"At 500 Hz you can reliably hear pitch differences of 2.1875 Hz, which means you did better than approximately 81.3% of people who took our test!"
With cheap earbuds and the washing machine churning away in the background. Will try with better conditions and phones later, though wouldn't expect much improvement.
I suspect having good headphones might actually be worse for this test. The more uneven the response, the more you'll hear a difference in volume as well. At least in theory.