In Australia we have "mandatory" voting. But actually it is only mandatory that you turn up -- you can deliberately vote "informal" if you don't actually want to cast a vote, and many people do just that (5.5% in the last federal election, although probably more like 2.5-3% of these are deliberate refusals to vote).

This is my preferred system. To me, you don't want to absolute force people to vote. But you do want to remove the bias that exists because turning out to vote is easier for some people than others (and it tends to be easier for the more privileged). Other factors help too: e.g. polling is on the weekend.

Re: apathy, the solution is not to ignore the disenfranchised, but to engage them. True representation is not about suiting those with the most free time and energy.