Microphones are ubiquitous. Chances are you’re reading this on a device that has at least one, either built-in or attached. How do they work? What types of microphones are used in music performance and recording? What are their key differences? Read on.
The purpose of a microphone is to convert sound energy to another form of energy that is more compatible with the recoding medium. In most cases, the air movement and/or pressure changes caused by sound waves are converted, into electrical impulses. This process is called transduction.
Types of Microphones
We will cover two mechanisms of achieving this transduction: condenser/capacitive and dynamic. Piezo microphones, while used in many music recording and performance applications are seldom used to record audio directly. We may cover them in a separate article. Other types of microphones, such as fiber optic see less use in the music world.
Condenser microphones place a thin diaphragm close to a back plate. Both are conductive and given an electrical charge either from a battery or via “phantom power” provided by an external source, like a mixer. Two separated electrically charged plates makes a capacitor. When sound pressure hits the diaphragm, the diaphragm moves closer to the back plate. This changes the capacitance, resulting in a voltage change. That voltage change is the electrical signal that we are looking for, but it is often converted into a current change using a transistor.
Simplified electrical diagram of a condenser microphone.
Special types of condensers, called electret condenser microphones, or just electret microphones use a material for the diaphragm that has a permanent electrical charge. This allows them to be smaller and more robust than other condensers. They are often used in cell phones, laptops, etc. though seldom in music recording.
Dynamic microphones use magnets and a conductive element that moves in response to sound pressure. When a conductor moves in a magnetic field, electromagnetic induction causes a current to be generated in the conductor. Variations in the current are the electrical signal dynamic microphones provide.
Typical dynamic microphones use a diaphragm of non-conductive material with a coiled conductive wire attached. The diaphragm moves in response to air pressure changes caused by sound waves. This compresses the coil, creating the movement that creates the current.
Simplified electrical diagram of a dynamic microphone.
Ribbon (Wait, Three Types?)
Ribbon microphones are dynamic microphones, in that they use electromagnetic induction. However, they are worth calling out separately. Instead of a separate diaphragm and conductive coil, they use a “ribbon” of metal that acts as both. This ribbon is suspended between the poles of a magnet. Ribbon microphones generate variances in current due to the speed the ribbon moves, which is directly proportional to the velocity of the air particles themselves. In almost all other microphones, including other dynamic mics, the generated current varies based upon the distance the sound pressure moves a diaphragm. The differences in construction and operating principles lead ribbon microphones to be used in different circumstances than other dynamic microphones.
Simplified electrical diagram of a ribbon microphone.
Choosing Between Condensers and Dynamic Microphones
Condenser microphones have a tendency to be “brighter” and “more live” than dynamic microphones. Essentially, they pick up high end frequencies better and tend to be more sensitive with a lower noise floor. For these reasons, they are often preferred in studio environments, especially when capturing or accentuating the high end is desirable.
Dynamic microphones are often favored in live environments where durability is required. They are the ones to use if you plan to “drop the mic”, though please do not do this with any of ours. The diaphragms and other components are generally far stronger, though not unbreakable. A side effect of the beefier diaphragm is that it is harder to move. Because of this dynamic microphones tend to be less sensitive. A more significant factor is that higher frequencies have less energy and tend to be lost more quickly. This is why condensers have a “brighter” sound. The lower sensitivity, especially on the high end, can be beneficial in live environments. It makes feedback less likely and reduces potential for picking up sounds from other instruments/vocalists. Dynamic microphones also generally require no phantom or battery power, though “active” dynamic mics do exist and provide a sensitivity or gain boost.
Ribbon microphones share many characteristics with other dynamic mics. The key difference is in the use of the thin ribbon as opposed to a heavy diaphragm. Ribon microphones have a comparatively flat frequency response. Where other dynamic microphones are characterized as losing the high end, ribbon mics are described as slightly accentuating the low end. Historically, the thin ribbon was a significant weakness for these microphones. Early versions could break while simply being moved across a room while uncovered. These days, materials are available to make them significantly more durable, though not quite as durable as non-ribbon dynamic microphones. That said, a high quality ribbon microphone will generally cost a lot compared to the other two types.
The other primary consideration when choosing a microphone is the directionality or polar pattern. We will discuss that in a future article. Stay tuned.
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