Little Mics Can Be Huge For Live
Design specifics and applications of headset, lavalier and miniature microphones...

May 07, 2014, by Gary Parks

microphones

It’s great to have microphones available that are small enough to hide on the bridge of a violin, on the bell of a sax, or near the mouth of a singer – and yet produce excellent sound quality with sufficient gain before feedback that they can be used for professional sound reinforcement.

Headset, lavalier, instrument and other miniature mics have become both smaller and better over the years, to the point where some sound engineers choose them over larger format models for certain applications.

Headsets and lavaliers are available in both omnidirectional and specific directional formats. Omnis are more forgiving in terms of placement and in how the user moves in relation to the mic, and they also exhibit reduced cable noise – but they’re typically more susceptible to feedback.

If the orientation of the source to the mic can be controlled, such as clipping a small mic onto an instrument and properly aiming it, a directional pattern can enhance isolation and increase gain.

Audio engineer Greg Cameron, who recently did the sound design for the Sierra Stages (Nevada City, CA) production of the musical “Company,” told me that he’s had some less-than-stellar experiences with cardioid-pattern headsets for theater.

Greg Cameron, sound designer for Sierra Stages.

“They’ve been overly sensitive when actors turn their heads from one direction to another,” he notes. “Though they can offer better gain before feedback, they’re not much good if an audience can’t hear dialog consistently during head movement.”

To create consistent directionality in a miniature template, precise design and manufacturing techniques are required. For example, the DPA 4099 Series of instrument mics integrates acoustic interference tubes into the assembly, balancing the tube length and porting to allow directional sound into the mic without interference, and acoustically canceling off-axis pressure waves as they enter the tube.

Countryman uses a micro-drilling technique to create arrays of holes as part of the porting, and during the process tests each capsule for maximum null depth and consistent frequency response.

The Audio-Technica BP894 headset has a rotating housing on the boom so that the mic can be pointed with precision.

For further controlling directionality, the company offers two “caps” that can be placed on the directional model of the H6 headset – one for a cardioid and the other for a hypercardioid polar pattern. The help enhance the response of higher frequencies to make up for off-axis placement, both companies also provide caps that press onto their omni mic capsules, with DPA providing either a +3 dB “soft boost” or +10 dB “high boost.” 

The Shure Beta 53 omni condenser headset also can be outfitted with caps for “mild” and “high” HF enhancement, while the miniature cardioid element of the Audio-Technica BP894 headset has a rotating housing at the end of the mic boom so that the coverage can be pointed precisely toward the corner of the vocalist’s mouth.

How Sensitive
To generate enough signal level from a miniscule diaphragm, these mics are invariably back-electret condenser types rather than dynamics. We can still find larger dynamic capsules on a handful of legacy headsets, such as the A-T PRO 8HEx; in contrast, the company’s recent BP-892c MicroSet headset incorporates a tiny 2.8 mm condenser with a sensitivity of -49 dB. 

To accommodate different input source levels, ranging from subtle speaker to shouting, the Countryman H6 offers three sensitivity levels for its capsule: -43, -53, and -63 dB. The maximum SPL before distortion increases by 10 dB with each capsule.

DPA also offers headsets with varied sensitivities, with the 4066 at -44.5 dB and the 4067 at -60 dB. And Avlex Mipro has optional Red Dot adapters for its headsets, which provide a -15 dB pad for use with a variety of wireless beltpacks.

Design Factors
Many of these mic elements are so tiny that a handful of them can be hidden under a quarter. Given their diminutive size, I was curious about how they work so well, and so I asked Chris Countryman about it.

Recognize this guy? It’s Microsoft co-founder Bill Gates giving a talk, outfitted with a DPA d:fine headset.

He began by noting that a well-designed mic produces a very flat, wideband frequency response – the process starting with making a diaphragm’s membrane “like a drum head,” and having a primary resonance “based on its stiffness and the damping provided by porting and the internal volume of air.”

Careful port design and internal layout are critical in controlling additional resonances so that response remains flat over the full frequency range, while tiny holes in the diaphragm or back plate provide pressure equalization and also control low-frequency roll-off.

Chris Countryman adds that lowering the mass of the diaphragm reduces membrane inertia and directly improves transient response and settling time. “Moving to a miniature size means that many of the tightest tolerance structures can be fabricated in one piece using precision etching techniques,” he states, also pointing out that high-quality electronic components with tight tolerances play a significant part as well.

Single Or Dual Ear
Headsets need to stay firmly in place while the performer moves, sometimes with great enthusiasm, with the mic element pointed optimally at the mouth. Both single- and dual-ear headsets offer a variety of mechanical solutions to permit stability along with the adjustability to fit all sizes of heads and position the mic where it’s needed. 

High- and mid-boost EQ caps for the Shure Beta 53 headset.

Dual-ear headsets wrap around the back of the head/neck and hang over both ears, creating a platform for the mic boom. Earlier attempts at this were often uncomfortable, but more recent advances in both materials and design have made many of them fit well while being visually undetectable.

Point Source Audio Series 8 headsets, available in both omni and directional versions, have a lightweight frame with earpieces that rotate at 90-degree intervals and lock in place so that the boom can be placed on either side of the face, and they can also be stored flat in a case. The Countryman H6 adjusts for head size with earpieces that smoothly telescope into the sleek frame.

