Understanding Bel vs Decibel in Microphone and Audio Engineering

Understanding Bel vs Decibel in microphone and Audio Engineering

In audio engineering and acoustic measurement, Bel and Decibel are two key units of sound intensity. Although we more commonly hear the term “decibel” in everyday use, its origin stems from the Bel unit. Understanding the differences between the two helps us more accurately assess microphone performance, environmental noise levels, and the dynamic range of audio systems.

This article will start with basic definitions, comprehensively analyze the relationship between Bel and Decibel, and explore their practical applications and impacts in devices such as wireless microphone, dynamic microphone, and condenser microphone.

1. What is a bel ?

A bel (Bel) is a logarithmic unit used to express the ratio between two power quantities or field quantities. It is named after Alexander Graham Bell and is commonly used in telecommunications, acoustics, and electronic engineering fields.

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

When using logarithms with a base of 10, the Bel is the unit for power quantities;  

Under the same conditions, it is also the unit for field quantities;  

Power quantities include sound power and sound energy;  

Field quantities include Sound Pressure, voltage, etc.

For example:  

If the power of one sound is 10 times that of another sound, it is 1 Bell higher.  

Although the Bell is a valid unit, it is not commonly used in practice due to its large numerical value. People typically prefer to use the more precise unit, the decibel.

2. What is a decibel (dB)?

A decibel (dB) is one-tenth of a bel, i.e.:

1 decibel = 0.1 bel

Since the bel unit has a large numerical value and is not precise enough for practical applications, people prefer to use decibels to express relative changes in sound.

Decibels can also be understood as follows:  

For power-related quantities (such as sound power), the formula is: dB = 10 × log(P₁/P₀);  

For field quantities (such as sound pressure or voltage), the formula is: dB = 20 × log(V₁/V₀);  

This is why we almost always use “decibels” as the unit when discussing Microphone Sensitivity, signal-to-noise ratio, and dynamic range.

3. Analysis of the Relationship Between Bells and Decibels

Bells and decibels are essentially different units within the same measurement system. Bells serve as the base unit, while decibels are their decimal subdivisions. This relationship allows us to flexibly describe changes in sound intensity.

For example:

If the power of a sound is 10 times the reference value, the difference is 1 bell, or 10 decibels;

If the power is 100 times greater, the difference is 2 Bells, or 20 decibels;

If the power is 1,000 times greater, the difference is 3 Bells, or 30 decibels.

As can be seen, the use of decibels makes the numbers more relatable to everyday life and easier to compare and express precisely. Therefore, in modern audio engineering, decibels have become the mainstream measurement standard, especially when describing microphone performance parameters.

4. Practical Applications of Decibels in microphone Systems  

1. microphone Sensitivity (Sensitivity)  

Sensitivity is typically expressed in mV/Pa or dBV/Pa, reflecting the microphone's ability to convert sound pressure into an electrical signal.

For example: The sensitivity of a certain condenser microphone is -38 dBV/Pa;  

This means that when an input sound pressure of 1 Pa (Pascal) is applied, the output voltage is 12.3 mV;  

The higher this value, the more “sensitive” the microphone is, making it suitable for low-noise environments such as recording studios (see “Detailed Explanation of microphone Sensitivity”).

2. Signal-to-Noise Ratio (SNR)  

The signal-to-noise ratio indicates the difference between useful signals and background noise, typically expressed in decibels.  

High-quality condenser microphone can achieve an SNR of over 80 dB;  

the higher the SNR, the clearer the recording and the fewer the interferences;

In wireless microphone systems, a reasonable SNR can reduce noise caused by radio frequency interference (see “Detailed Explanation of Phantom Power for microphone”).

3. Dynamic Range (Dynamic Range)  

Dynamic range refers to the range between the minimum and maximum Sound Pressure Levels that a microphone can capture without distortion, also commonly expressed in decibels.  

For example: A dynamic microphone has a dynamic range of 100 dB;

This means it can capture sound in very quiet environments and withstand loud shouting without distortion;

A wider dynamic range helps improve speech clarity (see “Detailed Explanation of Microphone Frequency Response”).

5. The Impact of Decibels on Different Types of microphone

1. Condenser microphone

Condenser microphone are widely used in recording studios and broadcasting due to their high sensitivity and wide dynamic range.

They have a stronger ability to capture faint sounds and require a higher signal-to-noise ratio;

The decibel rating directly affects their sound pickup accuracy and usability;

In high-fidelity recording, decibels become an important standard for measuring sound quality.

Mr Senam U87S large diaphragm condenser microphone

2. Dynamic microphone

Dynamic microphone have a simple structure and high durability, commonly used in live performances and speeches.

Their sensitivity is generally lower than that of condenser microphone;  

However, due to their strong interference resistance, their decibel performance is more stable;  

They can maintain good voice clarity even in noisy environments.  

Mr Senam S-ONE Dynamic Vocal microphone

3. Wireless microphone  

In wireless microphone systems, decibels are not only used to measure the microphone's performance but also involve aspects such as RF signal strength and reception quality.

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

RF gain, transmission distance, and interference resistance are all closely related to decibels;

when using an Antenna Distributor or amplifier, it is also important to ensure that the decibel gain is reasonable (refer to “Detailed Explanation of microphone Antenna Distributors”).

Mr Senam k58 portable Wireless microphone

6. Conclusion: Though small, decibels are ever-present—mastering the quantitative language of sound

Although the bel is not commonly used as a unit in practice, it lays the theoretical foundation for decibels. In fields such as audio engineering, acoustic measurement, and microphone design, decibels are the core tool for understanding and evaluating sound intensity.

Whether selecting the appropriate microphone, optimizing the recording environment, or setting up a wireless audio system, understanding the difference between bels and decibels helps us make more scientific and precise judgments.