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The scale of the audio spectrum to be reproduced imposes unavoidable physical constraints.
To appreciate this, you only need to consider the wavelengths to be produced.
The wavelength is expressed by:
λ = v/f
v is the speed of sound in air (340m/s)
f is the frequency of the signal to be reproduced
Therefore at 100Hz the wavelength
λ = 3.4m
At 1,000Hz the wavelength
λ = 34cm
And at 10,000Hz the wavelength λ = 3.4cm
The only solution to achieve a faithful reproduction of the original signal is to divide up this
reproduction through the use of optimized loudspeakers, the diameters of which are related to the
frequencies that they are designed to reproduce in order to obtain constant directivity for the
frequencies concerned.
For the bass, due to obvious size restrictions it would be impractical to use diameters running into
meters. Fortunately, directivity is not critical in view of the large wavelength of frequencies in the
bass register. In the midrange and treble, directivity has a major influence however, so here multiple
drive units are needed.
However, although this multiplication of sources is ideal for faithfully reproducing each of the
frequency zones, it does pose a problem of coherence. The sound from each of the drive units must
reach the ear of the listener at the same time (chronological synchronicity). If the midrange, the
treble or the bass is received ahead of any of the other registers, there will naturally be an impression
that the sound is distorted. Faithfully reproducing the original audio signal dictates that all
frequencies must reach the listener at the same time, perfectly in sync.
The Focus Time principle
The alignment of several loudspeakers on a flat front baffle inevitably leads to a small degree of
audio distortion. The treble will be heard first, followed by the medium and the bass - this time
smearing is heard as a blurring of transients. Naturally, it is possible to experiment with the
respective positioning of the transducers in order to compensate for this effect. Nevertheless, it is
obvious that the tweeter that emits the shortest (and therefore the most direct) frequencies must be
placed on the axis of the listener’s ear (at the same height). This means that in order that the mid
and bass frequencies arrive at the same time as the treble, the drivers designed to reproduce these
frequencies must ideally be positioned in a semicircle, the center of which is located at the same
height as the listener’s ear. This is the principle of Focus Time, in which all frequencies are focused
upon the listener and take the same time to cover the distance separating the loudspeaker from the
listener whatever the register, be it bass, mid or treble.
Towards the ideal of the single point source
As mentioned previously, the theoretical ideal for localized sources inevitably runs up against physical
constraints. This is even more evident when you add the notion of the directivity of the transducers
(see OPC filter) and the notion of energy reproduction, for the bass, arising from the movement of
the membrane which increases progressively as the diameter decreases.
The Focus Time solution offers an intelligent response to all of these problems by reconciling
temporal coherence and enhanced dynamic range. The final sound image is characterized by
excellent stability regardless of the amplitude concerned.
This is the best possible solution to simultaneously reconcile the criteria of tone, dynamic range and
the sound image.
Creating a special virtual source capable of delivering a coherent sound
without any loss of audio quality over space.
The various loudspeakers are aligned vertically on a traditional front panel.
The distance from the emissive center of each of these loudspeakers to the ear of
the listener is not identical.
The Focus Time structure: each of these loudspeakers is positioned in a
semicircle, taking the listener’s ear as its center.
Cutaway view of the Grande Utopia, clearly showing the Focus Time profile.
7
Focus Time
™
User manual Utopia Be line
notice utopia be 7 19/04/04, 15:32:43