By Gary Reber
I have been a long-time proponent of vibration isolation
materials and systems used in Widescreen Review reference
systems. For years I have used isolation platforms engineered
by Monster Cable and even air-type vacuum units to reduce
the sonic degradation cased by minute vibration.
Minus K Technology has developed and patented a passive
negative-stiffness vibration isolation tabletop platform
that significantly improves sonic performance over traditional
air tables and active vibration isolation methods. Dr. David
L. Platus is the inventor of negative-stiffness isolators,
and President and Founder of Minus K Technology, Inc.
This review encompasses the 25BM-8 with payload range from
10 to 30 pounds. The dimensions of the unit are 18 wide
x 20 deep x 4.6 high (in inches), with an approximate weight
of 40 pounds. The BM-8 series is also available in payload
pound weight ranges of 25 to 55, 50 to 105, 90 to 130, 125
to 155, and greater.
The design of the 25BM-8 is to support high-end turntables,
tube amplifiers, and optical disc players. Such internal
electronic components such as capacitors, resistors, and
transistors used in many audio systems are likewise sensitive
Vibration isolation in the playback process is crucial
to experiencing high-quality sound. Any external vibration,
no matter how slight, even someone walking near the turntable
or vibration from floor-mounted loudspeakers, is sensed
by the turntable's stylus movement. The sound waveforms
captured in the grooves with microscopic undulations affect
the sound being played back from the record. The turntable's
cartridge and stylus trace these minute
waveforms, play them back with very sensitive low voltages,
and convert them into an audio signal. This is how the sound
captured in the record grooves is reproduced. But this process
is extremely sensitive to movement and vibration. And the
human ear can detect movements of the stylus as small as
0.25 microns (250 nanometers, or 1/100,000 of an inch).
Why Vibration Isolation?
In an optical disc system, playback of the audio or video
from an optical disc can be interrupted by external vibrations
causing the datareading operation to mis-read on the optical
disc due to defocusing and mistracking of the laser pickup
head of the optical disc player system, whether a CD, DVD,
DVD-Audio, SA-CD, or Blu-ray Disc player. The optical
player system has a laser pickup head for reading data from
an optical disc; servo circuit for controlling the laser
pickup head; data processor for decoding the data from the
laser pickup head; memory circuit for temporary storage
of the output data from the data processor; microcontroller
for controlling operations of the servo circuit and the
data processor; and audio and, in the case of optical video
player, video reproduction components for reproducing the
output data from said data processing.
Vibrations that influence the sound reproduction in a home
theatre or stereo/surround system can occur in the range
of 2 Hz to 20 kHz. Vibration within this range can be caused
by a multitude of factors. Every structure is transmitting
noise. Within the home or building itself, the heating and
ventilation system, fans, pumps, and elevators are just
some of the mechanical devices that create vibration. Depending
on how far away the system is from these vibration sources,
and where in the structure the system is located-whether
on the third floor or in the basement, for example-will
determine how strongly the sound quality will be influenced.
External to the building, audio equipment can be influenced
by vibrations from adjacent road traffic, nearby construction,
loud noise from aircraft, and even wind and other weather
conditions that can cause movement and vibrations of the
These internal and external influences primarily cause
lower frequency vibrations, which are transmitted through
the structure, creating strong disturbances in sensitive,
high-end audio systems, making vibration isolation a necessity.
While sound quality is subjective, serious enthusiasts
tend to want to experience the full listening experience
without further coloration.
Turntable designers have long recognized the sonic quality
attributes of vibration and accordingly try to minimize
it in their turntable designs. Some premium turntables are
built with superb platter bearings to minimize rumble and
incorporate high-mass platters that are designed to increase
speed stability and reduce flutter. Designers will use exotic
materials to dampen vibrations without deadening the sound.
Tone arm geometry and vibration and damping isolation also
is important in turntable design. Quality turntables are
often factory-equipped with built-in vibration isolation
supporting the entire turntable. In such cases, additional
vibration isolation should not be used because two isolation
systems will interact, creating random resonances
that actually harm the audio quality.
But for the majority of high-end turntables that are manufactured
without factory-installed vibration isolation, the BM-8
vibration isolation platform is ideal. While there are air
systems and mechanical vibration isolation devices on the
market, they usually provide limited isolation performance,
especially in terms of horizontal isolation. The BM-8 platform
is designed to dissipate very low-resonance frequencies.
According to Jim McMahon, a technology writer for Minus
K Technology, several years ago, aware of the limitations
in even the best audiophile vibration isolators, The Audio
Archive began an extensive search for better vibration isolation
systems to facilitate the world-class sound reproduction
services that it provides to its clients, including some
of the world's leading archives, libraries, and record labels.
"Having thoroughly tested systems available to the
audio market and generally been unsatisfied, we then looked
outside of the audio world and conducted an in-depth search
of industrial vibration isolation systems," says Eric
Jacobs, President of The Audio Archive. "We learned
about negative-stiffness vibration isolation, which was
being used to eliminate vibrations in ultra-sensitive atomic
force microscopes, and in nanotechnology labs where objects
are literally built one molecule at a time. As we learned
more about negative-stiffness isolators, the more interesting
it seemed for audio vibration isolation."
