Content Summary
This article provides a detailed analysis of the definitions, calculation methods, and applications of average sound pressure level, weighted Sound Pressure Level, and A-weighted Sound Pressure level in audio systems.
By combining national standards with the fundamental principles of Bell and Decibels, it explains the differences and connections between sound pressure, sound pressure level, average sound pressure level, weighted sound pressure level, and A-weighted sound pressure level, and focuses on analyzing their impact on the performance of condenser microphone, dynamic microphone, and wireless microphone.
By understanding these key metrics, readers can more accurately assess a microphone's sound pickup performance and suitability for different environments.
In audio engineering, quantifying Sound Intensity is the foundation for understanding and optimizing microphone performance. To this end, we introduce several key physical quantities, such as sound pressure (Sound Pressure), sound pressure level (SPL), average sound pressure level (Average SPL), weighted sound pressure level (Weighted SPL), and A-weighted sound pressure level (A-Weighted SPL). These parameters not only help us describe the intensity of sound itself but also directly influence a microphone's ability to capture sound, its signal-to-noise ratio performance, and its suitability for various applications.
This article will systematically explain the definitions and relationships of these acoustic parameters based on national standards GB/T 2900.86-2009 and GB/T 3947-1996, and combine the basic principles of Bel and Decibel to explore their practical application value in different types of microphone (such as condenser microphone, dynamic microphone, and wireless microphone).
Additionally, we will combine the content previously introduced in “Detailed Explanation of Microphone Frequency Response,” “Detailed Explanation of Microphone Sensitivity,” and “Detailed Explanation of Phantom Power for microphone” to help you build a comprehensive audio knowledge system and enhance your professional ability to evaluate microphone performance.
Before discussing sound pressure level, it is necessary to review the units of Bel and Decibel (dB).
According to the definition in physics:
“Bel” is a logarithmic unit used to express the ratio between two quantities, commonly used for comparing power-related or field-related physical quantities;
“Decibel” is one-tenth of a Bel, i.e., 1 Bel = 10 dB;
For example:
When the energy of one sound is 10 times that of another, the difference is 10 dB;
If it is 100 times, the difference is 20 dB;
If it is 1,000 times, the difference is 30 dB;
In audio engineering, since the human auditory perception range is extremely wide (from the audible threshold of 0.00002 Pa to the pain threshold of 200 Pa), using Pascal (Pa) directly to describe sound pressure is not intuitive. Therefore, we typically use sound pressure level (SPL), a logarithmic form expressed in decibels, to represent sound intensity.
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. The unit is Pascal (Pa).
However, as mentioned earlier, due to the extremely wide range of sound pressure values, the concept of sound pressure level (SPL) was introduced:
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);
This formula is based on the logarithmic function, allowing us to express extremely large ranges of change using smaller numbers.
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 is as high as 120 dB, approaching the pain threshold;
This conversion method not only facilitates comparisons of the intensity of different sounds but also better aligns with the perceptual characteristics of human hearing.
The Average Sound Pressure Level (MSPL) is the logarithmic value obtained by averaging the squares of sound pressure over a period of time and comparing them to the square of the reference sound pressure. The unit remains decibels (dB).
According to the national standard GB/T 2900.86-2009:
“The average sound pressure level is the logarithm to the base 10 of the ratio between the time or spatial average of the sound pressure squared and the reference sound pressure squared, multiplied by 10.”
In simpler terms:
It reflects the overall loudness of a sound scene over a period of time;
It is commonly used to assess background noise, reverberation time, and comfort levels when exposed to a particular sound field over an extended period;
For example:
In a quiet recording studio, the average sound pressure level may be as low as 30 dB;
In a noisy street environment, this value may exceed 85 dB;
This metric is crucial for determining whether a microphone can operate stably in a specific environment.
Since human ears have varying sensitivity to different frequencies, engineers introduced the concept of weighted sound pressure level to describe sound intensity in a manner closer to human auditory perception.
According to the standard definition:
“Weighted sound pressure level is the logarithmic expression of the ratio of the measured sound pressure to the reference sound pressure, weighted by standard frequencies and standard exponential time intervals over a specified time period.”
The unit remains decibels (dB).
