Nearly every pair of headphones, every set of headphones ever made, works on the same basic principle. They are dynamic microphones working in reverse, miniature loudspeakers with diaphragms that vibrate in tune with the music, set in motion by an attached coil of wire moving within a ring magnet. Not so these OPPO PM-1 headphones, which create acoustic vibrations in air – the very sound of music – by the planar magnetic principle. See also: The best headphones of 2014 Planar magnetic headphones and loudspeakers are hardly new, with respected designs catching the ears of audio enthusiasts since the 1970s. But they are more difficult and expensive to manufacturer, and have traditionally been insensitive to input power, which means you need more powerful amplifiers to achieve the same volume. And in the case of planar magnetic headphones, they can be uncomfortably heavy from the added weight of magnets and supporting frames that fill each earpiece. Planar magnetic headphones consist of a sandwich constructed in three main layers. The two outer slices are usually made of a matrix of tiny but powerful magnets, carefully arranged with their norths and souths pointing in to and out of the sandwich. The filling in-between is a very thin plastic film, gossamer-like, but coated with a conductive trace of metal that may zig-zag from top to bottom. Through this is passed the alternating current of the music signal. With the help of the principles of classical electromagnetism, and following Fleming’s left-hand rule to indicate direction of oscillating motion, the lightweight membrane will vibrate between the two planes of magnets in accordance with the played sound. Also see: 6 best budget headphones
OPPO PM-1: build quality
The success of any pair of headphones can come as much from the comfort they offer. And frankly, their looks as well. In both these respects the OPPO PM-1 headphones can be seen as successful – they can be worn for hours with little or no fatigue, and their design is sleek and unostentatious. There’s more than a little of the timeless character of Bang & Olufsen here in the future-retro styling. As a circumaural design, they have ear pads that encircle the ear and rest on the head. Gentle but suitably firm pressure is applied from a sprung-steel headband, wrapped in latex foam and covered with even softer real leather. To accomodate different shapes and sizes of head, the driver housings pivot about their centre in metal loops, and the entire speaker driver units also rotate at the point they connect to the headband. Each side can rotate smoothly by 90 degrees in each direction, so you can turn the driver assemblies to lie flat – essential for carrying in the supplied zip-up denim case. Two sets of cables are included – a short, lightweight cable just 90 cm long that’s terminated with a 3.5 mm mini-jackplug, for use with portable audio devices. There’s no in-line microphone or playback buttons to allow them to be used as a remote-controlling headset. A longer, heavier cable, figure-8 section and covered in soft fabric braid, is finished with a high-quality metal-sleeved 6.35 mm (1/4-inch)s jackplug. This cable is specified with linear-crystal OCC copper conductors. Either set of cables is readily detachable from the headphones, plugging into 2.5 mm mono jack sockets on the bottom of each driver assembly. Also availableas an option is a balanced-audio cable with Neutrik XLR plug. There’s a choice of two sets of ear pads for the PM-1 included in the box. Already attached were the premium-feeling soft pads covered with nappa leather to match the headband. Or alternatively there is a pair of plush velour pads, a few millimetres thicker, which can be snapped on in place of the leather pads. The overall build quality of the PM-1 headphones is simply first-class, the swivelling parts moving slickly but precisely with no free play or stickiness. And in use, there is no creak or rattle to be conducted to the head, unlike even some high-end designs that can subtly grate as they flex on the head.
