Ongoing Innovation: Advances In The Art & Science Of Microphones
New technology for better capturing the acoustic sounds of voices and instruments...

March 06, 2014, by Gary Parks

earthworks

Particularly over the past couple decades, meeting the needs for greater freedom and flexibility in live performance has meant that microphone companies have expended considerable effort designing and building the hardware to deliver the output wirelessly. Virtually every mic manufacturer has its own brand of wireless, and these units make up a significant portion of their microphone sales.

Add the ongoing changes in the RF landscape and a voracious demand for spectrum from communications and consumer devices, and the pressure for manufacturers to pour resources into the wireless side of mic development becomes relentless. As an example, within the past three years we’ve seen new digital wireless systems – in some cases several models – from most of the established players.

But what about the microphones themselves? What improvements, technological advances, and innovations are being created within the transducers themselves to allow them to better capture the acoustic sounds of voices and instruments – before they’re delivered to the sound reinforcement system?

Critical Parameters
Mic designers work with a number of key parameters, including the range of frequencies the mic can effectively capture, the flatness of that response over those frequencies, the consistency of the coverage pattern over the relevant frequency range, sensitivity to the nuances of the audio sound, maximum SPL before unacceptable distortion is introduced into the signal, the minimum and maximum distances at which the mic can capture a usable signal, and gain—before-feedback in a live sound reinforcement setting.

Additional critical factors include the electrical noise floor the transducer system produces, resistance to breath and wind noises, attenuation of handling noise and other mechanical vibration, filtering and other internal equalization selections, amount of proximity effect when used closely, and a form factor that lends itself to the desired application. How are manufacturers balancing, varying, and improving these and other parameters?

Frequency Response
The goal is to achieve as flat and even of a frequency response across the desired spectrum – nominally 20 Hz to 20 kHz, yet with desirable variations to benefit certain applications. 

Having a vocal mic be sensitive to very low frequencies would do nothing for capturing a voice whose fundamental is more than two octaves above 20 Hz, and would pick up extraneous stage noise and lower frequencies from bass and drums; thus a mechanical, electronic, or combination high-pass filter is useful for vocals.

DPA d:facto II microphone, capsule for wireless, and wireless adapter.

A “presence peak” to emphasize some of the overtone frequencies produced by consonants aids intelligibility, and is commonly designed in. However, the ideal vocal mic might not have the low-end sensitivity to mic an acoustic bass or kick drum, and a flat response without a presence peak would likely sound more natural on an acoustic guitar or wind instrument.

With today’s sophisticated DSP options available for equalizing the mic’s raw signal, smooth adjustments for both tone quality and intelligibility can be made after the fact – as long as the desired frequencies have been captured by the microphone.

Frequency response of the Earthworks SR40V.

The design goals for several recently introduced vocal mics have included a very flat frequency response across the vocal fundamentals and overtones to yield a neutral, “transparent” sound quality. The Earthworks SR40V and the DPA d:facto II vocal mics emphasize linearity in their frequency response, and both companies’ background in creating measurement mics for acoustic engineering and system optimization applications contribute to this trait. 

Earthworks mics capture frequencies up to 40 kHz, according to Daniel Blackmer, because “the ear is highly sensitive to phase and time differences to localize a sound source and perceive it as ‘live’.”

Neumann KMS 105 and its onboard PCB.

On the other hand, DPA doesn’t emphasize these highest frequencies, yet within the full vocal range its frequency response stays within +/-2 dB.

The supercardioid Neumann KMS 105 and Shure KSM9 are also vocal condensers that exhibit a relatively flat, natural frequency response. Neumann varied the KMS 104-plus cardioid vocal mic specifically for female vocal in the pop and rock genres, with “a more extended bass frequency response.”

Polar Pattern Control
Continuing with the KSM9, Shure recently released a version called the KSM9HS, featuring switchable hypercardioid and the rarely used subcardioid patterns.

Both KSM9 variations use a dual-diaphragm design, which in general provides greater polar pattern control at lower frequencies than a single-diaphragm design. This technology attenuates these lower frequencies at the rear so the mic is less likely to pick up audio from behind and can be less prone to feedback.

From my tests with this mic a few months ago, the subcardioid pattern resembles an omni that is attenuated at the rear, with a wide frontal pickup having similar level and frequency response, yet being resistant to feedback. The audio quality of both patterns is almost the same, with the hypercardioid setting exhibiting moderate proximity effect when used closely.

