Wireless headphones have changed the way we listen, but not necessarily for the better. Because perhaps more than any other device category, they embody the shift to convenience over quality that's an unfortunate byproduct of some advances in personal listening.
True, the best wireless headphones sound very good indeed – almost as good as the best wired headphones, in fact. But to hear them at their best requires not only high quality sound files, but for both your headphones and digital music source to support a good quality wireless codec.
With so many competing codecs around – some of which are only supported by a tiny proportion of smartphones – this is easier said than done.
Surely there must be an easier way. And as of late 2025, there is, courtesy of the Sennheiser HDB 630.
These cans don’t just sound great, they include an ingenious solution to the codec clash problem plaguing so many wireless listening sessions. They come with a wireless dongle that's bursting with codecs. That way, even iPhone owners can enjoy the delights of the various flavours of aptX via their wireless headphones.
The HDB 630 quickly earned rave reviews, lodged themselves in our various lists of best headphones (including best over-ear headphones, best wireless headphones and best noise-cancelling headphones), and recently won a coveted What Hi-Fi? Award.
Here’s the story behind how they were made.
Research and you will find
The wireless headphone market is fiercely competitive, so making a pair that stands out and genuinely does something new is a very tall order. Rather than just offering the usual glut of minor upgrades and a tweaked design, the Sennheiser team went big on the research. And they discovered some interesting tidbits.
"Our research showed that, on average, audiophiles only listened to music for one, or maybe one-and-a-half hours a day. And we asked ourselves why that was – these people love music, so why aren't they listening to it for longer?" says Wee Hong Kuan, Sennheiser's Senior Product Manager.
They worked out it was due to what's involved in getting top quality sound.
"The best sound relies on being tied to a home system with an amplifier, so we asked ourselves: What can we do about this?" he says. "How can we cut loose this audiophile sound without losing the quality they demand? How can we get them listening not just for 90 minutes a day, but all day, wherever they are?"
Like other headphone makers, Sennheiser is obsessed with sound quality, so it was already hard at work on that front. But it realised this is only one side of the coin. Its research revealed another startling statistic: less than 16 per cent of phones are compatible with aptX Adaptive, and less than 1 per cent work with aptX Lossless. Having the best-sounding headphones in the world isn't much use if the sources feeding them audio aren't up to the task.
Which is where the dongle comes in.
An ingenious solution
The BTD 700 brings support for up to 24-bit/96kHz hi-res quality via the best wireless codecs (including aptX Lossless and Auracast). And it brings them to any Bluetooth headphones – just plug it into your music source and connect it to the headphones over Bluetooth. It went on sale a few months before the HDB 630 launched, but the decision to bundle the two together was a canny one.
To realise just how much of a gamechanger it is, it's worth considering the sheer number of Bluetooth codecs there are available: you’ve got SBC, AAC, aptX, aptX HD, aptX Adaptive, aptX Lossless, LDAC, LHDC, L2HC, LC3, LC3+... It's an alphabet soup dumped on top of a word salad, followed by acronym crumble and initialism custard. Talk about making a meal out of it.
How many people know which codecs their phone or laptop supports? And whether their headphones support the same ones? Chances are, not many.
To make things more complicated, even the same model of certain Android phones will support different codecs depending on where they're sold – some Samsung Galaxy S handsets sold in the UK have Samsung Exynos processors instead of those made by Qualcomm, and so don't support Qualcomm's aptX codecs, for example.
Plug in the dongle, and all of this complexity disappears. Sennheiser estimates that it ups the percentage of phones able to support aptX Adaptive to over 80 per cent (that remaining 20 per cent accounts for all the Lightning port-based iPhones that are still in use, which don't work with the dongle's USB-C connection).
"That's the purpose of the BTD 700 – to erase these worries," says Kuan. "You don't have to worry about which codec your phone supports. You just need to make sure it has a compatible USB-C port." And that your headphones support the best codecs, of course.
This wasn't actually the first time Sennheiser bundled a dongle with a pair of headphones, though its previous offering was aimed more at business folk than audiophiles. The Accentum Special Edition (which are still on sale) come with a USB-A dongle for lower latency video calls on a PC. Though perhaps it could've done with a sound boost – the dongle-less version only scored three stars in our review.
Nevertheless, Sennheiser applied learnings from the Accentum model to the BTD 700.
A dongle isn't the most exciting product to look at – it's a dongle – but a lot of thought went into its design. Sennheiser added a groove near the USB-C connector to allow it to fit a phone that's wearing a case, and it had to be slim enough not to block vents or other ports on any phone, tablet or PC with which it's used.
The downside, of course, is that it's yet another thing to carry, and due to its compact size, it could be easily lost. Some users have taken to carrying it in a coin pouch when not in use, which isn't ideal. (Kuan recommends keeping it plugged into the HDB 630’s USB-C port when not in use.)
And of course, it's still limited by Bluetooth's bitrate, which posed a quandary for Sennheiser. "We had a decision to make," Kuan says. "Did we want high resolution but in a compressed format? Or to maintain a lower resolution, but lossless? That's the trade-off that we had to make. To achieve true hi-res lossless playback, a higher Bluetooth bandwidth will be needed to support that resolution. Which requires industry effort."
Even without the dongle, the HDB 630 fared very well in our review, thanks to their excellent sound quality and customisable features – like the parametric equaliser, which lets you not only input an exact number of Hz for your tuning preference rather than adjusting a slider, but also share your tuning via a QR code for anyone to scan and try out your preferences.
It's a compelling package that just goes to show, when you do your research, the rewards speak for themselves.
MORE:
Read our Sennheiser HDB 630 review
Check out the best wireless headphones
