Bicycle Inner Tubes
Well, I popped into a bike shop to get a new air pump (my brother took away his Trek pump) and settled for a cheap $15 portable hand pump as well as a nice new inner tube for my Cannondale (whose inner tube I had patched several times). I must be behind the times cos' I didn't know that they had self-sealing tubes for bikes... amazing... but we'll see how it works out.
Anyway, I also decided to splurge a princely sum of $10 for 2 12" diameter inner tubes, not for my bike of course, but for hi-fi purposes :)
Digging around my house, I found 2 12"x10"x0.25" wood boards from my previous hobby of model kit/diorama making. The wood boards cost $2.30 each from an art supplies shop.
Sound under Amp
I placed the amp on the boards and the inner tubes under the boards. The tubes were only slightly inflated in order to get a lower resonant frequency. Listening to the usual CDs, I noticed a greater sense of space and detail retrieval and a fuller sound. The differences were consistent as I did a rigorous A-B-A-B (swapping in and out the tubes) comparison. For several hours of listening, I was so taken by the improvement that I couldn't really detect any shortcomings.
On the second day of A-B testing, I spinned some more CDs with pulsing bass beats (U2s Unforgettable Fire and the noisier tracks in Kendall Paynes Jordan's Sister), I detected a slight slowing of the pace of the bass. It was certainly not mushy, but it seemed a bit relaxed.
My initial conclusion is that the inner tubes win on points. I have still some more tweaking to do. First, I have to get a full sized board instead of 2 small boards so that I can arrange the tubes properly and get the amp levelled (during the trial, because of the swapping in and out, I didn't take much care to level the amp). Secondly, I will have to experiment with the correct material for the board (the particular type of wood may actually slow bass and I might even switch to a glass piece). Thirdly, I can try special feet under the board (instead of the DH squares which I'm using now) which are reputed to speed up the bass.
Sound on top of Speakers
Just for a lark and also partly due to a flash of inspiration, I decided to place the inner tube, the board, and 5 kg of weights on top of the speaker.
Prior to this, I had simply placed weights on top of the speaker and I found that it simply improved the bass. Therefore, I was presently surprised with what I heard.
Playing the raucous Supermodels from Jordan's Sister, I immediately noticed that the vocals were slightly clearer with better focus with the tubes and weights on the speaker. A/B testing was simple and quick (just remove the weights) and the differences were confirmed. Further, there was no detrimental effects to the sound that I could detect.
Though it seems strange, there is a theoretical explanation for the improvement - the inner tubes absorb some of the vibrations on the top surface of the speaker and when the tubes vibrate, a miniscule amount of the energy is converted to heat while on another level, the vibrations are tuned to a different frequency. Whereas, if you simply add mass to it, you're not absorbing the vibrations; you're simply coupling the speaker more securely to the floor.
At $5 an inner tube, why not have a go? If you hear an improvement, then maybe you can splurge on a Seismic Sink or Air Mass if you're concerned about aesthetics. The tubes are not a guaranteed easy improvement - I couldn't hear an A/B improvement on the downstairs system with the tubes under the SCD-777ES but there were other issues involved (not least that I'm not familiar with the system, the room is acoustically bad, and the ambient noise level was rather high at that time)