Electro-Voice has moved its proven Variable-D technology, which minimizes proximity effect when using a directional mic at close distances, into the RE320 dynamic vocal and instrument microphone. It’s especially useful when close-miking instruments with lower fundamentals such as acoustic bass or larger brass instruments, or to preserve the tonal quality and apparent level of a singer or speaker when they’re continually moving closer and farther from the mic. (The RE320 is the latest generation of the RE20 and RE27 designs.)

Shure KSM9HS offers a selection of polar patterns.

Miniature capsules and directional control aren’t an obvious pairing, yet both Countryman and DPA have made significant advances. With the new H6 headset, Countryman offers omni, cardioid, and hypercardioid patterns, enhanced with a set of acoustic “caps” that enclose the mic element.

The directional elements themselves use a “micro-drilling technique normally used to create cooling holes in jet turbine blades,” with precisely tailored arrays of holes that are smaller than a hair – with each capsule tested and adjusted for maximum null depth and consistent frequency response. The caps allow the user to select a polar pattern that is best for a given application, and go to another one at a different time. Other caps vary the high-frequency response from flat to enhanced.

In the 4099 series of instrument mics, DPA maintains directionality with the use of acoustic interference tubes integrated into the assembly. A precise balance of tube length, materials, and porting allow directional sound to enter the mic without interference, while off-axis pressure waves are acoustically canceled within the tube with minimal coloration.

This effective technology has been enhanced over the past decade, and is also used in the 4080 cardioid and 4081 supercardioid miniature instrument mics and the 5100 surround sound mic. The result is a smooth and accurate directional capture of the audio source.

Miniaturization
Tiny mics with transparent full-range performance extend the ability to unobtrusively place a mic on an instrument, vocalist, or actor/presenter in a live setting, and achieve sound quality akin to using studio-type models.

Audio-Technica BP894 with capsule within a rotating housing on the boom.

Audio-Technica has recently released the BP894 headset, with a miniature cardioid element. The capsule is contained within a small rotating housing at the end of the mic boom, allowing the active side to be precisely positioned toward the corner of the mouth. Different than most headsets where the capsule comes right off the side of the boom, A-T placed it at a right angle to the boom so that it has a T-shaped profile.

Countryman has pioneered miniaturization in headset applications. The H6 is offered at three sensitivity levels, to accommodate applications ranging from normal speaking to high-level operatic vocals. DPA also focuses on these applications, producing mics that are widely used on acoustic instruments, pianos, and more.

Proprietary pre-polarized backplate technology yields a combination of high sensitivity and extreme SPL handling. Both companies provide a wide variety of adapters for different applications and instruments, ranging from violin to woodwinds to acoustic guitars.

Countryman H6 with rugged cables and acoustic “caps” for the mic element.

Miniaturization means thin cables and tiny connectors, which must be extremely durable, as well as water-resistant and immune from RF and EMI interference. According to Chris Countryman, the H6 uses para-aramid fibers (in the Kevlar family) to “more than double the pull strength” of the mic’s cables, along with specialized polymers for the inner insulator and outer jacket to maximize puncture resistance while minimizing induced mechanical noise.

He adds that water resistance is a big focus, with combined custom connectors based on aerospace designs with housings made with medical-industry plastics and hydrophobic coatings helping to achieve an IP67 water and dust protection rating.

EQ, Filters, Switches
As much as designers strive to create a certain frequency response curve with their mics, sound engineers sometimes need to modify that response for particular applications. Some manufacturers offer internal circuitry for that purpose.

One of AKG’s latest achievements is Versatile Response analog filter circuitry. It can be found in the D12 VR large-diaphragm dynamic cardioid mic for vocal, bass drum, and bass amp applications. 

The newly designed capsule has an extremely thin diaphragm that is especially sensitive to lower frequencies, mated with the VR circuitry and the original transformer used with the classic 1970s-era C414 studio mics. When the mic is phantom powered, one of three switchable active filter preset can be selected to customize the frequency response; these settings are for open and closed kick drum, and “vintage sound.” The mic can also be used without phantom power and delivers the unfiltered response of the capsule.

