If you are disturbing others, then you should not do so that loudly.
The bottom line is this — you are 100% yotzei by saying Amen in a normal voice. If you want to do so in a louder voice and you think it’s the right thing for you to do with regard to your ruchniyus and connection to HKBH, then all the more power to you… but it can’t be at someone else’s expense. If it’s disturbing the person next to you to the point where they can’t concentrate on their davening or even if it just makes them uncomfortable, then you should not do so. You should not build your personal ruchniyus on the backs of other people.
The Wolf