My understanding is that it’s the same as the 1500. One is the international version and one is the Japanese version? I’m not positive. Anyway, The 1500 has similar mids and highs to FDX1 but a good bit bassier. Imo it was too bassy and sounded stuffy but a front tip vent mod helped greatly. The bass is slower, so it does sound warmer and lingers noticeably longer.