DPA d:fine headsets come in both dual- and single-ear formats, and additionally have a short-boom option for greater concealment. Avlex Mipro offers the low-profile HSP-09 single-ear headset, which weighs less than half an ounce and has a detachable cable, along with the HS-48 that provides a unique full-circle attachment for the ear.

I’ve found that a very comfortable and stable single-ear design features a bit thicker “C” of soft-molded plastic covering a malleable metal core that can be fitted precisely around the ear. Models in this format include the Mogan Elite Earset, Que Audio DA-12, and Galaxy Audio ES3. 

Reliable miniature models are a blessing for applications where it’s essential that the mics are virtually invisible, such as theatrical performances. They’re attached at the hairline or in a similar stable location on the talent, and are typically wired to a wireless transmitter.

The Sennheiser MKE 2 lavalier has long been a standard for concealed sound reinforcement, combining tiny size with moisture resistance and a wide frequency response. An omni element delivers a response within a +/-3 dB tolerance, and two “sound inlet caps” are available for tailoring high-frequency response.

By the way, the MM-MSLM MatchStick lapel mic from MMAudio is the aforementioned Cameron’s miniature mic choice for performers in Sierra Stages productions.

The venerable Sennheiser MKE 2 lavalier.

Off-Axis Response
When miniature mics are placed on instruments, it’s usually possible to position the mic on-axis to the sound source. But when using them for vocals, positioning is more difficult and can lead to excessive breath noise and plosives distorting the audio.

The typical ideal position for a headset mic is for the element to be just slightly behind the corner of the mouth, yet even with this placement, what is being received (especially if a directional headset is being used) has a different balance of frequencies compared with singing directly into a handheld. 

This tendency becomes more apparent when the mic must be placed on the head at a distance from the mouth, and can be extreme when using a lavalier mic at a neck or chest position. Omnis can be more forgiving here than directional models, while attaching the “high boost” caps can help overcome the natural attenuation of high frequencies off-axis.

Countryman even offers instructions for attaching a B6 lavalier to eyglasses with an O-ring.

Equalization is also often required. Cameron describes his basic headset EQ settings on the current production: “Once the baseline was established for the most easily over-excited frequencies, they were notched out on a 4-band parametric EQ on the main mix bus. I really only had to notch 8 dB at a couple of frequencies, with quarter-octave Q at about 350 and 800 Hz.

“During rehearsals,” he continues, “I noticed an overall lack of top-end sibilance on all of the mics, so I added a mild high-frequency shelf from 5 kHz on up, probably about 6 dB-per-octave of so. This gave a little more ‘air’ and definition to the actors and helped them cut through better.”

On the individual channels, Cameron found that several of the male voices had a bit too much down in the 200 to 300 Hz range, so he put in some soft cuts in that range to lightly boost intelligibility. Female voices tended to be more “boxy” up a little higher, around 300 to 450 Hz, so he applied some small cuts in that range.

Durable Links
Tiny mics have thin cables, so it’s essential to make them as rugged as possible to resist the bends, pulls, and other abuses of live performance.

Connectors must be water-resistant and long-term reliable. Kevlar and related high-strength fibers that used to be more closely related to bullet-proof vests, along with specialized alloys that combine flexibility with fatigue resistance, have become standard materials.

With the MKE 2, Sennheiser uses stranded stainless-steel reinforced cables to increase pull strength. For rigorous touring applications, DPA has just released enhanced cables for its d:screet mic line that include a stainless steel housing, additional strain relief, and a thicker 2.2-mm diameter.

The Countryman H6 uses Para-aramid fibers (from the Kevlar family) to more than double the pull strength of the cable, along with specialized polymers for the inner insulator and outer jacket to maximize puncture resistance while minimizing induced mechanical noise. Specialized plastics and hydrophobic coatings add protection from water and dust entering the cables, connectors, and mic elements.

Point Source Audio “x-tails” adapters for wireless transmitters. The top adapter is for Shure, Line 6 and other transmitters, while the bottom adapter is for Audio-Technica transmitters.

Making It Wireless
Given that headsets and lavs are designed to provide unobtrusive freedom of movement to performers, it follows that they’re usually connected to wireless transmitters. When used so close to radio-emitting sources, RF and EMI immunity of both the mic element and the cable is required. Also, with the variety of connectors used by different wireless manufacturers, offering mating connectors is a necessity.

Audio-Technica supplies versions of the BP-894 headset terminated with 3.5 mm, Lemo, Hirose, and TA-4F connectors. The H6 has detachable cables to fit virtually all wireless transmitters or wired connections, and DPA, Avlex Mipro, and others have adapters for the same purpose. Point Source Audio provides what it calls “x-tails” (X-Connectors) – short adapters featuring a variety of connectors that thread to a mini-connector at the end of the headset’s cable. 

When it comes to being discreet, light in weight, mobile, and close to the source, headsets, lavs and other miniature mics bring significant advantages. They’re available from a variety of quality manufacturers and at many price points, with some companies making a major commitment to the format and pushing the technology to new levels of performance. 

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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