Focal UTOPIA BERYLLIUM Série Manuel Utilisateur page 7

TFP port (Turbulence Free Port)
7
The bass reflex decompression port design is of paramount importance and has a direct
effect on the characteristics and performances of the loudspeaker in the bass range section.
The parabolic shape of the TFP (Turbulence Free Port) port has been designed to reduce
distortions produced by airflow noises and dynamic compression at high levels.
As regards bass reflex loudspeakers, their advantages and drawbacks are perfectly under control.
In addition to the setting up complexity, for which the manufacturer usually bears full
responsibility, this kind of tuning offers the main advantage of keeping an excellent frequency
response within the lower part of the spectrum, thanks to the tuned resonator, of which the energy
combines with the driver's energy. Therefore, this solution has been adopted for the Sub Utopia
Be, in order to deliver the best performances possible, more particularly in bass frequency range.
At the same time it is well known that subwoofers often come up against a recurrent problem:
a perceptible distortion, induced by airflow noises within the circular port, of which the section
is often much smaller than the driver's one. The induced overpressures are then at the source of
distortions and unpleasant mechanical noises.
Most used solutions
A common solution consists in choosing a port with circular section, with both extremities
bell-shaped, rather than a straight port. This relatively easy-to-implement shape makes easier the
progressive decompression of the airflow present in the port, thus reducing the airflow noises.
This most used solution proved to be inadequate for the Sub Utopia Be, even if it meets the needs
of most of other loudspeakers, thank to a great ability to reduce distortions. Actually, the combined
use of both a high efficiency 40cm (16") driver and a 1000 Watts RMS BASH amplificator allows
to obtain considerably high peaks, such as a pressure of 128dB at one meter. This induces strong
internal pressures and then leads to excessive flow velocity, which does not fit the current solutions.
The TFP parabolic port
The first taken measure to reduce these air flow noises lies in reducing the port section. Choosing a
rectangular port proves to be the best adapted solution, even if its implementation is more complex.
On the Sub Utopia Be, the opening has a 50dm² area (as opposed to a 17dm² section in the case
of a circular 15cm diameter port). Another solution consists in applying a bell-shaped opening to
this rectangular port, which has never been done before. After several simulations and successful
experiments, the ideal parabolic port has finally been created. The chosen design makes the airflow
noises imperceptible to human ears, even at nominal power level. The distortion rate has been
reduced by at least 10dB (the equivalent of 10 times less) over the whole part of the bass frequencies
response of the subwoofer. The improved airflow within the port enables a friction reduction,
which leads to a considerable dynamic compression at high level, phenomenon from which the
Sub Utopia Be is fully preserved.
Sophisticated massive building
The subwoofer performances also depend upon an additional factor : the enclosure's rigidity
The enclosure's walls are permanently undergoing significant internal pressures and are then being
bent, absorbing a wide part of the energy produced by the driver. As regards the Sub Utopia Be,
drastic measures have been taken : the bottom and top walls are made up with MDF 30mm thick,
50mm for lateral and side walls, and 65mm for the front panel. Filled with numerous internal
support pieces, the Sub Utopia Be enclosure ensures a perfectly inert mechanical reference, without
having any negative effects on the good working of the subwoofer.
User manual Sub Utopia Be line
The Sub Utopia Be features an exclusive back TFP port, which ideally
unwind the air flow within the port. Distortions prove to be considerably
reduced and dynamic compression phenomenon due to bass reflex system
is significantly reduced.
MDF -built walls reach an uncommon thickness of 65 mm for the front
panel. The TFP port, the internal support pieces and partitioning guarantee
an unprecedented stiffness.
Bass-reflex tuning functioning's principle.
The enclosure plays the role of a tuned resonator, of which the bell-shaped
curve superimposes itself with the driver's one. This interaction then allows
the frequency response to extend into the bass frequencies.
On a common port, the different frictions on the walls are slowing down the
airflow : the wave is then bent, giving rise to new distortions and turbulences
due to a violent output decompression producing noise. The TFP port ensures
a progressive air decompression in order to obtain a constant speed along
the whole part of the port's section and a coherent output wave form.