Hi Tom,
Thank you for your comments. It seems that I must have not been as clear as I intended. Please allow to explain again in more detail.
The vibration control system which I designed and described utilizes a high-mass, high-absorption platform directly under the speaker cabinet. The best implementation of this type of platform is the Big Rock which I created in 1985 and for which I was granted a patent in 1993. The Big Rock uses a quantity of sand to absorb and dissipate vibration from the components chassis or speaker cabinet that is placed on top of it. Virtually all sandbox type platforms which are discussed on the internet are copies of my original design. When used under a loudspeaker the entire bottom panel of the speaker cabinet is in intimate contact with the Plinth (top plate) of the Big Rock for maximum transfer of unwanted energy. Sand has the ability to absorb a huge amount of mechanical energy (vibration) by quickly and efficiently converting this destructive energy into more benign form thermal energy (heat). As we know from the laws of physics; ENERGY CAN NEVER BE DESTROYED IT CAN ONLY CHANGE FORM. I have used bold type because of the importance of this concept in our endeavor to control vibration. It encompasses every aspect of how vibration enters and contaminates the signal which flows through our audio and home theater systems and must be at the forefront of our thoughts as we design a vibration control system to most effectively address this problem.
There are multiple sources and multiple forms of vibration. The sources of vibration are:
1) Floor-borne vibration which includes; Vibration that is directly-coupled from the loudspeaker which transfers through the floor and up through the component stand into the feet of the component. Air conditioning and heating systems which send low frequency vibration through the buildings structure. Exterior traffic (trucks, busses, cars, freeways!, subways, trains, airplanes, etc.) which sends very low frequency energy up through the floor and into the systems components. Natural geological seismic activity which sends extremely low frequency energy up through the entire building which contaminates the systems components.
2) Air-borne vibration sent directly from the loudspeaker drivers through the air towards the chassis of the component (this also includes energy reflected off the walls, ceiling and floor).
3) Internally-generated vibration that is created within the chassis of the component by spinning motors, humming transformers and cooling fans.
Not all of these sources produce the same type of vibration. The vibration from the speakers as well as air-borne vibration are related to musical signal flowing through the system. Their sonic degradation to the system will be similar to a ghost image on a television. It will be vaguely similar but different in spectral content and have out of sync timing as compared to the original signal. The primary sonic symptoms of this type of vibration are a shift in tonal balance (typically excessive brightness and bloated bass), diminished transparency (detail and clarity) as well as degraded pace and rhythm. The secondary sonic symptoms include exaggerated dynamics for certain frequency groups and diminished dynamics for other frequency groups plus an alteration of imaging and soundstaging (either smaller than what is contained in the recording or an exaggerated version of what is contained in the recording).
The vibration from the other sources is not related to the musical signal which is playing through the audio system. The sonic symptoms of this type of vibration are diminished dynamics due to an increase in the noise floor and a general lack of coherence of the musical spectrum of each individual instrument and diminished coherence of the musical ensemble.
Mechanical vibration is a displacement of a physical body from its at rest position in reaction to the energy wave presented from the vibrating source. Some of these waves are vertically oriented (floor-borne vibration sourced from the loudspeakers and air conditioning/heating systems plus sympathetic vibration of the shelf directly under the component as it is excited by air-borne vibration) and some of the waves are horizontally oriented (air-borne vibration and the majority of the vibration sourced from exterior traffic and geological seismic activity). Furthermore, some of these waves are a combination of both. In addition, the horizontally oriented waves do not only come from one direction they enter the system from a number of different vectors.
Clearly, comprehensively addressing vibration will take much more than simply placing a few feet or a single slab of material under a component. Any vibration control product that does not take into account all of the above sources and forms of vibration will not adequately address the problem. In addition, it is critical that the vibration control device does not add any new problems that will affect the signal flowing through the component.
