What Does a Microphone Measure? A Beginner’s Guide to Understanding Microphone Specifications
A microphone is a device that converts sound waves into an electrical signal. But what exactly does a microphone measure? In short, a microphone measures sound waves by detecting the changes in air pressure caused by those waves.
The sound waves cause the diaphragm of the microphone to vibrate, and this vibration is then converted into an electrical signal that can be amplified and recorded. There are many different types of microphones, each with its own unique characteristics, but they all work on the same basic principle of converting sound waves into an electrical signal.
Understanding what a microphone measures is important for anyone who works with audio, whether you are a musician, a sound engineer, or a podcaster. By understanding how microphones work, you can choose the right microphone for your needs and get the best possible sound quality. So let’s take a closer look at the specifics of what a microphone measures and how it does so.
Basic Understanding of Microphone
A microphone is a device that converts sound waves into an electrical signal. This signal can then be amplified, recorded, or transmitted. Microphones come in different shapes and sizes, but they all work on the same principle.
When sound waves hit the diaphragm of a microphone, it vibrates. This vibration is then converted into an electrical signal by a transducer, which is usually a coil or a capacitor. The electrical signal is then sent to an amplifier, which increases its strength.
Microphones are designed to measure different aspects of sound. Some measure the pressure of sound waves, while others measure the velocity or acceleration of air molecules. The most common type of microphone is the dynamic microphone, which uses a diaphragm and a coil to measure the pressure of sound waves.
Another type of microphone is the condenser microphone, which uses a diaphragm and a capacitor to measure the changes in electrical charge caused by sound waves. Condenser microphones are more sensitive than dynamic microphones, but they require a power source to operate.
In addition to their design, microphones are also characterized by their frequency response, sensitivity, and directionality. Frequency response refers to the range of frequencies that a microphone can detect, while sensitivity refers to the amount of electrical signal that a microphone produces for a given sound pressure level. Directionality refers to the pattern in which a microphone picks up sound waves.
Understanding the basics of microphone design and measurement is important for choosing the right microphone for a particular application. By considering factors such as frequency response, sensitivity, and directionality, you can select a microphone that will provide clear and accurate sound reproduction for your needs.
What Does a Microphone Measure?
A microphone is a transducer that converts sound waves into an electrical signal. It essentially measures the sound pressure variations around its diaphragm within a range of frequencies. As the sound waves cause varying pressure around the mic diaphragm, the microphone produces a coinciding electrical mic signal.
Microphones are designed to measure sound pressure levels (SPL) and convert them into an electrical signal. The SPL is the amount of pressure exerted by sound waves in the air and is measured in decibels (dB). Microphones are also designed to measure the frequency of sound waves. The frequency is the number of oscillations per second and is measured in Hertz (Hz).
The microphone’s diaphragm is a critical component that determines the microphone’s sensitivity and frequency response. The diaphragm is a thin, flexible membrane that vibrates in response to sound waves. The diaphragm’s movement generates an electrical signal that corresponds to the sound waves’ frequency and amplitude.
Different types of microphones measure sound differently. For example, a pressure-field microphone is designed to measure the sound pressure in front of the diaphragm. It has the same magnitude and phase at any position in the field. On the other hand, a gradient microphone measures the difference in pressure between two points in space.
a microphone measures sound pressure levels and frequency. The diaphragm is a critical component that determines the microphone’s sensitivity and frequency response. Different types of microphones measure sound differently, depending on their design and application.
Types of Measurements
Microphones are used to measure various types of sound, and different types of microphones are designed to measure different aspects of sound. The three types of measurement microphones are free field, pressure field, and random incidence.
Free field microphones are the most common type of microphone and are used to measure the sound pressure from a single source directly at the microphone diaphragm. These microphones are designed to measure sound that is coming directly from the source, without any reflections from the surrounding environment. Free field microphones are commonly used in sound level meters, noise dosimeters, and other applications where accurate sound level measurements are required.
Pressure field microphones are used to measure sound in enclosed spaces, such as rooms or auditoriums. These microphones are designed to measure the sound pressure in the room, including the sound reflected off surfaces such as walls, ceilings, and floors. Pressure field microphones are commonly used in acoustic measurements, such as measuring the reverberation time of a room.
