Atmasphere said:
A correct platter pad will have the same hardness as vinyl so that any vibration from the LP can be absorbed.
Aluminum and any metal for that matter is far too hard.
Acrylic is too, but obviously less so than metal. IME, the harder the material, the more issues with high frequencies.
To expand on Ralph’s comments, you’re trying to absorb and transmit spurious vibrations away from the stylus tracking the groove so they don’t reflect back into the cantilever/motor assembly of the cartridge. The key to this lies in matching the speed of sound of the two materials (platter surface and record).
Our plain-Jane, PVC platter did this extremely well (the “V” in PVC stands for vinyl), but the market was fascinated with flame polished acrylic. The PVC was as much of a technical success as it was a commercial flop. And so it goes …
Now, you can work with aluminum but it gets tricky. In an after-market context, you can try playing with mats, but it will be a long, bumpy road (or … you might get lucky on the first try).
The key in working with materials that don't interface well with records (from a vibration transmission perspective) is to do this in stages - starting with an ideal platter surface, and working through intermediate material transitions,.
This is how we approached our composite (Gavia and Stelvio) platters.
Lew said:
For what it’s worth, I have not liked acrylic mats or platters in the past, but probably that’s just me. The only platter per se that meets your criterion pretty well, Ralph, is one of the several options offered by Thom Mackris on his Galibier turntables. It may be made of Delrin, but I cannot recall.
Top to bottom, the platters are carbon fiber, PVC (for the Gavia Platter) / Brass (Stelvio Platter - 14 Lbs. worth of it), and aluminum, along with damping chambers in the aluminum.
… Thom @ Galibier Design