Common frequency weightings include:
A-weighting: Simulates human hearing sensitivity to low volumes;
B-weighting: Suitable for moderate volumes;
C-weighting: Suitable for high volumes;
Z-weighting: No weighting applied, commonly used for technical measurements;
Time weighting includes:
F (Fast): Rapid response, suitable for rapidly changing sound sources;
S (Slow): Smooth response, suitable for sustained and stable sound sources;
I (Impulse): Used for sudden noises, such as gunfire or explosions;
Under normal circumstances, the default setting is A frequency weighting + F time weighting as the standard test condition.
The A-weighted sound pressure level (A-Weighted Sound Pressure Level, unit: dB(A)) is a sound pressure level that has undergone frequency weighting processing, specifically designed to simulate human subjective hearing in daily life.
According to the definition in GB/T 3947-1996:
“The A-weighted sound pressure level is the sound pressure level measured using an A-weighted network.”
Its core characteristics include:
Emphasizing the frequency range where the human ear is most sensitive (approximately 1–5 kHz);
Suppressing the influence of low-frequency and high-frequency components;
More accurately reflecting the “loudness” that people actually hear;
For example:
The self-noise of a certain condenser microphone is 15 dB(A), indicating extremely low background noise;
The background noise in a certain conference hall is 45 dB(A), which sounds relatively quiet;
A-weighted sound pressure levels are widely applied in fields such as broadcasting, recording, and occupational health monitoring.
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 suitable for scientific research, modeling analysis, and other fields.
Sound pressure level, on the other hand, is a logarithmic ratio based on sound pressure, with the unit being decibels (dB). It is a value obtained by comparing the actual sound pressure with a reference sound pressure, making it easier to intuitively express the relative strength of sound.
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.
Although both are used to describe the intensity of sound, there are fundamental differences between them:
Sound pressure level focuses on the specific sound pressure level at a particular moment or point;
Average sound pressure level is the result of averaging the square of the sound pressure over a certain time period or spatial range;
For example, when assessing the environmental noise in a meeting room, we use average sound pressure level to describe the overall sound level within the room.
Weighted sound pressure levels adjust the weights of different frequency components through frequency weighting to better align with human hearing characteristics. Common weighting methods include A, B, C, and Z weighting, with A weighting being the most widely used.
A-weighted sound pressure level is a special form of weighted sound pressure level that emphasizes the frequency range where the human ear is most sensitive (1–5 kHz) and suppresses the influence of low-frequency and high-frequency components. Therefore, A-weighted sound pressure level is commonly used to evaluate the signal-to-noise ratio and self-noise level of equipment.
Condenser microphone are widely used in recording studios and broadcasting due to their high sensitivity and wide frequency response.
A-weighted sound pressure level is commonly used to evaluate their self-noise, for example, if a condenser microphone has a self-noise of 14 dB(A), it indicates extremely low background noise;
Average sound pressure level can be used to assess the overall loudness of a recording environment;
Combined with “Microphone Sensitivity Explained,” this helps determine the microphone's pickup performance at different sound pressure levels;
Mr Senma f22S large diaphragm condenser microphone
Dynamic microphone are simple in structure and highly durable, commonly used in live performances and public speaking settings.
For high-intensity sound fields (such as drum kits or loud human voices), the average sound pressure level indicates whether the microphone is at risk of distortion;
Using A-weighting provides a more intuitive assessment of vocal feedback;
Combined with the “Detailed Explanation of Microphone Frequency Response,” this helps determine its performance in specific frequency bands;
Mr Senma S-ONE Dynamic Vocal microphone
In wireless microphone systems, sound pressure level also affects RF transmission quality.
If the input sound pressure is too high, it may cause signal clipping or compression;
Using A-weighting allows for more precise assessment of speech clarity;
In long-distance transmission, average sound pressure level helps determine whether the signal strength at the receiving end is stable;
Mr Senma k58s portable Wireless microphone
Whether you are a sound engineer, audio technician, or general user, when selecting and using microphone, you must not overlook the importance of average sound pressure level, weighted sound pressure level, and A-weighted sound pressure level.
They not only help us understand the physical characteristics of sound but also guide us in reasonably configuring equipment in different environments. By combining content from “Detailed Explanation of Phantom Power for microphone” and “Detailed Explanation of Microphone Sensitivity,” we can systematically evaluate the overall performance of microphone.
Only by combining theory with practice can we truly achieve high-quality audio capture and transmission.
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