Random incidence microphones are used to measure sound in a diffuse sound field, such as in a concert hall or other large space. These microphones are designed to measure sound that is coming from all directions, without any direct sound from a single source. Random incidence microphones are commonly used in acoustic measurements, such as measuring the absorption coefficient of a material.
the type of measurement microphone used depends on the type of sound being measured and the environment in which the measurement is being taken. Each type of microphone is designed to measure a specific aspect of sound, and choosing the right microphone for the job is essential to obtaining accurate and reliable measurements.
Measurement of Sound Pressure Level
When it comes to measuring sound, one of the most important parameters is the sound pressure level (SPL). SPL is the measure of the intensity of sound and is usually expressed in decibels (dB). A microphone is a device that is commonly used to measure SPL.
To measure SPL accurately, a sound level meter is used. The sound level meter consists of a microphone that converts sound waves into electrical signals, an amplifier that amplifies the signals, and a display that shows the SPL in decibels. The microphone is placed in the vicinity of the sound source, and the sound level meter measures the SPL at that location.
Sound level meters have various settings that can affect the accuracy of the measurement. The frequency weighting and time weighting/averaging should always be specified to ensure measurement accuracy. Classified sound level meters should be used to assure measurement accuracy.
It is important to note that the SPL measured by a microphone can be affected by various factors, including the distance between the microphone and the sound source, the direction of the sound source, and the ambient noise level. Therefore, it is important to follow standardized procedures when measuring SPL to ensure accurate and reliable results.
Measurement of Frequency Response
Frequency response is an essential characteristic of a microphone. It refers to the sensitivity of a microphone at different frequencies. A microphone’s frequency response curve shows how it responds to signals at various frequencies.
To measure a microphone’s frequency response, a signal generator is used to generate a test signal that covers the entire frequency range of the microphone. The microphone is then placed in front of the signal generator, and the output of the microphone is recorded.
The recorded output is then plotted on a graph, which shows the microphone’s response at different frequencies. The graph is called a frequency response curve, and it is used to determine the microphone’s sensitivity at different frequencies.
It is important to note that a microphone’s frequency response curve is affected by several factors, including the microphone’s design, the type of diaphragm used, and the microphone’s polar pattern. Therefore, it is essential to choose the right microphone for the intended application.
measuring a microphone’s frequency response is an essential step in understanding its performance characteristics. A frequency response curve provides valuable information about a microphone’s sensitivity at different frequencies and can help in choosing the right microphone for a specific application.
Measurement of Directionality
Directionality is one of the essential characteristics of a microphone. It refers to the microphone’s sensitivity to sound relative to the direction or angle from which the sound arrives. It is also known as polar response or polar pattern.
To measure the directionality of a microphone, sound engineers use a polar pattern graph. This graph represents the microphone’s sensitivity to sound from different angles around the microphone. The polar pattern graph is usually presented in a circular format, with the microphone at the center.
There are different types of polar patterns, including omnidirectional, cardioid, hypercardioid, supercardioid, and bi-directional. Each polar pattern has a unique shape on the polar pattern graph, which indicates the microphone’s sensitivity to sound from different angles.
For example, an omnidirectional microphone has a circular polar pattern, indicating that it is equally sensitive to sound from all directions. In contrast, a cardioid microphone has a heart-shaped polar pattern, indicating that it is more sensitive to sound coming from the front and less sensitive to sound coming from the sides and rear.
Sound engineers use the polar pattern graph to choose the right microphone for a particular recording situation. For example, if they want to record a solo instrument, they may choose a cardioid microphone to minimize the pickup of ambient noise. On the other hand, if they want to record a group of musicians, they may choose an omnidirectional microphone to capture the sound from all directions.
directionality is a crucial characteristic of a microphone, and measuring it requires the use of a polar pattern graph. Sound engineers use the polar pattern graph to choose the right microphone for a particular recording situation, depending on the desired sound and the recording environment.
Measurement of Sensitivity
Microphone sensitivity refers to the microphone’s ability to convert sound pressure into an electrical signal. It is typically measured in volts per pascal (V/Pa) or millivolts per pascal (mV/Pa). The higher the sensitivity rating, the more responsive the microphone is to sound.
Microphone sensitivity is usually measured with a 1 kHz sine wave at a 94 dB sound pressure level (SPL), or 1 pascal (Pa) pressure. The magnitude of the analog or digital output signal from the microphone with that input stimulus is a measure of its sensitivity. Sensitivity measures the voltage at the output pins of the mic for a given sound pressure level.
