Being from the Philadelphia area and having an interest in Band Organs
I have also wondered about the Knapp Barrel Organ Works.

The only mention I can remember is in Fred Fried's book "A Pictorial
History of the Carousel" where there are two sentences about The Knapp
Barrel Organ Works. "About 1903, Charles Looff was supplied with organs
by the Knapp Barrel Organ Works of South Howard Street in Philadelphia.
Knapp made organs for a short time, competition forced him to close."
The address is given in the book as 1407 S. Howard Street, Philadelphia.

Howard Kohlbrenner
Broomall, PA.