Headphones

With HiFiMan's UK distribution now switching to Signature Systems, we are at last able to get our hands on this idiosyncratic range of headphones from China. What makes them idiosyncratic is not merely their use of planar magnetic (aka isodynamic) drive units – something which is becoming increasingly mainstream – but that these drivers are reminiscent of isodynamic units of the past in respect of their low sensitivity. Recent years have seen not just a resurgence in planar magnetic headphones but, thanks to neodymium-iron-boron magnets and the use of finite element analysis to optimise the magnetic design, a notable improvement in their sensitivity. Indeed, the best examples now offer a comparable sensitivity to many moving-coil competitors.

Lust For Power
But that certainly isn't the case with the £475 Sundara, one of HiFiMan's least expensive 'Reference' models, of which there are 17 in total. Its sensitivity is so low, in fact – despite a 37ohm nominal impedance, which is at the low end for medium-impedance headphones – that it's only right to warn potential buyers that some music sources may not be able to generate sufficient output. Via my (1.4W/32ohm) Teac HA-501 headphone amplifier [HFN Apr '14], not only was the volume control setting much higher than usual, but there was little remaining adjustment once I'd achieved the desired loudness.

It's only fitting, given this, that the Sundara offers little indication of being intended for use with hand-held music sources, even though HiFiMan does picture it with its own MegaMini hi-res music player. At 1.48m in length its cable, which connects separately to each capsule via straight TRS mini-jacks and to the source via a right-angle TRS mini-jack, is a bit too long for convenient use on the hoof. On the other hand it's also too short for easy use with many a home hi-fi installation, although a clip-on gold-plated ¼in jack adapter is supplied to aid connectivity in these circumstances. No carrying case is provided and as for the capsules folding up into the headband or anything fancy like that – forget it.

One reason for the Sundara's low sensitivity is perhaps that – if HiFiMan's exploded diagram tells true – it has bar magnets arrayed only on one side of its NSD (NEO 'supernano' diaphragm). The advantage of this is that it saves weight, so the headset is relatively light for a planar magnetic headphone at 383g, although this isn't sufficient to ensure that the Sundara is notably comfortable to wear. In fact it loses points in longer listening sessions for having round earpads that aren't quite large enough – they squashed my earlobes – and for having a moderate perceived head clamping force. I say perceived because I measured this at 6.5N (across a default 150mm head width), which isn't excessive. But it feels distinctly higher than, say, the 5.2N recorded on the same test frame by the Quad ERA-1 [HFN Aug '18]. That said, the Sundara's wide headband strap spreads its vertical load sufficiently well across the scalp that even sparsely-thatched pates are unlikely to experience any discomfort. It's notable, by the way, that some other HiFiMan models – the Ananda and Arya, for instance – use elongated capsule/earpad profiles to reduce any earlobe squashing.

Open-Back Advantage
Like all open-back headphones, the Sundara offers only limited isolation from external sounds. By the same token, it can produce levels of high frequency sound that someone sitting nearby may find annoying. But there are also positives to an open-backed design other than the potential benefits to sound quality of not having a reflective, resonant enclosure behind the diaphragm. Unlike closed-back designs, open-backs are typically pretty relaxed about earpad sealing, losing much less low frequency output if the earpad is less than perfectly sealed to the sides of the listener's head.

I now supplement our usual frequency response tests, taken ensuring good earpad sealing, with two others in which more normal usage is simulated by using artificial 'hair' and a pair of chunky spectacle frames, both compromising the earpad seal. Compared to a typical closed-back design, the Sundara was substantially unaffected by either. The spectacles didn't cause significant LF loss until about 30Hz, the 'hair' until 50Hz, so the Sundara should deliver similar performance for a wide range of users.