Audio-Technica PRO 31 Cardioid Microphone (Discontinued) Leave a Comment / Uncategorized / By Alexander / February 19, 2018 89 GEARANK 89 out of 100. Incorporating 30+ ratings and reviews. Street Price: $39.00 Manufacturer: Audio-Technica Features: Cardioid Polar Pattern Frequency Range: 60 Hz to 13 kHz Neodymium Magnet On/Off Switch Ball-Type Grille