- September 2012
The below article was sent to Inner-Audio by Zebra Communications.
Zebra Communications specializes exclusively in the development
and execution of feature story PR campaigns for industrial and
high-tech companies. So while reading the article, please, take
into account that it does not represent standard journalistic
content. It is provided by the manufacturer and its ground crew.
Minus K vibration platform
But we found the article interesting and informative enough
to be included in the NEWS section, especially for those turntable
lovers who have not yet considered isolating their analogue
source from vibrations coming from outside the system. Another
encouraging factor is that MinusK products and technology are
used not just in audiophilia but in microscopy, micro-hardness
testing, optical systems, spacecraft testing, biology/neuroscience
by Jim McMahon
The impact of external vibrations plays a critical role
in the sound quality produced by turntables and tube amps within
high-end audio systems. Capacitors, resistors, transistors and
other electronic components used in many audio systems are likewise
sensitive to vibration.
|Vibration isolation in the playback process is crucial
to experiencing a high-quality audio. Any external vibration,
no matter how slight, even someone walking near the turntable
or vibration from floor-mounted speakers, is sensed by
the turntable's stylus and affects the sound being played
back from the record.
With recorded discs, sound waveforms are captured in the
disc grooves with microscopic undulations. The turntable's
cartridge and stylus trace these minute wave forms, 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.
Vibrations in the range of 2 Hertz (Hz) to 20,000 Hz will
influence the sound reproduction in audio systems. 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 audio system is from these vibration sources, and
where in the structure the audio 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
Negative-stiffness vibration isolation has significantly
improved performance over traditional air tables and
active vibration isolation methods, providing improved
sound quality for audiophiles with high-end sound systems.
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
To put this into perspective, a stereo LP groove is 0.0028 inches
wide (70 microns) and your typical sheet of 20-lb printer paper
is 0.0038 inches thick. The human ear can detect movements of
the stylus as small as 0.25 microns (250 nanometers, or 1/100,000
of an inch). It does not take much vibration to affect the sound.
"People who care about sound quality -- such as audiophiles,
musicians and recording engineers -- can have very strong,
subjective preferences about what constitutes good sound,"
says Eric Jacobs, President of The Audio Archive, which provides
consulting and audio transfer services to digitize, restore
and preserve sound recordings from a wide array of current
and obsolete analog media formats. "Some people like
resonances in their system that emphasize particular frequencies,
so they will insist, for example, that their equipment must
rest on a maple wood support because it has a certain resonance
to it that makes the sound more appealing to them. Others,
particularly those engaged in audio restoration or archival
work, want to experience sound as the mastering or recording
engineer intended it, without further coloration."
"Most manufacturers of high-end turntables
recognize that external vibration is a problem, and will go
to great lengths to minimize it in their turntable designs,"
continues Jacobs. "Quality turntables, for example, are
built with superb platter bearings to minimize rumble. Some
turntables can cost as much as $100,000 and use air or magnetic
bearings, and other sophisticated approaches. They often incorporate
high-mass platters that are designed to increase speed stability
and reduce flutter. They might use exotic materials to dampen
vibrations without deadening the sound. Tone arms have their
own set of vibration and resonance characteristics which manufacturers
attempt to isolate from the audible frequencies through geometry,
localized vibration isolation and damping. Turntable designers
go through this elaborate process to try and eliminate vibration
throughout the entire turntable playback structure."
High-end turntables are also sometimes factory-equipped with
built-in vibration isolation supporting the entire turntable.
These turntables are poor candidates for additional vibration
isolation because resting an isolator built into a turntable
upon an external isolator causes the two isolation systems
to 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, third-party
air-based vibration isolators have become a popular accessory.
These systems typically have a vibrating power pump to supply
air, with a tank that holds the pressurized air and delivers
steady pressure to the isolator. The noisy pump is usually
located outside of the room that has the audio equipment,
and the air hoses are run over to the tank and isolating platform.
"Air systems are usually a less than optimal set-up,"
explains Jacobs. "They do achieve some isolation, but
we have found that like most of the mechanical audiophile
vibration isolation devices, they provide limited isolation
performance. They do isolate some -- usually in one dimension
(vertically) with limited horizontal isolation -- but they
do not isolate to the extent that is really needed at very
low resonance frequencies."
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 Jacobs. "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
(*Note that for an isolation system with a 0.5 Hz natural
frequency, isolation begins at 0.7 Hz and improves with increase
in the vibration frequency. The natural frequency is more
commonly used to describe the system performance.)
Negative-Stiffness Vibration Isolation
Negative-stiffness vibration isolation has significantly improved
performance over traditional air tables and active vibration
isolation methods, providing improved sound quality for audiophiles
with high-end sound systems. Developed and patented by Minus
K Technology, Inc., negative-stiffness isolators provide a
unique capability to the field of audio fidelity. They employ
a completely mechanical concept in low-frequency vibration
Where air isolation systems deliver limited isolation vertically
and very little isolation horizontally, negative-stiffness
isolators have the flexibility of custom tailoring resonant
frequencies vertically to 0.5 Hz, and horizontally to 1.5
Hz (with some products as low as 0.5 Hz horizontally).
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.
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
"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 frequencies."
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 isolators.
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.
Negative-stiffness isolators resonate at 0.5 Hz. At this
frequency there is almost no energy present. 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.
Simpler is Better
If audio systems can be isolated from vibration without having
to deal with compressed air or electricity, then it makes for
a system that is simpler to install, easier to set-up, and more
reliable to operate and maintain over the long-term.
For example, because active system isolators run on electricity
they can be negatively influenced by problems of electronic
dysfunction and power modulations. And air tables need a constant
supply of compressed air, which requires a compressor to be
located near the audio set-up. Compressors are sources of both
mechanical and acoustic noise and have the potential to be part
of the problem rather than the solution. Not the best choice
from a vibration elimination standpoint.
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.
"These isolators provide a great deal of flexibility,"
says Jacobs. "For example, it is possible to configure
a state-of-the-art mobile turntable that can be moved around
a facility without having to worry about electrical power
and pumps, or whether it is located in the basement or on
the second floor. This was an unexpected bonus, and has helped
increase the flexibility of our studio."
"And then there is the sound, which is what really matters
most to our clients," continues Jacobs. "With negative-stiffness
isolators 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. Negative-stiffness isolators truly represent
a significant advance in sound quality for high-end audio."
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