"After extensive testing in our own audio laboratory,
which is outfitted with extremely sensitive and accurate
audio reproduction systems and measurement equipment, we
confirmed that negative-stiffness isolators are unrivaled
in vibration isolation for high-end audio reproduction,"
continues Jacobs. "Negative-stiffness isolators were
not just a little
bit better, they were significantly better. Whether with
turntables, tube electronics, CD transports or other audio
equipment, negative-stiffness isolators provided an unheard
of 0.7 Hz isolation performance vertical, and 1.5 Hz horizontal,
using a totally passive mechanical system-no air or electricity
required. We were not really expecting to find
a passive vibration isolation system that outperformed an
active system-that was a big, and very pleasant surprise
While we do not have the technical measurement equipment
to verify the findings of The Audio Archive, our experience
with the BM-8 is affirmative as to the sonic benefit of
this completely mechanical low-frequency vibration isolation
The BM-8 negative-stiffness isolators have the flexibility
to custom tailor resonant frequencies vertically to 0.7
Hz, and horizontally to 1.5 Hz (with some product models
as low as 0.7 Hz horizontally).
According to the company, vertical-motion isolation is
provided by a stiff spring that supports a weight load,
combined with a negative-stiffness mechanism. The net vertical
stiffness is made very low without affecting the static
load-supporting capability of the spring. Beam-columns connected
in series with the vertical-motion isolator provide horizontal-motion
isolation. A beam-column behaves as a spring combined with
a negative-stiffness mechanism. The result is a compact
passive isolator capable of very low vertical and horizontal
natural frequencies and very high internal structural frequencies.
According to McMahon, vibration transmissibility with negative-stiffness
isolators is substantially improved over air systems, which
can make vibration isolation problems worse since they have
a resonant frequency that can match that of floor vibrations.
Transmissibility is a measure of the vibrations that are
transmitted through the isolator relative to the input vibrations.
The negative-stiffness isolators, when adjusted to 0.5 Hz,
achieve 93 percent isolation efficiency at 2 Hz; 99 percent
at 5 Hz; and 99.7 percent at 10 Hz.
"Negative-stiffness isolators work with audio systems
in two ways, "continues Jacobs. "One, they cancel
out large vibrations, what we refer to as footfall. If a
turntable is set up on anything other than a concrete slab
floor or other large inert mass, then every time someone
walks in the vicinity of the turntable, the vibrations from
their footsteps are transmitted through the floor to the
support stand and into the turntable, and finally show up
in the recording. People will literally tiptoe around their
audio playback systems, but the playback process is so sensitive
that it will still pick up footsteps in the hallways or
rooms some distance away. And two, the negative-stiffness
isolators block out building vibrations in the higher audible
McMahon states, "transmissibility of negative-stiffness
isolators is also improved compared to active vibration
isolation systems. Also known as electronic force cancellation,
active isolation uses electronics to sense the motion, and
then adds forces electronically to effectively cancel out
or prevent it. Some active isolation systems can start isolating
as low as 0.7 Hz. But active systems have a limited dynamic
range that is easy to exceed, causing the isolator to go
into positive feedback and generate noise. Although active
isolation systems have fundamentally no resonance, their
transmissibility does not roll off as fast as negative-stiffness
McMahon says that "air tables will actually amplify,
instead of reduce vibrations in a typical range of 2 Hz
to 7 Hz because of the natural frequencies at which air
tables resonate. All isolators will amplify at their resonant
frequency, and then they will start isolating. So with air
tables, any vibration in that resonant frequency range could
not only fail to be attenuated, it could be amplified. In
this case, the low cycle perturbations will come straight
through to the audio system."
BM-8 negative-stiffness isolators resonate at 0.5 Hz. At
this frequency there is almost no energy present. McMahon
says that it would be very unusual to find a significant
vibration at 0.5 Hz. Vibrations with frequencies above 0.7
Hz (where negative-stiffness isolators begin isolating)
are rapidly attenuated with increase in frequency.
Another aspect that the BM-8 platform provides is the simplicity
of setup. One does not have to deal with compressed air
or electricity, which makes for a system that is simpler
to install, easier to set up, and more reliable to operate
and maintain over the long-term.
BM-8 negative-stiffness isolators do not require electricity
or compressed air. There are no motors, pumps, or chambers
and no maintenance because there is nothing to wear out.
They operate purely in a passive mechanical mode.
Of course, what really matters most is the sound-quality
performance that the BM-8 negative-stiffness isolator produces.
There is a sense of harmonic rightness. Instruments sound
much more like real instruments, and voices sound like they
are in a real acoustic space, with real air around them.
The ability to "see" clearly into the entire three-dimensional
soundstage is greatly enhanced. Improvements in rhythm and
pace are captivating. BM-8 negative-stiffness isolators
truly represent a significant advance in sound quality for
Wow! This is a phenomenal product that works as claimed!
Our worst-case challenge is to isolate external vibrations
from interfering with our turntable systems. Presently,
we use three reference turntables: the Linn Sondek LP12
with Linn Radikal DC motor, motor control unit and power
supply and Ekos SE tonearm with an Akiva moving-coil cartridge,
and the Thorens TD 350 and Thorens TD 2035. The Linn setup
is in Widescreen Review's reference system and the Thorens
in a secondary, Class A system. Both setups are prone to
vibration within a frame wood structure and concrete slab
foundation. In fact, one must walk with extreme care to
not cause the stylus to jump grooves. Thus, this was a perfect
test for the BM-8.
In both locations, with the Linn and Thorens supported
by the BM-8, the stylus jump condition was completely eliminated!
But the real benefit was the immediate sense of openness
to the sound that was obviously previously masked by vibration
and the seemingly complete absence of rumble and acoustic
feedback. The BM-8 has no competition in this regard and
is a MUST HAVE component in an enthusiast's system.
We also positioned the OPPO BDP-95 Universal 3D Blu-ray
Disc Player on the BM-8. While the sonic improvement was
not as dramatic an improvement compared to the turntable
performance, still a detectable nuanced clarity in the sound
resulted. The BM-8 is simply an amazing vibration platform
product that provides an impressive degree of isolation
from vibration distortions, resulting is definitive sonic