Yup, Bard 6 for Lore bard Secrets.
You could TWF for higher damage, but I personally think the drop in AC isn't worth it.
*May not point out that if you're looking for a blasty spell earlier than that, Thunderwave is available at Bard 1 and scales decently with higher slots (same damage as Shatter from 2nd level slots and up, plus a push effect).