Learn Finnish: Säädä voimakkuus alemmas, niin että basso ei kuulu liikaa. - Adjust the volume lower so that the bass is not heard too much.

Comparative adverbs of location inflect to show direction. When answering 'to where?' (like adjusting the volume down), we use the weak grade stem -mma- and add -s (or -ksi), creating alemmas. The strong grade stem -mpa- is used for 'from where?' questions, like alempaa (from lower).

Why is voimakkuus in its basic nominative form instead of the accusative?

Because it is the object of a command. When giving a direct command using an imperative verb like säädä (adjust!), the total object drops the usual -n ending and looks exactly like the basic nominative form.

The English translation says 'is not heard.' Why isn't ei kuulu in the passive voice?

The Finnish verb kuulua inherently means 'to be audible' or 'to be heard.' It is an active, intransitive verb, so you don't need a passive construction. You are simply saying that the bass doesn't 'sound' too much.

Why use liikaa here instead of liian?