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Loudspeaker Imaging

Achievements n

With the simple principle of progressive and tailored flex, through advanced cone profiling, our drivers achieve optimised imaging from a single focused source of finite diameter, using a single coil, or a vertical line array of such drivers. This is helped by an order of magnitude lower distortion at all frequencies and the ability to reproduce many frequencies simultaneously without problems with inter-modulation distortion, commonly associated with multiple frequencies from a single, centre-driven source.

Different frequencies are presented from different diameters within the cone simultaneously. This means voices, for instance, are far more revealing and realistic than the norm, intimately revealing the source in quality, dynamics and spaciality. The principles behind these benefits are explained below:

Imaging Fundamentals Explained

Sound waves propagate like waves on water. Imagine the effect of dropping stones into a large pool near to each other (multi-driver) - a complex interference pattern results, leading to a 'confused' pattern. This is more complicated by the fact that if you change position slightly you 'hear' different combinations of ripples. Now let it settle and drop a single large stone, followed by a smaller one at the same location (single driver) - there is a coherent spread of waves, forming a beautifully clear pattern that remains the same at the observer. For the best stereo imaging you actually also need detailed resolution across the whole frequency range and controlled sound dispersion (to minimise room reflections and channel blurring) from a single or vertically polarized (cylindrical wavefront) sound source.

The latter can be set up using several full-range drivers, sufficiently close/strategically placed so they effectively couple together to form a uniform cylindrical wavefront.

Focused Dispersion Explained

Imagine dropping a stone right at the edge of a small, irregular shaped pond. The energy cleanly propagates a long way across the pond, with no reflections from the side of origin. This is akin to focused dispersion. The effect is enhanced further by using a wave-generator of small but finite width instead of a stone (in audio reality you need a vertically polarised or 'cylindrical' wave), focused waves propagating a long way before they disperse. Compare this to dropping a stone into the centre of the pond (omni-directional). The energy rapidly dissipates in all directions and much confusion arises due to reflections from all the banks - the end result is random 'noise' throughout the pond and no real focus or coherence at a 'listening' point.

In Practice

These analogies explain why semi-directional 'finite single/vertical line source' is better than differing multi-sources or omni-directional point sources, and also why bass sounds more defined if the loudspeaker can be used next to a wall (the best-case scenario being the theoretically ideal infinite-baffle where the whole wall acts as a front baffle). In practice, the wall placement is not so critical as at fully omni-directional frequencies, the wavelengths are relatively large compared with the gap between speaker and wall, but the effect is still noticeable (and much more so than arguable differences between speaker cables).


Sound sources that span horizontally (for the same channel) or change in frequency vertically (except for non-directional frequencies – below 80Hz) are non-ideal for imaging. Imagine a wide, planar source. This gives coherent sound but poor imaging as the stereo information is no longer set up by 2 discreet horizontal locations. It is the high frequency sounds that convey most imaging information and which should have limited dispersion for true imaging.

In most multi-way systems that use high dispersion tweeters as the sole HF source, the dispersion from the woofer diminishes as the crossover point is reached and the tweeter produces a far greater dispersion when it takes over. This high dispersion means the volume drops off much quicker with the distance from the speaker compared with focused dispersion, meaning the nearest speaker takes precedence in the sound-field, blurring the instrument locations between the speakers. There is also a higher proportion of reflected to direct sound at the listener and a higher interference (diffraction) of sound at the cabinet edges, disturbing the stereo image.

Crossover Problems

There are also phase discrepancies due to the displaced drivers and crossover components employed. The high frequency components of the sound are segregated from the lower harmonics in dispersion, space, quality and phase and an element of distortion is introduced at all frequencies by the crossover, particularly those near the crossover point. Also, because the driver is operating in it's non-ideal range near anywhere near the crossover point the sound is far less than ideal. The quality of the sound always peaks around the region farthest from the crossover points/frequency limits of drivers.

Aurousal has No Crossover

The breakthrough with the AI Aurousal range is the driver, that it is driven from a single coil but is designed to change effective area in a finely tailored fashion with frequency so there is no peak in sound quality – you get unbridled 'LIVE' sound over a vast frequency range with no need for crossovers (see section below). Even if a crossover were employed the sound is still optimal right up to the crossover point as the driver still 'wants' to produce this frequency as well as any other. The crossover would still introduce deleterious effects of its own, however.

Even the Aurousal VS, which is actually a 1 way/1.5 way design, does not employ an actual crossover (full driver handover circuit).

Why not Pure-Piston?

Standard speakers are often designed to approach 'pure-piston' in action with minimal flex. Flex is actually quite necessary for some degree of frequency bandwidth and accounts for the standard cone loudspeaker's ability to produce different frequencies, but it distorts and ruins the sound if not controlled very carefully along with changing frequency.

Reducing this flex or leaving it uncontrolled gives an associated limitation on the useable frequency bandwidth. This is why more than one driver is traditionally employed (or single drivers driven from more than one point/coil).

AI: The Flexible Approach

Our drivers successfully control this flex over the whole audio frequency range, giving unprecedented bandwidth and quality from a single coil. The finely contoured diaphragm means the flex position changes in an ideal way according to frequency, the effective area of the cone reducing with increased frequency. The flex position, amount and frequency dependence has been finely optimised according to mathematical laws, calculated to within microns. This allows us a cone far lighter than the normal thick rigid cone, also affording the impeccable dynamics and resolution.

Why is pure-piston used then?

Optimum cone profiling is technically very challenging. If you are designing a dedicated unit that is designed to perform over a relatively narrow frequency band (the accepted norm) then it's easier to ignore the benefit of finely controlling flex and total rigidity is better than uncontrolled flex – this is why dedicated units/subwoofers traditionally try to approach pure-piston action, with relatively thick rigid cones. Pure-piston is never actually achieved in cone systems, but the effect of the small amounts of uncontrolled flex we are talking about here is minimised by the limited bandwidth.

The result of trying to increase the bandwidth just results in an increase in the inter-modulation distortion associated with a pure pistonic cone. A crossover is therefore employed to distribute frequencies between dedicated drivers and so we arrive at the celebrated multi-way speaker.

Aurousal Technology

At high frequencies and low volumes the flex (measured in microns) would be lost in the uneven surface structure of most cones, while our system, using profiled smooth light metal alloy foil, imparts an unrivalled resolution giving unparalleled realism. Metal foil is also more acoustically opaque than other cone materials, effectively separating the sound inside/outside the cabinet. Sound propagates along this material the fastest, giving an immediacy to the sound. Tailored flex also gives the extremely low distortion and a low-level resolution that preserves even the low-volume original recording room acoustics. The ultra-thin and strong cone also contributes to the dynamics and resolution.

A no-compromise approach has also been used for all other aspects of the driver design including a massive magnet assembly and optimised suspension, affording a high and extremely fast linear cone excursion.

Listening is the ultimate test - we are very confident you will hear a vast difference (see our Comments section).