Stereo Amplifier

Review: AKG K1000 Headphones

With this innovative headphone design, the AKG engineers in Vienna have moved the whole ear-speaker concept forwards, and upwards, both in terms of price (they are nearly four times more expensive than AKG's previous top model) and standards of spatial sound reproduction.

Clapping conventional headphones over our ears has always involved serious compromises. Traditional closed-back types (the oldest approach) have the potential to produce the firmest bass response and can be equipped with circumaural ear-pads to exclude outside noises. Yet they tend to generate dimensional cavity resonances in the midrange and, with almost no left-right ear crosstalk, they produce an overly divided sound picture from stereo recordings: the voices and instruments become concentrated in the two ears with any mid-stage images lodged inside the head or, worse still, at the back of the neck.

When open-backed and ultra-light head phone designs first appeared a couple of decades ago, they were widely welcomed for their more spacious soundfield, and they remain firm favourites with many stereo aficionados. The fact that the diaphragms are free to radiate outwards, as well as inwards towards the ear, gives some time-delayed crosstalk of left channel signals to the right ear and vice versa. This is a better approximation to the situation of listening to a pair of spaced loudspeakers, for which the recordings were balanced, where both ears hear the sounds from both loudspeakers (including a slight time delay from each loudspeaker to the more remote and shadowed ear). Accordingly most people find that open-back headphones produce less o that claustrophobic in-the-head effect.

On the other hand, open-back headphones have a number of serious drawbacks: they are generally less full in the bass; they fail to exclude outside sounds; and they can radiate tinny sounds strongly enough to annoy people in the vicinity. Thus we come back to that word I began with: compromises.

There is another drawback inherent in both of these types of headphone. Since they are held so close to the ear, the filtering or response shaping introduced by our cleverly contoured pinna, or outer ear, is more or less eliminated. We therefore lose that individualized characteristic to which we have unconsciously grown accustomed over the years, and this robs the signals of some directional information and a lot of their naturalness.

This new K1000 design incorporates stand-off pads at each end of the headband. These hold the entire earpiece assembly about 20mm away from the ear so that the plane waves from the diaphragm encounter all the nooks and crannies of the pinna and are thus 'processed' on their way to the eardrum very much as nature intended. At the same time the inter-aural crosstalk is increased to 30-40dB, enhancing the desired binaural, i.e. out-of-the-head, effect. As a bonus, the earpieces are mounted on a swivel suspension, like wing mirrors on a car, enabling the user to choose from a wide range of angles. Aimed most directly at the ears, the system gives maximum definition and immediacy. Progressively increasing the backwards angle has the effect of opening out the sound stage and putting a controllable distance between you and the nearest performers-the first time that this has been offered as a user option.

The transducers use the basic dynamic (moving-coil) principle in preference to the other, seemingly more esoteric, electrostatic and orthodynamic (distributed magnet) types. However, a new topography has been worked out to give maximum transparency, i.e. elimination of standing-wave forming obstructions in front of the ear. The diaphragm with its attached coil vibrates inside a radial magnet system built up from short high-flux neodymium bar magnets set inside a circular channel. Piston-like motion, free of break-up modes, is encouraged by assembling the 7 micron thick diaphragm from four layers of plastics foil, with elastic damping intermediate layers and a coating over the whole of the same hard organic varnish used by the famous old master violin-makers. The coil former is a ring of incredibly thin (80 microns) aluminium, which is fabricated on a computer-controlled machine, and acts as a heatsink. The response has been optimized for free-field operation, i.e. with no equalization to suit a head-coupler, the resulting interference-free plane wave then being subjected only to the listener 's personal spectral cues.

The transducer element is suspended in a square frame of light but strong fibre-filled plastics within an open-weave metal basket front and back. The minimalist headband comprises two red coated steel strips, terminating in plastic blocks. These carry two soft pads which press lightly on the temples and hold the earpieces away from the head as already mentioned. The front pad is fixed but the rear one can be adjusted fore and aft to suit the wearer's head and provide maximum comfort. A self-adjusting inner headband rests on top of the head.

