New noise-cancelling headphones are inevitably compared to the big kahuna in this game, Bose QC25s, and things were going well with the new Space Ones – with sound by Kef and aesthetics by Porsche Design – until I tried to change the battery. The Bose have a AAA, and changing it takes 20 seconds by opening a small door in the right earcup and sliding the old one out and a new one in. The Kefs also have a AAA, but it's in a cute secret panel that Porsche Design probably thinks will sell more units.

The quick-start guide provides a diagram of a finger reaching inside the right earcup, making the outermost trim panel, hinged at the top, pop open obediently. So I dug around in there trying to find the hidden button for the secret panel. There are lots of little lumps and bumps, but nothing made the panel pop. After 10 minutes I emailed the guy at Kef.

His reply told me what I already knew: "It's very hidden." Then he attached a copy of the quick-start diagram I was already looking at. It was reassuring, anyway, to know there was something in there to pop the panel; it was just a matter of finding it among the metal brace points and construction seams.

OK, I cheated. With a fine screwdriver I levered the panel open and located the pin that pushes the clasp out of its lock, releasing it. It was then simply a matter of finding the release button at the other end of the pin. It's deep within the base of the earcup, hidden under acoustically transparent material and, being flush, barely discernible to touch. If you're transporting diamonds, remove the battery and put them in its cavity, the bad guys will never find them.

By now I had developed a view on headphones designed by car guys and I wondered how much of the $700 price was going into sound and how much was about a Porsche moniker. The Space Ones are beautifully presented with a leather headband and earpads, and black detailing around a titanium finish, but they cost $300 more than QC25s, which look fine to me.

The Kefs are significantly heavier, 316g against 196, and the rigid carry-case is bigger, too. Such things matter if you're a frequent flyer. And it's difficult to get even a tiny portable music player in the case with them, but you will fit a spare battery and the airline entertainment adaptor plug. The Kefs have noticeably tighter clamp pressure but they're comfy enough, just not as comfy as the Bose. It's the same with noise-cancellation. They'll get 50 hours out of a AAA; the Bose get 30.

Sound quality? The Kefs romp it in. They're rich, beefy and solid, muscular, full-bodied and nicely defined. The bass is powerful, but doesn't intrude on the mids and highs, which can be entirely delicate. The Bose are more subtle, airier, clearer. They don't lack thump but do better in the mids and highs. Both sound way better than most noise cancellers. If you're into gutsy bass and can manage the bigger carry case, not to mention an extra $300, it's the Kefs. For accuracy and value, the Bose.

Coincidentally, I was trying Sennheisers' HD569s at the same time, the best looking and most comfortable Sennheisers I've used. They're not designed by Porsche and they're not noise cancelling, but they have a better balanced sound than both the others, doing a good job everywhere. And they're $300. Great value.