Ricolanominally Impedance: 15Ω, but if you using a standard dongle like lightning to 3,5mm jack with iphone, mid-bass starts scattering and crosstalking to other frequency bands which leads to tonal imbalance and uneven frequency response. a similar situation is observed at the upper-middle frequencies, which are colored by noticeable harmonics even at low volumes. i use Fiio BTR5, which eliminates the listed problems, and noticeably improves the tonal balance.