So, I just received the extra thick silicone mat that I ordered from Amazon to place beneath the HomePod, so it dampens the vibrations of the HomePod against my metal windowsill ... and it made a noticeable difference. I still don't think it's better than B&O but it definitely improved the sound of the HomePod. So I just wanted to send a little note to those still paying attention to this thread:
In the HomePod teardown we can see that the "tweeters" are downward firing, and the sound comes out of the bottom edge, similar to how the woofer is directed out the top edge. The sound doesn't fire out of the sides of the HomePod as the X-ray images would suggest. So the material you have the HomePod sitting on (as well as the vibrations), directly affects the sound. Some recommend elevating the HomePod off the surface where it's sitting, using books or a stand. Others would go as far as putting the HomePod on a specialized acoustic foam base. But if you lack the space for either, or would not find them aesthetically appealing ... you can try a silicone mat.
The one that I got was the:
Cok White Food Grade Silicone Pastry Mat Extra Thick on Amazon for $9
I cut mine in half down the longest side, because I wanted to double it, with the vibrations dispersing along the length. But I imagine it would be equally effective if you cut it into fours, or a circular shape. Just make sure that the circle is at least one to three inches larger than the base of the HomePod (2 to 6 inches greater in diameter than the HomePod), so that the sound is being directed onto the mat, instead of it reflecting off the table or whatever it's resting on. Perhaps, you can use a small pot, to trace / cut along the edge. There are other and even cheaper silicone mats in various colors if the translucent white doesn't work for you. I merely got that one because I wanted to make sure it was thick enough, and wanted it in white.
But if you're getting a set of 2 or 4 in a different color, for the same price or less, then the thickness of an individual mat probably doesn't matter. Just make sure it's silicone.
Anyway, enjoy!
--- edit 2/19/18 ---
In hindsight, thickness does matter.
This past weekend I received black silicone mats for my mother's HomePod. Although I cut it into four layers, and that rivaled the two layers of the extra thick white silicone mat that I used before, it did not have the same effect. The thickness of the previous mat gave it more of jelly-like sensation when pressed or wiggling the HomePod on top. But the black mat was so thin that it became a solid, non-jiggly base. It was essentially four layers of rigid silicone, less able to absorb vibrations and more prone to transfer vibrations to the surface beneath. So check the thickness of the silicone mat you're ordering. And if necessary, order the extra thick silicone mat and just place another colored mat on top (if you'd prefer something other than white).
Also, please be careful with placing the silicone on wood. The silicone base of the HomePod is leaving circles on oiled wood. I am unsure if these silicone mats will have a similar effect, so to be on the safe side I put my mother's mat on top of paper towels cut to the same shape and size. A breathable barrier / separation should mitigate wood + silicone issues, so if it's on top of a table cloth or something it should be fine.
