i know that "開ける" involves subject and object, like :
"窓を開けました"( windows opened, & implied someone did it ),
and "開く(あく)" only involves the subject, like :
"窓が開きました" ( windows opened, & implied no one, maybe by wind blow ),
but i can't make it very clear if "開く(ひらく)" is similar or equal to "開ける(あける)" which i found only very few examples says so.