Sound Vibration Isolation
to High-End Clients
integrators selling high-end audio systems or
audiophiles, explaining vibration isolation can open up
a potential upselling opportunity for vibration isolators
turntables, tube electronics or CD players.
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 structure.
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 isolation in the playback process is crucial
to experiencing 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 turntables 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 turntables
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.
Newly developed negative stiffness isolators for turntables,
tube electronics, CD transports or other audio equipment
provide 0.5 Hz isolation performance vertical, and 1.5
Hz horizontal, using a totally passive mechanical system.
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,"
Reducing Turntable Flutter
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
"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
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 worlds 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
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
Developed and patented by Minus K Technology, Inc., negative-stiffness
isolators provide a unique capability to the field of audio
fidelity. The companys employ a completely mechanical concept
in low-frequency vibration isolation.
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 0.7 Hz, and horizontally to 1.5 Hz (with some
products as low as 0.7 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
What is very advantageous about negative-stiffness isolators
is that they achieve a high level of isolation in multiple directions,
Jacobs says. Not just vertically, which is very important
for audio systems to isolate against footfall, but also in all
horizontal directions. The horizontal direction is often overlooked
because horizontal building vibrations that are transmitted
to the turntable are less obvious.
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
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.
version of this article