.The ER•4 MicroPro™ earphones are the next best thing to live music, with noise isolation far surpassing that of active noise-canceling earphones. The ER•4s require NO batteries, and can be plugged into any audio source. Their external noise exclusion35 dB with 3-flange eartips, 42 dB with foam eartips allows you to hear the full dynamic range of recordings without having to play them at unnaturally high and unsafe levels. Pack comes with an ER4P-24 conversion cable for a more neutral frequency response