Concrete tubes: hemholtz resonators? tubes?

They are not talking about "concrete tubes". They are talking about the hard cardboard tubes that are used to form concrete pillars. You pour concrete into them, and when it dries, you cut the cardboard off, and you have a pillar or piling.

These tubes come in sizes from about 6" diameter to about 24" diameter, and they are thick hard cardboard. The most common size I see are 8" and 12". They are often used in DIY projects to make tuned "t-line" type enclosures for subwoofers. Unfortunately, the single diameter tube doesn't have the actual correct tapering for a true t-line, and winds up giving "one note bass". It's not really that bad, but tapered would be a lot better.

They could be used as bass traps, if you make them correctly.

Ok, I'll bite. How can these be turned into bass traps? What would be involved?

A few years ago, there was an article about this at Headroom (the headphone people). Unfortunately, my company's firewall thinks the link to Room Tubes is about sex and won't let me open it. Maybe you will have better luck: http://web.archive.org/web/20000816145216/www.headphone.com/EditorialHeadroom/RoomTubes.asp

See Jon Risch's website under room treatments.

The hollow concrete tubes go by the trade name Sonotube. I've used 'em, but to build a deck and fence (I know, I've failed as a 'phile so far). The exterior of the tubes are shiny and if I had to guess, reflect more than absorb but I really have no practical audio experience with these. In any event you may want to check out HSU's subwoofers, I suspect they use Sonotubes in their design.

Tsouth, your company firewall blocking you is somehow amusing to me.