A Closer Look at Dynamic Microphones, Part 1

Microphones are the portal, the gateway into the world of audio recording, media production and live sound reinforcement. With near mystic qualities, the microphone transforms physical activity into electrical energy. But what happens inside a microphone isn’t magic; it’s science. And it isn’t just the science of electromagnetic induction.

Creating a microphone relies on all sorts of empirical understanding, from materials and construction to performance and application. To that end, there are now all manner of microphones, many touting their unique applications. But whether you are looking for a shotgun microphone, a stereo mic, a USB microphone, or the ubiquitous hand-held vocal mic, they all generally fall into one of two categories: Dynamic Microphones and Condenser Microphones. (Well, okay, three categories; there is a subset of the condenser family known as the electret condenser.)

The big difference is how the microphone transforms the vibrations in the air that we call “sound” into the electrical current that we call “signal.” Unlike a condenser microphone, the dynamic microphone is self-powered – no phantom or external power source is required.

So get ready to take a look inside and see what makes a dynamic microphone tick. In addition, you can review what qualities make for a great live mic – as well as pick up some EQ tips for achieving higher levels of performance from your hand-held dynamic vocal microphone. For this exploration, the Samson Q8x dynamic vocal mic will be the reference touchstone.

What Makes a Dynamic Mic Work?

Pass a bar magnet through the center of a spool of wire and an electric current is created. Perhaps you’ve seen such a demonstration in school or at a science museum. This is an example of electromagnetism at work. It works the other way, too; moving a coil past a fixed magnet also creates a current. Knowing that a Dynamic Microphone is also called a Moving-Coil Microphone may give you some idea how it all comes together. Inside the dynamic microphone is a thin membrane, known as the diaphragm. It is this diaphragm that moves in response to the pressure of the sound waves. Behind this diaphragm is a small coil of wire. The diaphragm and the coil are connected; together they move back and forth in opposition to the magnet. This motion creates the electrical current that ultimately becomes the audio signal. Seems simple, right? And in some ways it is. But as you’ve guessed, there is a bit more to it than that. The next section breaks it down piece by piece.

• The Diaphragm
  This is the key component in nearly every dynamic microphone. The challenge is to create a diaphragm that has a very low mass, allowing it to respond to every subtle nuance of the sound. In addition, the materials and construction of the diaphragm must balance strength against resilience. A semi-rigid film is often used. If the diaphragm is made strong, it may be too rigid to respond to delicate sounds, and could conceivably tear or crack. If the material is too soft, the diaphragm may vibrate excessively after an abrupt or sharp transient, resulting in a sound that lacks definition.
• The Coil
  The construction of the coil can also impact on the sound. The gauge of the wire, the number of turns (how many times the wire is wrapped onto the coil), even the precision and uniformity of the windings can be a determining factor in the overall tone, response and output level. The additional mass of the coil may diminish the extreme high-end response; however, that same additional mass allows moving-coil dynamic mics to tolerate higher sound pressures levels (SPL). The reference Samson Q8x can withstand a punishing 150dB SPL.
• The Magnet
  While there are certain limits to optimizing the coil, recent advances in rare-earth magnetic compounds have proved beneficial to microphone construction and performance. Neodymium magnets – like those found in the Samson Q8x – provide a much stronger magnetic field and have a much lower mass that other magnet materials. The result is a lighter body as well as a sound with improved definition.
• The Transformer
  Achieving the appropriate output and impedance levels is the job of the transformer. Saturating the transformer with too much input signal will create an overload situation and may cause the signal to clip, creating unwanted distortion artifacts. The Samson Q8x uses a more robust high-saturation transformer than those found in many microphones in order to minimize this type of clipping and to deliver a stronger output signal.

Together, the Diaphragm, the Coil and the Magnet are known as the Microphone Capsule. A few additional wires connect the capsule and Transformer to the microphone output connector. While the capsule is the electronic engine of the microphone, there are plenty of other performance factors under the hood.

What Makes for a Good Live Mic?

Using a microphone in a live situation presents its own set of unique challenges. If there are other singers and instrumentalists sharing the stage, a good mic can minimize any stray sounds from entering your microphone. Choosing the right pickup pattern can also eliminate the threat of feedback from the house mains and the stage monitors. If you are an energetic performer, you need a durable mic with a minimal amount of handling noise; one that is reliable and ready for life on the road. And of course, to sound your very best, you want a microphone that delivers excellent results across the vocal spectrum, allowing you to pop out of the mix with clarity and articulation.

Pickup Patterns

One of the most important factors in selecting a live sound dynamic mic is appreciating the different pickup patterns available – Omnidirectional, Cardioid, Hypercardiod/Supercardioid, etc. The pickup pattern is not a physical component added to the microphone; it is by and large the result of how the capsule is constructed. There is no “ideal” pattern; the choice is often dictated by application.

Omnidirectional

Omnidirectional mics pick up sound equally well in all directions – in front of the mic, behind the mic, off to the sides, etc. Unlike with other patterns, there is no degradation of the sound as the vocalist moves “off-axis” from the front of the mic. In an on-stage situation, however, the welcoming design of the omni-directional mic has some potential areas of concern.

