DONE Unit 48.2: Understanding Microphones: Dynamic vs. Condenser

Choosing the right microphone

So first of all, what actually is a microphone? A microphone is a piece of sound equipment which converts acoustic energy/sound into electricity. This is called the 'microphones signal'. This signal can be recorded, amplified or transmitted.

Depending on the purpose which you intend to use the mic for, you will require different types of microphones. For example, you probably wouldn't use the same microphone to record an orchestra as you would a vocal soloist. It is important to chose the right mic for the job, to ensure the best projection of the piece. Not only is it vital to consider what you are using the mic on, but also why you are using the microphone. Are you recording in a studio, or are you using the mics to amplify a live performance? There are many other factors that must be considered before choosing the right microphone.

In modern times we have an extremely wide variety of microphones, we are spoilt for choice! Today I'd like to focus on 2 types of microphones; dynamic mics and condenser mics. Both mics have a different operating principle, in other words their sound is converted differently into an electrical signal. This principle depends on the type of transducer that the microphone uses to convert sound into an electrical signal.

Dynamic Microphones

Shure SM57- a dynamic microphone. 

First of all, we have dynamic microphones. A dynamic microphone you may be familiar with is the Shure SM57, I chose this because it is quite a popular choice of microphone for musicians as it is produced by a well known and respectable brand, plus it is affordable with a retail price of around £85. This model has been in production since 1965, so obviously its been a pretty successful product.

A dynamic microphone makes a signal in result of motion inside the mic. When sound enters this type of microphone, sound waves strike a thin, plastic diaphragm causing vibration. A coil which is attached to the back of the diaphragm vibrates along with it, as the coil is moving back and fourth it passes through a magnetic field. This generates an electrical signal that corresponds to the original sound.

After the sound has travelled down the mic cable and been converted into an electric signal, the sound is too weak to be used. This is when a pre-amplifier comes in. A pre-amp amplifies a weak signal before it is sent to the main amplifier, Sometimes pre-amps are built into to amplifiers or mixers.

How a dynamic microphone works.

Dynamic mics are usually used with high sound level applications, like vocals or drums, as unlike condenser mics, they're less likely to overload when exposed to loud sounds. Therefore dynamic microphones aren't that great for recording distant or quiet sounds. This is because the sound waves would have to move the mass of the diaphragm and also the voice coil. If not enough acoustic energy is given, then these components won't move and the complete microphone signal will not be transmitted. With these mics, you will notice that often they are a lot heavier than condensers. Dynamic microphones have to contain a magnet in order for the diaphragm and coil to work, hence the fact why these microphones are heavy as they contain a magnet. This factor means that these mics cannot be made small, this limits mounting options. But, on the other hand this is a good thing as it makes the mics more durable, so they're perfect for the road and stage applications.

Condenser Microphones

 Another microphone type is a condenser mic, these work differently to dynamic microphones as they process the acoustic energy differently. In a condenser microphone, soundwaves also strike a diaphragm causing it to vibrate. But, in this mic the diaphragm is infront of an electrically charged plate. As the diaphragm moves back and fourth it changes the electrical field between itself and the plate. This then generates an electrical signal that corresponds with the sound. Quiet sounds can easily be picked up by this microphone type, as there is no voice coil needing to be moved. A dynamic mic requires more acoustic energy/sound in order to move the coil, but a condenser mic does not as only the diaphragm has to be moved which is the reason why condenser mics have better high frequency detail.

Condenser microphones are ideal for micing stringed instruments, percussion, piano or vocals. Generally, they have a higher output than dynamics, so they're really good at picking up distant or quiet sources. Unlike dynamic microphones, condensers do not have a magnet so they're very light.

These mics require power in order to operate as they have internal circulatory. The powered used by the microphones is called phantom power, usually it is supplied through the amp, mic cable, the mixer or recorder. Some mics can even run on an internal battery, but this isn't common.

In certain situation it is safer to use a dynamic mic as condensers overload when exposed to loud sounds. This outcome can be avoided by completing sound checks prior to using the mic to ensure that the mic you're using can cope with the sound levels from the source.

An example of a condenser mic is the AKGP170, which was released in 2007. This is a popular choice of mic to use in the studio and currently retails at around £70 (2015). The AKGP170 sources its phantom power from a preamp or an interface and then this electric allows the mic to produce signals. Another example of a condenser mic could be the C1000S. Alternatively, this mic gains power from a 9V battery, therefore this model would not need to be connected to equipment that supplies phantom power. Certain mics even have switches which can variate the sensitivity of the mic. One of the disadvantages of condenser mics is that they aren't as durable as dynamic mics due to their construction and their electronic property.

Frequency Response

The frequency response of a microphone is the sensitivity, which is effected by the diaphragm. If the microphone has a high signal then it will be more sensitive, whereas if the signal is lower it will have a lower sensitivity. This all depends on the size and thickness of the mic, what materials the mic is made out of and how the mic is attached. The frequency response of a microphone can be represented using a frequency response chart, this is a graphic representation of the mics sensitivity over its operating range from its lowest to highest frequencies (this can be between 20-20,000hrtz, human hearing).

Frequency Response Curve for the Shure SM58.

The graph above shows the frequency response of the Shure SM57, which is a mic that we use regularly in the studios at school. This mic has a tailored response as it is not equally sensitive to all levels of frequency. The chart tells us that this mic can pick up between 50Hz-15KHz. This pick up range is perfect for vocals and should brighten the mid range and bass rolloff.

A mic can have a 'flat response'. This means that the mic is equally sensitive to all frequencies within its operating range. The result of this is that sound is reproduced almost the same to the original sound, making it great for recording acoustic groups, vocal groups and orchestras. Another type of response is a 'shaped response', this response is more sensitive to some frequencies than others. For example; if a mic had increased sensitivity to the upper and middle range then it would add clarity to sounds. This response works well with guitar amps and drums. If a mic had decreased sensitivity to lower frequencies it would reduce the chances of picking up background noise and unwanted vibration. This property is great when recording close to the source, as it doesn't pick up the build up of bass, this is called the proximity effect.

Choosing the right frequency response is extremely important when recording! And the ideal response for the instrument you'd like to record should be researched before you record that particular instrument.

Polar Patterns 

We use polar patterns to see the strongest and weakest points a microphone picks up. This is shown using a circular graph that uses circles to represent how sensitive a microphone is in different directions. There are a variety of different pattens, but 3 popular structures are Omnidirectional, Cardioid and Figure of 8.

Omnidirectional

An Omnidirectional micpicks up noise from a 360 degrees radius/all directions. This is great for picking up natural sounds or for using in  a headset or tie-clip. All Omnidirectional microphones are pressure sensitive, this means that they will not be affected by wind noise or the proximity effect.

Omnidirectional Polar Pattern. 

Cardioid

Cardioid mics pick up sound from a 120 degree radius of the direction it is facing. This type of pattern is good for reducing feedback and recording a specific sound in a loud/noisy environment. Unlike Onimdirectional's, Cardioid's pick up wind noise and the proximity effect as they aren't pressure sensitive. Cardioid microphones are more sensitive at the front.

Cardioid Polar Pattern. 

Figure of 8

The 'Figure of 8' polar pattern, also known as Bidirectional, picks up sounds from the front and back of the microphone but eliminates sound from the sides. Similarly to Omnidirectional microphones, bidirectional do not change depending on the frequency. The main characteristic of a Figure of 8 microphone is that they produce a natural sound, which is why they are often used in interviews, broadcasting and in studios. All ribbon mics have a figure of 8 pattern.

Figure of 8 Polar Pattern.