Well... I believe in all their collaterals, promotions and website they specifically mentioned headphones because the technology is to let the headphone speakers work in a way that complements your ear structure.
By using in-ear buds, the bud speakers are also generating sound according to this algorithm but without the ear structure there to manipulate the sound, you end up the wrong sound that they are wanting to create.
Borrow a cheap headphone and I'm confident it'll be quite different.
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