The beauty of the Big Rock as a vibration control device is in its elegance and straightforward effectiveness. When the Big Rock is implemented as I recommend it has very high mass and is extremely absorptive yet is not significantly compliant. A speaker cabinet placed on the Big Rocks Plinth will not rock back and forth in reaction to the speakers drivers while a significant amount of unwanted stored energy will transfer out of the speaker cabinet and be dissipated in the sand bed the exit strategy if you will. In addition, a Little Rock pod (a very high mass damping and absorption pod) placed on top of the cabinet will damp excessive resonance in the speaker cabinet, absorb unwanted stored energy as well as causing the speaker to be planted more firmly to the top of the Big Rock making the transfer of unwanted energy even more efficient. Our upper model Little Rocks also incorporate EMI (electro-magnetic interference) shielding which is important when they are used with electronic components.
For ultimate effectiveness the Big Rock / speaker/ Little Rock should be placed atop one of our multi-cell Air Mass pneumatic mounts which will effectively decouple all of the above from the floor. This will stop the speakers mechanical energy from entering the floor and traveling towards the systems components. The speaker is also protected from the other floor-borne sources of vibration which can compromise its performance. When an electronic component is placed within an Air Mass / Big Rock / Little Rock combination it too is protected from floor-borne vibration as well as being critically damped from above and below while it is simultaneously in intimate contact with high absorption reservoirs from above and below which significantly minimizes the effects of air-borne and internally generated vibration.
This vibration control system places the highly absorptive energy reservoirs in direct and intimate contact with the speaker or component. The transfer of energy from the component and its conversion to benign thermal energy is immediate and very efficient without any intermediate structures.
Another virtue of the Air Mass / Big Rock / Little Rock combination is that it is very resistant to horizontal displacement because of its extremely high mass. Is also has a resonant frequency in the horizontal plane as low as 2.5 Hz and 1.5 Hz in the vertical plane.
Vibration control devices that employ rigid coupling as the principal method of execution require the mechanical energy to go through a number of structures before it can leave the locale of the components. They typically claim to route the energy into the floor but unfortunately the floor does not readily dissipate mechanical vibration. If it did, the vibration would not be entering the components feet in the first place and we wouldn't even be discussing the need for vibration control. Moreover, the floor is one of the primary SOURCES of the destructive vibration!
Merely placing a vibration control device under a component does not address air-borne or internally generated vibration. Even if the device below the component does route some unwanted energy out of the component it can only do so AFTER the vibration and resonance have had time to degrade the signal flowing through the component. How far does the horse have to be out of the barn before the door is closed? No amount of draining after the fact will restore the signal to its original, pristine state.
It is also extremely critical that the vibration control device not add any of its own degradations to the signal flowing through the component. Employing materials that ring (metal, glass, stone, etc.) or materials that are resonant (wood, acrylic, etc.) will virtually guarantee that they will affect the signal and restrict the ability of the system to faithfully reproduce what is contained in the recording.
The fact is that making ANY change to a system will result in a change in the way that system reproduces sound. Even moving the location of the equipment rack by just a few inches in any direction will alter how the various pressure zones in the room will interact with the various resonance frequencies and resonance characteristics of the equipment resulting in change in the sound of the system. Moreover, changing the support under a component will usually cause a significant change in performance. Most audiophiles simply listen to the difference and try to decide if it is "better" or not. There is some merit in that method but I believe that controlling vibration should have the goal of allowing the system to more faithfully reproduce the sound of the original musical instrument as it has been captured in the recording. That can only be accomplished when contaminating vibration is minimized as much as possible in the audio or home theater system.
In many cases, simply adding or changing a vibration control device will not give the full indication of whether the change brings the system closer to my stated goal or not. Trying to balance off or tune resonances within a system may be an interesting pursuit, it will not allow that system to faithfully reproduce the sound of the instrument as it has been captured in the recording. In some cases when contaminating vibration is eliminated it will more clearly expose the true nature of the system by letting one hear all of the previous choices of components, set up and applied accessories. If those choices were made while the system was being plagued by destructive vibration (which describes virtually all systems until a comprehensively designed vibration control system is employed) the devices and set up already in place may no longer be appropriate once the problem of vibration eliminated. If the change is simply compensating for a deficiency or problem elsewhere in the system the listener may reach an erroneous conclusion about the efficacy of the change.
Tom, please let me know if you have any questions.
Best Regards,
Barry
