spikes under a subwoofer ?

We have found the same problem Dinos describes above. We have found that spikes into a wood floor; even through carpet does indeed mess up the midrange etc. We have found that something simple and cheap under even stock spikes make a huge difference in the overall sound. Yes even coins placed under the spikes help. This is not as big of a deal when speakers were on concrete slab floors.

I think that you're going to get BIG differences if the floor is suspended or not when using spikes. Directly coupling it to a suspended floor with spikes can REALLY excite the floor, especially when we are talking about a downloaded subwoofer. As mentioned, driver to floor distance can also affect the loading characteristics of said speaker too.

One trick that you can use is to spike the speaker cabinet and then place that on top of a board or large flat surface. The surface should be slightly larger than the cabinet. The panel lies directly on top of the carpet, which spreads the load out on the floor somewhat. This rigidly couples the cabinet to the board while the board is somewhat isolated from the floor by the carpet and padding. You still get the correct loading for proper driver output due to the panels' flat and smooth surface AND minimize floor excitation due to the slight carpet / pad insulating effect. Playing with the type of and mass of the panel and adding weight via mass loading can be used to "fine tune" the results somewhat. I've found that adding too much weight to the cabinet will tend to deaden the bass and make it slower though, so be careful. Just a thought... Sean
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Perhaps I should add that the HGS series subs are front firing.

Good point : )

The effects mentioned above should still be similar but possibly not quite as drastic. Sean
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Have a look at this page: www.sonicdesign.se/sdfeet.html
Quite interesting, and to my knowledge, you can excite
resonances in the floor even if it´s made of concrete!
I have tested the SD-feet just in this case,(and at different places) and the improvment in sound quality was remarkable!
The Danish loudspeaker, CDP and amplifier- company Holfi is marketing simular soft feet, they also claim that floor and loudspeaker cabinet vibration is significantly lower with their softfeet(some thousand times lower vibrations, if I remember correct).
Of course,I have no commercial interest in either of these
companies.
You have to weight the front- and back-side of your loudspeaker or sub, to get the right stiffness in the feets.I think there are feets up to a load of about 450 Lb. They are made of a material that doesn´t have closed cells,therefore the feet wouldn´t collapse with time.
I can´t say what the prices for the SD-feet are at the moment(set of eight of them),but I believe that you should
be able to get a set at about $130 including shipment
to the US.

Regards
Håkan