The two-core oxygen-free copper signal cable divides to enter each earpiece via the bottom front corner. This cable is 2 metres long and is terminated in a 4-pin XLR plug. Some professional locations may be able to use this plug direct but the system comes complete with a thicker 3-metre oxygen-free extension lead (made for AKG by Monster Cable) having a matching XLR line socket at one end and ready-tinned bare wires at the other. This is where I have to explain that the K1000 sensitivity is too low to be driven satisfactorily from the conventional headphones outlet. The wire end s should be fitted with appropriate 4mm (banana) plugs or inserted direct into the amplifier's loudspeaker terminals or binding posts. This will present no problems with an amplifier already having alternative A and B pairs of output terminals. Simple A/B switching will then select either loudspeaker or headphone listening on demand, though I would recommend turning down the volume before switching at least until you have found a setting which gives safe and comfortable listening levels. With a single output amplifier, you will need to change plugs or buy a proprietary changeover switch-box. I gather that AKG are now marketing a suitable unit and are also claiming that the cord can be extended by a further 7 metres with no signal degradation. I did find that the bare wire cable ends have a limited reach of only about 12cm and will need to be extended if the left/right loudspeaker sockets on your amplifier are wider apart (e.g. on the Quad 606).

How they performed

You would need to be serious about headphone listening to contemplate buying a headset costing £499 which does absolutely nothing about isolating the wearer from extraneous noises. However, for such a listener AKG have produced an absolute winner which in my opinion leaps straight into the front rank and even rivals the legendary Stax electrostatics.

Bass and treble extend smoothly to the limits of hearing, except for mild roll-off in that elusive bottom octave, and the midrange response is remarkably steady and free of peaks or dips. The rapid attack gives transients a 'champagne'-like quality and indeed reveals an extraordinary degree of fidelity on individual voices and instruments from the best (usually purist miked) recordings. You would find it very difficult to choose loudspeakers (or a room) which could produce this degree of fidelity to the original sounds.

Of course we cannot shirk the bottom-line dilemma that all stereo recordings and broadcasts, except for a few experimental binaural and surround-sound ones, are designed to be listened to in the mandatory layout with the left and right loudspeakers and the listener respectively at the corners of an equilateral triangle. Only then will the recording engineer's efforts at establishing a believable arc of performers in a natural acoustic produce the desired effect. Even the best headphones spoil this spatial illusion, though to be fair some listeners feel more disturbed by it than others.

This K1000 design goes a long way to ameliorating the in-head restriction and I would expect most listeners to end up with a pretty satisfactory impression of space after a bit of experimentation, as follows. First adjust the movable pads, which have three click-stop positions, until the headset feels firm yet comfortable. Look in a mirror if necessary to check that the pad adjustment brings the earpiece centres slightly in front of the ears. Then adjust the earpiece angle for the most natural-sounding balance on your favourite music. You may end up choosing different angles for different recordings.

I found it useful to begin with something fairly specific like a well-recorded string quartet, or the unaccompanied voices of The Tallis Scholars or The Sixteen. With the earpieces at their innermost angle, the separation and definition are very impressive. The ambience can be heard to the full but there is a sort of forwardness and spatial constriction. The earpieces can then be turned outwards in small steps until the best mix of presence and airiness is heard. Over-doing this spatial effect is immediately apparent, and is accompanied by a steeper bass roll-off, so that the final adjustment can be very precise.

You will have gathered that I like these headphones-or should we call them ear-loudspeakers- very much. They have a remarkably smooth and well-balanced frequency coverage allied to splendid articulation. Perhaps more than any other design they tackle the loudspeaker compatibility question to produce a high degree of spatial realism. If you can afford to spend this much and are serious about headphones, do give the K1000 a try at your nearest AKG dealer.