High Definition Towers Mark II
Looking through the pages of Sterilized and Absolute Nonsense, one
can't help feeling that speaker design has changed very little since
the basic principles were laid down in the 1940s. Yes, we are seeing
the use of molded compounds and the rounding of sharp edges and corners
into Shmooaform contours. Progress seems to be coming from the driver
designs, computer modeling and the use of exotic materials but
beneath the refinement and tweaking there is the basic base reflex, air
suspension systems, horns and planar systems. There has been very
little innovation in the design of the speaker enclosure itself.
A person looking at the High Definition Towers Mark II for the first
time might assume that it was just another of a long line of
rectangular box designs. It has side firing woofers or passives so it
must be a sealed box. It probably has the standard Swiss cheese shelf
type bracing. And what's that stack of latticed panels on top behind
the tweeter supported by little bowling pins that looks like the top of
a 1930s refrigerator? Probably catches the back wave of the
tweeter. But a closer examination of the internal structure of this
speaker reveals that it stands beside only a handful of others as one
of the truly unique and innovative approaches to speaker design in the
last 70 years. Steve Deckert has been working on and perfecting this
design for almost three decades.
On the inside of the HD Mark II are five interconnected chambers one of
which is a transmission line. The front firing 8 inch woofer and side
firing 8 inch passives present a surface area at low frequencies
equivalent to a 24î speaker presenting as much surface area as a
Hadly! The woofer runs full range and the top mounted ribbon tweeter is
filtered in first order with a single capacitor.
Dave Wilson once told me while he was demonstrating the WHAM in his
home, that a little understood distortion in speakers was their
tendency to go into a kind of harmonic resonance where the whole
cabinet vibrates back and forth and from side to side. This is
different that the front and side panels moving in and out
independently and acting like diaphragms which can be addressed through
bracing. Do you treat that with diagonal bracing?" I ask. "No" he said.
He explained that in his speakers he adds and subtracts mass from all
of the panels so that the front and back and sides and top all have
different densities. Steve Deckert addresses this problem another way
so that the right front corner is braced against the left rear one and
the left front to the rear right. This is achieved not with mere struts
but with entire panels that run from the top most of the way down
dividing the box in the upper part into four triangular shaped, tuned
chambers, the rear one of which making up a transmission line.
Confused? Imagine you are looking at the cabinet
from above with the top removed. Imagine a rectangular panel of
mdf that runs from the right front corner to the left rear one dividing
the box diagonally in half. Now imagine another board crossing the
first from the left front corner to the right rear. Now you have an "X"
cross section forming four triangular chambers. Triangles are very
rigid structures and resist harmonic resonance in the first place.
Further more triangular chambers have no parallel surfaces so sound
doesn't bounce back and forth like it does in rectangular boxes.
Standard front to back and side to side bracing invites the kind of
vibration Wilson was talking about. When the front speaker moves
backward the back panel also retreats at the same time. The same for
the sides, especially if side firing speakers or passives are involved.
With diagonal bracing, the movement of the front of the speaker is
carried to the back corners making the transfer of energy non
symmetrical. The result of this approach is much less sound coming from
the cabinet which contributes to the Mark IIs remarkable ability to
disappear. More about this later.
On the bottom of the tower is a single chamber called the summing
chamber. Each of the three front triangular columns has a tuned tube
attached to its bottom connecting it to the lower box which
receives and blends the three Helmholtz resonances. The front tube is
tuned differently that the ones on the side. The combining chamber
opens into the back to the transmission line which carries the sum of
the three tubes upward, the rear triangular transmission line opening
completely on the top.
But somehow the sound has to get from the front column where the woofer
resides into the side columns in order to excite the passive radiators
and load the tubes. This is achieved by oval ports at speaker level,
one on each side. Why oval? So any sound bouncing back and forth from
the parallel surfaces of the ports would be different any where on the
ellipse. But Steve defeats this problem even further by scalloping the
edges of the port so there are no parallel surfaces at all. In fact,
the only parallel surfaces in these speakers at all is the top and
bottoms of the triangular columns and the inside of the combining box
which has foam egg crate foam damping on its bottom. There is an
additional duct in the bottom of the back panel at the level of the
averaging chamber. This further tunes the transmission line and
provides a way to recover lost articles that fall down it.
