Question re: Resonance in tall cabinets

[Ken C]

I've been toying with the idea of building another pair of tower speakers based on the bookshelf project I've got now. The bookshelfs are about 13 inches tall, and my proposed cabinet would add 24 inches below this for a total of 37 inches of height.

Every source and person I've encountered recommends keeping the same internal volume for the 2-way speaker (upper part), and then bracing the lower part and filling it with sand or leadshot.

What I'd like to know is if I can get away with not using sand or leadshot to "mass" up the cabinet. Is there anything else I can do to avoid adding a sick amount of weight to these? Bracing? How much, what kind?

I only have a few books in my library ( a few by Weems, V.D.'s Loudspeaker Cookbook, etc) and none really address the principles I think I need to understand all that well here. Are there any good online references or other material I could look at? Thanks.

[tg3]

Why not just build a nice stand for your current 'bookshelf' design?

[David Gatti]

It seems strange that you want to make the cabinet larger, but retain the same volume for the 2-way section. So what's the point of it?
As the previous person said, why not just make a good stand?
If you were to make a larger cabinet, mdf matrix style internal bracing & the volume filled with fibreglass would be the way to prevent both iinternal standing waves and wall vibrations.

www.gattiweb.com

[Ken C]

Just to clarify...
I'm quite happy with my bookshelf speakers...and I'm building a home theater based on 6 speakers and a center.
The wife says she'd really like the look of front towers, especially in the nice veneer I have, so I'm trying to accomodate.
It gets her off my back a bit if she's given input and buys into my projects.
Besides, with a cat, dog, and the occasional nephew running around bumping into things, the bookshelf gets moved a bit too often and drives me nuts when I try to line it back up right. My current speaker is fastened to the stand, and the little ****** knocked it over somehow.

You're right though, stands would be easier, cheaper, less complications, etc..
Just looking for ideas. Maybe a nice, thick necked stand with the same veneer finishing would be a better compromise.

[BillFitzmaurice]

If you add volume to the cabinet the speaker Fb will be lowered and the speakers won't work right any more. I'd conside making the cabinet internally divided, with a subwoofer driver in the bottom 2/3. The specs of the MCM 55-2421 may prove OK for a small volume sub.

[catapult]

If you like your bookshelves, you should keep the same internal volume. You can do that by putting a shelf across the cabinet interior at the right spot. There's no need to fill the lower section with something heavy but another shelf or two to damp panel resonances would be good.

You could also build it as two pieces where the bottom stand part is the same width, depth and finish as the upper speaker part. Something like this:

http://www.mksound.com/5-1_sys.html

[PooJou]

You could always make this work to your advantage, and attempt to extract some more lower end "Punch" from your current bookshelf drivers, if you know what i mean.
This would obviously require a redesign of the cabinet to take into account the extra volume
Hope this helps - Goodluck!