kubusi, thank you for the offer regarding the Leak article from Langford-Smith.
I will PM you my details.
The one I have is from the Internet and there is also one on the Internet dated June 1956 from
Langford-Smith where he used a speaker to conduct some tests on the Leak.
If I can remember correct, the Leak was developed after the Williamson amplifier and the Williamson
was the milestone in audio development.
The book from Stephen Spicer is a current publcation. Its ISBN number is 1-882580-31-1