Focal Utopia Beryllium Line Role of the Crossover, Mastering Directivity, Mastering Phase

9OPC crossover™ (Optimum Phase Crossover)

User manual Utopia Be line

The crossover is a key element in the design of a loudspeaker. Its role and

its development are very complicated, the personality of a loudspeaker depends on it.

The role of the Crossover

The crossover has the function of distributing the signal from the amplifier to the various drive units in a loudspeaker: bass, midrange and treble. The most critical area of filtering this signal, with out any doubt, is between the midrange and treble. A low-pass filter rolls off the higher frequencies of the midrange. A high-pass filter rolls off the low frequencies from the tweeter. This crossover point generally occurs in the region between 2-5kHz. This underlines a fundamental point in terms of realistic sound reproduction: “directivity”.

Mastering Directivity

The diameter of a drive unit designed to reproduce midrange frequencies is generally between 130 and 170mm. These dimensions correspond to a frequency of between 2 and 2.6kHz. The directivity, meaning the angle over which a drive unit will radiate its energy, reduces as frequency increases. For frequencies where the wavelength is smaller than the diameter of the cone, the sound becomes very directional. This means that the sound will be radiated in an increasingly narrow beam. As a consequence, the acoustic power radiated from the loudspeaker is not evenly balanced, principle criterion for the reproduction of a realistic image over a three dimensional space.

Here our inverted dome tweeter offers a unique advantage in that its design and conception allow it work down to frequencies sufficiently low enough to avoid the effects of midrange beaming.

Mastering Phase

In addition to the constraints imposed on the tweeter at low frequencies, there is also another very critical aspect: the phase behavior of the loudspeaker and crossover combination in this critical region. The ear and the auditive system are extremely sensitive in the zone 2-2.5kHz. The midrange drive unit and its crossover must display an amplitude response that is “the exact mirror image” of that of the tweeter and its crossover. For this criterion to be met, the phase between the midrange and tweeter must be perfectly matched for the two to overlap and sum perfectly and

create a balanced tonality. The difference in phase between the tweeter and midrange at the crosso- ver point must be zero. Thus, there is total summation between the two emission sources

at the crossover frequency. Out of phase, the loudspeaker should show a very deep and symmetrical hole in the response curve.

OPC Technology

These aforementioned steps form the basis of OPC technology. However, it would be naive to think that this ideal could be reached simply through an extensive development of crossover technology. It is necessary to have total control over the response and performance of the transducers themselves, as is only possible for a few manufacturers who develop their own drive units as Focal-JMlab: a specific drive unit is developed for each individual type of product. It's unrealistic to think that a mechanical deffect can be corrected electricaly.

With the OPC technology, we use an acoustic roll-off of 36dB/Octave for the slopes between midrange and tweeter along with a perfectly aligned phase. This translates into a sound that is extremely coherent and with a natural timbre. Imaging is extremely precise and at the same time dispersion wide so that the result can be enjoyed over a wide listening area.

The high and low pass crossover sections “calibrate” the electrical signal perfectly optimizing the range of frequencies passed to each drive unit.

5 000Hz

2 500Hz

A bass-mid drive unit will radiate sound in an increasingly directional manner as frequency increases. It becomes more directive. Therefore the crossover should introduce the tweeter before this phenomena starts to take effect.

Frequency response in and out of phase. The Grande Utopia shows a perfectly symmetrical cancellation out of phase indicating a perfect optimization of phase.

The OPC crossover offers a remarkable impulse response, even on a 4-way loudspeaker like the Grande Utopia Be.