Tuning in to ReSound’s LiNX Quattro (Part 1)

This is the third hearing aid review Tested Technology has undertaken in the past couple of years. Readers may be wondering why we’re paying so much attention to this niche market. Fair enough. Let’s deal with that question.

1. It’s not the niche business you might think. In 2017 the global market for hearing devices was estimated to be worth a little under $6.5 billion and is expected to reach over $9 billion in the next five years. Demand is increasing, but more importantly, the need is increasing even faster. This need will turn to demand at an accelerating rate as the price of the technology falls.
2. Falling prices will be driven by three main factors: the inevitable declining cost of technological components; the widening market for medical hearing devices; and—as we discussed in our initial review of the Teneo M+ hearing aids—the merging of the medical hearing aid market with the now rapidly evolving “hearable” consumer market.
3. Technological advances from the hearing aid manufacturers (like NFMI and balanced armature microphones and speakers) have already crossed over into consumer devices. These technologies and others currently in development in the medical field are arriving inside products anybody, hearing-impaired or not, can benefit from. By tracking these hearing aid developments Tested Technology hopes to give readers an informed glimpse of the future.

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I RAN INTO RESOUND AT THE VAST IFA technology Expo in Berlin last year. ReSound is a worldwide Danish manufacturer of medical hearing equipment under the ownership of GN Store Nord, a venerable firm founded in 1869 as “Det Store Nordiske Telegrafselskab A/S”, which translates as “The Great Northern Telegraph Company”.

As a communication technology, the telegraph, alongside (often literally) the railway infrastructure, dominated the second half of the 19th century. GN’s global reach grew rapidly. By the 1920s it had established a name for itself as one of only a handful of world-class telecommunication companies.

When the Second World War physically and metaphorically destroyed GN’s telegraph business, the company began to diversify into other related fields. By the end of the 20th century, GN was left focussing on just two core businesses: hearing aids and headsets, produced by GN Hearing and GN Audio.

The ReSound LiNX Quattro*

With the launch in November 2018 and the showing at the Consumer Electronics Show in January of this year, ReSound introduced the new LiNX Quattro. The improved chipset is built around  a much faster processor able to handle a wider range of high-frequency sounds.

This extended frequency—now up to 9.5 kHz—not only gives a fuller and more balanced rendering of music but, more importantly, provides more of the high-frequency cues that are valuable for better speech recognition.

On paper, 9.5kHz may not look impressive as the frequency ceiling. Hearing aid microphones and electronics have been able to cope with high frequencies for several years. The Sivanto Teneo M+, for example, could be controlled by inaudible ultrasound frequencies sent from a smartphone.

The limitation seems mainly to have been in the output transducer (still archaically referred to as “the receiver”).

Textbooks quote 20Hz to 20kHz as the range of human hearing. Each doubling of frequency represents an octave, so at 9.5kHz the Quattros are still missing just over one full top octave.

However, those textbook metrics are largely theoretical. The human ear is most sensitive in the 2kHz to 5kHz range. From the age of 8 years onwards we experience loss of those upper frequencies and very few adults reach middle age with the ability clearly to hear sounds above 15kHz. Male hearing tends to deteriorate faster than female hearing.

Traditionally, audiologists have focused entirely on the 120Hz to 8kHz range, crucial to speech recognition. Digital hearing aids have typically been designed accordingly, not only shortchanging musicians and music lovers, but also—as mentioned—depriving the general user of possibly useful high-frequency speech cues.

To be fair, there has been sensible science behind this limitation. There is no point amplifying frequencies that the impaired cochlea may be unable to deal with at any volume. And in any case, high frequency speech cues, most useful in noisy environments, can easily be drowned out by amplified noise in that same frequency range.

But ReSound is now able to venture usefully into these higher frequencies with the LiNX Quattro, thanks to two technological developments that have been transforming the hearing aid industry in general since the beginning of this century: frequency transposition and greatly improved speech in noise separation thanks to much better sound location.

ReSound calls this transposition “Sound Shaper”. It’s a similar strategy to the frequency compression used in the Teneo M+ . ReSound explains:

High-frequency sounds that are not audible due to high-frequency losses or cochlear dead regions are moved down in the frequency spectrum. A proportional relationship between input and output frequencies is maintained to minimise distortion.

This improves the audibility of speech cues that would otherwise have been lost, while maintaining the best sound quality possible.

More Juice, Longer Use

One immediately impressive feature of the LiNX Quattro is rechargeability. Instead of having to open the battery cases to switch them off at night, and periodically to remove the disposable batteries and replace them with new ones, you simply ensure that the built-in batteries are refreshed before they run down.

What makes this so important?

Since the turn of the century, most modern hearing aids have used near field magnetic induction (NFMI)* to intercommunicate through the skull. NFMI is a development of the ubiquitous older technology, the Telecoil or T-loop, that connects hearing aids directly to the audio output of venues like theatres, ticket offices and transport vehicles.

