Welcome to the third part of our microphone guide.

In the previous guides, we looked at moving-coil dynamic microphones and ribbon microphones. This time we are looking at another microphone type which can regularly be found in recording studios: the condenser microphone.

Condenser microphones tend to be more sensitive than moving-coil microphones and are often chosen when we want to capture more detail, quieter sources or sounds from a little farther away.

But first, let’s look at where they come from, who used them and especially how these microphones capture and convert sound waves to help with choosing the most suitable microphone for a recording.

Before we start: microphone type and polar pattern are still not the same thing

As we saw in the dynamic microphone guide, the microphone type describes the transducer principle: how the microphone converts sound energy into an electrical signal.

The polar pattern describes the direction, or directions, from which the microphone picks up sound.

A condenser microphone can therefore be cardioid, omnidirectional, figure-of-eight or have several selectable polar patterns depending on its design.

So, again, keep these two questions separate: ‘how does the microphone convert sound into electricity?’ and ‘from which direction does it pick up sound?’

A little history

The condenser microphone is one of the oldest electronic microphone designs. Its basic principle was developed in the early twentieth century. One of the important pioneers was E. C. Wente of Bell Laboratories, who developed a practical condenser microphone in 1916.

Early condenser microphones required comparatively complicated electronics and external power supplies but the technology developed considerably over the following decades.

By the mid-twentieth century, condenser microphones had become particularly important in broadcasting and studio recording. Manufacturers such as Neumann developed microphones which would become studio standards. Many of their microphone designs (and their descendants) are still used today.

The U47 became closely associated with some of the most famous recording studios in the world. Abbey Road used U47 and U48 microphones extensively during Beatles sessions, while the U48 — a closely related version with different polar-pattern options — was used for many of Frank Sinatra’s classic recordings at Capitol Studios.

How does a condenser microphone work?

A condenser microphone converts sound into an electrical signal using a capacitor.

A capacitor consists of two electrically conductive surfaces separated by a small gap. Inside the microphone these are:

1. a very thin diaphragm

2. a fixed backplate

The diaphragm forms one side of the capacitor and the backplate forms the other. When sound reaches the microphone, changes in air pressure make the diaphragm move backwards and forwards. As the diaphragm moves, the distance between the diaphragm and backplate changes. This changes the capacitance.

So the basic process is:

sound wave → diaphragm moves → distance between diaphragm and backplate changes → capacitance changes → electrical signal is produced

This is rather different from a moving-coil microphone where a coil moves through a magnetic field. The condenser capsule needs an electrical charge and the active electronics inside the microphone need power. In many modern microphones this is supplied through 48V phantom power from either a microphone preamplifier, mixing desk or audio interface.

Early condenser microphones used valves (tubes in American terminology) in their electronics. These were later increasingly replaced by solid-state electronics using transistors and particularly FETs (field-effect transistors). Some modern designs use integrated circuits (ICs) containing many electronic components on a single chip.

All of these can still be condenser microphones because the microphone type is determined by the capacitive transducer principle of the capsule, rather than by the following electronics.

In addition to the different electronics inside the microphone, some condenser microphones use a permanently charged electret material rather than an externally polarised capsule. The basic principle of detecting diaphragm movement through changes in capacitance remains the same.

What does this construction mean when recording?

The transducing elements can be extremely light and therefore have considerably less mass to move when changes in air pressure reach the diaphragm. The lower moving mass allows the microphone to respond easily to small and rapid changes in the sound.

As a result, condenser microphones are generally more sensitive than dynamic microphones and can capture very small details and fast transients particularly well.

With the help of the active electronics in the microphone they can produce a stronger electrical output. This makes them very useful when recording quieter sources or when the microphone cannot be positioned close enough to the source.

However, there is a trade-off: their high sensitivity means they may also capture considerably more of the surrounding environment. Imagine the microphone faithfully recording the singer, the room, the computer fan, the neighbour moving a chair next door or possibly a car passing by outside.

Microphones do not know which sound source was meant to be recorded. Unlike our brain, they do not selectively focus on the sound that seems important and ignore everything else around it.

Advantages and disadvantages

High sensitivity is therefore neither automatically good nor bad. It depends on who or what is being recorded and on the recording environment.

Where would we use a condenser microphone?

Condenser microphones are extremely common in studio recording and are often used when detail, sensitivity and transient response are important.

Typical applications include:

• vocals

• acoustic guitar

• piano

• strings

• drum overheads

• percussion

• choirs and ensembles

• room microphones

• orchestral recording

• Foley and detailed sound effects

• spoken voice and voiceover

They are also widely used as small-diaphragm condenser microphones for instruments where accurate transient response and a relatively neutral frequency response are useful.

• A pair of small-diaphragm condensers, for example, is extremely common for stereo recording.

• Large-diaphragm condenser microphones are particularly common for vocals, voiceover and many general studio applications.

The important principle is not that ‘condenser microphones are better’ or that they are automatically the correct studio microphone. Their construction simply offers a different set of characteristics.

Always listen to what the microphone captures rather than choosing it simply because it is a condenser.

Large diaphragm or small diaphragm?

Condenser microphones are commonly divided into large-diaphragm and small-diaphragm designs. This distinction is useful but it does not say anything about how a microphone will sound with a specific musician or object.

Large-diaphragm condenser microphones are common for vocals, voiceover and general studio recording as they can have a strong sense of presence. Many classic studio microphones belong to this category.

Small-diaphragm condenser microphones tend to have very light diaphragms and so have excellent transient response and consistent directional behaviour across a wide frequency range. This makes them particularly useful for sources such as acoustic instruments, percussion, piano, ensembles, stereo recording and on location (as boom microphones). As always, the actual microphone and the recording source matter more than the category alone.

Distance matters

Because condenser microphones are usually more sensitive, they do not necessarily need to sit extremely close to the sound source. Moving the microphone further away changes the relationship between the direct sound (i.e. sound travelling directly from the source to the microphone) and the indirect sound (i.e. reflected or reverberant sound from the room).

A very close microphone placement leads to recordings fitting into the category of ‘hyperrealism’ or ‘intimate performances’. Close placement generally gives us more direct sound and less room tone while moving farther away from the sound source allows more of the acoustic environment to become part of the recording.

With directional condenser microphones—just as with directional dynamic microphones—moving closer to the source can produce what is called the proximity effect. This means that microphone distance is not simply a question of getting enough signal. Distance becomes an attribute of the recording’s sound.

A note about phantom power

Most modern studio condenser microphones require power for their internal electronics and many use 48V phantom power. Other powering systems also exist, particularly in older or specialist equipment. Phantom power travels along the same balanced XLR cable which carries the microphone signal. This means that no separate power cable is required.

Some condenser microphones use batteries, dedicated power supplies or other powering systems but 48 V phantom power is by far the most common system encountered in modern recording equipment.

Always check what the particular microphone requires—especially before plugging it in or switching on phantom power.

Some well-known condenser microphones

Microphone	Typical use
	Historic studio vocal and instrument microphone
	Vocals, voiceover, acoustic instruments and general studio recording
	Vocals, instruments, piano, ensembles, room recording and general studio use
	Acoustic instruments, piano, percussion, ensembles and stereo recording
	Acoustic instruments, hi-hat, percussion and overhead applications
	Vocals, instruments, drums and general studio recording

I hope you enjoyed this introduction to condenser microphones. If you have any questions, drop me an email.

In the next episode, we can look at valve (or for our American readers 'tube') microphones which is another really cool-sounding type of condenser microphone.