I think this is as accurate a conversion of the 5e spell as I can get without becoming grossly overpowered. I used air geyser and battering blast as guides. It is more limited in damage since sonic damage is rarer than other kinds of damage (see battering blast, as that limits the damage to 5d6 and the original spell's maximum of 15d6 damage is far too powerful for a 3rd level Pathfinder spell). I'm leaving the push mechanic to not pushed away if the save is successful as that is mechanic for the original spell. Thanks for the help! This is now the updated version of the spell.
School evocation; Level bloodrager 3, druid 3, magus 3, shaman 4,sorcerer/wizard 3, witch 3
Casting Time 1 standard action
Components V, S
Range 15-foot cone emanating from you
Target Creatures and objects up to Large size
Saving Throw Reflex partial (see text); Spell Resistance yes
You evoke a whip-crack of thunder, creating a wave of energy that can sweep aside creatures and objects it contacts.
Each creature in a 15-foot cone originating from you must make a Reflex saving throw. If a creature fails, it takes 2d6 points of sonic damage plus 1d6 points of sonic damage for every 2 caster levels (to a maximum of 5d6) and the target is pushed 15 feet away from you plus an additional 5 feet per additional caster level. If it succeeds, it takes half as much damage and is not pushed.
In addition, unsecured objects that weigh less than 50 pounds are automatically pushed 15 feet by the spell's effect, and the spell emits a thunderous boom audible within 300 feet of it.