Bad Duck Luck?

[ibarbidahl]

(Look at my pictures - there is a band of 6-8wk bachelors at the kiddy pool that clearly displays this) also- you'd hear the difference.

 

[PirateGirl]

You definitely should be able to sex the older batch by voice. If they all sound the same they are probably all the same sex. The young males almost sound like they never outgrew their baby peeping and like their voices didn't change. Females will let out a loud quack or honk. At first it will just be once in awhile, but eventually it's consistent enough you should be able to figure out who it is coming from. When you have at least one of each sex it is really really obvious.