The new Telefunken Elektroakustik M82 large-diaphragm microphone also incorporates analog filter circuitry, with two switches that act independently to yield four frequency-response settings. These passive circuits are “Kick EQ” and “High Boost,” with the former reducing midrange frequencies centered around 350 Hz and the latter tilting up the mid and high frequencies with a knee at about 2 kHz. With both filters off, the mic can be applied to vocals, guitar amps, and brass instruments.

AKG D12 VR with Versatile Response analog filter circuitry.

The Avlex Superlux PRO-38MKII condenser vocal mic has an internal 12 dB/octave high-pass filter centered at 100 Hz to minimize pickup of stage noise. Its 1-inch gold-plated thin-film diaphragm is very responsive, as well as fostering a well-behaved cardioid polar pattern and a flat, uncolored frequency response.

Diaphragms
Mic diaphragms vary in size, thickness, tension, and material – each of which affects the sensitivity, frequency response, and a variety of other characteristics. Audix uses proprietary VLM (Very Low Mass) technology within its OM Series handhelds, based on “a very lightweight diaphragm that allows for extremely fast, accurate processing of incoming signals” that yields extended frequency response with high SPL handling.

The AKG D7 vocal mic employs a specially developed Laminate Varimotion diaphragm – which varies in thickness from center to edge – allowing response tuning within the mic assembly without the use of acoustic resonators. This technology is also used in the D5 vocal and D40 instrument mics.

Audio-Technica AT4081 ribbon with higher output from a neodymium magnet motor.

Ribbons
Traditionally, ribbon technology has been more delicate, and it’s use in live sound was pioneered by beyerdynamic. The company’s recently introduced TG V90r handheld vocal mic uses an ultra-light and thin aluminum ribbon for excellent responsiveness to transients, housed in a well shock-mounted body. The frequency response covers the vocal range, with specifications of 50 Hz to 14 kHz, with high SPL handling and an output sensitivity of -61 dBV.

Audio-Technica holds several patents in this technology, including the Microlinear ribbon imprint that protects dual ribbons from lateral flexing and distortion.  The AT4081 provides a higher output level with the use of a neodymium magnet motor structure, and it has the audio quality to be used for recording and the durability for live use.

Ribbon technology is also used in the Royer R-122 Live and Cascade Fat Head II for guitar cabinet miking and similar applications, while the AEA N-22 can be used for applications ranging from vocals to acoustic instruments to cabinets.

Shure KSM313/NE and KSM353 ribbon mics include proprietary Roswellite “molecularly-bonded film” ribbon material, which provides the tensile strength and durability to withstand high SPL applications. These mics are precisely manufactured, with each ribbon frame being optically measured and its ribbon then custom-cut with a laser to fit it exactly – to a tolerance of .001 of an inch.

These manufacturing processes are normal for Shure, notes John Born, product manager for wired microphones. An emphasis on documentation and process control in engineering and manufacturing, consistency, and optimization is central to a philosophy that states “performance shall not change” over the years and manufacturing runs for a particular microphone model – even as internal changes might be made to improve consistency or find substitutes for obsolete components. 

Adaptation
With the introduction of the Digital 9000 wireless system, Sennheiser also made changes to its mic capsule suspension. According to the company’s Brian Walker, the new suspension system “greatly reduces mic handling noise while maintaining excellent audio quality.”

Sennheiser’s new mic capsule suspension.

The bands hold the capsule from six posts, offering significant mechanical isolation from the rest of the mic assembly. Sennheiser has also standardized all of its wireless mic capsules to be used interchangeably across the evolution, 2000, and 9000 Series systems, so that an investment in a particular capsule may be separate from the wireless delivery method.

Across a variety of handheld mic brands and models, interchangeable mics heads thread onto the wireless using a 3-conductor, concentric-ring connector that mate with spring-loaded pins within the transmitter body. This innovation allows a preferred mic head to move across a variety of transmitters, rather than the former method of hard-wiring the head into the transmitter.

These are just some of the examples of the ongoing innovations in mic technology. What’s currently available provides many excellent choices, yet I strongly suspect the search for ever more transparent, unobtrusive, durable, and overall great-sounding microphones will continue.

Gary Parks is a pro audio writer who has worked in the industry for more than 25 years, including serving as marketing manager and wireless product manager for Clear-Com, handling RF planning software sales with EDX Wireless, and managing loudspeaker and wireless product management at Electro-Voice.



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Ongoing Innovation: Advances In The Art & Science Of Microphones
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