The Auckland Audio Society's February 23rd meeting hosted Richard Krebs who talked about his view of earthing v's the more typical isolating (e.g. using sobothane pucks) of audio gear. This is a summary of his address and demonstration.

Richard's thesis is that the most troublesome noises emanate from the equipment itself (not from foot-fall or resonances originating from the speakers) and hence should be mechanically earthed direct to ground, not isolated from external sources by for example sorbothane. Richard has a NZ certificate in engineering (his commercial business specialises in advanced hydraulics) and he is responsible for designing the OMA K3 and K5 turntables. He firmly believes in single point grounding, which parallels with conventional electrical star earthing. His recommendation for the latter is to use a single outlet for all equipment and if you use a junction box, plug the equipment with the greatest current draw closest to the power cord.

So the key to understanding his approach is the understanding that power transformers, diodes, capacitors and resistors not to mention ‘noisy’ CD transports and turntable motors are the source of the problem. (Suspended belt and rim driven turntables c.f. to direct drive turntables and suspended wooden floors may be an exception to the rule?) Speakers too he believes should be earthed (in practice most partially are through the use of spikes) because of the almost inevitable panel resonances that they have. What follows is a summary of his talk.

Richard first demonstrated his approach by using two SHIDA isolation platforms, one of which was used as purchased with the correct number of S55 elastomer isolation pucks inside for the weight of the CD player on it. It is critical when using this platform that the weight is supported by the correct number of pucks as per the manufacturer-provided table. Too much weight or too little weight results in diminished isolation. With the correct number of pucks, no external vibrations above 20hz can get through. The pucks from the second SHIDA platform were removed and replaced with dry silica sand, which it should be noted is non-magnetic. (Just as well, because Richard also puts some of this on inside of his amplifiers which then sit in a sand-tray). Richard recommends a minimum depth of 75mm of sand which is more than the SHIDA could contain. The normal hardwood tops of the platforms (Richard favours very dense bamboo ply) then stood respectively on either the pucks or the silica sand with no other changes. The consensus of the meeting was that the earthed platform provided a clearer sound. But that is not all.

As noted above single point isolation is the goal, but this in practice is impossible; the whole ensemble would simply fall over. To correct this two other ‘points’ are added, each of these using a different material. For example, Richard uses an oil-impregnated zinc block (roughly 70 mm square ) with a drilled hole into which a chrome steel ball bearing for the main support was placed, with the other two zinc blocks containing a copper / brass ball bearing and carrying minimal weight. The chrome steel topped zinc block should be placed under the most sensitive part of the device (the inputs of the CD player in his demonstration) or the weightiest or noisiest part (almost necessarily the power transformer in an amplifier). Richard noted that the cases of most of our equipment is flimsy and resonant, and so a lead weight or something similar on the top can also help; burying the bottom plate in sand as he does is another option! He also noted that most equipment racks and tables have four feet which makes them nigh impossible to level unlike a 3-foot stool. (Small pieces of lead flashing were put under the four spikes of the original SHIDA table – soft plastic pads are provided with it to achieve the same effect - and weight applied to prevent potential ‘chattering’). Richard thought that all equipment – including speakers which because of their typical height and weight require four zinc blocks, one having a chrome steel ball bearing and the other three having copper – should be locally grounded e.g. through a 75mm silica sandpit.

Richard also believes that critical mechanical damping returns the vibrating device to stasis the most rapidly in comparison to for example sobothane which takes time to recover. (I wondered whether the SHIDA platform with the appropriate number of pucks could be considered inversely to be critically isolated or damped?) Over-dampening leads to a slow and boring sound whilst under-dampening leads to a fast

but shouty sound. Three-point dampening using different materials (one ‘fast’ foot and two ‘slow’ feet) is more likely to result in critical dampening and greater clarity. Multiple routes to ground (e.g. in a typical rigid equipment table) results in phase and therefor time-smearing. Richard thinks that having multiple layers of grounding / propagation as for example in his oil damped zinc blocks, chrome steel/ copper blocks (soft wood in addition to a hard grounding material is another option) is essential.

Richard’s talk led to some critical thinking by attendees with the first issue inevitably whether we have focussed too much on external sources of noise rather than the true source, which is from the equipment itself. Whether to isolate or earth our equipment and how to best do this, is the question. Thank you Richard.

Edited March 7Mar 7 by Peter 0 C

Very interesting, thanks for posting.

Two thoughts from me:

1) The word "grounding" is problematic, because the same word is commonly used in the electrical sense. ie. electrically connected to earth. This can cause confusion.

2) The other point is the word "dampening", which means to make damp with moisture, whereas the word that means to decrease mechanical vibrations is "dampen".

Probably seems a bit nit-picky, but technical explanations need to be precise and use the correct technical terms.

Edited March 5Mar 5 by bob_m_54