Is this speaker okay?

Hey

Im currently listening to ultrasonics on my samsung galaxy s10 with dolby atmos.

It registers on frequensee at about -50 to -60 db at where my ears are.

Is this okay for sub use or should i invest in a speaker?

I think it should be fine

-60 to -50 is a good range when you’re measuring near your ear. That is just above conversational speech