Microphones Frequency Response Explained

What is microphones Frequency Response?

“microphones frequency response” refers to the ratio of the open-circuit output voltage of a microphones to a reference frequency (typically 1 kHz) under constant sound pressure and specified incidence angle conditions. This ratio is expressed in **decibels (dB)**.

In other words, frequency response describes a microphones's ability to capture sound at different frequencies. It is one of the key technical parameters for evaluating a microphones's sound quality reproduction capability, directly affecting the authenticity, clarity, and suitability of audio recording for various applications.

Frequency Response Range: Covering the Human Auditory Frequency Range is Fundamental

The range of audible sound frequencies for humans is approximately **20 Hz to 20,000 Hz (20 kHz)**. A high-quality microphones should maintain a uniform frequency response within this range to achieve high-fidelity recording.

However, not all applications require full-range response:

Vocal recording typically focuses on the 85 Hz to 8 kHz range;

Instrument pickup may require full coverage from 20 Hz to 20 kHz;

telephone communication only requires coverage from 300 Hz to 3.4 kHz.

Therefore, when selecting a microphones, it is important to determine whether its frequency response aligns with the intended application.

How to interpret a frequency response curve?

Many manufacturers include a frequency response curve in their product specifications to illustrate how the microphones's Sensitivity varies across different frequencies.

A flat curve indicates consistent response across all frequencies, making it suitable for professional applications such as broadcasting and recording studios.

A curve with peaks and valleys may have been specifically optimized, such as to enhance vocal clarity or emphasize low-frequency effects.

It is important to note that even if the specified frequency response is very wide, an unbalanced response may still cause sound distortion or coloration.

Differences in frequency response between analog and digital microphones

Although frequency response is a universal technical indicator, there are still some differences between different types of microphones.

Analog microphones

Common types include dynamic microphones and condenser microphones;

Frequency response is significantly influenced by diaphragm material, cavity structure, and preamplifier circuitry;

Physical resonance points may occur, causing fluctuations in the frequency response curve.

Digital microphones (e.g., MEMS microphones)  

Incorporate an ADC (analog-to-digital converter) and directly output digital signals;  

Frequency response is more stable and less affected by external circuits;  

Widely used in smart devices, voice assistants, and IoT applications.  

Whether analog or digital, frequency response is a crucial metric for evaluating microphones performance.

Frequency response characteristics of different types of transducers

Transducers with different transduction principles exhibit significantly different frequency response characteristics:

Condenser microphones

Wide frequency response range (typical value 20Hz–20kHz), excellent flatness (within ±1dB), and high-frequency extension up to 70kHz;

Suitable for high-fidelity music recording;

Core advantage stems from lightweight diaphragm design;  

Requires external polarization voltage or electret material to maintain operational state.  

Dynamic microphones  

Narrower frequency response range (80Hz–15kHz);  

Mid-to-high frequency bands often feature a moderate boost at 3–5kHz to enhance speech clarity;  

Robust and durable construction, making them the mainstream choice for stage performances.  

Ribbon microphones  

Known for their natural warmth in the mid-frequency range;

High-frequency extension is limited (typically <15kHz);  

Modern improved models gradually address this limitation by enhancing diaphragm rigidity.  

Analysis of Key Performance Parameters and Measurement Standards  

Frequency response evaluation relies not only on its nominal range but also on multiple key performance parameters. These parameters measure the microphones's response consistency across different frequencies, directional effects, and proximity effect characteristics.

Flatness tolerance: High-performance microphones must meet a fluctuation range of ±1.5dB within the nominal frequency band, in accordance with industry standards such as GY/T 373-2023. Professional studio-grade products typically require higher precision, up to ±0.5dB.

Effective frequency bandwidth range: Depending on the application scenario, requirements for frequency coverage vary:  

Conference microphones generally need to cover 50Hz–15kHz (dynamic) or 50Hz–18kHz (condenser);  

Music recording and broadcasting scenarios require a wider frequency response range, typically 30Hz–20kHz.

