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Bold Directions: The Future Of Stage Monitoring

Where to next? Looking at new and developing technologies to enhance the craft.

Ongoing Innovation

The technology surrounding in-ear monitor earpieces themselves has also come a long way since its inception, with models such as JH (Jerry Harvey) Audio’s Layla boasting as many as 12 balanced armature drivers. Some brands have a removable ambience attenuator tunnel, allowing for a certain amount of natural sound to enter, and Sensaphonics offers embedded binaural microphones to capture ambient sound with full 3D directionality. The ambience is routed to the compact bodypack mixer, where it’s combined with the monitor mix and delivered to the ears with zero latency. A toggle allows instant switching between Perform Mode (used while playing) and Full Ambient Mode (for communication between songs).

JH Audio Layla earpieces equipped with as many as 12 drivers.

My vote for the most exciting earbud innovation goes to Asius Technologies, the company founded by Stephen Ambrose, who you may remember from my previous article – he created the first homemade in-ear monitors way back in 1965. Ambrose introduced many musicians, such as Guns ‘n’ Roses, to IEMs during the course of his touring life, but when he discovered evidence that his invention could actually be causing harm to people’s hearing, he stopped touring until he found a solution.

When we hear a sound from an external source like a loudspeaker, the acoustic pressure waves enter the outer ear, hit the eardrum, and those vibrations are translated into nerve signals by the middle and inner ear. Because the outer ear – the trumpet-shaped ear canal between the fleshy part of the ear on the side of our heads and the eardrum – is an open system like a long cave, air can move in and out.

However, as we know, IEMs are tiny loudspeakers that sit inside the ear and they seal the entrance to that cave, so there is no natural “in and out” movement. The resulting pneumatic piston effect on the eardrum can cause the eardrum to move with a far greater amplitude than normal, and by way of self-protection, the acoustic reflex action takes place: the tensor tympani muscle contracts and pulls the malleus bone, which touches the eardrum and allows ossicular coupling to occur and transmit vibration down the tiny bones of the middle ear, away from the eardrum.

At the same time, the tiny stapedius muscle in the middle ear contracts to pull the stapes or “stirrup bone” slightly away from the oval window of the cochlea, against which it normally vibrates to transmit pressure waves to be converted into nerve impulses. These protective actions create a compression effect resulting in a 20–40 dB reduction in what we hear, so what happens? We turn up the volume… and so the vicious circle of hearing damage begins.

Ambrose found a way to break the cycle, backed by the National Institute of Health and the National Science Foundation. His invention, called ADEL (Ambrose Diaphonic Ear Lens), introduces a second, artificial eardrum into the equation to act as a pressure release valve. Meaning that the eardrums of the listener are no longer pounded with sound pressure waves from which they have no refuge, and listeners can turn their volume way down as the middle ear is no longer in defense mode and the stapedius and tensor tympani muscles can relax.

Pre-production ADEL earbud models.

By not prematurely tightening in-ear muscles (and so dramatically compressing the volume), loud sounds actually sound louder and require lower overall volume levels. A study by the Vanderbilt University Medical Center shows that using ADEL Drum earbuds allows listeners to enjoy “enhanced loudness perception” (lower volumes sound significantly louder, and better, over conventional devices). This provides them a louder, yet safer, high fidelity listening experience at greatly reduced power levels (1/4th to 1/16th typical levels) with no perceived loss in volume, allowing the eardrum to behave as nature intended rather than being subjected to pneumatic pressure.

The study by the Vanderbilt University Medical Center on ADEL Drum earbuds.

Additional Aspects

But ADEL technology doesn’t simply prevent hearing loss caused by IEMs, it actually has the capacity to allow those people whose hearing is already damaged to hear clearly again. While the drum earbuds described above use a passive form of ADEL, Ambrose and the Asius Technologies team have also created an active form of the invention which, rather than a standard rubber tip or custom mold, has a tiny inflatable balloon on the end of the earpiece which nestles inside the ear canal. The resulting resonance actually allows the bone conductivity of the skull – trans-cranial conduction – to restore hearing function to nerve-dead ears.

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When Ambrose brought this product into existence, AC/DC’s Brian Johnson had recently announced that his touring days were over due to hearing loss. Ambrose reached out to him via a viral YouTube video. The two men got together and Johnson was delighted with the result, saying: “It just totally works. I was really amazed to be able to hear music like I haven’t heard for several years.”

This is a medical breakthrough that has the potential to be life changing for millions of people. Truly a revolutionary advance in the future not just of monitors, but for the listening pleasure of everyone. (An information pack on ADEL is available for free download at

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