I T E... P A P E R
The RADIAL Loudspeaker
by Steve Deckert
RL-2 is a modified design of the RL-1. It incorporates
two fundamental changes. The first is a different
tweeter. The original tweeter is replaced with
a top drawer planar ribbon tweeter - basically the finest
I could find. Since the tweeter covers half of
the loudspeakers frequency range it stands to reason
that using the best available will elevate the fidelity
beyond what it already is.
second is related to the enclosure. Since an enclosure
is responsible for up to 70% of the sound quality of a given
speaker it stands to reason that improving it will elevate the
are the only two things I could think to do to the RL-1 since
the actual driver is at a peak in its development and I can't
think of any ways to make it any better.
paper will deal with the fairly radical enhancement to the enclosure
since there were no modifications needed to swap tweeters. The
crossover does not change.
original RL-1 cabinet is still used but with a different cabinet
base design. On the original RL-1 the cabinet is an 8
inch cylinder that terminates into a 10 inch diameter base.
The base is like a donut allowing the cylinder to vent
through the bottom. There are adjustable spikes on the
RL-1 cabinet base that allow you to change the height of the
enclosure in relation to the floor it sets on. In most
rooms carpet is required to be in close proximity to the base
if not almost touching it to prevent the somewhat colored sound
inside the cylinder to cloud the presentation.
Radial design in general has some difficult obstacles to overcome
where enclosures are concerned. Because the cone is both
very THIN and INVERTED it's very shape now becomes a microphone
to the inside of the cylinder. This is why carpet is recommended
under the base, to absorb some of this excess back wave. Whatever
energy is not absorbed and is reflected back to the cone will
be heard on top of music.
fundamental problem has been resolved in the RL-1 as far as
possible by designing the main driver with a large cast motor
assembly which largely blocks the reflected back wave off the
bottom of the enclosure. Add to that some trial and error
placement of different dampening materials on the cylinder walls
in the correct patterns and you have made it possible to get
very good sound out of an otherwise impossible design.
that, the question of how to improve the enclosure becomes how
to better control the back wave of the main driver.
vision I get in my head that illustrates what is happening inside
this or any tall narrow enclosure is as follows:
enclosure is like a large hallway, such as in an airport terminal.
The large hallway is packed with people all running around
in different directions with different objectives, and of course
some are just lost. Basically a scenario for chaos. All
of these people entered and continue to enter the hallway from
a door at one end. As the hall fills with people the chaos
increases. Well imagine if you could separate the idiots
from the orderly to reduce the level of chaos by installing
a lounge at the other end of the hallway. They all run
for the bar and you never see them again. In the RL-2
I've installed a bar at the other end of the hallway.
was accomplished by creating a cabinet base that would accommodate
a second woofer - magnet side down - so that it fits tight against
the bottom of the cylinder. The base design would also fix the
distance off the floor for optimal performance.
installing a second driver in the base we basically have a passive
radiator instead of a vero-vent which is what the RL-1 basically
is when it sets on the carpet. The passive driver still
has a motor assembly and voice coil but is not hooked up to
anything. In the case of a cylinder where the diameter
exactly matches the driver, placing a passive unit at the other
end creates almost a one way valve where energy is absorbed,
modified and dispersed into the room rather than back into the
addition the voice coil is used to modify the dampening factor
of the passive by placing different values of resistors across
the terminals. This enhances the thermal capacitor effect
of the passive by converting energy directly into heat that
is dissipated by the voice coil through the pole vent of the
response of the overall design remains largely unchanged since
the lower driver is tuned at the resonance of the cylinder.
However bass signature is largely improved since cabinet colorations
are no longer detectable.
are two other positive side effects of the RL-2 cabinet base
design. The first is that by raising the cabinet height
by 6 inches a improvement was noticed in overall sound stage
height when listening to the speakers too close or in none optimal
set-ups. This is frequent in smaller rooms. The
second is that by controlling and modifying the back wave and
dispersing it out of the bottom with what the floor sees as
another inverted cone, we get enough ambient sound information
out of it to largely enhance the overall size and palpability
of the sound stage. It's like two pillars that bloom with
sound making them even more impossible to locate when you close
your eyes, regardless of where you stand in the room.
this to the rather dramatic improvement in the RL-2 tweeter
and I believe these speakers rate up in the very top of audiophile
home speakers. One of the flattest sounding speakers that
never shout at you, yet have the highest level of detail on
both the top mid and bottom that I've only heard on the most
we did our serious listening evaluations primarily focused on
comparing the RL-1 to the RL-2, the first thing I thought about
was a $6500.00 price tag. As good as the RL-1's they just
aren't RL-2's. From one perspective they are very similar,
from the other perspective they're not even close. Our
in-house rating system involves several opinions including one
man who started listening to and building hi-fi in the 50's.
He is a character who has either owned, heard, or fixed
(usually all three) almost every piece of high end audio gear
ever made until about 1990 when he decided to give it rest.
He is always the hardest nut to crack - a man spoiled
by his own tube direct drive electrostatics to a degree that
he can't even stand to listen to a cone type speaker! He was
quoted as saying, "now that I've heard these I can admit
that I really didn't care for the RL-1's that much. They
were real good in some ways, but still not my cup of tea. The
RL-2's however actually got me exited a few times and I would
rate them as better than 95% of all audiophile speakers made,
price aside." With the exception of the Zen Triodes,
this man has never liked anything so we were actually shocked.
this aside we realized it now looks like a rocket and noted
that if we made the grill more pointed at the top and stuck
a fuse on it we could paint a pair white and put some USA decals
on them so they look like real missiles and call them the bin
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2007 2008 by Steve Deckert