Older readers might be suffering from a case of déjà vu - this product first appeared back in 1988, and disappeared by the mid 90s. But fear not, it's not you: the Aspri Acoustic Reverb is indeed back for 2013.
What is it? Essentially, it's a plastic-shrouded three-spring reverb tank that attaches under the strings and is held in place at the base of the guitar. It fits in a couple of minutes, and can be removed even more quickly.
Three metal inverted T-shaped 'pickup' legs sit under the strings and butt right up to the saddle. There are two versions: one for steel-strings, the other for nylons (the only difference seems to be slightly wider spacing of those 'pickups').
It proved an easy fit on our Alhambra classical, though slightly trickier on the angled compensation saddle of our Martin dreadnought.
The unit isn't heavy, but it is weighty enough to subtly change the seated balance of our test guitars. The pickup legs sit right under the strings, and impart a slight metallic edge and a little loss of body to the tonality.
In return, you get an easily audible hall-like reverb emanating from those springs. We preferred how it sounded on our classic guitar compared with a steel-stringer.