According to Yamamoto and 6moons, ebony footers under spikes make a positive difference. http://www.6moons.com/audioreviews/yamamoto3/footers.html
Can the density of the wood under the spikes actually produce an audible difference? I am using Cain & Cain Abbys (the same speakers under which the PB-10s were placed for this review) so I may have to try these out.
PB-10s as Speaker Footers
I've been using the PB-10s on my Cain & Cain Abbys for nearly 2 years. Initially I was looking for a cost-effective solution to protect my wood floors from the Abbys spikes. The least expensive solution which oddly enough turned out to be currency -- eight shiny pennies -- served this purpose but actually didn't work out for a number of reasons. With Lincoln's flattened profile providing the resting place for the Abby's spikes, any minor adjustment meant one or more of the pennies slipped from their spots and re-positioning became a real drag. I came across the Yamamoto footers on the Venus HiFi website and for $35 for four ebony footers, I thought it was worth a try. I've heard a number of positive reports on the effects of ebony including its use in Herbies tube dampers and Mpingo devices so I ordered two pair from Brian Bowdle, the US importer of the Yamamoto line.
When the PB-10s arrived, I placed them under the Abbys and there they've remained for these past 2 years. Why? Beyond the fact that they make positioning a breeze, protect my floors and stay put, I prefer the sound of the Abbys with the ebony footers. Compared to the pennies (nickels, dimes and quarters too) the PB-10 ebony imparts a tighter, fuller bottom end, improved resolution and I'd even go as far as saying the African ebony gives the Abbys a richer tonal flavor. I also prefer the PB-10s to the Abbys spikes going directly into my wood floors. So does my wife.