[rickkuy]

I recently purchased a sub woofer to augment the bass on my new RM-30C's. It's a Sub Table from Performance furniture, purchased mainly because of aesthetic concerns-- my wife loves the looks of the rosewood RM-30's (as do I), but wasn't too wild about putting a big box in the corner of the room. After less than a week the amp went kabutz in the new sub, which the company said they'd replace. Upon pulling the amp out, I discovered that there was no damping material in the sub box. I called the company and asked why this was so, and was told, in a mildly indignant tone that "damping material is not necessary if the box is designed properly."
When I said I'd never heard of a speaker, particularly a sub, without some sort of damping material he immediately replied that Wilson Audio products don't use damping material.
While I don't consider myself an audiophile, I am rather fanatical about this stuff and am in need of some education-- and from someone without an attitude!
It was my understanding that internal damping material is there to prevent the creation of resonances which could manifest in sound coloration. I have a hard time believing that if only Brian Cheney were a little smarter about this stuff, he could build speakers that don't need damping material, and the SR-71 sound coating would be irrelevant.
So anyway-- any insights for this relative newbie are appreciated. Should I consider adding damping material, or would I risk upsetting the balance in my audio universe?
Thanks, --Rick.

[Martyn]

In essence, the stiffer the panel, the higher its resonant frequency. For a sub, it's not hard to make the panels stiff enough to move their resonances above its operating frequency range. If this is accomplished, no fill is necessary.

[ctviggen]

The damping material also affects the Q of the subwoofer (or any speaker for that matter). This describes the various Q's:

http://www.bcae1.com/spboxad2.htm

Here's a description about why fill is used:

http://stason.org/TULARC/entertainment/audio/general/12-24-What-is-the-best-stuff-to-fill-a-speaker-cabinet-wit.html

As to whether a fill is necessary, I bet you could ask speaker designers this question and get different results. 

[PLMONROE]

If I were a manufacturer I might wonder about three things. How many people would ever look inside my subs. Of those how many would wonder at no fill? How much could I save in construction costs by leaving fill out of a run of 10,000 subs?

[rickkuy]

Thanks for the links-- some good background info there.
I gather then the main (only?) reason for the damping material is to tame the resonant frequency of the speaker box-- for a sealed enclosure. So if you have stout and/or short enough walls, no need for damping material?
Isn't there a concern about sound waves that would be reflected back to the driver itself?

Boy, I'd be pretty disappointed if a speaker manufacturer was trying to save a buck by not putting in fill-- especially at this price point. I understand saving a buck on a run of 10,000 though...

[Brian Cheney]

The damping properties of various fills are well known.  Fiberglass is the most efficient at low frequencies.

One of the main applications for filler material is to stiffen the air inside the enclosure and therefore mimic greater air volume.  Fiberglass does this very well.

Also, filler is necessary to damp out the "organ pipe effect" in tower type enclosures, which would otherwise resonate strongly at the frequency (and its harmonics) equal to the  vertical path length.

[ka7niq]

The damping properties of various fills are well known.  Fiberglass is the most efficient at low frequencies.

One of the main applications for filler material is to stiffen the air inside the enclosure and therefore mimic greater air volume.  Fiberglass does this very well.

Also, filler is necessary to damp out the "organ pipe effect" in tower type enclosures, which would otherwise resonate strongly at the frequency (and its harmonics) equal to the  vertical path length.

Brian is sure right about that.

I have been experimenting with my older RM 40's in an effort to get them to sound even more wonderful.

I pulled the fiberglass stuffing out of the inner chamber of the speakers.

Bass did SEEM to be a bit louder.
But there was too many colorations, and I put it back in.

No harm done, it is just fiberglass stuffing, goes right back in, the way it came.

I ONLY itched a couple of days, LOL