Microphones: The Basics

Pablo Bellinghausen

Before getting into the more practical aspects of microphones, it’s important to know a bit about how they work. There are many introductions to mics out there, but they are often rather dry and theoretical, whereas others, in an attempt to keep things simple, miss some technical elements that are actually very important when purchasing and using mics in the real world.

We’ll try to go through the essentials here in a clear and concise way that will hopefully be useful for beginners and experienced users alike.

What is a microphone?

In theory, a mic is simply a sensor that transforms sound waves into an electrical signal – it’s really as simple as that.

Their technical term is “acoustic-to-electric transducer”, since they convert energy from one kind to the other. In practice, the thousands of different models costing from pennies to several thousands of pounds show that it isn’t all that straightforward, however.

The main element of a microphone is a capsule, containing a diaphragm, or membrane, that is physically moved back and forth by the sound waves. This movement is converted into an electrical signal and then amplified by internal circuitry. The most common mic varieties, differing in diaphragm design, are condenser, dynamic and ribbon.

Microphone types

Condenser

The most common microphone variety in many studios is the condenser type. They are clean-sounding, accurate and will pick up a lot of low-volume detail, which can either be a good or a bad thing; it’s a common occurrence for home studio users to clearly hear the neighbours having a chat in the background of a recording!

This is a great advantage when working in controlled studio rooms; good-sounding rooms are picked up beautifully by high-quality condensers, giving a sense of organic realism to recordings. Most classic recording microphones are of this variety.

The Neumann KM 184, like the C414 above, is a condenser mic

Condensers are great for the highest sound fidelity, but their tendency to be rather fragile and their sensitivity to quiet sounds up can make them problematic in stage applications. Some older models can also be susceptible to overloading at loud levels, leading to nasty distortion.

A lot of improvements have been made in this technology in the last few years and there are some fantastic, rugged “live condensers” nowadays, but they will always end up picking up more extraneous sounds than good dynamic mics, which can easily cause feedback (that familiar high-pitched whine that is heard when a mic is placed in front of a speaker playing the same signal back). Condensers are best in quiet stages, far from any loud drums or amps, and ideally for musicians using in-ear monitoring.

The Sennheiser e965 is an amazing live condenser, but it’s not for everyone

Condensers need power, both to get the capsule to work and to drive the internal circuits. This is done via phantom power (usually 48 volts), normally supplied by the mixer or audio interface’s built-in mic preamplifier.

Some vintage-type premium models will use valve (or “vacuum tube”) circuitry and will be sold with a separate power supply unit. Valve mics will usually have a warmer, more complex sound which can be very flattering on many sources, particularly vocals.

Condensers will come in lots of shapes and sizes; one of the main distinctions is the size of the diaphragm. Technically, smaller diaphragms tend to have better transient response and fewer internal resonances and are in general more accurate than large ones, particularly for sounds reaching the capsule at an angle. However, there is just something subjectively nice about the sound of a well-crafted large diaphragm condenser, enhancing close-up vocals and instruments and making them sound “larger than life”.

The Telefunken CU-29 is a large-diaphragm tube condenser, shown here with its power supply

Electret Condenser

There is a particular type of condenser called electret, which is actually the most common variety outside of pro audio; it is found in most computers, telephones and portable recorders. Their capsule is permanently charged (or “pre-polarised”), so it doesn’t need phantom power; the microphone’s internal circuitry still does, but it can use a much lower voltage. Most consumer mini-jack mic inputs will supply 5 volts of “plug-in” power through the “ring” bit of the connector.

Cheap consumer model & Audio-Technica AT4033: two electret mics of very different quality

Electrets can be very small and very cheap to manufacture (good reasons as to why they’re so common) but until not that long ago they were all pretty bad! Consumer ones still tend do be rather poor, and many will lose their charge and stop working after a few years. However, electret technology has been refined to the point where high-quality models can sound as good as classic condenser models, and in use there is little difference nowadays.

The main difference in use between electrets and “true condensers” will be with headsets and lavalier “tie” microphones, which need to be fed a voltage no higher than about 10 volts; specific adaptors are therefore required when plugging them into an input with 48V phantom power; plugging it directly can damage the mic.

Dynamic

Dynamic microphones are far more rugged, being both resistant to impact and moisture; this makes them ideal for stage use. One of the most common models, the Shure SM58, is renowned for its durability and can be seen being subjected to some rather intense stress tests on the following (pretty funny) video by the Scandinavian magazine Studio:

https://www.youtube.com/watch?v=33QPLbQi9FI

Dynamic microphones will also tend to pick up a lot less extraneous noise than condensers, which besides helping immensely in cramped stages also makes them great for recording voice and instruments in rooms with poor acoustics. If rejection of sounds of any kind is a high priority, then a dynamic microphone is often a good choice.

Audix OM7: One of the “kings” of feedback rejection

The downside is that very small nuances in the original sound are often lost by all but the very best dynamics. The capsule is a lot heavier, which makes it harder to respond to very quick changes in volume (transient response). Compared to a condenser, the sound loses some detail and “liveliness” which cannot be recovered through tone adjustments; it does however impart a sound that works great for some vocals, and is very flattering to certain kinds of percussion, “fattening” the sound of toms, for example.

High quality dynamic microphones are also the norm for broadcast due to their rejection of poor room acoustics (often a problem in cramped radio booths), warm, flattering low-frequency response, and non-fatiguing, pleasing treble.

The Beyerdynamic M 99 is a great dynamic for broadcast and spoken word

Ribbon

There is also type of dynamic that uses a thin metal ribbon as a diaphragm. These used to be the standard studio microphone during the thirties, and they have been in use in broadcast and music studios ever since, most notably by the BBC. Although their popularity started to wane as soon as classic German condensers started to get a hold on the market in the fifties, there has lately been a resurgence of interest for them, and several innovative models have come out in the last few years.

