insulating after-market speakers


First off, I am a novice - thanks for your patience. I've had some luck "tightening up" some boomy subwoofers by lining the cabinet interiors w/high-grade speaker insulation(egg-crate style) purchased from PEx. Of course, these were budget subs. I am presently awaiting the UPS arrival of a replacement tweeter for a budget bookshelf speaker(ported in both the front & rear) and I'm eyeballing the naked interior of this cabinet. Very little insulation was provided. I realize that cabinets are tuned a certain way upon design but I ask the question:"Can I improve the sonic quality of the cabinet by lining it's interior w/a high-grade foam insulation as I did my old subs, or am I more likely to alter the sound in a negative way by changing the interior cabinet dynamics therefore altering the cabinet's tuning?" Of course, I would do it in a manner that would allow air flow to both ports. Somebody (w/a great deal of knowledge) suggested using dampening spray (usually used for car doors) as an alternative to foam, but I think he made THAT suggestion NOT KNOWING I can easily access the whole cabinet interior at this point in time. What are your thoughts on this? Foam insulation, dampening spray, or even the third alternative of using vinyl self-adhesive dampening sheets. Thanks for your input!
davesen
A long time ago I bought a pair of Wharfdale Diamonds. They were highly regarded, but I live in a relatively small town so auditioning was not an option. I sold the speakers I had to fund the new purchase.

When the speakers arrived I tried to be hopeful though they were smaller than I expected. I hooked them up and let them play for a couple of days. After enough time to break in I sat down to listen.

I almost cried, they sounded awful! I didn't know what I was going to do since I did not have money to buy something else, and this was long before AudiogoN. I decided a fix was more rational than suicide.

I opened the cabinet and rewired the whole thing with some AudioQuest cable I had left over from something.

I gave them a second chance, after appropriate break in. The speakers sounded a lot better. Good enough that when I had other 'audiophiles' listen to them blindfolded they were surprised to see how small they were.

To get back to your question; your speakers can sound much better with a little effort put into the cabinet. Polyfil is a good start, bracing can help, and using some good cable inside is worth the minimal cost. Try any or all of them, you should be pleasantly surprised.
Thanks Uppermidfi for the helpful anecdote. Now, any others on whether better insulating the cabinets could improve/harm the sonic qualities of the speaker in question?
Davesen
One good thing about doing it yourself is that it is just as easy to un-do. Give it a try, I would!