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Composite Plinth
Composite Plinth
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Old 18th July 2006, 01:11 AM   #1
Capt Zach is offline Capt Zach  United States
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Default Composite Plinth

I'm building a a new turntable, and thought about a whole lot of different materials to make it out of, finally siding with composites I decided to use a sandwhich-core of balsawood, laminated using carbon fiber, to make a lightweight, rigid plinth. This technique is used in all kinds of vibartion specific applications in aerospace (747 passenger compartment) floorboards in corvette. It is lightweight, rigid, strong, and has high-damping characteristics.

I constructed a plinth made from layers of balsawood, leaving a channel in the center of the construction. WIthin this, I added a mix of sand and silicone, topped off so it was level, then sealed with another thin layer of balsa. The final core is pretty solid and dead. Its fully sanded and shaped, ready for me to lay up the fibers.

I've been having second thoughts about using carbon fiber, however. Its very expensive and hard to find right now. The reason I've been told is due to an "international carbon fiber shortage." I've never used carbon fiber, and would hate to make any expensive mistakes.

I've considered swichting to fiberglass, which I've already got lots of here leftover from other projects. I'm a bit concerned though about its effectiveness in audio applications, how it would sound. One sees carbon fiber used in a lot of audio products, but not much fiberglass. It isnt as strong as carbon fiber, or as good at damping, from the limited information I've been able to get, but much better than aluminum, for instance. I could try to compensate by making much thicker layers of the fiberglass. Does anyone have any ideas if this would work or if Im making a mistake?

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Old 18th July 2006, 04:32 AM   #2
Nanook is offline Nanook  Canada
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Default i'd try..

Polyureathane paint or arbrite. The paint would be lighter and it's tough as nails.
stew -"A sane man in an insane world appears insane."
Let's help Ruth and Dave
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Old 18th July 2006, 06:36 AM   #3
fortitudine is offline fortitudine  United States
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Try Soller composites for carbon fiber. Its in stock. Buy the uni directional and use two or more layers at 90 degrees.

Soller Composites

I just bought their 9 oz uni. The price is good and its a superiour product.
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Old 18th July 2006, 08:42 PM   #4
SPU_SPU is offline SPU_SPU  United States
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I'm in the process of (re)building my plinth as well. This unidirectional carbon fiber fabric -- do you use it in between layers of wood or do you wrap it around the plinth/paste it to top or bottom? Sorry, I've never seen this kind of fabric before, but I think I might give it a try. Either that or some kind of dampening rubber (is this advisable?). Jeremy Epstein looks like he uses some kind of rubber in his DIY Teres plinth: http://home.earthlink.net/~jeremyepstein/teres.html

(i have a similar DIY Teres)
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Old 18th July 2006, 11:14 PM   #5
EC8010 is offline EC8010  United Kingdom
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It strikes me that it all depends on what you're trying to do...

If you're making a suspended subchassis turntable, you want tha mass of the platter to be dominant and the mass of the subchassis to be negligable in order to minimise bearing noise.

Conversely, if you're making a more traditional sort of a plinth (Garrard 301 etc), you want as much mass as possible to sink any vibration.

Without knowing which approach is being taken, how can we comment?
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
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Old 24th July 2006, 08:40 PM   #6
steenoe is offline steenoe  Denmark
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"international carbon fiber shortage."
Thats correct. Its all being eaten up by partly the aeroplane industry, and the rest is used for fishing rod's (A little portion is used by other industries such as racing) One wouldnt beleive that, but the market for fishing gear is huge. Especially the more exotic fibers are sought after. IMX fibers and T3 fibers top the list. They are super high modulus graphite fibers. The most exotic brands like G. Loomis and Orvis cant get enough of the newest high tech fibers. They want the latest stiffest and strongest fibers at all times to produce the lightest flyrods and the flyfishers are prepared to pay for it! 1000-1500usd for a flyrod wouldnt scare away a serious flyfisherman Not to mention the handcrafted rods that sold for a minor fortune

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