Virtually free system upgrade?

I had a recent experience that I want to share with my fellow (and lady :-) ) Audiogoners. I added a Hsu VTF-3 subwoofer to my system a couple of months ago. It came with a test tone CD and correction factors for using a Rat Shack sound level meter with it to check the freq. response of the bass. On nearly every bass tone, I heard stuff rattling or buzzing, and I realized that I could not get accurate measurements with the extraneous noises. By banging my fist on the walls where the noises originated, I found and quieted a picture frame and window screens that were rattling, found the sheetrock on one wall rattled at 20 Hertz (nothing I can do about it unless I want to shoot screws, spackle and paint the whole room, which I don't), but I found the major problem to be the baseboard heaters along the wall behind the speakers/sub. I spent over an hour working on the b'boards and got 'em MUCH quieter. I wasn't in the mood to take measurements at that point, so I put my CD changer on random play for background music, but before I could leave the room I realized the sound was much better, and not just the bass. A certain overhangy quality in the bass (a sound I used to think was inherent to Hsu's subs) was completely gone (I detest the constipated bass most reviewers seem to crave, but sloppy bass sucks, too!) and the bass sounded much cleaner, but the real surprise was that the attack and clarity of EVERYTHING (including xylophones and cymbals) improved radically, too.
I'm still trying to get the measure of the extent of the improvements a week later. I've come to realize that the baseboards were causing problems long before I got the sub (I confirmed this by turning off the sub and noting the improvements over what the system had sounded like before getting the sub), and in most, if not all, of my previous systems. Try it for yourself. I used toothpicks, piece of rubber and pliers to quiet the baseboards. I wedged the toothpicks between the vane that opens or closes to control the heat and the hinges for it, and used the rubber and pliers on the baseboard covers and their attachment points. I'll probably redo it with self-adhesive foam (it's a pain in the butt when the rubber falls out).

If anybody tries this, post the results here.
BTW, I don't think I made it clear in my post above that I never heard any buzzing or rattling while music was playing, but the sound still suffered.
Thanks for the post Alrau. You are right in pointing out that secondary, sympathetic vibrations from other parts of the listening room can muddy the sound. That's why it's important to have very stiff surfaces or non-resonating absorbers (e.g., curtains, cushions, sandbags) in the room. I'd wager the floorboard was acting as a third speaker, but out of phase and with poor resolution -- it was resonating with the music.

The floor was probably not contributing as much as you'd think. When I had the addition with the music room put onto our house, I specified that they put the floor joists on 10" centers rather than 16" centers (and I think they sized the joists one size larger than code), with carpet and padding over the 2 layers of 1/2" plywood. I also have about 200 pounds total of weights in various places between the speakers (plus a 36" direct view TV). All that weight did improve the bass significantly; I discovered this when I chucked out a 40" projection TV that weighed 195 lbs. and noticed all the bass had disappeared. Borrowed some weights from my neighbor, and, voila! Bass again.

While I'm sure the floor must "sing" to some extent, it doesn't obscure detail. The baseboard did.
Ozfly, you were right, when my Andra,were in my living
room,my floorborad was acting the third speaker, I
did not notice it, until I transfer them back to my family
room,concrete below with tar on top.Thank you
for bringing this topic.I totally, totally, agree
on this.The diffrrence is huge.
If you think all that is bad,try mounting a couple of 15 inch JBL woofers right in your rec room wall (infinite baffle)!If you want to hear true one note cancelled bass listen to how much louder they are upstairs than down!
Alrau, I meant to say the baseboard rather than the floorboard, but either could wreck things as Jayctoy attests. Large solid surfaces that resonate with the music can wreck havoc.

I heard a Bosendorfer speaker not too long ago during a private audition. It had a solid wood side that was allowed to move and was designed to act as the woofer. It worked (though quite honestly, I've heard better low end in most other speakers). Moving wood does act as a speaker.

Alrau, good thinking to add the joists. I redesigned my flooring support to overkill the loading as well. I'm glad things are working out for you now.
Absolutely. I have done this using a very low tone on the sub , with all other amplification off to identify what is rattling , and yes the baseboard heat, pictures on the wall, cd racks , vases . Definetly worthwhile.
I'm a heating contractor and familiar with "buzzing" baseboard; there are a couple of alternatives available. One would be switching to cast iron baseboard, which is very non-resonant, but also much more expensive than regular copper and tin b/board. The other alternative would be to add under floor heat to the room and eliminate the baseboard altogether. There are relatively inexpensive ways to do this, using your current boiler. If you have access to the floor joists under that room it is very simple; you can utilize your current 180 degree (+/-) boiler water without getting a hotfoot. A good hydronic heating contractor in your area could help you out, and much nicer heat, too.

I have the baseboard problem pretty much under control now(and my system has been absolutely transformed). The original heat in this place was radiant heat using copper in the cement slab. It broke and was replaced with electric b'boards before I moved here. I installed a kerosene furnace when we moved in (heated 1200 sq. ft for $300 or so a year), but ultimately we put in hot water b'boards throughout when the addition went up. And you're right--radiant heat is nice. My wife loved putting her feet on warm flooring!