Evan Roberts and fellow revivalists in Loughor in about 1905

The National Screen and Sound Archive of Wales in Aberystwyth, says it is the only recording of Evan Roberts.

A wax cylinder that contained the recording in 1905 was brought back to life by an expert in Los Angeles.

At the beginning of celebrations to mark the anniversary, the find is particularly poignant, say officials.

The voice of Evan Roberts was heard for the first time in decades - and in Los Angeles of all places Dafydd Pritchard

Mr Roberts, a miner and blacksmith from Loughor, near Swansea, was one of the central figures of the revival.

"Although we have written testimony of powerful oration and second hand accounts of the feelings created by revival meetings, it's hard to imagine today the full power of the words and the message as they were spoken," said Dafydd Pritchard of the archive.

"This unique recording takes us a step nearer the excitement of the age.

"It is remarkable that the recording exists at all, and another coincidence that it has come to light a century after it was made."

Evan Roberts recorded voice was heard again first in Los Angeles

In 2002, the archive received a donation of six wax cylinders from a Barrie Davies from Tredegar.

Among them was one which had a label in pencil which read: "Revival Address, By Rev E Roberts, 18 Jan 1905 (ER)."

But of the cylinders in the collection the one containing the address by Mr Roberts was the only that was damaged.

The broken voice of Mr Roberts was flown to Los Angeles where Dr Michael Khanchalian, a dentist with an interest in wax cylinders, began the restoration process.

"Dr Khanchalian has developed an unique technique, by using many of his dental skills - and tools - to do the work," added Mr Pritchard, who took the cylinder to the US.

"We were full of doubts that perhaps it would turn out to be music on the cylinder, and maybe it wouldn't be the voice of Evan Roberts after all.

"After a week of painstaking work the big moment came when we dared to play the cylinder.

"By placing the needle on the cylinder the voice of Evan Roberts was heard for the first time in decades - and in Los Angeles of all places."

A digital copy was made in a studio in Pasadena and further work carried out at the British Library in London.

"The process of restoration has proved once again the importance of safeguarding our screen and sound heritage," said Iestyn Hughes, head of the archive.

"Rediscovering and restoring a voice that had such an impact on the spirit and history of our nation is an important and timely event for the archive and Wales."