Earworn Monitors: All Foldback, No Feedback (Part 2)
Inside the modern earpiece - Core technologies for personal monitors system

By Jerry Harvey

As frequently is the case in LSMAG!, what follows is manufacturer generated text which explains a brand specific solution to a common production challenge.

Personal monitors have been a viable sound source alternative for touring musicians since the mid 1990s. Instead of relying on floor wedges and side fills, engineers can deliver a customized audio mix directly to each band member.

Photo #1: Ultimate Ears Ambient Series

THE MEAT OF THE MATTER During the past few years, significant advancements in design and exponential improvements in audio quality have been made. Multiple companies offer both generic and custom fit earworn monitors, with an assortment of options available to the consumer.

The goal of this article is to present the current monitor technologies on the market, and to discuss their associated benefits and limitations. This article will not highlight or evaluate the transmitter and receiver systems, but will focus only on the delivery system - the earpiece itself.

Remember, the most advanced RF system can be crippled by the use of an inferior personal monitor. The system can only sound as good as the monitor. With this in mind, lets examine the three core technologies for personal monitors.

DIAPHRAGMS

One type of personal monitor relies on a sound driver that originates from the consumer market, a diaphragm speaker, sometimes referred to as an ear bud. Because a diaphragm is a speaker and the tuning of a speaker is relative to the size of the enclosure, this means that no two diaphragm monitors will ever sound identical.

In fact, frequency response will not be the same between the right and left ears, since no two ear canals are the same size or shape. Besides the sound fluctuations, diaphragm systems offer little in the way of precision audio quality. This is caused by two distinct facts:

1.) High frequencies (HF) roll off at 4kHz and;
2.) Overall frequency response is not close to being flat or natural sounding.

Figure #1: One feature of the diaphragm model, that may or may not be considered a benefit, is that it only isolates around –12dB because the speaker allows sound to bleed through it.

SINGLE ARMATURE The more advanced personal monitors are based on a sound driver that was developed and perfected for the hearing aid industry. This driver is called a Balanced Armature. Basically, it is a small rectangular aluminum box with an enclosed magnetically balanced shaft or armature. Because of the way an armature works, it is not reliant on the enclosure size for tuning.

Attached lengths of tubing and acoustic filters tune the armature, resulting in a more consistent sound from earpiece to earpiece. There are subtle sound differences, but not as drastic as a diaphragm driver. This configuration also allows for a noise reduction of ­26dB. This presents the opportunity to run a lower dB level at the ear with enhanced hearing protection.

Figure #2: Single Armature Earpiece Response.

Although the sound quality is notably flatter than that of a diaphragm system, the high frequencies still roll off at 4kHz. (see Figure #2) In addition, the single armature earpiece will over saturate if you try to get it to reproduce a fat bass response with a significant EQ boost. The predictable results are a distorted sound.

DUAL ARMATURE

To address the limitations posed by a single armature monitor, Ultimate Ears created the first commercially available, dual armature - passive crossover personal monitor, the Ultimate Ears UE-5PR.

In this configuration there is a passive crossover with one large armature that reproduces the low frequencies and one smaller armature that reproduces the high frequencies in each earpiece. The dual armature monitor produces a much warmer frequency response which allows for a much more natural sound.

Figure #3: Dual Armature Earpiece Response.

The highs are extended to 10kHz before rolloff occurs. It also provides more headroom than the diaphragm and the single armature models (119dB@1mW versus 108db@1mW for the diaphragms and single armatures). In its fully sealed mode, the UE-5PRO earpiece has -26dB of isolation from stage volume. (see Figure #3)

The above categories represent the three major classifications of personal monitors based on current technology: diaphragm, single armature, and dual armature.

Consider these categories to be the underlying internals of the monitors that define the available sound quality in an earpiece.

Figure #4: With the dual armature based ambient monitors, frequency response stays more linear than a diaphragm except that as the earpiece is made more ambient, there is a natural high pass of low frequencies. (This can be corrected with an outboard EQ if desired).

PUSHING THE ENVELOPE Ultimate Ears has developed some new and innovative earpiece designs that will augment the personal monitor experience. As shown above, the sound quality is directly correlated to the internal driver and to the personal monitor’s ability to seal the ear canal. Both the single and dual armature drivers create ­26dB of noise reduction; however, this isolation has led some artists to feel separated from the stage and the audience.

To address this issue many engineers typically use room mics to deliver the room ambience directly into an artists mix; however, now there is a more natural method to control the ambient level of the monitor. Ultimate Ears has developed a dual armature ambient monitor.

Figure #5: As mentioned, the ambient effect achieved with the diaphragm systems is more accidental, the diaphragm usually comes with different size ports that go into the back of the earpiece. The only problem is by changing the ports, the frequency response varies radically.

Ambient monitors offer the user the ability to control the amount of bleed from the sounds produced by either the PA system or floor wedges, while still delivering a precise mix directly into the ear. Performers now have the ability to walk into sound pockets on stage, while constantly maintaining a mix of the mics or instruments they desire to move along with them. This is accomplished through the use of specialized filters called Ambivents™. The filters allow for a spectrum of sound ranging from a completely open sound, roughly ­5dB of isolation, or -12dB of isolation, to a fully sealed mix of ­26dB of isolation.

THE ELUSIVE 16K

For the most demanding artists and engineers, Ultimate Ears has developed a personal monitor that is the first to deliver a flat frequency response of 31hz to 16k. With standard dual armature earpieces having a HF roll off starting at 10kHz, the Extended™ Series has notably more HF information.

Figure #6a

Cymbals and vocals seem to have more “air” yielding a more natural response. The Extended Series earpiece also, if needed, has the ability to output a totally flat frequency response.

Figure #6b

Further, the Extended Series can manipulate frequency response to meet any particular artist’s requirement, including compensation for hearing loss. Figures #6a, #6b and #6c display precise, customized response curves using Extended Series technology.

Figure #6c

The UE5 Extended series is only available through Ultimate Ears, Inc. This feature is available for dual armature models, and is even available with the dual armature Ambient series (see Photo #1). It is an outboard processor based system, and the processor is distributed as a separate device.

TO CONCLUDE

Please review your needs and compare them to the technologies available. It may well be your application doesn’t require advanced earpiece technology.

Do not buy what you don’t need, but conversely, don’t buy an inferior technology you will quickly outgrow and soon regret.

Approach this purchase as you would any serious technology commitment, be it a mixing desk, personal computer or automobile.

I hope that this article has provided enough technical data for you to be intellectually prepared to compare earpeice options when the time comes for you to purchase your first earworn or next earworn monitor system.

Jerry Harvey has been a touring monitor engineer since 1985 with such acts as Van Halen, KISS, The Cult, Morrissey, and k.d. lang, and is a founding partner of Ultimate Ears, Inc. For more information on any of the above technologies, you can contact Harvey at (800) 589-6531 or email him at ultimate@ultimateears.com. The Ultimate Ears web site is www.ultimateears.com

September/October 2001 Live Sound International