Why Use Aluminum for a TT Platter?

I think the key to an aluminum TT platter is to properly damp the aluminum to reduce resonance. This is often done within the platter and/or on top of the platter as in the case of SME. Mass does matter depending on the drive system and what problem the designer is attempting to solve.

Regarding the whole belt vs. DD discussion here, I agree with Dan ed, though this is far too complex a topic to discuss on this thread and I think we should stay away from gross generalizations regarding TT drive systems. It's how its implemented that counts.

Aluminum is used for several reasons. The first is that it is non-magnetic. This keeps it from messing with the cartridge. Aluminum is also relatively cheap, as it is one of the most abundant metals. Its also easy to machine.

An aluminum platter should be damped in some fashion for best results. If this is done it will keep up with any other material with no worries.

And this is why you as a consumer payed so much for the Goldmund to get it somewhat right. The reason I say get it somewhat if you took off the platter and watched the spindle spin it looked like paint can shaker at your nearby HD.

02-09-11: Dan_ed
This is also why so many DD tables have light-weight platters. The motor on a DD is designed to directly manipulate the platter in order to correct speed. The platter is supposed to have it's acceleration constantly manipulated.

i think the reason why direct drive tables tend to have light-weight platters is for fast acceleration. club dj's are among the most enthusiastic users of direct drive turntables. when you are a club dj you want to be able to cue up the record and have it accelerate to speed as quickly as possible on the break.

one of the drawbacks of direct drive turntables is the possibility that vibrations from the motor would couple into the turntable and get picked up at the cartridge. since the vibrations would likely be relatively low frequency, it would likely be in the frequency range that gets amplified in the phono stage. so a higher mass platter would require a more powerful motor, which i would think, would increase the likelihood of vibration.

I am in the process of building a turntable made entirely of Delrin which I understand is as close to a metal as you can get in a polyvinyl product. Fabricators love it because it machines so well, and holds its shape under load. Enought that you can use it for a bearing surface without a sleeve. I hope to see what a turntable with a Delrin plinth and platter sound like compared to a similar ridgid deck.
However, a 3" thick piece of Delrin is about $250 per square foot. Dont want to make too many false cuts or holes in that.