OPPO PM-1: design
In contrast to most planar magnetic headphones before them, the PM-1 headphones are relatively efficient and we found they could be driven to decent volumes by even an iPhone and other portable devices. Their high sensitivity is a product of a novel design that uses a double-sided diaphragm, with twice as many aluminium conductors as other designs, working within the strong flux of an orthoplanar magnetic field created by neodymium magnets. And the conductors are arranged not in a concertina-like collapsed line, but in a circular or spiral array. Also see: 6 best budget headphones
OPPO PM-1: sound quality
The OPPO PM-1 headphones provide uncannily smooth, wide-band sound reproduction, with firm but subtly textured bass and a glare-free treble. We compared them against a range of premium headphones old and new, including the capable and solid-sounding Denon AH-D600 – a closed-back dynamic circumaural design originally priced at £500 but available now for as little as £160; the Sennheiser IE 8 and Etymotic Research ER-4PT earphones; and another planar-magnetic design, the Audeze LCD-2 (£900). We also found ourselves reaching for a classic reference, an electrostatic earspeaker design, the Stax Lambda Nova Classic with SRM-3 energiser unit. Source material was DSD and high-resolution PCM recordings as well as lossless CD rips played from a Mytek Stereo192-DSD DAC with built-in headphone stage. Against any traditional moving-coil design we tried it was immediately obvious that the planar-magnetic PM-1 headphones were in a different league. There was a crystalline clarity that showed instruments in their natural state, with no added body or blurring that normally robs us of their unique character and detailing. Yet nor was there any disturbing lispiness or high-frequency spit that can accompany this kind of treble clarity. Percussion was rendered quickly, without the common dragging of the beat or smearing of its punctuation. Drum sounds of all flavour were heard with almost original impulsiveness – regular snare strikes, rimshots, tom-tom rolls, hi-hats and assorted cymbalry. Compared to reference Stax ‘phones, the PM-1s couldn’t quite deliver the same extended shimmer that rises stratospherically in ride cymbal playing, for example, but here in turn they made most regular headphones’ attempt sound like they were following a tired cassette tape. Against Audeze LDC-2 too, the PM-1 headphones were perhaps a trace behind in transient response, although the OPPOs certainly had the more authentic overall tonality, revealing more of the source material, for better or for worse; the LCD-2s could major in their relaxed, organic presentation with highly dynamic bass but just lost out to the studio monitor-like levelness and insight available from the PM-1s. Vocals were another obvious forté of the OPPO planar-magnetic design. That falsely fulsome chestiness, a coloration of many dynamic headphones, can sound like that from close-miked vocal techniques. Here it was lifted entirely so we could hear with ease the natural timbre of male voices in particular. This may take some getting used to if you’ve only ever heard sound and music reproduced by moving-cone loudspeakers and headphones. With electrostatic and planar magnetic technology, familiar recordings can sound almost empty from the absence of thickening colouration that is so often layered into the music by the material components of moving-coil designs, such as paper or plastic membranes and rubber suspension. Switching genders, we heard higher register female vocals could soar and dive with essentially none of the synthetic screech or metallic edginess that can also be inadvertently added. Many vocal performances seemed set slightly lower in level, easily followable but not shouting out of the overall mix. If anything, the PM-1s would benefit from a little more reach into the extreme high frequencies, as they did seem to tail off from the very highest of HF extension. We particularly enjoyed the sound of guitars through the OPPOs, the way they could be picked out by their metal stringy, buzzy character or the natural resonance of bodies and sound boxes; the same with banjo and mandolin. Fret buzz, squeaks, plectrum clicks were somethines readily audible, the kinds of sounds recording and mastering engineers think they’ve erased but were still thankfully present under the microscope of the Oppo headphones. Against the Stax reference, they had one trump card in particular – the bass slam and kind of drive that makes rock rock. If anything the Stax Lambda headphones could reach lower in bass depth – but you had to listen for it. Funky basslines on the other hand would get lost if you weren’t focusing in that direction. Through the PM-1s there was no chance of losing sight of these bass parts; in fact we heard whole new bass-guitar figures revealed in the chorus of an extremely well-played song that proved a startling revelation. Stereo soundstage placement was truly excellent, placing instruments in easily spottable positions, and fixing them there. As an open-back, or perhaps semi open-back design, we have the benefit of a more open-sounding soundstage. Images could be heard from a sphere that seemingly extended perhaps 20 cm about the head. Compare this with even the best in-ear earphones which have more limited span in virtual space; but the PM-1s were still some way behind the three-dimension masters of space we hear in electrostatic designs.
Oppo PM-1: On the move
The OPPO PM-1 headphones are essentially an open-back design, although there appears to be plenty of damping material on their converse side, such that they’re not as noisy to other listeners as the truly open-backed. That said, we wouldn’t use them on public transport – for the obvious reasons of sound leakage but also because they still allow a great deal of ambient sound to filter through. In a less-than-peaceful environment you may hear plenty of background noise, which could encourage you to turn up the volume to drown it out. On a bus, train or maybe worst-case, plane, you’d be playing unwisely loud to hear your music clearly. See also: The best headphones of 2014
