The Ultimate Ears 18 Pro in-ear monitors pack 6 high fidelity speakers in each handcrafted earphone creating more detail and soundstage than ever before: 2 dedicated woofers, 2 speakers for the mids and 2 speakers for the highs. In addition, this is the first time we separated the music with a true 4 way cross over, and a new patented 3 sound channel design that separates the lows mids and highs until the reach your ear and blend naturally. Input Sensitivity: 110.6 dB @ 1 kHz Efficiency: 115.6 dB @ 1mW Frequency Response: 20 Hz to 18,000 Hz Impedance: 21 ohms @ 1kHz Internal Speaker Configuration: