Audio Eng. Microphones 1
Overview: mics as the inverse of speakers
A speaker converts electrical voltage into acoustical sound waves; a microphone does the opposite: it picks up acoustic waves and converts them into an electrical signal (voltage/current).
Conceptual takeaway: microphones are transducers that turn sound energy into electrical energy for recording or amplification.
There are many mic types and designs; the key differences come from how the diaphragm and capsule/element respond to sound, and how the electronics shape the signal (polar patterns, sensitivity, SPL handling).
Key concepts and terminology
Diaphragm: the thin membrane that vibrates in response to sound waves and initiates the transduction process.
Materials: typically Mylar or metal; condensers often use gold-plated membranes.
Some condensers have two diaphragms (back-to-back) to enable different polar patterns; in a two-diaphragm setup, a figure-eight pattern can emerge because each diaphragm can be tuned to a cardioid pattern and combined.
Capsule: the housing around the diaphragm that, with circuitry, determines directionality and sound capture.
Polar pattern (directionality): how a mic responds to sound from different angles.
Common patterns: omnidirectional, cardioid, figure-eight (bi-directional).
Ribbon mics are typically bidirectional by nature; dynamics and condensers can be configured for various patterns.
Front address vs side address:
Front-address mics: you face the mic when recording; typical for many small-diaphragm condensers.
Side-address mics: the front of the mic is oriented to the side; you look for a logo on the front indicating the side to face the source.
Preamp: a device (often inside an audio interface or standalone) that amplifies the mic’s very weak signal to a usable level for A/D conversion.
Phantom power (48V): DC power supplied through the XLR cable to power condenser microphones and some active circuits; typically labeled as +48V. Formats vary by equipment (global vs. per-channel);
Important safety practice: turn off phantom power before unplugging mics to avoid sudden power surges to ribbons and other sensitive elements.
SPL (sound pressure level) and headroom: measures how loud a source is that a mic can handle without distortion.
SNR (signal-to-noise ratio): a measure of how much background noise is present relative to the desired signal; condensers tend to be more sensitive (higher SNR but potentially more noise floor in non-studio environments), ribbons tend to be less noisy in controlled studio contexts but are highly sensitive to high SPLs and environmental noise.
Basic mic physics equations (transduction origins):
Dynamic microphone: voltage generated by a moving coil in a magnetic field; the electromagnetic principle can be summarized by E ≈ B l v, where
E is induced voltage,
B is magnetic flux density,
l is conductor length (coil),
v is diaphragm/coiled motion velocity.
Ribbon microphone: a thin aluminum ribbon vibrates in a magnetic field, producing voltage in the same electromagnetic fashion as a moving-coil mic, but with a different mechanical arrangement and typically bidirectional pattern.
Inverse-square law reminder (typical live sound principle): SPL decreases with distance according to the inverse square law. A quick practical rule of thumb:
Doubling distance reduces SPL by about 6 dB: ext{ΔL} \,\approx\, -20\log{10}\left(\frac{r2}{r_1}\right), and for r2 = 2 r1 this gives \Delta L ≈ -6\,\text{dB}.
Types of microphones and their roles
Dynamic microphones (moving coil):
Characteristics: rugged, affordable, durable; can handle high SPL; less delicate than condensers; do not require external power.
Typical uses: drums, guitar amps, loud sources; good for live sound due to high gain before feedback.
Typical limitations: narrower high-frequency response compared to condensers; not as detailed for vocals as condensers in studio.
Common moving-coil (dynamic) mics:
Shure SM57: classic workhorse; widely used for snare drums and guitar amps; introduced 1965; front-loaded design; robust and reliable.
Shure SM58: similar era; tailored for lead vocals and stage performance; durable, with wind protection.
Sennheiser MD421: versatile for bass amps, kick, and other loud sources; known for its robust build and DL-type settings.
Electro-Voice RE20: introduced 1960s; features a five-position bass roll-off switch (M and S positions) to tailor response for music vs speech; used for voice, kick, and radio; built-in tailoring filter reduces pops/noise.
AKG D12E: introduced 1953; dynamic cardioid with low-frequency boost; historically popular on bass amps and kick drums; later reissued as D12DR.
Notable construction notes:
Dynamic mics typically use a moving coil around a magnet; signal via electromagnetic induction as the coil moves with the diaphragm.
Some dynamic mics are front-address; others are side-address depending on capsule orientation and clip design.
Availability of rugged, affordable models makes them common for live and on-the-road use; many classic models have been replicated or continued due to reputation (e.g., Unidyne lineage related to the 57/58).
Practical tips: choose based on pickup pattern, proximity to source, and context (live vs studio); assess whether the mic will be facing the source during performance; observe logo placement to identify the front side for accurate orientation.
Condenser microphones (capacitors):
Characteristics: high detail and transient response; more fragile than dynamics; typically more expensive;
Power requirements: require external power (phantom 48V is standard) to bias the condenser capsule; some models include a battery or can be powered by an external DI or preamp.
Common uses: vocals, acoustic instruments; excellent detail but require careful handling in live settings due to sensitivity.
Important practice: always ensure phantom power is correctly configured; turning phantom power on/off improperly can damage certain capsules, especially ribbons; when unplugging mics, power should usually be turned off first.
Notable notes about condenser mics:
Two-plate (capacitor) design: a fixed plate and a movable plate (diaphragm) create a variable capacitor; small changes in distance create large voltage changes.
Some condensers use two diaphragms (pressure-gradient designs) to shape polar patterns and frequency response; this contributes to the common studio practice of using condensers for detailed vocal work.
Neumann mics (and other brands) emphasize premium capsule construction and meticulous quality control; Neumann production processes include capsule assembly, gold-coated diaphragms, backplates, and electronic components;
Phantom power distribution: typically +48V supplied through XLR, biasing both plates; applied to pins 2 and 3 (positive and negative) with pin 1 ground.
Example concepts touched in class: active DI boxes with 9V batteries to provide local power when phantom power is unavailable or globally supplied, though most condensers rely on phantom power from the mixer/preamp chain.
Practical tips: use condensers where you want detail and sensitivity (vocals, acoustic guitar, piano, etc.); in live settings, be aware of proximity effect and proximity-induced bass boosts; consider a pad or high-pass filter when capturing loud sources or dealing with proximity.
Ribbon microphones: a distinct class within dynamic-type designs
Core concept: a very thin aluminum ribbon between strong magnets; ribbon movement in the magnetic field creates the electrical signal.
Characteristics: typically bidirectional (figure-eight) by nature; very delicate and fragile; highly sensitive to high SPLs; usually best kept in studio due to environmental sensitivity and cost; older ribbon mics can be extremely fragile and expensive; modern ribbons (e.g., Royer R-121) are more rugged but still require careful handling.
Common ribbon mics discussed:
RCA 44: historic, warm tone; used in old broadcast and recording contexts.
RCA 77DX: multiple pattern selector via a rotating shutter controlling a ribbon; patterns include cardioid, omnidirectional, and bidirectional.
Beyerdynamic M160: double ribbon with a fixed hypercardioid pattern; notable for its unique form factor and tone.
Coles 4038: rounded, classic ribbon microphone; very common in studios for warmth and natural room tone.
Royer R-121: introduced 1998 to reintroduce ribbons in a practical, robust package; durable and capable of handling high SPL; lifetime warranty; widely used for guitar cabinets and drums; often paired with a dynamic mic for versatility.
Kohl’s Electroacoustics 4038 (older model): predecessor lineage; part of the historical development of ribbon mics.
Practical notes and studio usage:
Ribbons provide warm, smooth mid-to-low frequency response; less top-end sheen than many condensers, which makes them desirable on guitar amps or voice for certain tones.
Fragility and care: ribbons are very delicate; avoid exposure to strong air blasts (wind, loud pops) and manage humidity and temperature; avoid powering ribbons with phantom power or excessive SPL close proximity; in many cases, a second dynamic or ribbon backup is used in live setups.
