In the realm of horror, often it is what’s heard, suggested and alluded to, rather than physically seen, that injects the lasting feeling of terror. Filmmakers such as Steven Spielberg and Ridley Scott embraced this with Jaws and Alien respectively, in which the terror of the titular monsters was reserved for the perfect time, when the audience’s guard is down. Instead, both of these films ingeniously heighten the tension using cinematography, clever lighting techniques and, most importantly, the soundtrack.
Source: The 10 greatest horror movie soundtracks of all time