Directional response: Non-omnidirectional microphones (such as cardioid) exhibit shifts in their frequency response curves at different incidence angles. International standards stipulate that at a 180° reverse incidence, the sensitivity attenuation must exceed 12dB to ensure good directional control.

Proximity effect: Pressure-differential microphones (such as dynamic and ribbon microphones) exhibit a significant increase in low-frequency sensitivity at close distances, typically adding 6–10 dB of low-frequency response. To avoid sound muddiness, it is recommended to compensate with a high-pass filter.

Correlation between measurement methods and sound field types  

Frequency response measurements must strictly distinguish between sound field environments:

Free-field measurement  

Simulates a reflection-free acoustic environment in an anechoic chamber;  

Measures the original sound pressure value before the microphones is placed;  

Reflects the actual sound wave incidence characteristics (labeled as Free-field Response).

Sound pressure field measurement  

Directly reads the pressure on the diaphragm within a sealed cavity;  

Ignores sound wave scattering effects (labeled as Pressure Response);  

Diffuse field measurement simulates a reverberant environment.

The three types of sensitivity have a conversion relationship:  

Free-field sensitivity ≈ Sound pressure sensitivity + Scattering pressure correction value (differences of over 3 dB may occur in the high-frequency range).  

The international standard GB/T 12060.4-2012 specifies detailed testing procedures, which must be conducted in conjunction with a sound calibrator to achieve precise measurement.

The relationship between microphones frequency response and practical applications

The frequency response characteristics of a microphones directly affect its performance in different application scenarios. Depending on the intended use, the requirements for the frequency response range also vary.

In vocal recording, the focus is typically on the frequency range from 80 Hz to 15 kHz, with particular emphasis on the clarity of the mid-to-high frequency range to ensure accurate capture of vocal or singing details.

For instrument recording, microphones with a full-frequency response from 20 Hz to 20 kHz are preferred to fully reproduce the low-frequency dynamics and high-frequency overtones of instruments, achieving high-fidelity recording results.

In voice communication scenarios such as video conferencing systems, the primary task of the microphones is to ensure speech intelligibility, so coverage of the 100 Hz to 8 kHz frequency band is generally sufficient to meet requirements.

For environmental monitoring or special applications, such as ultrasonic detection or infrasonic analysis, microphones may need to have frequency response capabilities beyond the conventional audible range, which can be flexibly selected based on the monitoring object.

The relationship between frequency response and microphones sensitivity

In the previous section, we introduced the technical parameter “microphones Sensitivity Explained.” While the two are related, they have different focuses:

Sensitivity describes the efficiency with which a microphones converts sound pressure into an electrical signal;  

frequency response reflects its consistency in response across different frequencies.  

Combining both provides a more comprehensive assessment of a microphones's performance.

The impact of frequency response on audio quality  

Frequency response characteristics directly influence the final audio quality:

Voice clarity optimization: Conference system microphones often limit the frequency bandwidth to 100Hz–10kHz to attenuate low-frequency noise and extremely high-frequency feedback;

Music detail reproduction: Condenser microphones with wide frequency response (>20kHz) can capture instrument overtones, but require low-noise preamplifiers (equivalent noise <23dBA);

Subjective Listening Calibration: Home Hi-Fi equipment may intentionally boost low frequencies (80–120Hz) and high frequencies (8–12kHz) to form a “smile curve,” while professional monitoring equipment aims for an absolutely flat response;

In practical applications, parameters such as dynamic range (>100dB) and total harmonic distortion (<1%@1kHz) must be balanced to avoid performance degradation caused by frequency response optimization.

Summary: Frequency response is one of the core criteria for selecting a microphones.

microphones frequency response not only affects sound clarity and realism but also directly impacts its suitability for specific applications and overall sound quality. Whether used in recording studios, live performances, video conferences, or embedded voice devices, frequency response is a critical technical parameter to consider when selecting a microphones.