Electret microphone how does it work

In fact, many intercom systems use small speakers with lightweight cones as both a speaker and a microphone, by simply switching the same transducer from one end of the amplifier to the other! Dynamic microphones are renowned for their ruggedness and reliability. They need no batteries or external power supplies.

Output level is high enough to work directly into most microphone inputs with an excellent signal-to-noise ratio. They need little or no regular maintenance, and with reasonable care will maintain their performance for many years. Condenser or capacitor microphones use a lightweight membrane and a fixed plate that act as opposite sides of a capacitor. Sound pressure against this thin polymer film causes it to move.

This movement changes the capacitance of the circuit, creating a changing electrical output. Condenser microphones are preferred for their very uniform frequency response, and ability to respond with clarity to transient sounds. The low mass of the diaphragm permits extended high-frequency response, while the nature of the design also ensures outstanding low-frequency pickup.

The resulting sound is natural, clean and clear, with excellent transparency and detail. Two basic types of condenser microphones are currently available. One uses an external power supply to provide the polarizing voltage needed for the capacitive circuit.

These externally-polarized microphones are intended primarily for professional studio use or other extremely critical applications. A more recent development is the electret condenser microphone Fig. In these models, the polarizing voltage is impressed on either the diaphragm or the back plate during the manufacturing process, and this charge remains for the life of the microphone.

The best electret condenser microphones are capable of very high-quality performance, and are used extensively in broadcast, recording and sound reinforcement. Due in part to their low-mass diaphragms, condenser microphones are inherently lower in handling or mechanical noise than dynamic microphones.

For all of its electret condenser designs, Audio-Technica has elected to apply the polarizing voltage, or fixed-charge, to the back plate rather than the diaphragm. By doing this, a thinner material may be used for the diaphragm, providing a considerable performance advantage over electret microphones of conventional design.

Condenser microphones have two other design advantages that make them the ideal or the only choice for many applications: they weigh much less than dynamic elements, and they can be much smaller. Attempts at miniaturizing dynamic microphones result in greatly reduced low frequency response, overall loss in acoustic sensitivity, and higher mechanical or handling noise.

Phantom powering is a technique which delivers a DC voltage to the microphone through the same shielded two-conductor cable that carries the audio from the mic. As previously mentioned, the electret material allows for a fixed electric charge across the parallel-plate capacitor.

This fixed charge, again, is necessary from ECM capsules to function properly. The transducer element and the electrostatic principles that govern it are pretty clever. The condenser capsule must maintain a very high impedance in order to keep the stored charge across the plates from leaking away. Similarly, it is essential to have an impedance converter immediately after the capsule to take the audio signal from the ECM capsule effectively.

A JFET is an active electronic device with three terminals. This effectively sets up the source-drain terminals to have electrical current flow through them. This current is relatively low-impedance and can be sent through the rest of the microphone and the final mic output. The current between the source-drain can be thought of as the JFET impedance converter output. This is where the impedance comes in. To learn more about transistors in microphones, check out my related article, titled Do All Microphones Have Transformers And Transistors?

Depending on the particular electret condenser microphone, there could be additional circuits for the mic signal to pass through before being outputted from the microphone. ECMs have [practically] permanently charged capsules and do not require an external polarizing voltage to apply a fixed charge across their plates. That being said, electret condenser microphones are still active microphones. Their impedance converters require power provided by external means to function properly, as do the components mentioned in the section above.

In consumer devices, which commonly use electret microphones, the mics are powered by the same battery, power supply, or power mains that power the rest of the device. At the beginning of this article, I mentioned that electret condenser microphones are one, if not the most, commonly used microphones on Earth. The applications of the above microphone types range from telephone calls to blockbuster movie audio; hit records to helping those of us with hearing impairments.

To really learn about electret condenser microphones, we should take a look at some examples:. The Earthworks M50 link to check the price at sweetwater is an excellent measurement microphone with an electret condenser capsule.

It has a wide frequency response ranging all the way from 5 Hz to 50, Hz the human range of hearing, which most EMCs aim to reproduce, is only 20 Hz — 20, Hz. This microphone tells us that electret microphones, with the right design, can be top performers and incredibly accurate transducers. The DPA A link to check the price on Amazon is a top-of-the-line microphone in general not only compared to other electret condenser microphones.

This pencil microphone performs nearly as precisely as a measurement microphone but is not marketed that way. Rather, the A is produced to be a go-to microphone for accurate and detailed sound production in the studio. The Sanken COSD link to check the price on Amazon is an industry-standard lavalier microphone for film, television and other screened media. These small pin-type project ECMs would be very similar to what we would expect to find in consumer-grade electronics.

MEMS mics are much smaller and becoming cheaper to build and, in some ways, outperform ECMs particularly in consumer devices like cellphones. What is a FET microphone? A FET microphone is a solid-state active microphone that utilizes a FET field-effect transistor , as opposed to a vacuum tube, as its impedance converter. FET mics are typically condenser microphones but can have dynamic transducers as well. What is an active microphone? An active microphone is a mic that requires power to function properly.

All condenser mics are active, and some ribbon dynamics are active. Your email:. This really explain much. Looks all electrec microphones are quite similar. Differencies are only dimensions and frequency areas. What it mean? Thanks, decibel seems almost same in all the eletret mic datasheet, so I am not sure how it can be so crucial. I think the biasing resistor decides the sensitivity level of the MIC which can be tweaked easily.

Could you please expand on the differences in construction of omnidirectional versus unidirectional microphones? Thank you for liking the post. Your email address will not be published.