Welcome to Android Central! Which phone? You've made sure that the Alarm volume slider (which is separate from the Ringtone/Notification slider and Media slider) is turned up, correct?
If none of the other preinstalled alarm tones aren't loud enough, then you could look online for an inherently louder tone. Download it to the phone, and use a file manager to move the sound file to the /Alarms directory. See if that works better.