Final answer:
The librarian is asking to change the volume of your speech, which means you should speak more quietly by reducing the amplitude of your voice waves.
Step-by-step explanation:
The librarian is asking to change the volume of your speech, which means you should speak more quietly by reducing the amplitude of your voice waves. When the librarian asks you to 'speak softer', they are requesting you to change the volume of your voice; you should speak more quietly.
The volume of sound is associated with its amplitude. To speak softer, you would need to decrease the amplitude of your voice waves, which effectively reduces the loudness of your sound. This does not involve altering the pitch (frequency) of your voice, the timbre (color or quality) or the tempo (speed) of your speech—just the volume. To do this in practice, you could try to project your voice less and use less breath when speaking, making your voice quieter.