Coles 4038 and sE VR1 ribbons: traditional vs modern

Their sound is similar to dynamic microphones, but with a smoother and slightly more natural mid and treble response; most models will be rather dark-sounding but they retain detail that most dynamic mics will not; newer ones have been designed to be a lot brighter to make them more versatile. Most will pick up sound from the front as much as from the back, which can make them a bit awkward for positioning, but there are models that will try to enhance their directivity. We will go through directivity and polar patterns in detail in our next instalment.

Old ribbon mics have a very low level output and are quite fragile; the ribbon itself can break if the mic is dropped, and is susceptible to blow out if phantom power is applied to it. Newer models are a lot more resistant, and their output level will often rival that of condensers, whether through innovations in the ribbon’s design or through integrated amplification circuits. Despite all these improvements however, ribbons are still a very unusual sight outside recording studios or broadcast booths.

Next time we will look at some of the technical characteristics that define the sound of a mic, such as the frequency response, polar pattern and proximity effect, as well as how to read the measurement graphs that represent them. Until then, happy recording!

 

Pablo Bellinghausen
Pablo Bellinghausen is a part of the technical sales and support team at Studiospares. After studying Sound Engineering at the SAE London he has worked as producer and remixer for acts such as Neonfly, A New Tomorrow, Andrea Balency and Monarchy. His alternative rock project The Distorting Glass digitally released their debut album in early 2014; a remastered physical version will be out in mid-2014.

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Novation Rockin Glastonbury 2014

Connecting Microphones to a Computer

by Pablo Bellinghausen

Consumer microphone inputs

Connecting a mic to a computer for recording sounds like an easy task: just plug the cable into the mic input on the computer and you’re good to go, right?

It’s not that simple, unfortunately; there is a very big difference between consumer and professional audio electrical standards, and mixing them up can create problems that vary from a distorted and noisy sound, to no signal at all, to actual damage to your equipment.

The standard consumer mic input on most computers (usually looking like the one in the above picture) is a rather budget affair, the whole circuit usually costing a few pennies. It tends to have very low gain, wildly variable impedance, and a small amount of DC power (normally 5 volts) supplied in a way that can damage some professional microphones, whilst remaining too low to power others. The incoming signal is then fed into an inexpensive analogue-to-digital converter that can further degrade the sound during the critical task of converting the signal into a digital stream to be sent to your recording software.

This input expects the kind of microphones that can be bought in computer stores. Consumer computer microphones will use a mini-jack connector; they will tend to have high output levels, high distortion and noise ratings, and uneven, spiky frequency response and polar patterns. In other words, they sound pretty bad!

Professional Mic Inputs

Professional microphones will still vary in electrical specifications, but the differences are small enough that they’re all mostly inter-compatible. All pro mics (with the exception of portable wireless systems and some vintage-style tube designs) will use a male XLR socket; they are designed to have the best possible sound quality and lowest noise level, at the expense of overall signal strength (which can be up to 1000 times lower than that of consumer mics). To make up for this, microphone inputs have internal amplifying circuits called preamps, which correct and raise the signal to a standard “line” level.

Sennheiser e965 and its male XLR socket

A pair of female XLR sockets

Condenser microphones like the Sennheiser e965 above have internal circuitry that requires phantom power (usually 48 volts, although it’s often a bit less), whereas dynamic designs don’t require it. Microphone inputs on a professional device will normally have a phantom power switch, and are kitted out with female XLR sockets like the above, so you can use industry-standard XLR leads with them.

Audio Interfaces

So, how does one plug these microphones in? Well, some motherboards have line inputs into which a stand-alone preamp can be plugged, but even then you might run into noise and operating level problems. The low quality of analogue-to-digital (A/D) converters also remains an issue, often giving you a diffuse, watery sound that can defeat the purpose of improving the rest of your gear.

By far the best way to connect professional microphones is through an external sound cardor audio interface – basically a box that takes over all the audio signals going in and out of the computer, including headphone and speaker outputs. Audio interfaces have the circuitry required to work with many other types of signal, like synths, electric guitars, MP3 players, and tape recorders.

They have high-quality electrical components and very clean converters, which convert the inputs from analogue to digital, and the speaker and headphone signals from the computer from digital back into the analogue realm to ensure maximum quality when recording as well as when listening to the playback. They are usually plugged in through USB, Firewire or Thunderbolt, and upon being selected on the computer these ins and outs effectively supersede the built-in connections.

Audio interfaces come in many different sizes, depending on how many separate inputs and outputs are required. Some, like the Scarlett 2i2 above, offer a simple, no-frills experience, with only two inputs and a stereo speakers and headphone output; the largest ones by Avid or Apogee have complex routing options and input numbers that can go well into the triple digits.

In our next instalments we will be taking a closer look at audio interfaces and what to look for when purchasing one, as well as differences between vocal microphones and their relative uses. Until then, happy recording!

Products mentioned:

454570 – Sennheiser e965 Handheld Condenser Mic

http://en-uk.sennheiser.com/vocal-condenser-microphone-studio-live-recording-e-965

http://www.studiospares.com/invt/454570

389820 – Focusrite Scarlett 2i2

http://uk.focusrite.com/usb-audio-interfaces/scarlett-2i2

http://www.studiospares.com/invt/389820

Pablo Bellinghausen
Pablo Bellinghausen is a part of the technical sales and support team at Studiospares. After studying Sound Engineering at the SAE London he has worked as producer and remixer for acts such as Neonfly, A New Tomorrow, Andrea Balency and Monarchy. His alternative rock project The Distorting Glass digitally released their debut album in early 2014; a remastered physical version will be out in mid-2014.

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