Which keypad and door station models are you using?
The KP06 and KT03, and DS01 have better performance for eacho cancelllation that other door stations and keypads
One mistake when having low volume to door station speaker is to adjust the door station volume louder. This will not work because the system does echo cancellation. If the total volume gain is high the system will reduce the gain of one side
Instead reduce the volume from Door station to Keypad
Figures 4 and 5 show the block diagram for KP to DP intercom
Tuning Parameter 81 (AFE DP Mic Gain) default is 3. Reduce to 1 to reduce the gain of DP Mic to KP speaker.
Reset the system
Try the volume at both sides before anything else
For KP03 as well as the above steps, reduce the volume control so that the volume of the person talking at the Door station is not loud. This will allow the keypad to door station volume to be louder The more you make the door station to keypad louder, the softer will be keypad to door station
Make sure the KP03 has the internal black accoustic filler. If that is removed then it will be difficult to get adequate volume