But what about the low frequency energy coming up the transmission line
and firing upward toward the ceiling. That's where the strange looking
diffusion panels on the top comes in. On the top of the HD Mark IIs are
two rectangular panels, one atop the other with hemispherical
indentations cut out for the tweeter. The diffusion panels are
supported by four heavy metal spikes resting on the part of the top
above the "X" bracing. Inverted spikes also support the upper diffuser
to the lower. The lower diffuser panel has a triangular opening in it
positioned above the opening of the transmission line, but the triangle
is reversed in orientation to the opening of the T line. This
allows some of the wave to go through to the upper panel and some to
into the lower. This diffusion apparatus dose several things.
First it adds considerably more base. With the diffuser panels removed,
the speaker sounds very clean and precise and the base has more of a
point source quality. When they are added back there is a sense of much
more base coming from the speaker and the radial distribution of the
low frequencies sounds more realistic and contributes to the ability of
the speaker to disappear.
Furthermore, the diffuser panels slot loads the base lowering its
frequency, and acting as an acoustic lens, it stops the wave of low
frequency energy coming out of the transmission line from firing up at
the ceiling and bends it into a three hundred and sixty degree circle
coming out at ear level. Steve Deckert has explored radial sound
dispersion in some of his other speakers and he has concluded that the
lower and midrange frequencies are best served by this method while
imaging is preserved by the use of a point source tweeter.
With the front and side firing woofer and passives, the rear port, and
the omnidirectional dispersion pattern of the transmission line the
Mark IIs project a quasi radial wave front in the lower frequencies.
Because of its radial dispersion in the low frequencies, the Mark IIs
radiate base in multiple phase angles and can actually be plaid out of
phase without the expected cancellation. How can more than one phase
angle be good? Wouldn't there be lots of distortion? Actually all
real sound sources project their sound in quasi omnidirectional
dispersion patterns. In the low frequencies this improves the amount
and smoothness of the base and there is less awareness of the sound
coming from the speaker.
But with all that base firing into the delicately supported structure,
wouldn't the diffuser panels themselves vibrate and radiate out of
phase energy in all directions, mixing it with the primary wave from
the transmission line? Indeed it would, but Steve solves this problem
in a most ingenious way. The upper and lower panel are connected within
the aria of the tiptoes, by a threaded bolt that screws in to an nut
embedded in the lower one. By tightening this bolt, the upper and
lower panels are drawn closer and closer together applying a large
degree of torqued pressure on them, tightening them like the head of
drum. This not only completely stops the diffusion panels from
resonating, but if offers a degree of acoustic tuning where the actual
quality of the base can be adjusted from a livelier sound to one more
damped. It is very important to tighten this bolt more than you might
at first think. It takes a full turn and a half to eliminate the out of
phase resonance that is otherwise produced. The adage "do not over
tighten" does not apply here.
The same design for the cabinet of the Mark II is used in the other
High Definition Tower speaker that Decware produces which is designed
for full range single drivers such as Fostexs or Lowthers. This
model uses more internal damping, different passives and a different
tuning on the tubes.
The 8 inch Woofer is a Silver Flute. The cone material is made from
wool fiber which while dense and rigid enough to resist breakup
is very damped as far as cone resonance is concerned. Lightly tapping
on its surface is like tapping of a wool suit.
The tweeter is a transformerles ribbon design. Its narrow width and low
mass allow it to be extremely fast, more so even that some larger
designs with bigger magnets and larger ribbons. It images
extraordinarily well projecting a rock solid, holographically
delineated sound stage and when the cap brakes in, is extremely
natural. If you hear any roughness or edginess from this tweeter its
not the speaker but something in the source material or system.
The Mark IIs have an efficiency of 94dB making them ideal for low power
gear. On the other hand, they really respond to higher powered amps of
the 8 to 20 watt range creating a larger scale presentation and more
base and slap.
What about the sound?
My first impression in listening to the Mark IIs was that they were
extremely wide range and very smooth in their execution of the
frequency range. Some speakers sound best at certain frequencies and
show their limitations in others. The Mark IIs sound good everywhere in
the frequency sweep; wherever the music goes the speaker follows. This
offers a very full, flushed out sound which while being extremely well
delineated, never sounds thin.
The base from the Mark II is absolutely astounding! It is so
clean and tight and goes down so deep that it truly does not require a
sub woofer to sound complete. The one exception might be full
orchestral classical music where a sub adds a more realistic sense of
scale, especially in larger rooms. I find that a sub woofer adds to the
effect of home theater movie soundtracks. In some speakers the higher
frequencies float on a cloud of diffuses base energy but here the base
is part of the structure of the sound-shape. The holographic sonic
images have hard edged outlines and the base is contained in the image
and does not spill out into the surrounding space. If there is no base
in the score, there is no base from the speaker but when a really
demanding low frequency passage comes along, it is unbelievable how
much these speakers put out.
