The 19Hz story, and why your phone cannot tell it
In 1998 Vic Tandy, an engineer at Coventry University, published an account of a laboratory his colleagues considered haunted. The account is well known in this field and is usually retold badly, so the Survey is holding this page until the original paper has been read rather than summarised from memory. That work is scheduled.
What can be said now is the part that concerns the instrument itself. Very low frequency sound — below roughly 20Hz, which is where human hearing gives out — is difficult to produce and easy to claim. A phone speaker is a few millimetres of moving surface. It cannot shift enough air at those frequencies to produce anything you would feel, and any handset that appears to be doing so is producing audible harmonics instead.
So Instrument 21 will be a curiosity with a good story attached rather than a working device, and the page will say so plainly at the top rather than at the bottom.
The Survey would rather ship an honest disappointment than a dishonest effect.