Added mass is bad, because it reduces the combined structure's resonant frequency. This increases the excursion of the vibrations and makes it harder to tame them with other means.Constrained-layer damping forces the damping gooey material to be placed into what is called "shear" in order for the structure to vibrate. This dissipates a lot more energy per unit weight of the damping material, so you get a lot more damping action without adding a lot more weight.
The aluminum layer on Dynamat X-treme is designed to give good damping with typical car body sheet metal. That it also works on most audio component box and chassis metal is good for us, because it is sold into the car market rather than the high-end. There are plenty of extremely expensive high-end alternatives that are probably more effective under the right circumstances, but much more costly than what this experimenter is willing to pay.
To finally answer your question, now that you know why it is there, no it is not likely to give good shielding. For one thing, it is not grounded by installation, and grounding it securely would be a major PITA. It is not designed to have thickness or resistivity appropriate for electrical shielding. Since it is usually attached to metal, having it there is not necessarily bad. However, there may be cases where the fact that it is electrically floating would cause problems.
If you need to have additional shielding, you can attach an appropriate copper sheet with polyurethane construction adhesive to the aluminum side. This would increase the constrained-layer damping effectiveness, as the polyurethane rubber is also a dissipative material.
Be careful with Dynamat X-treme on thick metal objects, like the typical upmarket component front panel. It is not effective on such objects, and makes their ringing worse by lowering their resonant frequency.
for effective shielding to occur, you would need to completely surround the object you're trying to shield, and also connect the shield to ground. I'm definitely not an expert on shielding, though. If you don't soon get some good answers, you may want to try re-posting with a more specific subject line (something like 'Foil Shielding - advice wanted)- lots of people with good information only have time to scan the subjects and will only read the ones which look interesting to them.
N/T
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