Interchangeable Capsule Series. The B4 capsule is ideal for live and orchestral applications. Blue's Bottle Caps are interchangeable capsules designed for any mission. The Interchangeable Capsule series contains microphones capable of providing a wide palette of tonal characteristics and pickup patterns to satisfy even the most discriminating tastes. The series integrates the best of Blue's discrete Class A circuitry with a unique and revolutionary system of interchangeable capsules that provide the engineer a wide range of potential tonal characteristics. This series is employed in the world's most respected studios, and is recognized by industry insiders as the world's premiere microphone system.