The Sennheiser e 901 is a specialized half-cardioid dynamic boundary microphone engineered specifically for capturing the full impact and tone of a kick drum. Its unique half-cardioid polar pattern is designed to be placed directly on a surface—in this case, often inside the kick drum on a pillow or damping material, or just outside the drum's sound hole on a stand. This positioning leverages the boundary effect, which increases bass response and provides a tight, punchy sound with enhanced low-frequency extension and controlled attack. The microphone's tailored frequency response emphasizes the fundamental thump and beater click while minimizing boxy midrange resonances.

Built with a rugged, low-profile housing, the e 901 is designed to withstand the high sound pressure levels inside a drum. It often includes versatile mounting options, such as a rubber isolation pad or a dedicated stand adapter. By combining boundary microphone technology with a drum-specific design, the e 901 offers sound engineers an alternative to traditional kick drum microphones, capable of delivering a powerful, focused, and well-defined kick sound that requires minimal equalization, making it a popular choice in both live sound and studio recording.