What is another word for not loud?

Here are some words for "not loud," depending on the specific nuance you want to convey:

General:

* Quiet

* Soft

* Silent

* Still

* Subdued

* Mellow

* Peaceful

* Tranquil

More specific:

* Muffled (sound is muffled or dampened)

* Faint (barely audible)

* Whispered (spoken very softly)

* Soothing (pleasant and calming)

* Discreet (low-key and unobtrusive)

For people:

* Reserved

* Shy

* Unassuming

* Modest

The best word will depend on the context of your sentence.