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.