I almost forgot about the last part of Gsm18439 question: And how/why do they work?
Some years ago, I attended a lecture given by a chemical engineer. The lecture was given to prospective chemical engineering students and it was about the different fields that a chemical engineer can be involved in as a professional.
Among other topics, he talked about the field of vibration control in the automobile industry. He showed two balls of some viscoelastic material of approximately 3/4" in diameter. Both balls were made from the same formula, but one of them had a different molecular configuration in the formula. The viscoelastic material was at the time being developed to be used in the design of car bumpers.
He dropped both balls to the floor. One ball bounced, the other one didn't. This was a memorable experience as I right away said to myself: I wonder how this would impact vibration control in the audio field.
The idea presented was that this material was designed to absorb a great amount of the energy generated in a car collision, if the bumper was involved. Hence transferring less of that energy to the rest of the structure of the vehicle. Another application was, he said, that it could also be used as a vibration control throughout the vehicle in order to prevent road vibrations and airborne vibrations from reaching the cabin.
I for some time searched into vibration control materials being used in the automobile industry. I found that it is a very popular field given the fact the sales of luxury vehicles was increasing. Eventually, I found that viscoelastic materials are greatly responsible for the quiet ride you can experience in most luxury cars in the market today.
I then started to look at the different companies that were using the same approach to control vibration in audio equipment. I found that HRS, EquaRack and Silent Running Audio were using viscoelastic materials in their vibration control designs.
All three companies take into account the weight of the audio equipment that requires vibration control. EquaRack and Silent Running Audio also take into account the weight distribution so that their devices can be optimized independently according the the weight balance of the audio equipment.
HRS platforms (I have one under my turntable), because they are mass-loaded, are less sensitive to weight imbalance, assuming that the equipment in isolation is within certain weight range. They have developed a viscoelastic disc and plate that can also dampen mechanical vibrations and airborne vibrations.
SRA platforms are custom designed for the exact equipment weight and weight distribution they are supposed to hold and, as far as I know, do not address airborne and mechanical vibrations, but only external mechanical vibration coming to the audio equipment.
The Equa Footer has an aluminum disc with a viscoelastic layer at the base. This disc holds various viscoelastic pellets on top. Each pellet can support up to three pounds. Then there is a top aluminum disc with another viscoelastic layer on its upper area. The pellets are sandwiched between the two aluminum discs.
The idea behind the Equa footers is that you weight your equipment with a home scale to determine the weight and weight distribution of your audio equipment. The wight distribution is for determining how many pellets each foot should hold in order to have the footers optimized for the weight balance of a particular equipment. This design also allows you to reconfigure the footers in case of an equipment change or upgrade.
Among the three products I mentioned, the Equa footer is the only design that tackles mechanical, airborne, and structure vibrations with a single device. Mechanical vibrations from the floor onto the audio rack is handled first by the viscoelastic layer at the bottom of the lower disc. Any vibration not being absorbed by the first viscoelastic layer is handled by the aluminum discs and the pellets. The pellets also contribute to absorbing horizontal vibration. The upper disc with its viscoelastic layer on top handles vibrations generated by the equipment itself, either self-generated or as a result of airborne energy producing a "ringing" effect on the exposed surfaces of the equipment, which is usually metal for most audio equipment in the market.
Let's keep in mind that vibration in most cases exhibits a random behavioral pattern. It's not just horizontal or vertical. Because of this, the vibration control device must be able to channel and absorb vibration energy from all directions. The device or platform must also be able to absorb vibration operating in a wide frequency range.
The HRS and SRA platforms, and the Equa footers are very clever designs. Only lots of research can yield solutions like these. I'm very satisfied with the my HRS platform and the Equa footers. The price, flexibility and performance of the Equa footers are hard to beat IMHO.
This turned out to be very long and I want to apologize for taking so much space.
Regards,
iSanchez,