For example, a microphone with a sensitivity rating of 13 mV/Pa means that an air pressure oscillation with an amplitude of 1 pascal (94 dB SPL) at the mic capsule would produce a voltage oscillation with an amplitude of 13 mV at the XLR pins. Gain is basically the ratio of output level to input level.
Almost all microphones will have sensitivity specifications of less than 0 dB (a negative number) because the reference voltage is 1 Volt and the voltage produced by the microphone under test is typically less than 1 Volt. A microphone with a sensitivity rating of -60 dBV/Pa, for example, produces a voltage of 1 microvolt for a sound pressure level of 1 pascal.
Understanding microphone sensitivity is important for choosing the right microphone for a particular application. A microphone with high sensitivity is ideal for recording quiet sounds, while a microphone with low sensitivity is better suited for loud sound sources. It is important to note that sensitivity is just one of many factors to consider when choosing a microphone, and other factors such as frequency response, directionality, and noise level should also be taken into account.
Measurement of Impedance
Impedance is an important specification to consider when selecting a microphone. It is measured in ohms and can be thought of as a type of “AC resistance” in an AC circuit. Audio signals are AC voltages since they have both negative and positive voltages (the positive and negative amplitude of the signal). Impedance, as it applies to microphones, refers to the resistance that the microphone presents to the input of the preamp or other device accepting the input from the microphone.
As a rule of thumb, the load impedance of a preamp or other device accepting the input from a microphone should be about 10x the output impedance of the microphone. On any given microphone’s spec sheet, you’ll find a value for its output impedance. This value can vary widely depending on the type of microphone, with dynamic microphones typically having a lower output impedance than condenser microphones.
Measuring the output impedance of a microphone can be done using a simple test setup. First, set up the sound source and measure the microphone’s output amplitude without any load. A high-impedance scope probe should work fine without loading the microphone. Next, load the microphone’s output with a resistor equal to your best guess of the output impedance. Measure the output amplitude again. The ratio of the two output amplitudes will give you the output impedance of the microphone.
It’s important to note that the impedance of a microphone can vary with frequency. Some microphones may have a flat impedance response across their frequency range, while others may have a more complex impedance response. Understanding the impedance characteristics of a microphone can help you select the right preamp or other device to match the microphone’s output impedance.
Measurement of Signal-to-Noise Ratio
One of the key metrics used to describe the quality of a microphone is the signal-to-noise ratio (SNR). This metric measures the ratio of the power of the desired signal to the power of the background noise. A higher SNR indicates a better quality microphone as it means that the desired signal is stronger relative to the noise.
SNR is typically measured in decibels (dB) and can be calculated using a base 10 logarithm. The formula for calculating SNR depends on how the signal and noise levels are measured, but a common formula is S/N = 20 log10 (Ps/Pn), where Ps is the power of the signal and Pn is the power of the noise.
When choosing a microphone, it’s important to consider the SNR as it can have a significant impact on the quality of the recorded audio. A high SNR is particularly important for recording in noisy environments or when recording low-level sounds.
It’s worth noting that the SNR is not the only factor that determines the quality of a microphone. Other factors such as frequency response, sensitivity, and distortion should also be considered when selecting a microphone for a particular application. However, a high SNR is generally a good indicator of a high-quality microphone.
Conclusion
microphones are essential tools used in various fields, including audio engineering, broadcasting, and telecommunication. They are transducers that convert sound waves into electrical signals, allowing us to capture and record sound.
There are different types of microphones, each with its unique characteristics and applications. Pressure-field microphones are designed to measure sound pressure, while other types, such as ribbon and condenser microphones, are more sensitive and can capture a wider range of frequencies.
When selecting a microphone, it is essential to consider its specifications, such as frequency response, sensitivity, and signal-to-noise ratio. These specifications can affect the quality of the recorded sound and its accuracy.
It is also important to note that while microphones can accurately measure sound waves, they are not perfect. Our ears can perceive sound in a more nuanced and complex way than microphones, and they can also adjust to different sound environments. Therefore, it is crucial to use both our ears and microphones to achieve the most accurate and high-quality sound recordings.
microphones are powerful tools that allow us to capture and record sound in various applications. By understanding their capabilities and limitations, we can make informed decisions when selecting and using microphones for different purposes.
