Theories and opinions abound on vibration control for audio equipment: Is vibration control needed? If so, which products work best? Let’s start with how vibration affects sound quality.
Loudspeakers — To reproduce sound from a source, a moving component in the loudspeaker (a dynamic driver, a ribbon, an electrostatic panel) must vibrate and cause change in air pressure. “Good” vibrations replicate the recorded signals. But other characteristics of the loudspeaker (cabinet resonance, crossover components, driver specifications) may introduce unwanted vibrations.
Vibrations from loudspeakers are transmitted elsewhere through the air or to the floor through the stands, causing more vibrations in the listening environment. The aggregate effect can interfere with the listener’s perception of certain frequencies and processing of complex harmonics. It can also result in indirect reflections of low bass frequencies.
Other Audio Components — Vibration can create electro-magnetic fields around wires inside an audio component. It can cause the transport mechanism in a CD player to shake. In an analog setup, it can move the stylus in the record grooves in unexpected ways.
There are many vibration control approaches on the market. Some seek to isolate the components from vibrations in the environment while others try to channel vibration away from the components. The material used ranges from soft iso-elastomers to hard metallic cones or balls. To evaluate the effectiveness of a solution, we need to establish how to measure the results.
Accelerometers — Applying a vibration control device to a component should result in less vibration. The easiest way to quantify the difference is to compare signals from identical accelerometers, one mounted on the component with the treatment, the other on an identical component without the treatment. This test may be impractical because it requires two identical components operating under identical conditions except for the vibration control device.
An alternative way to quantify the difference is to mount one of the accelerometers on the component, the other on the shelf directly under the vibration control device. If the device does anything to the vibration, the accelerometer on the component should show less vibration than the one on the shelf.
A/B Listening Tests — The effect of reduced vibration on the sound quality should be verified in blind listening tests with multiple test subjects.
Vibration Control Methods
The spike-based method encompasses any variety of feet used to support audio equipment.
Most audio components have rubber feet. Regardless of the material and durometer of the feet, their purpose is to cushion the chassis and lessen the vibration that can channel up from the rack shelf to the component.
Most speakers come with spikes that are typically made of metal (steel, aluminum, copper, bronze, etc.). Spikes couple the speaker cabinet to the floor and prevent the cabinet from moving with the drivers thus smearing the sound. They are also meant to channel vibration away from the cabinet, but this notion is often challenged.
Suspension-based devices work like shock absorbers on cars. The vibration transfer is reduced in both directions, to and from the component in question. The suspension can be air-based, spring-based, or both. The stiffness of the suspension can be tuned to match the weight of the component to optimize performance.
Different materials have different resonances and affect vibration differently. Judicious use of layers of different material to provide a base for components can reduce vibration across the frequency spectrum.
|Spikes||• Provide a firmer base for the speaker or component.|
• Reduce vibration transfer by isolating the bottom of the speaker cabinet or component chassis from the surface it rests on.
|• Even when the difference in vibration can be measured, improvements tend to be small.|
• The spike material will have its own resonance that can affect the final result.
|Suspension||• Can be tuned to suit the application and optimize performance. Reduction in vibration can be measured as the suspension is tuned.||• Can be difficult to balance and level.|
• When not configured properly, can cause the supported component to be unstable.
|Constrained-Layer Damping||• Simple to design and manufacture, once the combination of materials and construction technique has been selected.||• The materials used may have their own resonance that can affect results, depending on the applications.|
• The thickness of the base adds to the overall height of the component.
Theories Versus Practices
Although spikes are meant to channel vibration away from the speaker cabinet to the floor, tests using accelerometers have shown similar vibration between the accelerometer the floor and the one on the cabinet. This may be because the spike transmits vibration in both directions.
We find that a suspension-based approach works for most audio components. Gingko Audio’s Cloud platform combines the suspension provided by rubber balls with the rotational movement of the balls on dimples in the platform base. The Cloud platform works great for turntables and similar components. But it does not work at all for speakers because it wobbles under the load, especially when the speaker plays music.
A constrained-layer approach requires careful design, testing, and measurements to ensure positive results across different components. As an example, Gingko Audio’s ARCH is a multilayered band in a curved shape that acts as a leaf spring, turning vertical vibration energy into horizontal vectors under load. The choice of materials and construction technique must take into account different component weights.
Theories and measurements aside, if the listener can hear the effects of a vibration control device and concludes that they yield more enjoyment of the music, then it is the “best” device for his/her application. Not everything works well in all situations, so by definition, the “cost-effective” device is one you can return and get your money back if you are not satisfied with its performance.
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