How to respond 'Amen'

Hi,

"How is it known that one who replies 'Amen' should not raise his voice above that of the person who recites the actual blessing?

"It is written, 'Elevate Gd with me, and we will exalt His Name as one.'"

(Talmud, Berachot 45a)

Have a great day,
Mordechai