I tested the two new models, the mid-range MA600i and range-topping MA750i.
Both models come with at least eight pairs of interchangeable ear buds to ensure a perfect fit. Picking the best from the almost bewildering array of choices - from small to large, and simple to double-flanged - isn't straightforward but it's time well spent, as choosing a good fit makes a huge difference to the quality of sound.
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The models are also similar in their overall design, using RHA's aerophonic (inverted trumpet) shape which it claims channels sound more naturally into the ear. It works: both models create a wide sound stage that seems to extend well beyond the listener's head, while retaining a level of clarity that surpasses most of their rivals.
The key difference between the two models is in their materials and finish. The 600s are machined from aluminium while the 750s are made from high-grade stainless steel. And where the 600s use a production line speaker, the 750s feature a handmade unit.
The MA600i headphones are the more conventional of the two models, though they still have their quirks, most notably their braided fabric cable. RHA has learned from previous models, now sheathing the fabric cable in clear plastic to avoid the scratching sound that often resulted from the fabric cables rubbing against clothes.
On a practical level this works brilliantly, making the 600s among the quietest headphones I've tested on the move, but aesthetically it troubles me. I'm being picky, but the wrapped-in-plastic look takes me back to memories of 1970s furniture protectors.
The MA750i headphones opt for a more industrial aesthetic, replacing fabric cables with functional grey rubber terminating in a knurled jack plug with a chunky strain relief spring.
Of the two models tested, the 750s are the weightier, mostly due to their heavy-duty cable. In use, that extra weight is almost imperceptible, thanks to the looping, round-the-ear design of the cable.
Both models were reviewed in their Made for iPhone guise, with a three-button remote and microphone built into the cable. The remote controls everything from track selection to Siri on compatible Apple devices, while the microphone does a decent - if not stellar - job of allowing hands-free voice calls. In both cases a non-iPhone version is available which loses the remote and shaves £10 off the price-tag.
The MA750i aren't a fashion accessory but sound great while coping with abuse. If they were a car they'd be a Land Rover Defender.