Choosing a Dynamic Workhorse: Electro-Voice RE20 vs. Sennheiser MD 21-U

When building a studio or assembling a field recording kit, professional dynamic microphones often become the backbone of the operation. Unlike condenser mics, which require external power and tend to pick up every minor background noise, moving-coil dynamic microphones are valued for their durability and predictability.

Two models that have maintained a presence in professional audio for decades are the Electro-Voice RE20 and the Sennheiser MD 21-U. Both tools enjoy a reputation for reliability, yet they were designed with fundamentally different philosophies, pickup patterns, and intended environments. Comparing their technical designs, sonic behavior, and practical limitations shows where each excels.

The Core Design Philosophies

Every microphone dictates how you interact with the acoustic environment based on its polar pattern and internal capsule housing. This is the primary dividing line between these two models.

Electro-Voice RE20: Controlled Isolation

The RE20 is a large-diaphragm directional microphone designed primarily for controlled environments like broadcast suites and recording studios. It utilizes a cardioid polar pattern, meaning it is highly sensitive to sound coming from directly in front of the capsule, while rejecting sound originating from behind it.

The defining technical feature of the RE20 is a proprietary design called Variable-D. In a standard directional microphone, moving closer to the grille causes a dramatic buildup of low frequencies—a phenomenon known as the proximity effect. This can make voices sound boomy, muddy, and unclear. Variable-D uses a series of acoustic ports along the length of the microphone body to cancel out these low-frequency build-ups. No matter how close a speaker or instrument gets to the capsule, the tonal balance remains virtually identical.

Sennheiser MD 21-U: The Bulletproof Omnidirectional

The MD 21-U represents a completely different approach to capturing sound. It is a small-diaphragm omnidirectional microphone housed in a rugged, blocky metal chassis. Because it is omnidirectional, it picks up sound with equal sensitivity from all angles—front, back, and sides.

Omnidirectional capsules naturally do not suffer from the proximity effect, so the MD 21-U does not require complex internal porting to keep the bass frequencies stable when used up close. Sennheiser designed this model specifically for demanding field work, news gathering, and outdoor broadcasting. The housing is built to minimize handling noise, ensuring that when a reporter moves their hand along the body during an interview, the friction noises are not transmitted to the recording.

Frequency Response and Sound Character

While both microphones deliver a clear midrange that preserves the intelligibility of the human voice, their frequency curves and general presentations differ significantly.

[Electro-Voice RE20]  ---> Tight Cardioid ---> Focused, dry, flat low-end
[Sennheiser MD 21-U]  ---> Wide Omni     ---> Room ambience, open, bright top-end

The RE20 Sound

The RE20 provides a flat, uncolored frequency response across the spectrum. It does not feature the aggressive presence peaks (boosts in the upper-midrange) common in many vocal microphones. The low end is smooth and extended, while the top end is rolled off gently, avoiding harshness or sibilance. The result is a heavy, authoritative sound that feels immediate and dry, especially because the cardioid pattern keeps room reflections out of the signal.

The MD 21-U Sound

The MD 21-U has a remarkably linear frequency response through the bass and midrange, but it features a noticeable rise in the high frequencies, typically peaking around 10 kHz. This slight boost compensates for the natural loss of clarity that occurs when recording outdoors or off-axis. Because it captures the surrounding environment alongside the direct source, the overall sound character feels open, airy, and deeply tied to the space where the recording takes place.

Practical Applications in the Studio and the Field

Because of these design choices, swapping one microphone for the other alters the workflow and the final audio track significantly.

Voice and Speech Applications

For solo spoken-word tracking, such as podcasting, voiceover work, or radio presentation, the RE20 is a standard choice for a specific reason: isolation. In a room that lacks professional acoustic treatment, the RE20 helps mask the sound of hard walls, computer fans, or distant traffic by ignoring off-axis sound. The lack of proximity effect allows talent to move naturally in front of the microphone without creating sudden changes in volume or bass response.

The MD 21-U handles speech differently. If used for an interview in a quiet room, the recording will include the natural acoustics of that room. In field journalism, this behavior is often preferred. When interviewing someone on a busy street or at a sporting event, the omnidirectional pattern captures the environmental noise smoothly, placing the listener directly into the scene without letting the background sound distort or clip the input. Furthermore, because the pattern is wide, a reporter does not need to perfectly aim the microphone back and forth between themselves and the guest to get a balanced level.

Instrument Tracking

In music production, both tools find frequent use, though on entirely different sources.

• The RE20 on Low-Frequency Sources: The ability to handle high sound pressure levels combined with a flat low-end response makes the RE20 a staple for kick drums, floor toms, bass guitar cabinets, and brass instruments. It captures the punch and weight of a kick drum without overloading or creating artificial sub-bass boom.

• The MD 21-U on Acoustic Elements: The omnidirectional nature of the MD 21-U makes it highly effective as a room microphone for drum kits, or as a close mic for acoustic string instruments like guitars and violins. When positioned correctly in a good-sounding room, it captures a balanced blend of the instrument’s direct strings and the natural reflections of the space, avoiding the boxy sound that directional mics sometimes produce.

Direct Comparison

The selection between these two units depends on the recording environment and the level of ambient isolation required.

Technical Considerations: Preamps and Gain

Before deploying either microphone, understanding the downstream signal chain is necessary. The Electro-Voice RE20 is notorious for its low output sensitivity. To get a robust signal from a speaking voice without introducing hiss, you need a high-quality audio interface or an external preamplifier capable of providing at least 55 to 60 decibels of clean gain. If the preamplifier is low-grade, turning it up high enough to satisfy the RE20 will often introduce audible noise into the track.

The Sennheiser MD 21-U is more forgiving in this regard. Its output level is slightly higher, and because it captures ambient energy along with the source, it generally sits comfortably with standard audio interfaces and field recorders without requiring inline gain lifters.

Conclusion

The Electro-Voice RE20 and the Sennheiser MD 21-U are both durable, high-fidelity dynamic microphones, but they serve opposite acoustic functions. The RE20 is built to focus directly on a single source, control bass fluctuations, and reject the surrounding room, making it optimal for studio speech and heavy instrumentation. The MD 21-U is built to embrace the environment, providing an open, uncolored capture of both the source and the space, whether that space is a live concert hall or a busy public street. Selecting the correct tool comes down to whether you need to shut out the world around your sound source, or invite it in.