Hi Keith sound like "the trumpets of Jericho" which was one of the last secret weapons of the German in second world war II. You can destroy a lot of material with bundled ultra low frequencies of great distances. Reminds me of the movie "earthquake", it was the first to my knowledge with low bass frequencies producing some vibrations :-)
Markus > Seems to me I recently read about this happening, and the article > described a military use for it, for disabling troops with unbearable > sound intensity...