NFMI and Telecoil both allow for highly energy efficient short-range communication. But more recently, with the ubiquity of smartphones, hearing aid manufacturers have vied with one another to include Bluetooth for more general connectivity.

Classic Bluetooth is a notorious power drain, something that becomes immediately apparent to users of small Bluetooth devices like hearing aids, even though these will typically be using a (sometimes proprietary) version of so-called Bluetooth Low Energy (BLE).

The Evotion Oticon uses Bluetooth to communicate with the Evotion-provided Samsung A3 smartphone so that usage data can be conveyed back to the Big Data pool the project is collecting. These hearing aids run on disposable zinc-air 312 batteries for an absolute maximum of five days. My previous hearing aids, the Teneo M+ (admittedly using the slightly larger size 13 battery) would run happily for up to 11 days between changes. These did not use Bluetooth.

Zinc-air is a remarkable technology and weight-for-weight has a much higher energy density than the Li-ion chemistry that fuels rechargeables.*

So today’s tiny rechargeable batteries powering hearing aids can’t be expected to match the longer runtimes of traditional disposables. Add to this the requirement to power Bluetooth streaming and rechargeable hearing aids seem condemned to impracticably short use between charges.

ReSound’s LiNX Quatto ingeniously works around this problem with three key design decisions.

1. Don’t pursue the trend to ever smaller devices. Build the hearing aids around sensibly sized rechargeables (approximately size 13 equivalents) that can hold a whole day’s charge.
2. Provide a “seamless” charging solution that is as simple as returning the hearing aids to their case.
3. Build the case itself around a much larger rechargeable battery, making it fully portable and independent of the mains supply.

(There’s a fourth consideration around how the manufacturer chooses to implement Bluetooth. We’ll come to that later.)

The batteries in these small devices recharge automatically and wirelessly every time you return them to the case. The case itself contains its own rechargeable battery, which in turn can be recharged through a standard microUSB connector. The hearing aids can run for more than a full day on a single charge and the case holds several days worth of recharging power.

An update from ReSound says:

We have also recently changed the battery in the hearing aid charger. Initial tests show the charger can recharge two hearing aids four times before it runs out. The new battery takes 3.5 hours to charge from completely empty.

Made for Android?

At its first announcement (as reported here by hearing aid blogger Geoff Cooling) the LiNX Quatto was described as “the first ever to be Made for Android”. The idea was that Android users would at last be able to join the iPhone crowd, who for a couple of years now have been able to stream audio directly from their phones to the hearing aids of several different manufacturers with no intermediate device.

The “Made for Android” label came with some qualifications. ReSound is “in partnership with Google” about this, from which we can gather that direct streaming of this kind requires a special variant of the normal Bluetooth protocol that isn’t yet rolled out into Android devices.

This “Made for Android” variant of Bluetooth is based on the existing Bluetooth Low Energy protocol. As its name implies, BLE’s primary objective is to limit power use, which—as Tested Technology has often discussed—is Classic Bluetooth’s Achilles’ heel. To this end, BLE reduces its range to something more appropriate to a body area network (BAN) and removes some of the functions associated with Classic Bluetooth.

One key function missing from BLE is audio streaming. This is why hearing aids like the Oticon Evotion can be controlled from a smartphone app via Bluetooth, but can’t directly receive music or speech. It’s what makes intermediate devices like the easyTek neck loop and ReSound’s Phone Clip+* necessary.

Apple’s own “Made for iPhone” (MFi) Bluetooth variant that enables streaming to hearing aids is a twist on BLE that adds a limited version of audio streaming without excessively increasing the power requirement. Sadly (but typically) this is a development that Apple has kept to itself, depriving the overwhelming global majority of smartphone owners* with hearing aids from being able to make phone calls and listen to music through a direct connection to their phones.

Belatedly, Android is now playing catch-up. The Bluetooth Special Interest Group (SIG) has nursed Bluetooth through its multiple iterations for the past twenty years. In conjunction with GN and other interested manufacturers (including Apple), the Bluetooth SIG is now working to develop a new standard called “Audio Streaming for Hearing Aids” (ASHA).

Not all Android phones will have the hardware capability to support ASHA. Those phones that do will need a firmware update, and a corresponding update to the LiNX Quattro hearing aids will also be required.

The initial date for direct streaming to Android was thought to be mid-2019. At the time of writing, we’re still waiting to hear from ReSound about this and the official information is that there’s no official information when this might be.

You can get the full (very technical) heads-up on Audio Streaming for Hearing Aids from Android’s own Web page.

In the next part of this review, we’ll be looking at the various intermediate streaming devices that connect LiNX Quattro users wirelessly to their TVs and phones and also provide the very best way of hearing speech in noisy surroundings.

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Chris Bidmead