Cardioid

Once referred to as uni-directional, the cardioid (“heart-shaped” – it shares its roots with the words cardio, cardiology, etc.) pattern may be the better choice. The cardioid pattern narrows the pickup zone in front of the mic, and rejects sounds coming from behind the microphone, preventing feedback from the onstage monitoring system and ill-placed mains, plus the cardioid provides better isolation from other vocalists or instruments sharing the stage. The tradeoff is a more pronounced drop in bass response and fidelity when moving away from the center axis of the microphone.

Hypercardiod/Supercardioid 

These designs narrow the cardioid pickup field even further, delivering even higher levels of isolation. The tradeoff is the further diminishing of the microphone’s off-axis response. One other consideration is the proximity effect, which is a phenomena exhibited by the hypercardiod/supercardioid designs. The proximity effect produces a noticeable bump in the bass response of the microphone as the singer draws extremely close to the grille. The touchstone Q8x mic was designed with a super-cardioid pattern. Together, the isolation of the narrow pickup pattern and the benefits of proper mic handling technique allow the onstage vocalist to maximize their sonic impact. Experienced vocalists will match their performance style to complement the super-cardioid design by maintaining a suitable distance from the mic, by singing on axis, and by holding the mic further back on the body. The interference caused by cupping the hand around the ball end of the microphone, or from holding the microphone directly behind the grille, may cause the mic to capture sound using more of an omnidirectional pattern, thereby lowering the isolation and increasing the potential for feedback.

Noise Abatement

Noise is the enemy of audio fidelity. Once noise enters an audio system, it gets amplified and processed with the signal itself and can compromise any performance. Microphones designed to deliver excellent results in a live venue should be able to minimize noise on a proactive level. There are all kinds of noise in the audio world – RF (Radio Frequency interference) noise; Hum (electrical) noise; and … well, just plain old physical noise. Keeping noise at a minimum should be a goal for any live-use microphone.

• Filters
  Filters provide noise protection from the popping Ps and sibilant syllables that can add explosive percussion during a performance. While everyone is familiar with the “Clown-Nose” windscreen filters added to the outside of a microphones, many microphones employ an internal filter that lines the interior surface of the grille.
• Isolation/Shockmount
  The shockmount isolates the microphone capsule from the body itself, and thereby reducing handling noise. Different schemes offer different levels of protection. One consequence of hyper- or super-cardioid pickup pattern is the tendency to create a small “bubble” of sensitivity directly behind the capsule – which could potentially increase handling noise with certain performers. The Samson Q8x uses a unique pneumatic shockmount that provides excellent protection for the capsule in all situations, and keeps handling noise to a minimum.
• Electronic and RF noise
  Using a low-impedance (Lo-Z) microphone live is one of the best steps you can take to hold noise at bay. The low impedance (<600Ω) configuration requires a 3-conductor cable, with separate conductors for the negative audio line and the shield. Unbalanced high impedance (Hi-Z) cables combine these two. The 3-conductor configuration effectively eliminates RF interference and noise originating in other electrical components. Inside, a high-performance live microphone such as the Samson Q8x is equipped with a high-saturation audio transformer which improves the signal-to-noise performance and acts to reject hum.

Built to Last

Life on the road is just as hard on the equipment as it is on the performer. Moments of glory give way to grueling hours of travel, preparation and performance. Your live microphone has to be able to stand and deliver, night after night, without compromise. While it may seem trivial, the construction of the microphone affects durability, reliability and ultimately the value of the microphone. Looking at the Samson Q8x, the body is die-cast using a zinc alloy, providing both strength and protection from corrosion. Components added to enhance performance also affect long-term reliability. The pneumatic shockmount diminishes handling noise, but it also protects the capsule from damage when the mic is dropped or mishandled. The filter lining the grille can prevent excess moisture present as the singer exhales from reaching the delicate capsule components. The Samson Q8x offers a spring steel grille, and structural supports inside the grille help it to keep its shape.

Hearing is Believing

So what does it take to for a microphone to have a great sound in a live performance venue? Certain factors – frequency response, dynamic range, bass roll-off, etc. – seem universal in any discussion of audio performance. Optimizing those factors to create an outstanding vocal mic is the challenge. Again, let’s look at the Samson Q8x. The Q8x can withstand dynamic Sound Pressure Level spikes of up to 150dB SPL, providing ideal performance in the live sound arena. The frequency response of the Samson Q8x is smooth and even across the audio spectrum. The low-end response begins to roll off at about 150Hz, and decreases a full 10dB by about 50Hz to prevent rumble and to reduce bass “boominess.” The rest of the Q8x frequency response remains primarily flat, with just a slight lift in the upper midrange. This lift adds presence to the vocal signal, providing greater clarity and helping the vocals to project over the music. All of these key elements – SPL level, bass roll-off, the midrange lift and even the pickup pattern itself – are the result of careful engineering of the microphone components, the capsule porting and other vital elements by the engineering team at Samson.

Read Part 2 here