⏰ In A Nutshell
If there's no issue with the speaker, you would have either set the volume too low or activated "Gradually Increase Volume" feature.
⏰ To Elaborate
1) If you set the volume to "Low" when setting the alarm
Did you set the volume to maximum when you set the alarm? (There is a volume control gauge in the screen). When the alarm rings, the volume is automatically adjusted to what you set. So, It is very important to set the volume to maximum when you are setting the alarm!
2) If "Gradually Increase Volume" is activated
If this feature is enabled, the alarm starts off with very weak sound. If it is set on a longer time, the volume will be small for a much longer time.
Please check if this feature is enabled!