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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Copper Plates or Copper Paint? posted by rober on April 29, 2007 at 12:12:37:
Steel is a poor material for amplifier chassis. One thing that makes it especially bad is the way its magnetic properties turn the chassis into a microphone. Consider that all the signals conducted by wires inside the chassis have some magnetic coupling to the sheet metal. Vibrations in the sheet metal will induce voltages in the wires.Heavy objects mounted to sheet metal will have low fundamental resonance frequencies. These may be in the range of bass to mid-bass, and will make reproduction of instruments with power in this range vague and unsubstantial. I found this problem with an InnerSound ESL-300, which has the heavy power transformer mounted near the center of the sheet steel bottom chassis plate. Stiffening the bottom plate (by supporting it on Deflex rubber sheet over a thick butcher-block cutting board) greatly improved the image palpability and realism of bass instrument reproduction. In your case, be sure any heavy objects are supported by braced sections of the chassis.
The TI shield suggestion below is a good one. This material is designed to dissipate RF energy, so it will reduce the internal electrical resonances of the chassis box. However, mechanical stiffening and damping are also important. I've had good results with Dynamat X-treme, a constrained-layer damping composite sold to the automotive sound industry for damping car body sheet metal. This is a damping rubber with a thick aluminum foil on one side and adhesive on the other. Apply the Dynamat first, then attach the TI shield to the aluminum layer with polyurethane construction adhesive.
You could combine the electrical and mechanical damping solutions by lining the chassis with carbon fiber cloth instead. Epoxy will hold the carbon fiber to the steel and stiffen it for mechanical damping. The conductivity of carbon fiber is in the range where it works as an effective RF absorber (think of stealth aircraft technology), and is already used by Oyaide and Furutech to make AC outlet cover plates that dampen RF resonances on power cords.
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Follow Ups
- Mechanical strength. - Al Sekela 09:48:28 04/30/07 (0)
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