Ok here comes the very first post !
Topic 1 - All about microphones
Active vs Passive Microphones
An active microphone contains an internal amplifier and requires a power source, such as a battery or phantom power, to operate. The amplifier inside the microphone boosts the audio signal, which results in a stronger and clearer output signal. the amplified signal can withstand the signal loss that often occurs over long cable runs.
A passive microphone, on the other hand, does not have an internal amplifier and does not require a power source to operate. Instead, the microphone converts sound waves into an electrical signal that is then transmitted to an external amplifier or recording device for further processing.
When it comes to voice assistants, such as those found in smart speakers, the type of microphone used is usually an active microphone.
Active microphones are preferred for voice assistant applications because they offer greater sensitivity and signal-to-noise ratio, which are important for accurately capturing voice commands and reducing background noise
In addition, active microphones are often designed with features such as directional sensitivity, beamforming, and noise cancellation, which help to optimize voice recognition and improve the user experience.
Passive microphones are less commonly used in voice assistant applications, primarily because they lack the built-in amplification and noise reduction features of active microphones.
While passive microphones can still capture voice commands, they may be less effective at distinguishing between speech and background noise, which can lead to errors in voice recognition and a less reliable user experience.
Diaphragm
A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.
A microphone diaphragm is a thin membrane that moves in reaction to external sound pressure variation. A microphone diaphragm is a key transducer component in converting acoustic energy into electrical energy.
There are 3 main types of microphone diaphragms:
- Moving-coil diaphragm (dynamic)
- Ribbon diaphragm (dynamic)
- Front plate diaphragm (condenser)
Refer to above link for more information on microphone diaphragm !
MEMS Microphones
MEMS (Micro-Electro-Mechanical Systems) microphones, on the other hand, use a tiny diaphragm that is etched onto a silicon wafer using microfabrication techniques. The diaphragm is suspended by thin, flexible arms that vibrate in response to sound waves, generating an electrical signal.
MEMS (Micro-Electro-Mechanical Systems) microphones can be either active or passive.
Active MEMS microphones have an integrated amplifier circuit and require a power supply, such as a battery or phantom power, to operate. The amplifier circuit provides gain to the microphone signal, which makes it stronger and easier to process. Active MEMS microphones are often used in applications where high sensitivity and low noise are required.
Passive MEMS microphones, on the other hand, do not have an integrated amplifier and do not require a power supply. Instead, the microphone element produces a small electrical signal that must be amplified by an external circuit or device. Passive MEMS microphones are often used in applications where low power consumption and a small form factor are important, such as in hearing aids and other medical devices.
In general, active MEMS microphones are more commonly used than passive MEMS microphones due to their higher sensitivity, lower noise, and greater ease of integration into electronic systems.
Electret Microphones
Electret microphones use a polarized electret film as a diaphragm that produces an electrical charge when it vibrates in response to sound waves.
An electret microphone can be either active or passive.
A passive electret microphone relies solely on the charge stored in the electret diaphragm to generate an output signal. It does not require any external power or amplifier circuitry, and its output voltage is typically quite low.
An active electret microphone, on the other hand, includes an amplifier circuit that boosts the output signal from the electret diaphragm. Active electret microphones require a power source, such as a battery or phantom power, to operate. The amplifier circuit in an active electret microphone can provide higher output voltage and improved signal-to-noise ratio compared to a passive electret microphone. Active electret microphones are commonly used in consumer electronics applications
Electret and MEMS microphones in voice assistant applications
Both Electret and MEMS microphones are commonly used in voice assistant applications
Electret microphones are often used in consumer-grade voice assistant devices because they are inexpensive and can provide good enough voice recognition performance for many applications. They are also relatively easy to integrate into electronic systems and require minimal power. Electret microphones are well-suited for use in devices that are not battery-powered, such as smart speakers and home automation systems.
MEMS microphones, on the other hand, are preferred for more high-end voice assistant applications, such as those found in smartphones and wearables. MEMS microphones offer high signal-to-noise ratio and superior voice recognition performance, which is essential for accurate and reliable voice control. They are also extremely small and low power, making them ideal for use in compact, battery-powered devices.
Type of microphones used in Alexa, Siri and Google Voice Assistants
In Alexa, Siri, and Google Voice Assistants, both electret and MEMS microphones are used depending on the device and its specific design requirements.
For example, in Amazon Echo devices, which use Alexa voice assistant, both electret and MEMS microphones are used depending on the specific model.
For instance, the original Amazon Echo used a 7-microphone array that included both MEMS and electret microphones, while the Echo Dot uses a single electret microphone.
The newer Echo and Echo Plus devices use a 7-microphone array that includes MEMS microphones.
Similarly, in Apple’s Siri-enabled devices, such as iPhones and HomePod, MEMS microphones are used for their high sensitivity and low power consumption. Apple’s AirPods also use MEMS microphones for voice recognition.
In Google Home devices, which use Google Assistant, both electret and MEMS microphones are used depending on the specific model.
For example, the original Google Home device used two MEMS microphones, while the Google Home Mini used a single electret microphone.