The new cat's miaow in wireless earbuds is something called an 'open' design, where the driver housing does not require a neck that needs to go into your ear canal to create a seal, but rather sits just above your aural opening (read: earhole) – see Sony's Linkbuds or the sportier Cleer Audio Arc for examples.
The benefit of such a design, as you might have guessed, is that it allows you to maintain greater awareness of your surroundings while enjoying your playlists. And unlike with bone conduction headphones, there's no band going around he back of your head to contend with.
But never has a pair of earbuds given you the choice of either letting ambient sound in, or blocking it out with an actual, transformable physical barrier – until now.
Enter the JBL Tune Flex. Out of the box, they sport an open design, but simply add on the ear-sealing tips (thus deploying something JBL is calling Sound Fit technology) and they become a pair of noise-isolating pair earbuds, essentially giving you two sets of earbuds in one.
Heading out to try and beat your 10k time? It's possibly ill-advised if you're in the UK and enduring the current heatwave, but for everyone else, wear them in the open style and you'll hear traffic, buses, dogs and the like as you hit the road.
Need to focus? Pop on those ear-sealing tips (three sizes are provided to help you achieve an ideal seal) and you should be able to block out extraneous noise.
And it's not just about the passive isolation – you can further tailor the sound using the JBL Headphones app, which includes access to six levels of active noise cancellation (ANC). Apparently, you can even use these profiles when wearing the JBL Tune Flex in the open design – although how that would sound (or actually work) remains to be seen.
Claimed battery life is eight hours (irrespective of whether you're going open or closed) plus an extra 24 hours from the case, although that's with ANC off.
You're also getting an IPX4 splash-resistant rating (so they're good for the gym), Google Assistant support for hands-free controls, and three finishes, plus three 'Ghost' special edition color options.
Opinion: open earbuds are the most exciting development in wireless headphones yet
The idea of open-back and closed-back headphones is nothing new in the world of over-ear headphones – see the Philips Fidelio X3 or Grado GW100 for starters. In the over-ear headphones realm, the benefit of an open-back design is oodles of extra clarity, detail and insight.
How come? Open-back headphones allow air to pass through the ear cups from the rear (read: back) of the speaker driver, so that low-frequency build-up caused by the closed nature of other cans is no longer a problem. All of which is a roundabout way of saying "they usually sound better".
And the downsides of an open-back headphone? Sound leakage – everyone on the train carriage is going to judge you on your taste in music – plus the fact that these over-ears are often harder to drive, and they're otherwise known as high impedance headphones.
But here's the thing: none of that applies to 'open' true wireless earbuds because the headshell (the actual unit that houses the driver) either goes into your ear, or it doesn't. And JBL claims to have taken care of the rest.
While I'd certainly expect to hear a marked difference in audio quality when listening in open or closed mode, depending on how these earbuds have been tuned, JBL is a hugely talented audio specialist so I'd dearly love to be proven wrong… and at this price, I think I won't be alone in wanting to give them a whirl.
The JBL Tune Flex will be available from September for just £90 / €100 (around $110, AU$160) and while I've yet to have the pleasure of trying them out – so we can't say whether they'll make it into our best wireless earbuds buying guide – they're certainly unique.
Remember, not even the best AirPods can offer this feature – in fact, many wearers claim that by design, Apple's non Pro-suffixed 'toothbrush head' in-ears can't provide the necessary passive sound isolation to facilitate great-sounding music.
In my humble opinion, JBL's new Tune Flex are a truly intriguing proposition.