It'd actually help if you sang to them. Plants love CO2. The plants would receive the same effect if you stuck your head near them and breathed. Music however is pointless because plants don't have ears or brains. They have no clue you're putting out the vibe. If you think an audio frequency somehow benefits them, everyone in class would love proof, evidence and facts. In the millions of years of evolution how on Earth could audio therapy been developed in cannabis? The only sound they would very seldom be exposed to is thunder, wind, trees falling, rocks rolling, water flowing, and animals making noises. All of these noises would be rare and varied enough so that the frequencies of these noises would never proliferate long enough for any substantial influence what so ever. If you enjoy doing it, that is all that matters. Stay happy and keep putting out the vibe.