In an effort to recreate
a sound that happened in some other place, in some other time, audio
engineers are constantly trying to find the best means to record and
reproduce the sound as exactly as possible. If we could have absolutely
accurate replica of recorded sound at the end of an audio equipment
chain, than the sensation that we would have, would be the same as we
actually participated in the recorded event.
Of course, absolute accuracy is not possible. Fortunately enough, it has been proven that it takes a certain level of reproduction accuracy to make the human or animal ears experience no difference to original. Impressive achievement, but with ridiculously expensive and impractical laboratory equipment and conditions.
Our goal is to bring the most of that experience to everyday life.
Since RAAL was making various kinds and sizes of custom true ribbons for more than a decade, we could see through the years of experience, what are the biggest disadvantages in using them in high-end systems and how to solve the existing problems.
technology: The magnetic field in RAAL ribbons is homogenous. Regarding
the width of the gap, it is designed to have the same strength at the
ribbon edges, as well as at the ribbon middle portion. It reduces the
stress at the ribbon foil dramatically. The distortion, too. To get the
precisely shaped field, through the gap width and depth, we’ve
extensively used the FEM and BEM magnetic circuits analysis software. In
order to obtain such a field in real magnetic circuit, very strong NdFeB
magnets have been precisely machined, prior to magnetisation, in very
special shape. Making the magnetic field homogenous, sacrifices the
strength of it, but efficiency should easily be changed for low stress
and low linear and nonlinear distortion.
technology: Homogenous field has one, much more interesting result and
that is the possibility to use non corrugated, thin,
no-excess-weight-sandwich, flat aluminium ribbon. We are using just
slightly structurally shaped pure aluminium foil, of just 0.004 mm of
thickness, to yield the best possible performance. FLATFOIL?
although very thin, is much more resistant to high signal input, and
unable to go out of optimum magnetic field, thus providing the non
compressed dynamic output and much lower distortion at high SPL output,
achieving the dynamic capabilities of horn loaded drivers with
technology: Very important part of signal handling is its path to the
ribbon ends. Almost all of today’s ribbon drivers are using the layout
which loops around the whole magnetic structure, which is, in fact, the
single winding solid iron core inductor, connected in series with
ribbon. This is effectively depriving the ribbon of high frequency
signal. The solution for this problem is, RAAL’s unique signal leads
path, which doesn’t put the signal leads around the iron. The signal is
fed to the ribbon through two symmetrical leads above the iron yoke,
which effectively widens the bandwidth considerably. This layout also
acts as a RF signal cancelling circuit, to stop the power amplifier
being fed with radio frequency signals which might be picked up by
ribbon acting as an antenna.
TRANSFORMER: The impedance matching transformer is made to transfer the real power without distortion. Not just the shaped noise signal for power measurement methods, but real high-power signal peaks can be transmitted to the ribbon, which preserves the natural dynamics recorded. The primary inductance of the transformers in RAAL ribbons is set to a value which corresponds to the second coil of 4th order L-R high-pass filter at the appropriate cut-off frequency, depending on the model in question.
Recently, we finished
development of Amorphous C-cores application in our ribbons. Some years
ago, we were the first to introduce large gap approach in building
ribbon transformers and now we are the first to use AMCC's in ribbons
for absolutely uncompressed high power transient transfer and, at the
same time, even further improving already the best low-level performance
in the world today, by decreasing the width of hysteresis compared to HF
ferrite cores. For direct coupled tube SE-ribbon, we succesfuly
developed 175:1 ratio, -3dB at 120kHz Amorphous C-core transformers that
can carry DC idle current of SET. Impedance conversion is about 30000:1,
bringing the 0.1 Ohm ribbon up to 3kOhm, good for plate loading of most
triodes in HF.
One of the big existing problems is the use of thick front plates, so
common in true ribbon designs, which are then bevelled to minimize their
acoustical influence. On the other hand, bevelled front plate act as a
wave guide somewhere in higher kHz range, ruining the linearity, so that
has not solved the problem yet. RAAL’s unique front plates are very thin
with no bevels, and our research brought us to the making of the zig-zag
“acoustically invisible?front plate ribbon opening. The benefit is
“non-wave guide? seamless coupling or ribbon air loading to the open
space, because of the “distributed parameter?edges of the opening. By
that, we achieved the unmatched linearity in the upper kHz region and
exceptionally “clean?impulse response.
FOAM DEFLECTOR PADS: Wide angle polar response is of great importance for the natural reproduction, therefore using the larger ribbon drivers bares a problem, since they are showing very intensive “beaming?of high frequencies, as they are line sources far bigger than the wavelengths of high frequencies in audible range. For model 140-15D, we found the solution for that problem in using the specially shaped foam pads in front of the ribbon. The dispersion pads are working as an acoustic lens, by slowing down the velocity of sound and thus shaping the sound wave front from cylindrical to spherical. The parasitic effect of partial sound absorption is inevitable, but acceptable. The pads are magnetic and they can slide on the front plate. By adjusting the distance between the pads, sliding them toward or apart each other, it is possible to shape the on-axis linearity vs. wide angle vertical polar response. In this way anyone can adjust the high frequency output by his-hers own liking. If the pads are
completely removed, 15 kHz on-axis response is increased in level of about 7 dB.
sub-critically damped compression chamber of ideal proportions provides
the exceptional amplitude linearity and impulse response.
RIBBON REPLACEMENT KIT: ribbon replacement is made easy by our ribbon replacement kit, which is easily replaced by the user. This “kit?is in fact our SYMMLEAD?signal leading frame, holding the stretched ribbon, allowing it to snap into perfect position between the magnets.
This feature might be an obsolete one, because RAAL ribbons are destructible only by really extreme abuse or curiosity. In two years, we sent away only 3 replacement kits to customers who destroyed the ribbons by opening the drivers out of curiosity. Aside from that, our reliability record is 0% failure rate.