Testing, testing, 1-2-3
I’ve been learning about music production recently. Part of the process is understanding how to get the sound you want out the recording equipment you have. At the heart of all recording is the microphone, and the way the microphone takes mechanical vibrations and transduces them into electrical signal is quite interesting.
The first device widely accepted as the first microphone is the carbon button microphone. Before that, Alexander Graham Bell created a liquid transmitter that involved parchment, wires, water, and acid, among other components. It didn’t make the most portable device, not to mention the added perk of having to work with exposed acids. The carbon button microphone offered a nice alternative.
Carbon is a resistor. It’s one of the most common materials used to make the resistors used in circuits. However, when carbon molecules are compressed, they become more conductive. The carbon button microphone was composed of grains of carbon between two plates, which were connected to wires that connected to audio receivers. One of these plates was the diaphragm that vibrated when hit with sound waves. That vibration put a compressive pressure on the carbon molecules and changed the electrical resistance between plates. With the power of a battery to create current flow, the changing resistance between the plates created an electrical current that had the same variances in the signal as did the mechanical sound vibration hitting the diaphragm, and transduced sound. Carbon button transmitters were used in rotary telephones for several decades until they were replaced by push-button (aka “Touch-Tone”) telephones. The carbon button microphone was susceptible to great background noise, and occasional crackling.
The condenser microphone is the modern descendant of the carbon button microphone that operates under similar principles but deals with background noise more effectively. The diaphragm and back plates act as capacitors, and when they’re closer, their capacitance increases, and similarly decreases with distance. In order for this to happen, an electrical field must be generated between the plates, and this is done either through an internal battery, or an external power source, which is often referred to as phantom power. This allows for the signal produced by the vibration of the diaphragm to be amplified and transduced into an electrical signal.
Another common type of microphone is a dynamic microphone, and it is a bit of a different beast. The dynamic microphone features the same diaphragm plate that a condenser microphone uses, but in place of an additional plate to act as a capacitor, the dynamic microphone has a coiled wire surrounded by a magnet. From the study of electricity and magnetism, we know that a changing magnetic field can generate an electromotive force, which then causes electric current to flow. That current is what we need to power the microphone. So, in this case, the vibrating diaphragm will displace the wire coil, and that creates a current that is proportional to the speed of the movement from the mechanical sound wave hitting the diaphragm, and the signal is transduced.
Now let’s talk about the different physical spaces microphones can capture sound from. You might remember the cardioid from calculus class. You can also recognize it as the shape of a halved apple. Cardioids and other polar patterns also play a role in sound recording and help describe how certain microphones should be placed for optimal pickup while minimizing background noise.
An omnidirectional microphone picks up sound from all directions but cannot be targeted toward one sound source; the field of sound it can pick up is like a sphere. A cardioid microphone picks up sound mostly in front of it, and captures tapered sound to the sides, and takes the shape of, you guessed it, a cardioid. A super-cardioid microphone has an area behind the microphone head that is also sensitive to sound. This means you need to be aware of where your microphone is placed in reference to the rest of your amplification system. I know I’ve definitely gotten screamed at with some feedback when I was singing into a microphone too close to a speaker.
There are a lot of ways you can manipulate microphones during the recording process to get the best-quality sound for your money. For directional microphones, there’s a concept called the proximity effect, which is an increase in lower frequencies as you move the sound source closer to the microphone. This makes vocals sound a bit more full and clear. To avoid popping sounds due to the mechanical impact of air on the microphone when singing or speaking, a pop filter can be placed between you and the microphone when recording. You can make a decent pop filter on your own, which I have actually done, and I’ve found a few YouTube videos that teach you how to do it. For what it’s worth, I’ve personally found that unidirectional condenser microphones on low volume settings do well for recording acoustic piano.
If this inspired you to go out and play around with microphones to see what you can make, happy recording!