Sound Pressure and Sound Pressure Level in Microphone Technology

Sound Pressure and Sound Pressure Level

Understanding Sound Pressure and Sound Pressure Level in Microphone Technology

In audio engineering, sound pressure

and sound pressure level (SPL) are core physical quantities for measuring Sound Intensity. They not only determine the loudness of the sound we hear but also directly affect a microphone's ability to capture sound, its distortion performance, and its Dynamic Range.

This article will comprehensively analyze the definitions, calculation methods, and practical applications of sound pressure and sound pressure level in different types of microphones based on national standards GB/T 3947--1996 and GB/T 2900.86-2009, and discuss their important roles in scenarios such as recording studios, live performances, and remote conferences.

1. What is sound pressure?

Sound pressure refers to the difference between the pressure in the air or other medium when sound waves are present and the pressure in a static state. Simply put, it is the pressure fluctuation caused by the vibration of air due to sound.

According to the national standard GB/T 3947--1996:

“Sound pressure is the difference between the pressure in the medium and the static pressure when sound waves are present.”

The unit is Pascal (Pa), which is the standard unit for pressure in the International System of Units (SI).

Common Terminology Explanations:  

Effective Sound Pressure (RMS Sound Pressure): The root mean square (RMS) value of instantaneous sound pressure over a period of time, typically used to describe the average intensity of a sound;

Peak Sound Pressure: The maximum instantaneous pressure value of a sound wave;

Peak-to-Peak Sound Pressure: The difference between the maximum and minimum instantaneous pressures;

Average Sound Pressure: The average pressure value over a cycle or extended period of time.

These different types of sound pressure are of significant importance in audio system design, equipment selection, and environmental noise assessment.

2. What is Sound Pressure Level (SPL)?

Although the unit of sound pressure is Pascal (Pa), in practical applications, due to the extremely wide range of values (from the audibility threshold of 0.00002 Pa to the pain threshold of 200 Pa), using Pa directly to describe sound intensity is inconvenient.

Therefore, the logarithmic unit Sound Pressure Level (SPL) was introduced to express sound intensity.

According to the national standard GB/T 2900.86-2009:  

“Sound pressure level is the logarithm of the ratio of the given sound pressure to the reference sound pressure. The sound pressure level expressed in Decibels (dB) is 20 times the common logarithm of this ratio.”

The formula is as follows:  

SPL (dB) = 20 × log(P₁ / P₀)  

Where:  

P₁ is the measured sound pressure (in Pa);  

P₀ is the reference sound pressure, typically 0.00002 Pa (i.e., the lower limit of human hearing);  

For example:  

A sound with a sound pressure of 0.2 Pa has an SPL of approximately 80 dB;

When the sound pressure reaches 20 Pa, the SPL reaches 120 dB, which is close to the pain threshold.

This conversion method not only facilitates comparing the intensity of different sounds but also better aligns with human auditory perception characteristics.

3. The Relationship and Differences Between Sound Pressure and Sound Pressure Level

Although these two concepts are closely related, there are some key differences between them.

Sound pressure is a specific physical quantity representing the pressure changes caused by sound, measured in pascals (Pa). It describes the actual physical intensity of sound and is applicable in fields such as scientific research and modeling analysis.

Sound pressure level, on the other hand, is a logarithmic ratio based on sound pressure, measured in deciBels (dB). It is derived by comparing the actual sound pressure with a reference sound pressure, making it easier to intuitively express the relative intensity of sounds.

In summary:

Sound pressure is the physical manifestation of sound;

Sound pressure level is the quantitative expression of this physical phenomenon; The two complement each other, together forming the foundation for our understanding of sound.

4. The role of sound pressure and sound pressure level in microphone systems

A microphone is essentially a sensor that converts changes in sound pressure into electrical signals. Understanding how sound pressure and sound pressure level affect microphone performance helps us make more reasonable choices in scenarios such as recording, sound reinforcement, and live streaming.

1. Impact on Microphone Sensitivity

Microphone sensitivity (Sensitivity) refers to the magnitude of the output voltage under a given sound pressure input, typically expressed in mV/Pa or dBV/Pa.

Higher sound pressure results in a stronger output signal;

High-sensitivity microphones (such as condenser microphones) are more suitable for low-sound-pressure environments, such as podcasting and recording studios;

Low-sensitivity microphones (such as some dynamic microphones) can better withstand high sound pressure and are suitable for live performances and loud shouting.

2. Determining Dynamic Range and Distortion Risk

A microphone has a sound pressure range within which it can operate without distortion, known as the maximum sound pressure level (Maximum SPL).

If the sound pressure exceeds this range, it may cause clipping or distortion;  

For example, if a condenser microphone has a maximum SPL of 130 dB, and the input exceeds this value, the recording will exhibit noticeable distortion;  

Dynamic microphones typically have higher tolerance and are suitable for high-intensity sound field environments.  

3. Impact on wireless microphones

In wireless microphone systems, sound pressure also affects RF transmission quality:  

Excessive sound pressure may cause the microphone circuit to overload, resulting in unstable signals;  

In long-distance transmission, high sound pressure may increase background noise and interference;  

Properly controlling input sound pressure helps improve the stability and signal-to-noise ratio of the wireless system (see “Phantom Power for microphones Explained”).  

5. Differences in Sound Pressure Response Among Different Types of Microphones

1. Condenser Microphones

Condenser microphones are widely used in recording studios and broadcasting due to their high sensitivity and wide frequency response.

Advantages: Can capture subtle changes in sound pressure and reproduce details accurately;

Disadvantages: Prone to distortion in high sound pressure environments, so input volume must be limited;

Application scenarios: Recording studios, podcasts, voice synthesis, and other applications requiring high fidelity.

Mr Senma f22S large diaphragm condenser microphones

2. Dynamic Microphones  

Dynamic microphones are simple in structure and highly durable, commonly used in live performances and speeches.  

Advantages: Strong shock resistance and ability to withstand high sound pressure levels;  

Disadvantages: Lower sensitivity, less effective at capturing faint sounds compared to condenser microphones;  

Application scenarios: Concerts, conference speeches, outdoor interviews, and other noisy environments.

Mr Senma S-ONE Dynamic Vocal Microphones

3. Wireless Microphones

In wireless microphone systems, sound pressure not only affects sound pickup quality but also impacts the stability of radio frequency (RF) signals.

Receiver signal strength is commonly expressed in dBm (relative to 1 milliwatt);

RF gain, transmission distance, and interference resistance are all related to sound pressure;

Before use, test the environmental sound pressure level to ensure the system operates within its optimal range.

Mr Senma f7 portable Wireless microphones

6. Sound pressure and sound pressure level serve as the bridge between the physical world and audio systems

Sound pressure is not only the physical manifestation of sound but also one of the core factors determining a microphone's ability to accurately capture sound. Whether selecting the appropriate microphone type, optimizing the recording environment, or setting up a wireless audio system, understanding the essence of sound pressure and its relationship with decibels, sensitivity, and dynamic range helps us make more scientific and precise decisions.

Combining the content we previously introduced in “Detailed Explanation of Microphone Frequency Response,” “Detailed Explanation of Microphone Sensitivity,” and “Detailed Explanation of Phantom Power for Microphones,” it can be seen that excellent audio performance is a systematic engineering project constructed by multiple technical components. Only by comprehensively considering microphone performance and its coordination with peripheral devices can high-quality audio capture and transmission be truly achieved.