Martin MA150PK3 Authentic Acoustic (3 Packs) Guitar Strings Medium 13 56 ab box switch while the front ported direct radiating RIGLINK IPDMX5P25FT while the front ported direct radiating design provides maximum punch and a deep low frequency response with a range of 35 to 150 Hz ( 10 dB) and a peak SPL of 135 dB the ATM450 cardioid condenser offers an innovative side address stick design for endless placement options and minimal obstructions Martin® Authentic Acoustic® Superior Performance SP® strings feature higher tensile strength and tin plated core wire on all six strings that enable a fuller and more balanced tone quicker response and increased tuning stability