In live contexts, ribbons are less common due to fragility and cost; in studios, they are valued for their tonal color and natural warmth.
Construction and operation (neat production notes from Neumann video-style walkthrough):
Ribbons are aluminum strips (very thin; equivalent to about a human-hair thickness when stacked as multiple sheets).
The ribbon is mounted between two strong magnets inside a transducer; the signal is produced as the ribbon vibrates in the magnetic field.
Manufacturing involves careful assembly: cutting casings, creating slots to allow sound, applying micro-structure to the ribbon, conditioning and tuning before final assembly; the process involves precision to minimize noise and distortion.
The magnets are often neodymium-based (“super magnets”) for higher energy extraction from the ribbon.
Ribbon quality control includes tuning to reduce molecular noise, ensuring proper mass and stiffness, and ensuring the ribbon is properly tensioned.
Ribbon mics require protective grilles and dust screens to prevent damage to the ribbon; the generator/transducer and transformer stage boosts the signal for XLR output.
Practical safety and usage notes:
Do not power ribbons with phantom power in some cases unless specified by the manufacturer; powering ribbons can damage the delicate ribbon and alter response.
In live settings, pair ribbons with robust dynamics or use as close-mic options to avoid direct exposure to loud near-field sources.
The condenser mic section (high-detail, high-sensitivity)
Core concept: condenser mics use a capacitor with a fixed plate and a movable diaphragm; sound causes the diaphragm to move and change the capacitance, converting acoustic energy into an electrical signal.
Power: requires external bias/phantom power to operate; typical phantom power is +48V (sometimes labeled PS or panel power).
Phantom power is DC power delivered through the XLR pins; it biases the condenser circuit to enable operation.
Some units may include internal batteries or require local power in DI boxes or preamps; it’s important to verify power requirements before connecting.
Practical notes on phantom power:
Most condensers fail-safe with phantom power when connected properly; some individuals advise turning phantom off when unplugging to protect ribbons (though condensers are generally robust).
It is common practice to turn off phantom power before disconnecting or reconfiguring a mic to avoid any transient power surges or short-circuit scenarios.
Neumann overview (typical premium path):
Neumann capsules are assembled with care: backplates, gold-coated membranes, multi-layer meshes, and precise alignment of two capsules to enable selectable patterns and frequency response.
Capsule pairs can be combined to create variable directionalities; electronics and software in quality Neumann mics enable detailed responses to a wide array of frequencies and angles.
A mic’s response is tested on multiple frequencies and angles to ensure consistent performance before shipping.
Practical choices for condensers:
Use condensers when detail, transient response, and high-frequency extension are desirable (vocals, acoustic instruments, room mics, etc.).
Be mindful of proximity effect and ambient noise in non-studio environments; consider high-pass filtering for proximity or loud sources.
Consider impedance, preamp matching, and gain staging to avoid noise and distortion.
Practical usage tips and real-world considerations
Orientation and face direction:
Most mic issues come from facing the mic the wrong way; logos often indicate the front side for many models.
Side-address mics require the user to position the mic so the sound source is directed toward the side where the capsule is sensitive; front-address mics are pointed at the sound source.
Selection based on context:
Dynamics for ruggedness, live sound, and high SPL applications (drums, amps, broadcast VO); good for on-stage use due to durability and cost.
Condensers for studio detail, vocals, acoustic instruments; ensure proper power supply and environment.
Ribbon mics for warmth and vintage character in studio settings; careful handling and protection in live settings.
Specific practical examples and anecdotes mentioned:
The Shure SM57 is widely regarded as a workhorse; often used on snare drums and guitar amps.
The SM58 is a classic vocal stage mic; when used on a stage, it’s common to see both it and other mics in redundant configurations for broadcast or streaming setups.
The Sennheiser MD 421 is a versatile mic noted for its low-end response and robust build; some models include a low-cut filter and a high-pass control tailored to music vs. speech.
The Electro-Voice RE20 is well-known for radio and broadcast work; has bass-roll-off switch (M vs S) and a special low-end shaping feature for kick and voice.
