I use a source of information that has been a reference point within the HiFi community for many years, it is used both by Professional and Amateurs to extract information.
I have used the resourcefulness of the producer of the information further and they have received materials I am using and New to them for testing.
I have made it one of my goals to become quite familiar with materials used for Plinths that are described as having optimum damping, and the result is that I have become very impressed, and have moved away from the Massey Plinth Designs as the mounting methods.
I am keen to maintain the experiences had from being demonstrated the materials with a obove optimum damping measurement, hence my having access to Densified Wood and acquiring a supply of Permali and Panzerholz which carries a considerable expense.
The Polybentonite Resin is in my view a Massey Plinth Design, when produced it has very high measurements compared to other Massey Materials, the Resin measures above optimal damping, but the sonic is different from Densified Wood.
To put a further perspective on the above Materials that are with High Intrinsic Damping, when compared to other regularly mentioned materials such as Slate 0.017 and Aluminium 0.004 it can be seen the divide in the measurements are quite vast and the stone and metal fall way short of optimum damping.
The following is the words of the technician who produces the testing and recording of a wide variety of materials:
When a sample of material is struck, it vibrates, the frequencies at which it vibrates is dependent on its dimensions, its stiffness (Young's modulus), density and how much it deforms when compressed (Poisson ratio).
How long it vibrates for is a function of its damping factor. Have a look at the trace below. My three axis accelerometer was taped to this material, and struck. The sound was captured on a computer, and recorded using Audacity software. You will notice the rate of decay is quite well defined, fast at first, and becoming asymptotic towards the end. The damping factor is calculated by looking at successive peaks, and measuring their heights from the zero line. This gives the 'log decrement', and from this the damping factor is calculated.
The damping factor, Greek letter eta, n , is a dimensionless number which represents the amount of intrinsic damping a material has. The property is like density, it is irrespective of other properties, including dimensions.
A material with a damping factor of 0.07, or above, is said to be damping, above 0.1 and it is a good damping material, and as the damping factor is twice the ratio of its damping compared to critical damping, a value of 2 represents critical damping. Most materials encountered in hifi products have a damping factor between 0.01 (or below) and about 0.2, so they are well below the critical damping figure.
The trace below shows how a slate tile rings for about a second, when struck, (and they say it makes a good plinth material). Its damping factor is 0.017, very poor! Amplitude up the y axis, time (seconds) on the x axis.