Down Firing Speaker Ports: Carpet vs Hard Surface

Calling for thoughts, experience, and/or technical of speaker port theory....

I have had, and still own several speaker models and subwoofers utilizing downward firing ports. In most cases, I have always had carpet to content with, and even though all of my speakers have had spikes, I've wondered on the ideal setup scenario. I have tried the following:

1) Granite tiles under the speaker spikes to get the speakers up and allow better air flow. 1a) tiles split to allow the port air to hit carpet. 1b) Tiles together to allow the ported air to hit a reflective surface., or 2) spikes into the carpet which lowers the speaker toward the carpet and somewhat lessons air flow.

The best results seems to be with the tiles only partially gapped.

Any Ported Speaker theorists out there?

Thanks in advance.
I have ProAc Studio 140's and have put large spikes (2 inches) on them and they sit on granite slabs. The spikes rest on shoes. Sound was greatly improved from the spikes just sitting on the carpet. The large spikes make a difference.
I have some ProAc Studio 148s on order and had the same question.  I hope to use some Soundocity SEV9 outriggers either with or without the plinth.

@tiger, did you get extra large / long spikes or just use the ones that were included?  TIA
I think the answer is to mount the mains to the ceiling upside down and raise your listening spot somehow…ropes? A table with a chair glued to it? Listen standing? You’re welcome.
I use Auralex Subdude  platforms under my bottom ported Ohm 100s.   These are available on Amazon and will not break the bank.  Very effective in preventing speakers or subs from interacting with the floor acoustically which with many home floors is undesirable and results in fat bass that is hard to tame otherwise and obscures detail elsewhere.  I find it always best to eliminate floor interactions any way possible and tweak from there to fine tune the sound.  

You’ll probably end up with a marginally lower effective tuning frequency with the port downfiring onto carpet, assuming the feet are fairly short.  That’s not necessarily a bad thing.  Whether or not the difference will be audibly significant, I don’t know.  Which surface is better, well that depends on which results in the best in-room response, and too many other factors come into play for me to be able to predict. 


occasional subwoofer designer