This page is from April 2000
Surfing the net, as one does in the late of night, I called up my favourite search engine to see what I could find out about the bass response of Guitars. Email readers know I have a special interest in the Guitar Orchestra family, and by coincidence, fellow Guitarist Wayne Lines was asking about getting deep bass from a normal guitar.
I chanced upon a British patent, of all things, number 0042723
I've downloaded some images of the thing which I've put on my website for luthiers and others to look at. Basically, it's so simple! We all know the Donald Duck effect from breathing helium. This patent uses a device a bit like a Dampit, but instead of water, it holds dry ice. Dropped into the lower bout, the carbon dioxide vaporises and fills the lower half of the guitar with cold heavy gas which lowers the air mode frequency. Because only half the guitar is filled with CO2, the effect is not isotropic, and this broadens the resonance peak and extends the bass still further.
Of course, the CO2 diffuses out via the soundhole; it's a heavy gas, however, and the lower bout tends to stay full. A small cube of dry ice keeps the lower bout replenished for a couple of hours - enough for some serious practice or even a recital. Any excess CO2 spills out of the soundhole as the dry ice evaporates.
The patent is for the idea as well as the dry ice holder.
WIth true British humour, the name takes a swipe at the Dampit, as it's called the Drywit!
Footnote : The patent, by the way, is for the British Dyson Vacuum Cleaner. Because like my April Fool, it sucks....