AKG D12E is an older dynamic cardioid with a low-frequency boost, historically used for kick and bass; newer versions exist (D12DR).
Ribbon mics are typically used in studio contexts; Royer R-121 comes with a lifetime warranty and is designed to tolerate high SPLs; ribbons are fragile and not typically used in rough live environments.
Some classic ribbons (RCA 44, RCA 77) have historically shaped broadcast and studio tones and are still revered for warmth; early designs influenced by line-array concepts.
Practical gear and collaboration notes:
Renting mics can be a cost-effective option for sessions; studios like Blackbird and others offer mic rental options for a day or session.
When assembling or repairing mics, note the complexity of ribbon construction and the precision necessary for capsule alignment, backplates, and membranes.
Danger and safety notes (from demonstrations):
mics and protective grills can be damaged by high-impact events if they are not properly protected; high SPL events (jet engines, gunshots) require careful distance and padding/filters when recording and require hearing protection for operators.
The discussion about protection and durability emphasizes that extremely loud events will overwhelm even sturdy mics unless properly placed and gain-staged.
The broader context and historical notes:
The “Unidyne” history connects to the early evolution of cardioid designs; the 57/58 lineage demonstrates long-lasting design principles.
Ribbon mics have a long history (1930s–1950s) and are prized for a certain warmth; modern designs attempt to blend vintage flavor with practical ruggedness.
The Neumann manufacturing walkthrough highlights the precision, quality control, and multi-step assembly that goes into premium mic production; it illustrates that a microphone is more than just a single capsule—it’s a system of mechanical parts, electronics, and testing.
Final practical takeaway:
The right mic depends on the source, setting, and desired tonal character; consider the source’s SPL, the space, proximity, and the expected noise environment; ensure proper power and orientation; and remember that many iconic microphones have deep histories and nuanced performance goals.
Quick reference: common models and their roles (summary)
Dynamic (moving coil) mics:
SM57: workhorse for live/snab drum context; rugged and reliable.
SM58: vocal stage mic; robust and widely used for live vocals.
MD421, RE20, D12E: provide specific tonal shapes; RE20 offers bass-roll-off options; D12E adds low-end boost characteristics.
Common features: no external power need; cardioid or similar patterns; robust for high-SPL sources.
Ribbon mics:
RCA 44, RCA 77DX, Beyerdynamic M160, Coles 4038: warm, smooth tone with figure-eight patterns; fragile and typically studio-oriented.
Royer R-121: modern ribbon with robust build; high SPL handling; lifetime warranty; commonly used on guitar cabinets and drums.
Condenser mics:
High-detail, sensitive, requires phantom power; used on vocals and acoustic sources; careful with phase and proximity.
Neumann capsules exemplify premium manufacturing and multi-pattern capabilities; quality checks include frequency/angle response measurements.
Math and concepts recap
Transduction equation for dynamic mic (simplified):
E \,=\, B \; l \; v where E is the induced voltage, B is magnetic flux density, l is the coil length, and v is the velocity of the diaphragm/coil.
SPL drop with distance (inverse-square-like behavior):
\Delta L = -20\log{10}\left(\frac{r2}{r_1}\right)
Example: if distance doubles, \Delta L ≈ -6.0\text{ dB}.
Phantom power: a DC bias applied through XLR pins to power condenser capsules; typically V_{phantom} = 48\text{ V} (± variations by gear).
Quick tips for exam-style familiarity
Always identify mic type (dynamic vs condenser) and its ideal use case before choosing placement.
Remember common models and their spatial behavior: SM57/58 for rugged live use; RE20 for broadcast voice; D12E for bass/low-frequency emphasis; ribbon mics for warmth in studio but fragility to loud SPL.
Recognize that condensers require phantom power; ribbons may require caution with phantom power depending on model; always check manufacturer guidance.
When troubleshooting mic problems: check power, orientation, proximity to source, and whether the mic is appropriate for the SPL of the source.
For studio tone shaping, note that mics come with built-in switches (high-pass, roll-offs) that tailor response to music vs speech or to reduce proximity effects.
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