Andrew Gabriel wrote:
What size and spacing of studs would be recommended for a stud wall
10' long by 10' high?


400mm centers and 2x4 minimum for a sound proof wall. Use noggins half
way up.

What infill would be recommended to reduce sound transmission (no
thermal insulation required).


No infill unless you can put sand in. Make sure its airtight and use two
thicknesses of plasterboard each side..

Airttightness will do far more to reduce HF transmission than any
infill. If you want to go even better, get some car soundproofing
material and stick it inside the panels before you sheet the other side.
It has excellent mass and panel resonance absorption qualities.Tat
reduces MF and LR transmission.