Microphones

Brief Introduction To Microphone Specifications

Microphones are one of the most important things to think about when setting up a recording studio, the quality of the microphone determines the quality of the recording.  There are a lot of different things to take into consideration when choosing the right microphone, things like polar patterns, frequency response, frequency range, the instrument or sound source, the connection, what it is being connected to, the sensitivity, the type and whether it requires phantom power.  The two most common types of microphones are condenser and dynamic.  All microphones are transducers, meaning they take one form of energy and turn it into another.  A microphone takes mechanical acoustic energy and turns it into an electrical signal which can be recorded and edited.

Microphone types

There are several different types of microphone, the two most common being condenser and dynamic.  A condenser microphone is more favored for studio use because of its extremely high quality, high sensitivity and usually flat frequency response as were a dynamic is favored for live performance as it doesn’t require phantom power and is very robust and inexpensive, it can also pick up very loud signals without the signal becoming distorted.  A dynamic microphone is also good for the recording of guitar amps and drums because of its ability to pick up high SPL instruments.  A condenser microphone can be good for recording acoustic instruments like guitar and piano, because of its usually flat frequency response.

Polar Patterns

The polar pattern of a microphone is how it picks up sound on the directional field, there are a number of different polar patterns, some more common than others.  An Omni directional polar pattern has a pickup of 360° which means it picks sound up from every direction, this polar pattern can be used if you want to record several sources in different directions or if you’re doing an interview in a quiet enviroment using this polar pattern will mean that using one microphone will pick up everyone equally.  Cardioid polar pattern gets its name from the word cardio as the shape of its pick up resembles a heart,  cardioid picks up best at the front while reducing pick up from the sides by 6dB and reducing sources at the rear by 15-25dB depending on the distance of the source.  Hypercardioid is similar to a cardioid but it picks up slightly more at the rear, the shape of the hypercardioid polar pattern almost resembles a mushroom it picks up best at the front  and slightly less at the rear, while reducing the sides by 12dB and has a weakest pick up 110° from the front on each side.  Supercardioid is similar to the hypercardioid pattern but it picks up slightly less from the rear.  It picks up best at the front and slightly less at the rear, while reducing the sides by 8.7dB and has a weakest pick up 125° from the front on each side.  Figure of 8 gets its name because the shape of its pick up resembles the number eight when seen from above.  It picks up equally at the front and rear, while rejecting the sides at 90° from the front. Figure of 8 could also be used for use in an interview if two people are sitting directly across from each other, this will ensure both sources are picked up equally while rejecting any ambient background noise that might be picked up from the sides.  Some microphones will also have the option to change the polar pattern, via a switch on the microphone, buying a microphone with this option could save money as it could then be used to record a large number of sources where different polar patterns would be needed.  A microphone such as the AKG C414 has this option, a switch on the front of the microphone lets the user switch between, omnidirectional, hypercardioid, cardioid and figure of 8.

Frequency Response

The frequency response of a microphone tells you how sensitive it is to certain frequencies on the frequency spectrum.  The frequency response of a microphone is an extremely important factor to take into consideration when choosing the correct microphone for the source you are planning to record.  Some microphones are designed to specifically record sources like vocals or a kick drum, these microphones have a shaped response as were other microphones can be designed to sound as natural as possible by their frequency response being as close to flat as possible, a flat response will give you an equal level over all frequencies these microphones are good for the recording of acoustic instruments such as guitar or piano.  A microphone like the AKG D112 which is designed specifically for the recording of a kick drum will boost certain frequencies on the spectrum in order to give the kick drum a realistic sound. Boosting at around 100Hz and 3kHz-5kHz will give the recorded sound the character of a real kick drum and will allow it to sound realistic in the mix.  It is also designed to handle high level transient signals without distortion.  Microphones with a boost in the upper mids such as an AKG C414 will give clarity and crispness to a source such as vocals.  Some microphones also have roll off options which will be selectable via a switch somewhere on the microphone, if the lowest frequency your source can produce is higher than the frequency the microphone will roll of it can be useful to use a microphone with this option as rolling of the low frequencies can be useful for preventing things like room noise, vibration and unwanted ambiance during a recording.

Frequency Range

The frequency range of a microphone refers to the range on the frequency spectrum it can pick up, the threshold of human hearing is 20Hz – 20kHz so a microphone with this range will be suitable for most instruments, although there are some microphones designed with a specific range to record specific instruments.  Some microphones frequency range will roll off in order to stop things like unwanted noise and vibration a roll off does not mean it rejects every frequency past this point, it will still pick up the frequencies but they will be lower in amplitude.

Sound Pressure Level

Sound Pressure Level or more commonly known as SPL is the loudest signal a microphone can pick up before it starts to overload.  A good SPL level would be anything above 120dB which is extremely loud to the human ear.  It is important to know the max SPL of your microphone so you do not clip when recording a source.  A dynamic microphone has a high SPL compared to a condenser microphone which has a lower SPL, making it useful for recording sources such as drums and guitar amps.

Operation

The operation of a microphone is how the microphone takes the acoustical energy and transforms it into an electrical signal, the operation in a condenser microphone and dynamic microphone are both different.  A condenser microphone is made up of a diaphragm and a back plate which is mounted directly behind the diaphragm,  sound waves strike the diaphragm causing it the vibrate back and forth, as the space between the diaphragm and back plate increases and decreases it changes the electrical signal generated.  A dynamic microphone works in a similar way but it is made up of different components such as, a diaphragm, a magnet and a voice coil.  Sound waves strike the diaphragm which vibrates a voice coil suspended in front of a magnet, the voice coil moves back and forth through a magnetic field generated by the magnet, which creates an electrical signal.

Connection

It is important to know the correct connection of the microphone you’re using so that you get the best quality recording with no problems, most microphones use a balanced XLR cable and some use a USB cable.  An XLR cable consists of three pins the bottom the pins will have the same signal flowing down them, one out of phase and one in phase this is so at the end of the cable when it enters the device it is connected to the out of phase signal is flipped and put back in phase which puts any interference picked up along the way out of phase and it is cancelled out and will not be audible. The top pin of an XLR cable is the ground.

Microphone Sensitivity

Microphone sensitivity is how sensitive a microphone is to sound.  A high sensitivity microphone will be able to record quiet sounds or a sound in the distance as were a microphone with low sensitivity will only be able to pick up louder sounds and sounds at a closer range.  A microphone with low sensitivity is a better choice when recording high SPL instruments like guitar amps and drums because it is less likely to clip the signal.  A condenser microphone will have high sensitivity making it more suitable for distant sounds or low level sounds and a dynamic microphone has a lower sensitivity making it better for high level sounds like a guitar amp or drums.