[CrazY.]

If your server is regamedll, set sv_alltalk to 4. If not, set it to 1 and use this plugin

#include <amxmodx>
#include <fakemeta>

public plugin_init()
{
	register_plugin("All Talk", "1.0", "Crazy")
	register_forward(FM_Voice_SetClientListening, "Voice_SetClientListening")
}

public Voice_SetClientListening(receiver, sender, bool:listen)
{
	if (is_user_alive(receiver) == is_user_alive(sender))
	{
		engfunc(EngFunc_SetClientListening, receiver, sender, true)
		forward_return(FMV_CELL, true)
	}
	else
	{
		engfunc(EngFunc_SetClientListening, receiver, sender, false)
		forward_return(FMV_CELL, false)
	}
	
	return FMRES_SUPERCEDE
}