The tweeter and woofer blend extremely well are very similar in
character in the sense of being fast and clean.
The Mark IIs are a very analytical speaker but not in the sense of
being cold or aloof or intellectuality detached. With the right source
material they are utterly emotionally absorbing in their presentation.
They are like microscopes for examining the program material and the
component chain. In this capacity they can be rather critical of edgy
resonances in some digital components or recordings. You tend to
want to listen to your best recordings. They are very good for
evaluating other components in the chain articulately revealing subtle
changes in interconnects, amplifiers, cartridges and other devices.
These speakers are designed to play and sound exceptional when driven
by components made by Decware which can stand beside some of the best
sounding high end gear in the world. They are in no way limited to this
Decware electronics, however. This means that no mater how good your
equipment is, you will not outgrow these speakers as you upgrade, nor
will they ever become the week link in the audio component chain,
The Mark IIs excel in the near field where listening room coloration's
are secondary to the direct voice. In this set up they can play to full
capacity with amplifiers as small as two watts. Their imaging is so
good that they can actually produce sounds that seem to come from
behind you! I never heard that before in a two channel setup.
They sound excellent as well in the far field and in larger rooms, but
here a larger amplifier improves the presentation. The Mark IIs really
excel with jazz, acoustic instruments, string quartet, new age and
ethnic music. They love close miked material and they are suburb at
reproducing the human voice. In contrast, they coherently resolve the
acoustic space of live recordings in large rooms, halls or auditoriums.
In the near field with the right recordings they produce a rock solid,
four dimensional, holographic sound stage with very precise location of
sonic objects. There is lots of back wall and it is easy to visualize
details of the recording session such as which way the piano was
They disappear as well as any speaker I have heard. The ability of a
speaker to disappear results from the ability of the enclosure to not
radiate any sound of its own except for that which is coming from the
drives, passives and ports.
Does it play all of your records? well no. The Mark IIs are so
revealing and peers so deeply in to the deepest layers of the sound
pool, that if a recording sounds hard or edgy or has phase anomalies
from microphone misphasing or from the mix, this will be very apparent
and the listening session. Untamed digital sources and some video sound
is ruthlessly revealed for what they are and are not masked by
coloration's like some speakers present.
I must qualify these comments by saying that if you want to hear the
kind of sound I am describing, the speakers must be braced with small
dowels beneath the woofer and the passives extending to the rear corner
of the columns. These prevent the front and side panels from acting
like diaphragms, as the speaker go back and forth. These braces are
supposed to be standard in all factory made versions of the Mark IIs
but their have been cases where they were accidentally omitted.
By the way you can buy plans and blueprints for these speakers if you
or a friend are handy at woodworking and you can buy parts kits,
passives and diffuser panels to finish them off. .
So what do these speakers sound like? What does a mirror look
like? They sound exactly like the source material and the whole
component chain from front end to speaker wire and everything in
between. What did the turd say to the mirror? "You look like shit. " if
your house is in order and you have your electronic ducks in a row,
they you are going to love them. If not, you will hear perhaps for the
first time where your problems are.
If you like a speaker that is extremely fast, detailed and transparent
with superlative imaging and a wide and deep holographically defined
sound stage, this might be the one for you. If you want to really hear
what is going on in the recording and in your system, these speakers
will excel. It you want a speaker that will reveal the warmth and
beauty and emotional depths of music and allow you to loose yourself
and sooth your soul and let you get lost in that rock and role, you
should audition the High Definition Towers Mark II.
Zen Triode Monoblocks model SE84ZSM
Steve Burger Stereo SE 45/2AC amplifier with Sophia Princes 2.5
volt mesh-plate 300Bs.
Bruce Tilden 300B SE monoblocks with Sophia Princes mesh-
Prometheus transformer coupled passive line stage.
alternately, Select Zen Preamp model CSP2
Select Zen Phono stage model ZP3
Early Kuetsu Onyx MC cartridge recently refurbished with a new
cantilever and stylus by Vandenhul.
Tamura moving coil transformer
Eminent Technology air bareing tone arm with teflon tube.
Wisa air pump with a regulator and Herb Wolf surge tank.
Ultra high mass Final Audio Research (of Japan) turntable on a
Vibraplane Isolation table with a Verus direct drive motor from Teris
DSRII 1.0 Silver Interconnects from Decware.