OPPO PM-1 review
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.
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.
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.