Around 2015, the first product announcements for True Wireless Stereo (TWS) earphones surfaced mostly on crowdfunding sites like Kickstarter, including a couple of teams that were well-funded, determined, and had serious engineering talent. Those watching their efforts could see that there were challenges to overcome such as reception stability, high packaging density and complexity, and inadequate battery life along with high costs.
|
|
|
This is a projection of wireless headphone market growth presented by Sony at IFA 2017. TWS models account for less than 8% of the wireless segment. Click the image to see related announcements.
|
Why was implementing TWS in a pair of Bluetooth speakers workable yet problematic with earphones? The bottleneck was forwarding a quality audio stream from ear to ear. This is notoriously difficult using existing 2.4 GHz RF solutions as the signal is mostly absorbed by human body tissue. Bluetooth is in the microwave band and the brain is quite a good microwave absorber so achieving stable performance requires some effort.
The very tight mechanical packaging of TWS challenges the production tolerances and general reach of many of the smaller Chinese factories, although quite a few of the more competent factories have succeeded. For sure, not much space is left for a decent sized receiver (speaker). Typically, the driver in TWS is 6 mm diameter or an expensive armature transducer. While 8 mm diameter receiver is more common in in-ears, 6 mm drivers have to "work harder" to achieve good sensitivity, high output and deep bass and require excellent production techniques or automation. The high-density packaging requires multi-layer circuit boards, together with non-standard MEMs mics in smaller ultra-tight pitch SMT. Overall mechanical design is comparable to an in-the-ear (ITE) hearing aide.
I have always marveled at how much hearing aid dispensers charge ($2000 per ear is not considered expensive) while TWS stereo earphones have to retail for $300 a pair or even half this. Factory OEM pricing from Asia ranges from less than $30 from some funky vendors to $60+ from the more credible choices. High price translates to high consumer expectations.
|
|
|
In September 2016, Apple announced its truly wireless AirPods, with a truly unexpected design. Yet, Apple grabbed more than 80% of the truly wireless earbuds market, selling millions of units.
|
Apple's AirPods certainly have brought TWS earphones mainstream, but with their own proprietary silicon and advanced construction. Samsung's Iconx had a first attempt at TWS earphones with some performance shortcomings, and it took the next gen Iconx 2018 to create acceptable performance. Bragi, now affiliated with Starkey, a long-established hearing aid company, delayed their initial Dash TWS earphone offering and eventually re-engineered its earphones, now available as the Dash Pro and the Headphone. What Bragi, Earin, Nuheara and many others have learned is what the hearing aid industry has long embraced - Near Field Magnetic Induction (NFMI). With legacy TWS, where audio is relayed between earphones using Bluetooth, the transmitting antenna propagates electromagnetic waves which are mostly absorbed by the wearer's brain. Conversely, NFMI enables wireless design by coupling a low power, non-propagating low frequency field that is not absorbed by the wearer's head. For sure the TWS earphone of the future will be a sleeker, smarter and more intuitive user experience.
Assuming that stable reception and longer battery operation will become commonplace, designers will focus on adding features, functions and more natural user interaction. Getting your phone calls is "must-have" for any TWS Hearable product and intelligible voice communications at least as clear as your smartphone is demanded. Older configuration Bluetooth earphones placed the mic in the remote-control dongle, or on the neckband (horseshoe) or on a mini-boom attached to the ear. TWS earphones present more of an acoustical challenge as the mic(s) are at your ear(s) and quite a distance from your mouth. After getting rid of the wires no designer is going to think about sticking back in a boom mic emerging from the listener's ear (well, maybe Apple with the AirPods...)!
The smarter TWS designs employ multiple microphones - often forming an array between the mic in each earpiece along with voice signal enhancement techniques enabling phone calls with good intelligibility even in noisy environments. A number of research groups such as Vocalzoom and SINEF are developing optical mics that can "read" your voice from the vibrations on your cheek yet ignore street noise or a blaring radio or TV. As the call is heard in both ears (as opposed to the old mono Bluetooth headsets) and the earphones block most of the extraneous noise, good performance comparable to or better than a smartphone can be achieved.
Above all, product developers will strive for autonomous operation without requiring the use of a smartphone. As the latest Apple smartwatch has added direct telephony operation even without a link to the user' smartphone, the market for TWS will also pull in this direction, although not anytime soon. On the other hand, on-board streaming of audio from the TWS earphone's memory rather than from your smartphone has already arrived on the Bragi Dash, the Samsung IconX, and other coming TWS earphones. Another exciting capability is stereo recording using the microphones embedded in the TWS. With sound pickup by the TWS mics in each ear, a true binaural recording is achieved with playback qualities with all the directionality and spatial perception of the human hearing system.
|
|
|
Introduced at IFA 2017, Sony's WF-1000X truly wireless earbuds introduced active noise cancelling technology in the TWS category, albeit limited to three hours per charge.
|
Passive earphones typically have a high level of noise isolation due to their mechanical construction, but active noise cancelation improves low frequency isolation while enabling more comfortable eartip design and user-control of outside sound feed-through for situational awareness. Active noise cancelation is another enhancement, with the Sony WF1000 leading the TWS pack, and quite a few others that will be launched at CES 2018.
One last frontier is user interface - and I mentioned that the present solution of tapping on TWS devices in your ear is far from elegant. As TWS earphones pack more and more computing intelligence in their confined space, the most natural user interface of all, voice, will be the path dominant for user-control. Not just for the TWS earphones, or your smartphone, but extend to all the smart home devices. Anyone using TWS earphones soon realizes how awkward it is to fumble around poking your ear, holding buttons for a couple of seconds, multiple taps, etc., to manipulate functions. The voice interface will evolve from simple local Voice Commands, thru smart phone-enabled Voice Queries (such as the Siri interface offered by the Apple AirPods) to embedded Natural Language Processing with a direct interface to the Cloud, to make the human interface of a Hearable as seamless and natural as possible.
On a future report, we will discuss Near Field Magnetic Induction and its impact on enabling stable and extended battery operation for TWS as well as applications beyond TWS earphones. If you missed Part 1 of my article, click here.
