Note: Please test the drivers first earlier than soldering, replacements usually are not available as soon as drivers been soldered TWFK-30017 Knowles Balanced Armature Driver Speaker Receiver CIEMs TWFK-30017 is the smallest twin balanced armature speaker, It is designed for professional audio in-ear purposes Enables customized crossover systems to achieve target frequency response in a equipment size, smaller than the ED Series TWFK-30017 is a mix of FK-30018 and WBFK-30019 The one with 3 solder facets is FK-30018 as mid-frequency/mid-low frequency, and the only with 2 solder aspects is WBFK-30019 as excessive frequency Commonly use white, brown or inexperienced damper to fit it, TWFK-30017 + CI-22955 is the most well liked combination to make a 3-way IEM (In ear monitor),O other mixtures like 30017+ 31618, 30017+30008, etc, also are very good Specifications: Frequency Range: 200Hz ~ 6 Impedance: 43 Ohm Sound Pressure Level: 95dB Port Location: Side Termination: Solder Pads Size: 0" L x 0" W (5 x 2) Height - Seated (Max): 0" (3) SENS(dB SPL) TO 100mV / TO 1mW: 106/112 MAX SPL 10% THD 1kHz(dB SPL): 117 THD@94dB SPL/THD@100dB SPL: 0%/0% Vented: Yes Feature: 1, Extreme wideband ability 2, Unique woofer/tweeter design 3, Mechanical shock resistance 4, Single sound port for simplified earphone design 5, Enables leading edge earphone designs for miniature size and performance