Thrown for a loop - a day with ListenTech

How AV friends! Sorry to have been quiet here over the past weeks; we'll try to get this blog back up to at least weekly updates. There's always more to talk about. HDMI 2.0! 4K! OLED! Curved flatpanels! Today I'll start with one of the ways we can improve peoples' lives and experiences. Today we're talking about assistive listening systems, specifically inductive loops.

Some possible layouts of loop systems, with
coverage patterns

Earlier this week I had the the opportunity to meet with the good folk at ListenTech for a single day training session on the theory, design, and implementation of inductive loop systems. This was a quick but thorough single-day class with a combination of theory and hands-on demonstrations. Students included a mix of integrators, consultants, and even a family of audiologists there to keep current on how AV technology interacts with hearing aids.

For those not in the know, a loop system uses magnetic induction to send audio directly to a coil in either a hearing aid or belt-pack receiver. It's considered a better system for assistive listening than the more common IR and RF systems for a few reasons.

• No need for many users to ask for special equipment. They can see the sign for a loop system, flip on the T-coil on their hearing aid, and get the audio without having to ask.
• None of the directionality issues an RF system has; there are no risks of falling into a "shadow" or turning so one is no longer covered. 
• Hearing aids are often tuned to a specific user's hearing loss. Using the hearing aid will give superior sound quality.

The first factor is, for me, possibly the most important one. Loop systems welcome those with hearing loss into spaces and experiences in ways which other systems do not. This is the dominant technology in much of Europe, but here in the US we've been slower to adopt it. Part of this is cost, part is poor perceptions caused by some very poorly done early hearing loop systems consisting - in some cases - of little more than an audio amplifier and some phone wire. Today, of course, we can do better. 

With the ANSI adoption of the IEC 60118-4:2006 standard (ANSI 117.7) there's now actual regulatory pressure in the US to deploy loop systems which meet standards. In addition to the requirements of the standard, ListenTech's Mike Griffit gave us a list of other "best practices" to create the best possible user experience.

The IEC requirements are as follows:

1. EM Background noise must be 32dB or lower (A weighted)
2. Field strength should be 400mA at 1 meter for a 1kilohertz sine wave. 
3. Field strength should be even throughout the covered area, with variations of no more than +/-3dB.
4. Field strength should be constant over the 100Hz to 5kHz frequency band, with variations of no more than +/- 3dB

In addition, one need to pay attention to coverage area, creating adequate signage, and insuring that the proper mix of audio is sent through the loop system. As is the case with many regulations, local regulation might trump nationally-recognized standards. The state of California, for instance, requires an entire venue to be looped so as not to discriminate against the hearing-impaired by forcing them into one area. As is the case with any regulatory issue, check with your AHJ (authority having jurisdiction). Listen also certifies both consultants and integrators in loop systems, and encourages the writing of these certifications into specifications. This is one way to insure that the people who design and install systems do so to an acceptable standard.

Wire layout for a phased array system. Loops colored
in red and green for clarity.

The most interesting thing with modern loop systems is phased arrays; instead of a single perimeter loop, two loops would be placed with the audio signal ninety-degrees out of phase. This technique allows greater areas to be covered and makes it easier to compensate for signal loss due to metal content in floors or ceilings. The most important thing to remember? Be careful to lay the patterns of loop wire (or flat copper tape) exactly as designed. Otherwise, you might end up with current in one leg running in the wrong direction and creating interference.

This wouldn't be a manufacturer-led training class without at least a moment of self-promotion, but to their credit it was brief. I also have to admit that ListenTech's loop drivers are nice bits of hardware; the "Multi-loop driver" contains both two drivers and a phase-delay in a single 1 RU chassis, greatly simplifying integration. Somewhat disappointingly, there's no Energy Star rating yet, but they are more efficient than earlier-generation models, more attractive, and even have basic monitoring.

The "figure 8" test pattern. In reality, the loops
would me precisely measured to give a calibrated
result.

The day wrapped up with a hands-on demonstration of how to commission a loop system and how to make test measurements using a "figure eight" pattern to measure metal loss. This is actually quite an easy thing to do; a field-strength meter was provided to measure the signal in various frequency bands.

Overall, this is a technology about which all of us in the industry should be educated. In addition to complying with the spirit and letter of the ADA, there is a moral responsibility to give everyone the best possible experience - regardless of their disabilities. Hearing loop systems are one way we can do that - in which we can do good as a part of our jobs. My thanks to ListenTech for the lesson, and I'll keep them in mind in the future.

At the end, they gave a certification to all of us who passed the test.
Hooray!