Extra monitor for my Emac?

Hi I'm new here so please be gentle with me.

I have an Emac and want to add another monitor.
I have the right adapter and screen spanner software but:
What monitor can i use? (just using Logic not any graphics).
Ive got and old apple studio display (ADC) but god knows how i connect that!
any help gratefully received

cheers shadow.

i think a VGA to ADc converter is quite pricey so i guess its worth getting a new monitor