如果只是做副词的话,loudly与loud一样用来说明声音的强度,意思是"高声地,喧噪地",只是在动词后面loud比loudly更常用些.
因此没什么区别
Don't talk so loud (loudly)----you'll wake the whole street.
别那么大声说话,你快把左邻右舍都吵醒了.
Someone knocked loudly (loud) at the door.有人在大声敲门.