Buzzer Installation

Looking for some help with buzzers. I have a 2 story house with panels upstairs and down. When I hook up buzzers behind both panels the buzzer sound seems to fade to the point of not achieving desired effect. Does the multiple buzzers drop voltage too much for sound or do I need some louder buzzers? Right now I have 2 small buzzers similar to V2 kit buzzer wired in parallel using the Add-On board output pins alongside 5V output. Would splitting a buzzer to another output help? I have the last output terminal on the Add-On board and Zone 1 on the Main Board open for use. Any suggestions would be appreciated.